Home

Ground loop problems and how to get rid of them

1. We are sorry but the URL you are trying to access could not be found or is not available any more Please check the URL proceed to our homepage or use our search functions to find the information you are looking for webmaster feedback main index back site search acronyms discussion mail to a friend post message Building your own antenna isolators Antenna cable isolator is basically quite simple circuit but it must be built correctly Improperly built antenna isolator can can cause RFI problems and even screw up the building antenna network operation Antenna isolators work at very high frequencies up to 500 MHz where even a very small construction details and component specifications can have a highe difference on circuit operation If you are not experienced and knowleadge at building high radio freqeuency circuits recommend that you buy a ready made isolator instrad of try to build it yourself Build your own antenna isolatation transformer Best solution to antenna cable caused ground loop is to add a 1 1 transformer in the antenna signal floating the VCR with respect to the cable tv ground This solved the hum no need for a messing with the audio signal and the tv image quality did not suffer most tv s get an overdose of signal from the cable tv anyway You can simply make such a 1 1 transformer e Take two strands of insulated wire length 10 20 cm e Twist the tw
2. index back site search acronyms discussion mail to a friend post message Ground loop problems and how to get rid of them Written and copyright by Tomi Engdahl 1997 2000 NOTE The information presented here is believed to be correct and is made available here by the author The author of this document is not liable for any effect this information or any use thereof may have The documents have been used and recommended by many people and are belived to be accurate So accurate that they have also been featured as GB AUDIO Ground loops DATA SHEET on their web pages with permission from me Basics A good power distribution system is essential for proper operation of audio system Professional audio systems just doesn t work well with normal extension cords running hundreds of feet to a stage Besides the power feed the good grounding of thw whole system is essential Ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground When two or more devices are connected to a common ground through different paths a ground loop occurs Currents flow through these multiple paths and develop voltages which can cause damage noise or 50Hz 60Hz hum in audio or video equipment To prevent ground loops all signal grounds need to go to o
3. site search acronyms discussion mail to a friend post message Naming Electricity System Earthing Arrangements The information on this document is based on UK DIY FAQ part written by Andrew Gabriel European naming conventions Mains electricity systems are categorised in the many European countries Finland UK etc according to how the earthing is implemented The common ones are TN S TN C S and TT Note that in these descriptions system includes both the supply and the installation and live parts includes the neutral conductor Description of letters First letter T The live parts in the system have one or more direct connections to earth I The live parts in the system have no connection to earth or are connected only through a high impedance Second letter T All exposed conductive parts are connected via your earth conductors to a local ground connection N All exposed conductive parts are connected via your earth conductors to the earth provided by the supplier Remaining letter s C Combined neutral and protective earth functions same conductor 5 Separate neutral and protective earth functions separate conductors Valid system types in the 16th Edition IEE regs TN C No separate earth conductors anywhere neutral used as earth throughout supply and installation never seen this TN S Probably most common with supplier providing a separate earth conductor back to the su
4. Any modification of the above 3 wire mains system completely eliminates the protection given by the three wire configuration The integrity of the separate ground path is also directly related to the quality of the receptacle and the wiring system in the building itself The neutral grounded conductor must be solidly connected bonded to the home s ground system at the first disconnect main panel This keeps large voltage differences from developing between the neutral and ground Currents in grounding wire Ground wires should not carry current except during faults If the ground wire carries any current there will be a potential difference between different grounding points bacause the current flowing in wire causes voltage drop because wire resistance This is why a common wire which works as neutral and grounding wire is very bad thing When there is separate wiring for grounding you can t still completely avoid the current flowing in grounding wires There will always be some capacitive leakage current form the live wire to the ground wire This capacitive leakage current is caused by the fact that the wiring transformers and interference filters all have some capacitance between the ground and live wire The amount of current is limited to be quite low limited to be between 0 6 mA to 10 mA depending on equipment type so it does not cause dangers and big problems Because of this leakege current there is always some current flowing in the
5. However the California Public Utilities Commission has specified that the service voltage shall be kept in the range 114 120V with some exceptions This was done because some studies showed a reduction in energy consumption at the lower voltages Information on NEMA plug configurations is available in NEMA Configuration Chart Form No H4513 For availability check http www hubbell wiring com Single phase power in Europe The nominal European voltage is now 230V 50 Hz formerly 240V in UK 220V in the rest of Europe but this does not mean there has been a real change in the supply Instead the new harmonised voltage limits in Europe are now e 230V 10 6 i e 207 0 243 8V in most of Europe the former 220V nominal countries 230V 6 10 i e 216 2 253 0V in UK former 240V nominal his is really a fudge and means there is no real change of supply voltage only a change in the label with no incentive for electricity supply companies to actually change the supply voltage To cope with both sets of limits an equipment will therefore need to cover 230V 10 i e 207 253V This will actually become the official limit for the whole of the EU in 2003 Single phase power in rest of the world A listing of nominal voltage frequency and plug socket types used in many countries is given at http kropla com electric2 htm Three phase distribution The 3 wire system that the user sees is typically derived from three pha
6. The grounding is most commonly done using the small bare metal parts on the sides on the the connector you can see one near the pace where the wire leaves and another on the the opposite side There is also a hole for a separate grounding pin used in some countries UK style grounded mains connector Maybe the most common electrical outlet used around the worls is the UK style 3 pin mains connector BS 1363 That connector is used in UK Ireland and most of the countries which were once part of the British imperium This makes this mains connector maybe the plug which is used in most countries 4 a This connector is designed so that it can be only fitted in the wall in one way so it is laways know which pin is which The toltally metal pin up in the picture is the ground pin Those pins which have part of them insulted are the live and neutral pins The speciality in the wiring used in UK is that there is a fuse placed inside the mains plug The size of that fuse is to protect the equipment wire from overheating in case of short circuit fuse size is determinded by the equipment wire size because the main fuse which powers many electrical outlets is typically quite large up to 30A The maximum current which can be taken from one outlet is 13A Ungrounded equipments Many small home electronics and light equipments designed for use inside house do not use grounding Those equipments are built using double insulation or insulating case
7. a trace on a printed circuit board a metal chassis virtually anything that conducts electricity Ideally it should be a perfect conductor but in any practical system it is not As the complexity and size of the system is increased the imperfect conductivity of the common ground conductor inevitably causes problems Hum and buzz 50Hz 60Hz and it s harmonics occur in unbalanced systems when currents flow in the cable shield connections between different pieces of equipment Hum and buzz can also occur balanced systems even though they are generally much more The cable shield currents and ground voltage differences are caused by several mechanisms The second most common source of hum and buzz is the voltage difference between two safety grounds separated by a large distance or the voltage difference between a safety ground and an Earth ground such as a grounded satellite dish or cable TV source This problem is usually called ground loop This is the most common one in severe humming problems Hum and buzz can also be magnetically induced or capacitively induced directly into signal cables Or the noise current can leak from mains input through capacitance between the A C power transformer primary and secondary windings which causes that a portion of the A C line voltage will ALWAYS be capacitively coupled directly to audio circuit ground This capacitivly coupled power line signal will usually contain significant harmonics out to 1MHz or mor
8. for example for 3 phase distribution you might see sometimes a 4 or 5 wire cable and a separate safety ground cable bundled on the side of the cable In some countries for example in USA in some case the metallic piping used to protect the mains carrying wire inside the walls can be used as safety ground conductor not usually very good or reliable in practice think but is allowed in some cases How power is delivered to the house Typical one phase feeding to building One phase distribution is typically used in small residental building The power company feed live wire and neutral gound wire to your house The power in the power company system is typically three phase power and the power company then feed one phase to your house you neighbour can have their power from other phase for even distribution of load Power Company Your House Mains Outlet Distribution Distribution Transformer Panel Phase Conductor Live wire Hot Grounded Conductor HV Line Neutral Ground Neutral Bonding Jumper Ground Wire g Grounding Electrode Building Grounding Electrode Single phase power in North America ANSI C84 1 Electric Power Systems and Equipment Voltage Ratings 60 Hz sets the preferred nominal voltage at 120V and allows a range of 114 126V 240V nominal range 228 252V Equivalent Canadian spec is CAN3 C235 Voltage at a 120 volt nominal single phase receptacle should be 110 to 125V under normal conditions
9. 06 4370 Ground Isolators which are 1 1 audio isolation with 10 kohm impedance cost around 20 have used this isolator successfully in some audio installations and am quite satisfied with that as a problem solver have found that the transformers in this product will attenuate the low frequency signals if the transformer is driven by high impedance output because the impedance gets quite low on lowest frequencies For professional audio use buy high quality commercial audio isolation balancing transformers those are very handy to keep around to solve unexpected ground loop problems Balancing the line and removing of humming in PA systems instrument connection can be achieve too by using passive DI boxes available at your local music stores Many DI boxes are active and can be almost useless in getting rid of earth loops and stopping buzzes amp hums etc A GOOD passive DI which provides isolation is proven only way to go Active ones work also if they are properly designed and provide necessary ground isolation Commercial products e Biltema 31 441 check measured results of performance text in Finnish e Cordial CLT 1 600 600 Ohm line transformer for the galvanic separation of the sound signal e Furman Iso Patch P 2 transformer isolator Monacor FGA 40 Best Nr 06 4370 Ground Isolators 1 1 audio isolation with 10 kohm impedance e Jensen Transformers company which makes audio isolation transformer and DI boxes e Leon Au
10. Europe is made by 230 400Vac 3 phase four wire Multiple Earth Neutral MEN One two or three phases are brought into the customer s premises depending on the maximum demand This applies to both residential and business premises For those not aware of the MEN system the neutral bar is connected to an earthing stake driven into the ground as near as possible to the customer s switchboard All earth wiring from power points etc is connected to the neutral bar In the UK the same practice is called Protective Multiple Earthing PME With P M E the neutral and earth conductors of the supply are combined The supply company connects the neutral solidly to earth frequently throughout the distribution network At the customer s connection point the company supplies an earth which is actually connected to the neutral to which all the installation earths and equipotential bonding are connected Another approach to bring grounding to the building is to bring it through armouring of the supply cable If the electricity company cannot easily supply or guarantee an adequate earth conductor for example supply comes on a pair of overhead wires the ser is generally responsible for the adequacy of the earth electrode The method of earthing can normally be found out by tracing the wiring from the meter consumer unit It is usually fairly obvious How Good Should the Earth Be This is a difficult question to answer in general the impedance of the earth c
11. Hz between the cable its shield and the audio video system and at the same time provide a low impedance path for RF signals The lowest signal frequency for which the impedance must be very low with respect to the 75 ohm cable impedance is around 50 MHZ That is about 1 000 000 times higher than 50 Hz A 10 nF capacitor has an impedance of less than 1 ohm at 50 MHz and over 200 000 ohms at 50 Hz Therefore isolating the cable s center conductor and shield each with a 10 nF capacitor from the input to the cable tuner will eliminate the 60 Hz ground loop current and resultant hum without attenuating the RF signal level Capacitor isolator approach is an old trick used in TV industry When the old TVs had their chassis at mains potential they used this kind of approach to make sure that the dangerous voltage can get to the cable from the TV but the RF signal goes nicely to TV Isolator used in one old TV had 330 pF 500 VAC capacitor which connects the center of the coaxial cable to tuner and the shield of the coaxial cable was connected to TV chassis through 820 pF high voltage feedthrough capacitor value unknown A commercial isolator which plugs to TV cable made by J EBSEE uses 11 nF capacitor for connecting coax cable center wire and 22 nF capacitor to connect the shields together The easiest way to build the isolator is to use two chassis mount antenna cable connectors typically EIC antenna connectors on Europe and F connectors on USA Connect
12. Me Hum a Few Bars information on ground loop problem solving on home theater setup Ground Loops or let me hum a few bars many home theatre video and audio systems hum usually a result of the matching of components their earthing scheme and the power lines within your home ISO MAX Toubleshooting Guide contains lots of useful technical information on groundloops and troubleshooting tips Kill Studio Hum and Buzz at the Source article will address some common causes of hum and describe ways to reduce it or even eliminate it entirely o My system hums what should do o Solutions for Ground Loop Interference o Thoughts of a road technician Equipment design o A New and Important Audio Equipment Evaluation Criteria what kind of equipments are potential noise problem makers o Audio Transformer The Ultimate Noise Killers application note article on audio transformers o Considerations in Grounding and Shielding in Audio Devices engineering report from Rane in pdf format o Proper Grounding Inside Equipment Avoids Ground Noise Coupling aka Pin 1 Problems 15KB PDF o Star Grounding one of the best amplifier power supply grounding schemes is a star ground system where all the local grounds for each stage are connected together and a wire is run from that point to a single ground point on the chassis back at the power supply ground Useful sites o Electrician s Too
13. The on site work required to find the problem usually starts at the computer equipment under question and works backwards through the electrical distribution infrastructure Branch circuit are examined for total harmonic distortion THD conductor resistance rms voltage and grounding methodology Pay attention to mains connections of connected equipment Every desktop PC has its cover as well as the ground pins connected to the center wire of the mains plug protective earth If you have two PCs connected to different mains plugs that you intend to connect together it is possible that each of them is connected to a different branch of your home electrical wiring Although these are connected together at the switchboard they may have different voltages if a heavy load is connected to one of them e g washer dryer etc causing a voltage drop Single pulse can reach the order of tens of volts This voltage difference then appears at the inputs of the PC EASILY DESTROYING the parallel or serial port hard drive controller sometimes even the whole mainboard Therefore it is a good idea to connect only PC s powered from the same mains plug or at least connected by a single extension cord The same applies to monitor printer and other connections Recommendations on grounding in computer networks Nowadays the shielded LAN cable is becoming common Shielded cable become grounded in every connection point both ends of the cable In this kind
14. always current flowing in the same wire which should distribute the same ground potential to different places If your building has four wire 3 phase wiring you can expect quite noticable ground potential differences of the power taken from different distribution panels The practice where safery ground is connected using the same conductor as neutral is called PEN TN C and practice where there is separate ground wire in whole system is called PE TN S Two wire 1 phase grounded outlet And worst of all is a 2 wire 1 phase jack wiring where neutral and ground share a common wire This practice is very often used in older buildings in Finland and causes terrible ground loop problems even between nearby power outlets If your are planning to install any dedicated equipments computer connected to LAN interconnected audio or video equipment etc to building which has this kind wiring system is advicable to get a lincensed electrician to rewire the room with proper outlets This wiring has also some other problems and that s why it is not allowed anymore in new installations in Finland Circuit breaker boxes The main breaker box to the building is the single location where the neutral and the ground wires come together The electrical service will be grounded at this point IN ALL DOWNSTREAM BREAKER BOXES BOTH THE NEUTRAL AND GROUND WIRES MUST BE KEPT APART FROM ONE ANOTHER Otherwise you will have neutral currents flowing on the ground wire This is ext
15. cope this If the voltage difference between your neutral and ground is much larger than few volts or there is very good propability that there is somethign wrong on you main wiring So it is best that an electrician goes and checks your wiring before more problem and damages happen In some cases the neutral actual to ground voltage is not the problem but the wavefor of the voltage Non linear loads like computer power supplies and light dimmers can cause some considerable noise between neutral and ground Such noise can be more problematic than just a simple voltage difference but equipment should still be able to cope quite fair amount of it EMC regulations etc If you have considerable amounts of noise on neutral wire used by nonlinear loads then you can again blaim the improper design of the electrical wiring This kind of problems can be solved by good wiring design practices separate electrical wiring from main panel transformer to the equipments which cause noisen and to equipments which are sensitive to it This is good practice and keep problems away If you would have on those cases had a wiring with common neutral and ground wire you would have terrible ground potential diffeences between different outlets In cases were ther problems neutral to ground voltage differences in separate ground and neutral wire wiring start cause problem a wiring with common ground neutral wire there would be so much ground potential differences between out
16. ground leakage detector in wiring it will cut the power to the outlet e Live or neutral cut Equipment just stops getting the power e Ground wire cut The safety ground to equipment is lost It continues to work nicely and there is no danger as long as there is no fault inside the equipment Potentially as dangerous situation as using ungrounded outlet in same place bur no immediate danger So any single failure does not cause great danger So the for safety sense separate ground and neutral wires are a very good idea 2 Minimizing the ground potential differences between outlet grounds In an ideal reparate grounding wire system there is no current flowing in ground wire network so there is no voltage difference between grounds on different outlets Unfortunately in real life systems there is always some current leakign to ground but that current is very small only propably milliamperes compared to the current flowing on line and neutral wires usually amperes If the neutral and ground were shared on same wire the current flowing on neutral wire would easily cause a large voltage difference up to many volts on different outlets grounds The ground potential on any outlet will then depend on the load current neutral wire resistance and the mains phase it is connected to Conclusion For the conclusion we can say that separate ground and neutral conductors are a very good thing in providing good electrical wiring security and minimizing
17. ground potential difference between different outlets So it is no wonder why modern electrical wiring regulations call for this arrangement in many applictions If the neutral to ground difference a problem when separate wires ared In large computers neutral to ground voltages are originated because nonlinear currents flow through the neutral wire In general always when there is some current flowing in neutral wire there will be a ground ot neutral wire voltage difference on output end because there is no current flowing on ground wire In some computer systems the voltage differences are considered to be problem because it has been reported to cause cause improper behaviour like hangouts on some computer systems It is true that in some special cases neutral to ground voltages can cause this kidn of problems but in those cases it is not to blame the separate wires because the problem lies in some other place In properly built electrical wirign network the neutral to ground voltage differences will never be more than few volts and any properly designed electrical equipment should not be disturbed of this kind of small voltage differences If the equipment gets disturbed of this small main frequency voltage claim the manufacturer designer of that particular equipment for doing bad job Computer equipments can be easily deigned to cope few volts of voltage differences between neutral and ground Most of the modern euquipments are designed to
18. if you connect sensitive audio equipments to such UPS you can get all kinds of noise problems Mains quality problems are usually solved by using mains filters and isolation transformer Many professional studios used high quality on line UPS equipments to power the whole studio This UPS will filter out any problems from the incoming power and also useful protection against short mains power breaks Sources for hissing noise Sometimes the phumming in the audio system is nor the main problem but he hissing like noise Here are few noise sources and how to avoid that noise First and foremost there s what is called thermal noise It is generated by all active and passive electronicd components ncluding cold solder joints and is simply a result os all those un cooperative electrons smashign each other The only way to avoid the hermal noise in components is to make them very cold but this is not an option in audio electronics The gain structure of your system becomes on important to get madimum signal noise ratio Radio frequency interference RFI is a big source of all kinds of noises Many RFI interferences are easily un detected if you can t hear the actual radio signal Radio interference can easily take the form of hash that sound like white noise Proper grounding and shielding practices are your only real defence against RFI Digital noise usually takes a form of high pitched whine usually round 15 kHz or so but at lowe levels can
19. impedance isolation between the the cable TV conductor and the A V system and the cable TV shield and the A V system And the right adapter for this is the same isolator to the antenna wire discussed eariler on this document This method is usually the most effective and is the most inexpensive solution The picture below shows one possible interconnection of PC with DVD drive AV amplifier and a TV cable TV video cable audio cables video cable Here is another quite propable configuration you might encounter This is an example of properly wired system with a TV and an ampldifier with a tuner and both wired to the antenna connection on the wall isolator PER _ TV Computer cable TV video cable audio cables II isolator lt k AMP radio antenna As you can see you need two antenna isolators for this case One for TV input for solving video humming bars problem and another for tuner antenna connection for solving audio humming Audio video and computer systems with many grounded equipments Even if you have multiple mains sockets in your room to take the power for everything from a single socket run it through a mains filter if you want then connect everything to that as a tree Sometimes buildings are wired with a lot of electrical distance between the separate socke
20. in applications where complete electrical isolation is necessary There are some this type of isolation devices on the market and some special video distribution amplifiers have this kind of option built in Ground loop elemination does not always ask for a complete isolation of the grounds There are passive hum suppressor transformers which will very effectively remove the hum from the video signal typically around 40 dB hum level reduction but do not effect the video signal otherwise Those special transformers act like a common mode coils which stop the annoying ground loop currents on the shield of the coaxial calbe but provide a straight path for the signal inside the cable This kind of devices are capable of passing the signals from DC to tens of MHz without problems This type of hum suppression transformers have found their way to the professional video application rental companies and comouter video applivations computer to video projector connections The transformers of this type are usually called hum bug transformers humbucking transformers anti hum video transformers or hum suppressor transformers Generally term hum bugger refers to any circuit often a special coil that introduces a small amount of voltage at power line frequency into the video path to cancel unwanted ac hum There are also special wideband isolation transformer which can isolate video signals A transformer which can nicely transfer the whole video freque
21. in the NEC Shared neutral problems Non linear loads do not draw current in phase with the voltage waveform This causes distortion and harmonics to current waveforms As the result of this the currents sent back to the source in neutral wire is additive the currents do not cancel each other like the case in neutral load case NEC allows multiple circuits to share a common neutral wire which can lead to overloaded neutral wire if all the circuits are loaded fully with non linear loads IEEE standard 1100 specifies the need for dedicated circuit for computer equipment and neutral conducting impedance and sizing requirements Use of the counduit as ground According NEC the conduit or piping that electrical wires is run is allowable as ground IEEE standard 1100 recommends that electronics loads be grounded with separate equipment grounding conductor and this equipment grounding conductor must be insulated from the conduit ground Isolated Ground wiring practices Isolated circuits were supposed to solve the grounding issues faced by today s computer equipment In reality the installation of those those circuits is seldom done correctly The NEC gives very little details about installing the isolated grounds where IEEE Emerald Book gives specific procedures for installation and mainteance of isolated ground circuits The users of computer systems are suffering this discontinuity between IEEE and NEC guidelines Finding the power problems
22. metal parts on the equipment Within the building the grounding connections of all electrical receptacles are wired to one another and are connected to the water piping This ensures that all electrical equipment with exposed metal parts has these parts electrically connected to each other and to exposed metal fixtures in the building such as water fixtures The hot and neutral wires are interchangeable as far as the equipment is concerned Both are power carrying wires One of the power carrying wires is grounded for reasons of safety Grounded equipments Grounded equipment wired from mains voltage has three wires going to the equipment live neutral and ground Live wire is one of the the phase wires from the 3 phase distribution systems Neutral and ground wires are the same as in 3 phase distribution systems The equipment load is connected between the live and neutral wires like in the picture below Here the two upper wires are the live and neutral wires There is not much difference which one of those is live and which one is neutral because modern equipments are designed so that this does not matter In some countries the power connector is designed so that you always know which wire has live and which has neutral in it In some countries for example Finland the power connector is designed so that it can be put to the connector in two ways The third wire the lowest one is the ground wire The ground wire goes to the equipment metal c
23. noise and hummign problems are the reasons to go to digital audio transmission and it is quite sad that some manufactuers put out products which can t usually fulfill their promises in real life applications because of the S PDIF interface ground loop problem Solving the problems with S PDIF If your sound card equipped with optical S P DIF Toslink inputs and outputs try to use them instead of coaxial ones The optical cable will mode the digital audio signals but at the same time provides a complete galvanic isolation between equipments So optical interfaces are free from humming If you want to use the coaxial output and your equipment with S PDIF output lacks the output isolation transformer on S PDIF connection you have to make your own extra isolation transformer Elector Electronics magazine issue 7 8 1999 recommend building the transformer for S PDIF isolation in the following way The transformer must have good coupling factor so the transformer core must be a toroidal core made of high permiability material The prototype described in the magazine uses Philips Type TN13 7 5 5 3E25 core which has permiability rating yt of 4500 THe primary and secondary windongs consisted of 6 turns of 0 5 mm diameter enamelled copper wire laid on opposite sides of toroid The transformer used in this prototype was described to have a bandwidth raged from 50 kHz to 17 MHz which is more than adequate for an S PDIF link The transformer should be fi
24. often injected into the circuit by filter caps or bypass caps that were placed into the circuit to filter a signal or chip So the best way to keep this noise out is to create a separate analog ground Separate grounds does not always mean totally separated Most analog ground and power splits are done by either just isolating the plane and not allowing the digital signals to flow over it There is generally a single point connetion between the DIGITAL and ANALOG grounds More than one point opens up the possibility of ground loops which cause the ground noise form the digital side to enter to your analogue electronics ground You should not run digital signals over or directly next to your Analog signals or planes This will result in capacitive inductive coupling to the quiet Analog planes and or result in horrible signal quality on the digital signal as its return current which normally returns on the plane directly below the signal is forced to travel around the isolated analog planes The need to have separate grounds in a printed circuit board or in a system is usually discussed and decided upon before the design begins Often when noise and other problems are perceived to be a possible problem the designer will use separate analog and digital grounds in an effort to be conservative Sometimes he s right and sometimes the grounds are separated needlessly The worst possible outcome is to design and build a printed circuit board with a comm
25. problems when all of the following thing are true e None of the wires in the loop carry any current e The loop is not exposed to external changing magnetic fields e There is no radio frequency interference nearby If there is any current folowing in any wires there is then some potentital difference which causes current to flow in other wires also which causes problems The loop will also act as coil and pick current from the changing magnetic fields around it Wire loop acts also like an antenna picking up radio signals What size of ground potential difference problems we are talking about Literature is speaking about Common Mode Noise of 1 to 2 Volt in well grounded plants and over 20 Volts in poorly grounded plants Literature is also speaking of the current measured on a main service grounding in a large building in terms of Amps Where does this current and voltage difference come from Current leakage of condensators between hot and ground and between neutral and ground in for instance main filters cause current in ground wires and ground loops The leakage current is typically measures in milliamperes typically less than 1 mA in computer equipments per equipment When you sum up maybe hundreds of such equipments you can easyly get amperes The capacitance between line and ground of large heaters and motors for example can be much larger than the capacitance in filter capacitors Currents from this source are usually of t
26. reducing the current flowing in the loop which will reduce the voltage dops on the cable shields and equipment that reduces hum Those coils can reduce the currents on cable shield very effectively because they have very high impedance at 60 Hz and above and there presents a high impedance to common mode signal differentials between the input and output Earth loops typically have low resistance a quite the inductance will not have to be very huge to start to help The coil itself will then have quite much voltage difference on the input and output grounds the potential difference is now over the transformer insted of distributed to whole cable but the common mode coil construction guarantees that this difference is not supped to the differential signal inside the cable Since the signal and ground lead are coincident the differential signal is unaffected Hum reduction transformers or common mode coils are constructed with either 75 Ohm twisted pair made of fine wire or coaxial cable wrapped around a very high permeability core Most basic hum isolation transformers are basically just coax cable wound on a toroid type core They work by mutual inductance The coax cable is wound around a transformer core so that both the inner and shield of the cable become inductors The tight coupling ensures that any voltage in the shield caused by variations in earth potential are transformed into the inner conductor The method is an ancient idea and can cope wit
27. separate ground path is directly related to the quality of the chassis green wire ground pin combination When the ground pin is removed the separate ground path is destroyed and then fault conditions may cause shock hazards Grounding and interference susceptibility Whenever audio equipment is operated without a ground floating chassis strange things can happen Under certain conditions the amplifier will be more susceptible to radio frequency interference picking up radio stations or CB radio Also without a suitable ground amplifiers sometimes hum more when the musician picks up his instrument and provides a pseudo ground through himself The only solution is to find a ground point to connect to the chassis Sometimes this may just cause more problems than it helps Grounding in wiring Today s modern US mains cable consists of three separate wires black white and green The green wire is always connected to the large ground pin on the plug and the other green end connected to the chassis of the equipment The black wire is always considered to be the hot wire and as such is always the leg which is connected to the switch and fuse The white wire is always the neutral or common wire European coloring is a little bit different The ground wire is here green wire with yellow stripe Neutral wire is blue Live wire in Brown additional colors for the live wires used in 3 phase systems are black and black with white stripe
28. signal transferring and must use shielded wire for optimum performance The only option then is to eliminate the difference in potential between any points wired with cable Star grounding solution There are a number of ground schemes intended to eliminate ground loops The most common is called a star ground In astar ground a point is chosen as the lowest potential There are conductors radiating in as many directions as necessary from that point hence the star name Those points should end up in every room that will have equipment with signal cables When all the ground conductors to star central point are of equal length all theends of the star are by definition at the same ground potential and signal wiring between any equipment grounded to any of the points of the star will also be at zero potential Therefore no ground loops are created The idea that the ends of the star are at equal potential because they are equal length is critical to the success of this configuration In order that the ends of the star are very low potential low resistance they must be large gauge wire Wiring between buildings You can almost guarantee a s serious ground loop if you are running between two buildings This is because each building probably has its own source for power from the power company and each building has its own central safety ground point Since this point is not the same point for both buildings and since the ground in one buildin
29. simple Many audio manufacturers conciously or unconsciously connect balanced cable shields pin 1 in XLR connector sleeve on 6 3 mm jack to audio signal ground instead of the equipment case ground where is is suppored to be originally connected The result of this design choise is that any currents induced int the shield modulte the ground where the shield is terminated This also modultes the signal referenced to that ground and the result is typically annoying humming noise Unfortuantely the practice of connecting noisy cable shields to audio ground is very widely spread This improper arrangement of shield grounds amazingly sometimes achieves somewhat acceptable performance It performs well in many stadard qudio equipment bench test but tge peformance on the field can be quite much varying This means that getting good performance from such system need quite much testing and tweaking including ground lifts and isolation transformers The hum and buzz problems with too many balanced equipments with signal grounded shields habe given balanced equipments a bad reputation This has created great confusion among system designers and users Unfortunatley this is the situation where we have to live in The truth of a balanced interconnection is that a properly designed and built balanced interconnection is very much better than any unbalanced interconnection in rejecting humming noise Properly dessigned balanced interconnection means that for fully bala
30. so that danger of electric shock is prevented in this way Ungrounded power connection needs only live and neutral wires oag m Connectors used in ungrounded equipments The most common connector in small electronics in Europe is so called EURO connector and is standardized in EN 50 075 This connector is designed so that it can be used in most parts of Europe EURO mains connectors can typically handle only 2 5 ampreres of current Typically the connector is a molded plug which is permanently connected to the cable and the plug can only be bought with the cable included Mains plug used in USA Ungrounde plug is quite commonly used in small light and home electronics like TVs VCRs etc Nowadays many two prong devices have one prong wider than the other This is so that the device could rely not guaranteed on one specific wire being neutral and the other hot This is particularly advantageous in light fixtures where the the shell should neutral safety or other devices which want to have an approximate ground reference ie some radios Many television and stereo components as well as appliances are being fitted with polarized plugs which have a wider spade for the neutral line cord wire In some equipments a bypass capacitor which is wired between the white neutral wire and the equipment chassis ground Capacitor offers a relatively low impedance to high frequencies such as generated by radio stations an
31. to makse sure that the the fuse blows when something gets short circuited to ground wire for example cable insution breaks inside the equipment and touches the grounded metal case The grounding system is primarily designed for electrical safety in mind The Protective Earth connection should be able to carry a heavy current to protect the user from live to chassis faults by ensuring that the fuse or circuit breaker will operate so the requirement is that the Protective Earth conductors can carry a 25A fault current for at least 1 minute The grounding system in the building electricity distribution has only effect on the electromagnetic environment inside the building which you must understand Unfortunately all building have big electrical equipment such as air conditioning units refrigerators washers dryers and other high current devices connected to the building ground the same ground you use for your AV system Computers and other equipments which use stiched power supplies generate harmonics to the electrical power which usually end up being noise in the gounding system Light dimmers are also a storng source of interference and some of it typically ends to the ground wires also Thus the chances of getting a clean ground in a typical audio visual installation is slim especially in large commercial buildings hotels hospitals or convention centers Grounding practices in buildings Electric power distribution throughout Finland and many parts of
32. video systems around which need particular DC reference level but there are many which are AC coupled Some of the isolation transformers are only designed for CCTV other not so demanding applications application where more signal distortion is accepted than in broadcast industry So a video isolation transformer might be OK for a security camera installation if a complete isolation is needed but I would not put it on any professional video studio system More information Extron Electronics has a good articles about video cabling ground loops their web site Those documents are really worth to look at Commercial video ground loop problem solution products Here is a list of products have seen on the web to reduce video hum have not tested any of those products Active devices e CVDA 6 MX one input six output isolating composite video distribution amplifier from Extron Electronics e Hum Nulling Video Distribution amplifiers from Video Accessory Corporation e Kramer Electronics OC 1N Optic Ground Isolator e Multidyne VPDA 100 distribution amplifier with back porch clamp for hum cancelation e Practel GA 409 Isolating video amplifier e HBVB VDA Video Brick Humbucking Video Distribution Amplifier e VL 2 Video Line Isolator from Video Accessory Corporation provides 1500V peak isolation with optional audio isolation Passive devices e ADC HUM 1 e Allen Avionics Video Hum Eliminators and Video Isolation Tran
33. wire exposed to avrying magnetic field will have an AC voltage induced to it To avoid magneticly picked noise in the cable it is a good idea to keep the audio cables at some distance away form devices like high current carrying cables light dimming systems transformers any equipment which has big transformers and large electrical motors All of those can be a serious source of electromagneti noise which can enter to audio cable and cause humming noise Unbalanced audio connections will pick magneticly coupled noise easily The normal cable shield which is very effective in shielding against capacitively coupled noise has almost no effect on magnetically coupled noise Only effectively ways to fight against magnetic noise in unbalanced connections are keeping the cables away form magentic noise sources magnetic fields drop very rapidly with the distance from the source so even few centimeters movement of cable can help to reduce the problem or placing lot of iron or other magnetic material between the noise source and the cable like putthing the audio cable inside an iron tube The only cable mechanical constuction which can avoid magnetic noise pickup in audio cable effectively is making cable such that two signal conductors have exactly the same distance to the magnetic source Thightly twisting of balanced signal conductors help to make average distance of each conductor to any doutside magnetic field source the same Combination twisted pair
34. If you can t get clamp on meter you can try to measure the current flowing on audio cables by removing the cable from one and and connecting an ordinary multimeter between the ground pin in the audio wire and the audio connector ground pin in you equipment it was connected to How to make connections to other equipments not part of the system When connecting a system which has well done non humming grounding and a system running from another power source the signal grounds of the systems need to be isolated With balanced audio signals lift the shields at the inputs With unbalanced audio or video signals use an isolation transformer or wire the signals to balanced input where the ground connection is left open Ather rack wiring ideas where ground loops are not a problem If all your equipments are just in one rack then you can also use another wiring method Instead of avoiding gound loop you can try to make the whole system to have a very stable common grounding This stable common grounding can be achieved by making sure that all equipments have very good connection to metal rack The mains power to all equipments mut be take from one power distribution unit installed to the rack case If all wirign is done using short wires the system does not have grounding problems because there can t be any significant ground potential differences because all equipments are well tied to one very low resistance ground the audio rack the metal equipment cased ti
35. Three phase distribution is a very common in big houses offices shops factories etc where lots of power is consumed and big motors are quite propably presents In Finland and many other countries 3 phase distribution 230V from phase to ground and 400V from phase to phase is very common in even smaller houses typical house in Finland has 3x25A three phase main feed Three phase power most oftehn used in permanently wired electrical equipments like electrical ovens and large motors In normal residental homes there are no normally anu power outlets for 3 phase power In places where there is need to power equipments which consume more power than what is available from one mains outlet there are usually 3 phase connectors available Examples of this kind of places are constructuction sites factories places where large electrical tools are used and entertainment venues for large PA system and lights The most common 3 phase outlet you might to see is 16 ampere 3 phase 400V voltage between phases outlet which uses round red CEE 17 connector Other popular models of this same round red connector can handle 32A 63A and 125A Three phase distribution in USA You re most likely to encounter a 3 phase circuit that shows 110 volts between any hot and ground and 208 volts between any two hots Those 3 phase distributions are commonly used in place where there are large motors or otherwise much consumption of electricity Examples of this kind of places
36. a day when audio transformers were commodity items and they were in everything but now they aren t so common and as a result the cheaper ones aren t in the catalogues any more and the better ones ccost more than they used to because there aren t the economies of scale If you get a cheap transformer you will eventually get depressed with the way it sounds and you ll be spending the money on a Jensen a Reichenbach Sowter or Lundahl or any other reputable manufacturer anyway So you might as well just get it now and save the wasted time effort and money Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Digital audio and groundloops Basics of digital audio interfaces Digital audio connection AES EBU and S PDIF are not by themselves sensitive to groundloop problems A small ground loop hummign does not change the digital data at all If the ground loop problem is really serious then some problems are possible Basically in digitla interfaces the signal either get through correctly or not Although the digital audio connections themselves are not much disturbed by groundloops they can be sometimes the connections which form the loop and cause a noise entering to the analogue connections of the equipments on the both ends of the digital connection AES EBU and S PDIF connections were originally designed so thet they should be free from gr
37. age on both failing to get the circuit to work as expected no isolation and some that the circuit works well Radio Shack cat s 15 1140 and 15 1253 It is hard to say for sure what is the problem could the product with same code vary in this sense though product code staus same It is best to test by outself that the baluns you plan to use are really isolating If the balun is isolatating can be tested with multimeter measure the reistances between all input and output pins If there is no conenction found between input and output then this balun is suitable for this circuit If you experience radio interference picked by this circuit you can can try the following method to make shilding ogh the circuit better You can wrap the whole little assembly in aluminium foil and ground the foil to the cable cable shield But don t let it touch the other ground Aluminium Foil Shield connect to shield of incoming coax Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Ground loop problems in video lines What ground loops do to video lines As the source and destination of a video signal can be at differing ac or dc earth potentials earth loop currents flow and cause longitudinal hum to be introduced into the video signal Video hum is low frequency 50 or 60 Hz mains frequency or it s harmonics noise from the ground lines which has influ
38. al circuit or equipment and the earth or to some conducting body that serves in place of the earth When talking about grounding it is actually two different subjects earth grounding and equipment grounding Earth grounding is an intentional connection from a circuit conductor usually the neutral to a ground electrode placed in the earth Equipment grounding is to ensure that operating equipment within a structure is properly grounded These two grounding systems are required to be kept separate except for a connection between the two systems to prevent differences in potential from a possible flashover from a lightning strike The purpose of a ground besides the protection of people plants and equipment is to provide a safe path for the dissipation of Fault Currents Lightning Strikes Static Discharges EMI and RFI signals and Interference Improper grounding can create a lethal hazard Correct grounding is essential for correct operation nad safety of electrical equipments Grounding can solve many problems but it can also cause new ones One of the most common problem is called ground loop What causes the humming in audio systems Audio and video systems need a reference point for their voltages Generally referred to as common or ground although it may not be actually connected with the earth this reference remains at zero volts while other signal voltages swing positive above and negative below it Physically the common may be a wire
39. ality telephone line coupling transformers which have 600 ohm impedance This is the most commonly transformer type used in high speed modems Best of those are quite wideband devices far more bandwidth than usual 300 3400 Hz as used in telephone Using two of those transformers and few RCA connectors made quite satisfactory but not really hifi audio isolator The connetion is easy connect primary side of the transformer to one audio connector and secondary to other used EOP Z1612 transformers in my test circuit and got quite acceptable frequency response of 1 dB from 40 Hz to 20 kHz as you can see in figure below The bass frequency below 40 Hz is not good mink doe oo om Cc 100 1000 10000 The frequency measurements were made with Nacamichi T 100 Audio Analyzer and the isolator circuit was connected between it s 600 ohm output and 50 kohm input don t know if EOP Z1612 transformers are still available at Farnell but you can try If you are looking for other high quality transformers which could be a used would try ETAL P2001 haven t been able to test their performance in this application but they have proven to good transformers in other laboratory test and applications Avoid cheapest telephone and audio transformers because their performance is very poor at frequencies over about 5 kHz for example Radio Shack 273 1374 Transformer isolation using audio transformer One way got my hands on the component of
40. als guarantees that there will be voltage differences from one part of the building to another Running a shielded cable between the ends virtually guarantees a ground loop and there hum or interference of some kind The effect of this huge amount of noise varies In video circuits it show up as hum bars buzzing slow moving bars which wipe across the screen diagonally In audio it can be heard as hum buzzes or other constant interference In data circuits it can cause bit error rates which can shut down a system where nothing else is actually wrong Quick fixes for problems Quick fixes are available for all these problems which attempt to eliminate the problem without addressing the actual problem of poor grounding In the video world one can purchase a hum bucker This is a torroidal transformer wound to reject 50 Hz or 60 Hz the frequen cy of the power line and most prominent frequency in the noise of a ground loop They are generally quite good in rejecting the mains induced frequency but are generally a little bit bulky somewhat large and heavy to be put in the middle of the cable connection expensive usually 100 200 per line and hard to find For audio wiring the insertion of an isolation transformer provides galvanic isolation which prevents ground loops Transformers are passive devices which use two coils of wire wound on one core made of magnetic material like iron or ferrite While the signal can cross between the two c
41. an cause problems from very distorted video signal to damaged differential video amplifier If the voltage difference is a substantial proportion of the DC supply voltage of the amplifier you will probably have trouble using an amplifier alone It is a good idea to measure the voltage difference before using differential video amplifiers to be sure not to damagze them Measuring can be done using a multimeter check using both AC and DC ranges or better using a scope earthed to the mains supply and put the probe on the earth connection of the incoming video cable If you many potential difference which are many volts then you have quite propably something wrong in the grounding of the building and you should consult a qualified electrician to check and correct this potentially dangerous problem Good back porch black level clamp If the video signal input has well designed fast black level clamp circuitry that can also solve small common mode noice problems caused by ground loop Back porch ground level clamp circuit adjusts the black level of the video circuits according the incoming video signal If black level clamp circuit is active circuitry which samples the black level saparately for every can line the ground loop bars are quite effectively eliminated because the the low frequency noise 50 Hz power or harmonics is sampled at start of every scan line and suppressed then from the rest of the line This works quite nicely with those low frequency hum
42. and money Multiple room systems Depending on your local electric wiring regulations the potential of the ground terminal in the wall outlets will be slightly different in different rooms due to other loads in the building and the potential will also be different than at a grounded antenna or CATV feed The voltage difference is small usually about 1 V If you have grounded equipment either through the wall outlet or through the antenna system in different rooms and you connect an unbalanced cable directly between the equipment a large current up to several amperes will flow in the shield and it still can not completely remove the voltage difference between the rooms and you have hum added to the signal When this ground loop current flows in the shield it will also induce some hum current into the signal lead worsening the situation even further So if you are running signals from one room to another it is a very good idea to isolate all the unbalaced connections using suitable audio isolation transformer Other possibility to get rid of that problem is to use ba anced interconnections if your equipments have such those are uusally only available on professional audio systems equipments Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Other than ground loop sources for humming Not all humming and noise is causd by ground loops Th
43. are factories big shops large office houses and similar buildings Getting a 3 phase feed to your home house in USA can be ridiculousiy expensive or impossible Residential houses are typilly wired using normal 220 110 wiring where there are two 110V live wires 180 degrees in phase with each other and they share a common neutral wire Normal electrical outlets are wires between one 110V live wire and the common neutral wire Some high current loads air conditioning etc are wired between two phase wires so they get full 220V voltage Grounded outlets While you may initially assume the three pronged cords to be inherently better due to their ability to introduce multiple grounds to the audio system they actually serve to further complicate the ground looping problems Three pronged grounded outlets are better for electrical safety Grounded outlets they are also good when the electrical distribution and audio wiring is well designed and constructed The 3 wire system that the user sees is actually derived from three phase distribution which uses a 5 wire system In the 5 wire system there are 3 hot wires 1 neutral wire and 1 grounding wire The common 3 wire receptacle uses only one of the 3 hot wires A typical office wall outlet has three electrical connections which are the hot neutral and grounding wires All office equipment requires only the hot and neutral wires to function The third or grounding wire is connected to exposed
44. as an AM radio antenna Any large loop of wire makes a good AM antenna These antennas are especially adept at picking up AM broadcasts if most of the loop is vertical e Cross Talk Ground loops can cause one signal to interfere with another because every cable should ideally return through the corresponding shield conductor but there s an alternative path through the other shield conductor which causes undesirable voltage differences to nearby cables Ground loop isolation in video lines Isolating video signal is more complicated than isolating audio or antenna signals because the DC level of the video signal is important and video signals have very high frequency spectrum normal composite video can have bandwidth from 50 Hz to 6 Mhz Isolating video signal needs typically active technology which involves electro optical isolation or differential amplifier with a floating ground on the input connector Those both technologies are usable in real world situations Differential input with floating ground works nicely for small ground potential differences and this approach is used in some professiona video equipments some video projectors have seen have had differential inputs and option to disconnect input ground connection Differential inputs are also used in applications where a video signal is transmitted through twisted pair wiring some CCTV applications which use twisted pair interfacing equipments Electro optical isolation works well
45. ase and is there for giving safety to the user When the metal case is tighly connected to the ground through the grounding wire then if there is something wrong in the equipment like broken insulator or water leaks inside equipment you just blow the fuse instead of getting lethal voltage to the case Grounding system is carefully designed so that it provides safety to the user This includes the color coding that the safety ground wire is never mixed with any other wire nowadays the safety ground wire must be alway yellow green colored in Europe The electrical connectors must be designed so that the safety ground connects before other pins and disconnects last When wiring the safety ground wire to connectors the wire to it must be a little bit longer than what goes to other pins so that if the cable gets loose it is the last one which looses the connection Connectors used in grounded equipments USA mains connector The power supply cord used on most modern electronic equipment has a three pin plug NEMA 5 15 The connector has place for two flat power pins for live and neutral wires and third round pin is ground Typican mains receptable in wall in USA nowadays is a grounded 15A power outlet A correctly installed receptacle should always be vertical with the ground pin beneath the two parallel blade slots There is also a 20A version of the mains connector which is used in some heavy equipments where 15A of 120V power is not enough Man
46. asily indice magnetic field around them and pick up magnetic fields If your power cables are tightly coiled they can cause large magnetic fields and heat too much up if loaded very much Coiled audio cables can easily pick up interferences If you have spare cables you need to put somewhere do not coil them just to a single coil but instead put them on 8 shape to ground this shape greatly reduces the magnetic interference problems Star Grounding One Path to Ground Star grounding is the name Audio and Electrical engineers use to describe a wiring system where all the electronic SIGNAL grounds cable braiding jack sleeves or pin 1 on an XLR either e Flow through in a serial manner without coming into contact with the electrical or chassis ground on the way or e Join the mains power supply ground the really really big thick green wire at the one place and one place only This system removes the possibility of a potential difference between mains grounds or the connection of mains grounds being duplicated in an Audio system With star grounding systems the centre that is usually chosen is either the Main Mixing Console or the multicore snake or patch bay that is usually plugged or hardwired into it The reason for this choice is that most Audio Systems only have one main mixing console and the vast majority of devices are connected to it Conformity with this grounding system will usually ensure that your system no matter how large will remai
47. ated sources of humming e Why do you have to use a separated conductor for grounding and for neutral Consumer audio and video systems e Audio signal grounding in audio equipments e Solving AV problems in typical home system Professional audio systems e Why professional sound systems suffer from ground loop humming e Advice on setting up hum free safe PA system e Balanced power systems e How to correctly wire audio equipment racks e Methods for breaking ground loop e Reducing microphone hum e Wiring audio equipment racks and studio e Ground lift circuits e Audio isolation circuits and how to build your own e Digital audio and groundloops e Grounding and Rack Installations Professional video systems e Antenna cable isolators and how to build your own e Ground loops in video systems e Grounding and Rack Installations Data networks e What causes computer problems e Datacom isolation e Mains isolation possibilities and why does it not help always Laboratory environment e Mains isolation possibilities Design tips e Design tips for balanced audio connections e Ground loops inside circuits Other related information e Other noise and hum sources than groundloops Useful links to other sites and articles General tutorials Curing Ground Loops Grounding tutoral on grounding and groundloops Ground Loops Wha
48. atre system with TV VCR and radio reciever all connected to the mains antenna outlet The system components have all ungrounded 2 pin power connectors The ground loop is formed through antenna wires but the loop is small and there is normally nor current flowing in those wires so no humming problems are expected unless there is strong magnetic fields nearby If there is magnetic fields nearby then the problems can be reduced by keeping antenna and audio cables near each other Example systems with two ground connections and potential ground loop humming problems e Typical home stereo system where all components have ungrounded two pin mains connectors The stereo system is connected to PC soundcard PC has grounded powwr connector and the receiver is connected to the wall antenna connector Problematic ground loop is formed by the connection between the ground pin in PC mains connector and the antenna connector shield in the wall e Typical home theatre system where all components have ungrounded two pin mains connector The ground ground connection is formed through TV and VCR which are connected cable TV feed e Typical home theatre system where all components have ungrounded two pin mains connector The ground ground connection is formed through TV and VCR which are connected cable TV feed and through PC connected to system e The audio system has two or more equipments which have grounded power connector and which are connected to different
49. ay have been converted e g an old TT system might have been converted to TN S or TN C S but the old earth rod was not disconnected index back site search acronyms discussion mail to a friend post message Solving the humming problems of computer soundcards and home theatre systems Getting rid of ground loops is not easy Finding them is even harder LiveDV magazine has published a good tutorial Soundings Getting Wired January 1996 how to find and solve ground loop problems in typical home AV system which consists of computer and other AV equipment receiver amplifier VCR etc The only acceptable method for testing is to remove and disconnect everything Then reinstall the equipments and connection piece by piece Stop when the hum becomes audible and fix the problem in the last piece of equipment that was installed If you have equipments connected to many power outlets then try to connect them all to one grounded extension cord and then plug this cord to one grounded outlet This solves usually many problems because this creates star like grounding scheme for those equipments But the following star grounding scheme is effective if the equipments do not have any direct connection to other equipment grounded elsewhere transformer isolated connections are ok Computer soundcard problems Typical computer soundcard ground loop situation Typican ground loop humming problem occurs when you connec
50. be mistaken for hiss Digital keyboards lighting computers effect processors and just about everything which uses fast clock pulses can cause this problem This includes the switched power supplies in many modern audio equipments and some amplifiers Some poortly designed equipments can radiate excessive levels of digital noise often via mains AC cord Carefully routing the AC power cords and audio cables away from each other can help to avoid this problem Digital noise can also be in forma of radio frequency interference so do not place a wireless microphone receiver near difital effect units and computers An electronics component which is failing can be a source of noise You cqan identify this hiss because it is not consistant It will vary fairly rapidly depending on run time and temperature The noise can also be popping noises similar to popcorn To get rid of the problem locate the bad part equipment and get it replaced or repaired One problem is the poorly designed equipments Some companies use active components with poort noise performance You can get rid of this kind of problem by replacing the nasty components or the whole equipment If you must use the existing equipments as it is then careful gain structure adjustment can usually keep the noise at acceptable levels Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Why do y
51. between the 2 hots is 240 and the voltage from either hot to the neutral is 120 half Normal electrical outlets are connected between the neutral and one hot wire Some heavy loads like air conditioners are connected between those two hot wires and receive the full 240V load House wiring details What does a typical power outlet look like A typical office wall outlet has three electrical connections which are the hot neutral and grounding wires All office equipment requires only the hot and neutral wires to function The third or grounding wire is connected to exposed metal parts on the equipment Within the building the grounding connections of all electrical receptacles are wired to one another and are connected to the water piping This ensures that all electrical equipment with exposed metal parts has these parts electrically connected to each other and to exposed metal fixtures in the building such as water fixtures The hot and neutral wires are interchangeable as far as the equipment is concerned be warned that there are some exceptions in some countries Both are power carrying wires One of the power carrying wires is grounded for reasons of safety In many parts of Europe nordic counties Germany etc the normal 3 wire receptacle is symmetrical so that the neutral and hot wire connections can be swapped by simply rotating the plug A A J Earthing of Electrical Installation Each circuit requires an earth conducto
52. bstation TN C S Protective Multiple Earthing Supply combines neutral and earth but they are separated out in the installation TT No earth provided by supplier installation requires own earth rod common with overhead supply lines T Supply is e g portable generator with no earth connection installation supplies own earth rod Ways to provide grounding Inside or nearby your consumer unit fuse box will be your main earthing terminal where all the earth conductors from your final subcircuits and service bonding are joined This is then connected via the earthing conductor to a real earth somehow The following earthing conventions are used in UK TN S The earthing conductor is connected to separate earth provided by the electricity supplier This is most commonly done by having an earthing clamp connected to the sheath of the supply cable TN C S The earthing conductor is connected to the supplier s neutral This shows up as the earthing conductor going onto the connection block with the neutral conductor of the supplier s meter tails Often you will see a label warning about Protective Multiple Earthing Installation Do Not Interfere with Earth Connections but this is not always present TT The earthing conductor goes to one or more earth rods one of them possibly via an old Voltage Operated ELCB which are no longer used on new supplies There are probably other arrangements for these systems too Also a system m
53. check by disconnecting everything and putting everything back together The check gave following conclusions e When I only disconnect my computer s power cord 3 prong the buzz goes away e When I only disconnect the soundcard from my receiver the buzz goes away e When I disconnect my TV and VCR the noise goes away Basically the hum buzz goes away when any of the following altered 1 Sound Card disconnect from receiver 2 Computer unplug from power strip 3 TV disconnect from receiver 4 Cable TV disconnect from wall How the isolators can be used to solve the problem The most effective way to stop this 50 Hz or 60 Hz noise is to break the galvanic connection which causes the ground loop You can either connect an isolator to the antenna wire b oe paanan isolator 555 lt a 2222nenn TV AMP Computer cable TV audio cable audio cable This is the only effective and safe solution to problems which deal with grounded outlets and radio TV cable antenna connection TV and audio system If you connect your TV or VCR to otherwise humless audio system you will quit epropably hear a humming noise 50 Hz or 60 Hz depending on the mains voltage frequency caused by current flowing between your equipment and the antenna connection in the TV The following example is a typical home setup where you have your multimedia computer TV and connected to your stere
54. ching the metal wiring conduit Twisted Pair Ethernet 10Baset T Ethernet used twisted pair wiring and RJ 45 connectors The wiring is completely transformer isolated in network card and HUB end 10Base T network using unshielded twisted pair wiring does not cause any ground loop problems If you are If you are working in enviroment where ground loops are very problematic then 10Base T network using unshielded twisted pair cables is one of the the safest choises It can cost a little bit more but is very flexible and you will save very much in long run in network trouble shooting costs The same which applies to 10Base T applies also to 100 Mbit s Ethernet which used unshielded twisted pair wiring 100Base TX Fiber optic links If you use Ethernet cabling with fiber optics those fiber optics links are free of ground loop problems because the systems on the ends of the cables are optically isolated from each other by the long optical fiber between them MIDI MIDI interface is designed for controlling musical equipments and the possible ground loop problems in audioo systens are taken to acount MID interface is designed so that the interface is isolated in the receiving end so that it does not make ground loops if wired correctly Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Isolatings mains power in laboratory enviroment Recomme
55. ction which is grounded only at the separately derived system from which the circuit is supplied It is permitted to pass through panelboards junction boxes etc without being bonded to the equipment grounding conductor which serves those devices thus minimizing electromagnetic interference It must be used in conjunction with an isolated grounding receptacle to be effective More details of isolated ground can be found at NEC 250 74 Exc 4 My understanding on using a term isolated ground is mostly for marketing purposes feel that their purpose is a marketing response to inadequate design by some electronic equipment manufacturers and to inadequate grounding practices by some electricians The ground terminal is isolated from the mounting yoke in conventional receptacles the yoke and the ground terminal are connected The idea is that the electrician connects a special clean ground to the ground terminal while the yoke and all other non energized metallic parts are connected to the dirty equipment ground How to avoid ground loop problems Most electronic equipment is sensitive to ground loops and ground induced noise A proper earth ground at the building services entrance is the first step to avoiding such problems In many cases a proper earth ground is provided by a connection to the steel rebar in the building s foundation All outside service grounds must be solidly connected to this ground point including power telephone and cable
56. currents into voltage fluctuations As a consequence of ground loop induced voltages the ground reference in the system is no longer a stable potential so signals ride on the noise The noise becomes part of the program signal Ground loop is a common wiring conditions where a ground current may take more than one path to return to the grounding electrode at the SERVICE PANEL AC powered computers all connected to each other through the ground wire in common building wiring Computers may also be connected by data communications cables Computers are therefore frequently connected to each other through more than one path When a multi path connection between computer circuits exists the resulting arrangement is known as a ground loop Whenever a ground loop exists there is a potential for damage from INTER SYSTEM GROUND NOISE A ground loop in the power or video signal occurs when some components in the same system are receiving its power from a different ground than other components or the ground potential between two pieces of equipment is not identical Usually a potential difference in the grounds causes a current to flow in the interconnects This in turn modulates the input of the circuitry and is treated like any other signal fed through the normal inputs Here is an example situation where two grounde equipments are interconnected though signal wire ground and the mains grounding wire In this situation there is 1A current flowing flowing in
57. d CB radios thereby providing them with a short path to ground in order to eliminate this type of interference and offers a high impedance to low frequencies not much mains current passes through it so there is no significant shock hazard Neutral wire is not very good ground in radio frequencies so this connection might cause more problems than it solves Sometimes the coupling capacitor from the neutral to the case can be up to 0 1 uF and if the neutral and live are for some reason swapped you can get over 4 mA of current flowing to the equipment case This kind of arrangement that live and neutral wires are handled differently inside equiments has not been recommended by international safety regulations for long time but it has been allowed practice in USA If you determine that you have a hot chassis with a system connected like this the solution is to simply reverse the plug if you can can Reversing the plug can sometimes solve interference problems In some instances in transformerless consumer receivers where the case was connected to the neutral side of a polarized a c plug via a 0 1 uf capacitor Since at the mains the neutral is grounded there may develop a small potential between the amp case and extended mains ground If there is any heavy power draw in the vicinity of the same circuit the potential may increase if wiring conductivity has decayed for various reasons Tomi Engdahl lt Tomi Engdahl iki fi gt index back
58. ding and Shielding for Sound and Video Clean Signals Pitfalls in Audiophile Systems for most designers technicians and users system interfacing and grounding practices are considered a black art but this column is intended to increase your understanding of these interfaces and offer guidelines for preventing and solving the inevitable real world problems Hum amp Buzz in Unbalanced Interconnect Systems pdf file Interconnection of Balanced and Unblanced Equipment Keeping Quiet learn to handle hum and buzz with a critical look at system noise from the ground up Power amp Grounding for a Post Facility Unconventional Approaches describes concepts like lean tech power and balanced power Sound System Interconnection RaneNote 110 describes the correct wiring methods for different audio cables Understanding Ground Faults loops Problem solving Getting Hum amp Noise to BUZZ OFF EARTHING Deerfield Lab Ground Loop Analysis and Solutions information on video interface ground loops Do You Hear Something Eliminating Hums and Buzzes Earthing Your Hi Fi Tricks and Techniques Equipment Maximization through Electrical Minimization tips for finding out ground loop problems some solving methods are questionable because of grounding safety issues Fixing Cable TV Hum in Audio Systems Ground Loops and Autosound Systems Tracking Down Ground Loops technical paper in pdf format Ground Loops or Let
59. dio Active Direct Box includes earth isolation e Leon Audio Passive Direct Box audio isolation transformer e Lundahl Transformers XLR inline transformer units for breaking up ground loop in audio systems e Pyramid RCA Isolation Transformer stereo isolator with RCA plugs designed for car audio e Radio Shack Ground LP Isolator 270 0054 cost about 15US RCA plugs for car audio Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message How to build your own audio isolator Building yourself an audio isolation transformers If you want to build one yourself you have to get two audio transformers which have 1 1 transformation ratio and greater than 1 kohm impedance There are high quality audio transformers in the markes that meet those specs but those can be quite expensive Another option it to use 600 600 ohm isoltation transformers widely available for telecommunications and other uses Those are not that high quality as good audio transformers but can be well adequate for many not so demanding multimedia applications like computer audio if suitable transformer is selected Isolation for unablanced lines Td Notice one thing in the transformer wiring Many transformers have the coil starting marked with dot If you put the audio signal to the transformer in such way that the center wire in RCA connector is always co
60. dio world there is a solution to ground loops called telescopic ground and Faraday shields A telescopic ground works only with a cable which is a balanced line that is one which has two wires to carry the signal and a separate shield In a telescopic ground the shield is connected only at one end This prevents the completion of the ground loop Best telescoping shield cables true telescoping shields are constructed so that they have two shields which are insulted form each other The idea is that you connect the inner shield to ground only at receiving end and the outer shield to ground only at the transimitting end In this way the ground loop is effectively broken but the RF shielding properties of the cable are still very good Double shields and the capacitive coupling between they are near each other in cable form a good shield for radio frequencies It has been claimed that telescoping a shield in cables with hybrid unbalanced banaced audio ystems is often very successful at removing noise The telescoping shield protects the inner conductors and drains away that unwanted noise to one location Shield effectiveness gets less and less as you travel further from the grounded end Telescopic grounds cannot be used in unbalanced circuits such as unbalanced audio interconnections and video coax as the two conductors necessary to send the signal include the shield That is the shield is both the noise reduction portion of the cable and a s
61. e These signals will cause currents to flow in the cable shields thus adding this noise directly to the audio signal Why grounding without problems is do difficult Virtually all data and broadcast construction projects run into problems of grounding These problems occur primarily because there is a conflict between issues of safety ground ing to prevent electrical shock and electronic noise reduction using ground as an electronic dump for noise and inter ference These two uses are often not compatible and can sometimes be in direct conflict with one another The ultimate purpose of good groundind scheme is he preservation and adherence to the safety aspects while obtaining the maximum noise reduction possible That is not usually an easy task to do Why ground loop is a problem Ground loops are a mystery to many people Even college trained electronic engineers may not know what ground loops actually are Engineers have either concentrated on power distribution for the electric company or on equipment that happens to plug in to the power distribution system Not much thought has been given to power distribution and equipment as a single entity where ground loops arise Ground loops are the most common cause of AC line frequency hum in sound systems Ground loops can be geenrally identified by a low hum 60Hz in the US 50Hz in Europe through the sound system A ground loop in the power or video signal occurs when some components in t
62. e ground currents on cable shield On the other hand EMC books and text talk about how important is to connect the cable shield on both ends to get good shielding against interference trying to get out from the cable and into the signal in the cable from external sources Cable shield connections are still controversial There are strong valid arguments both ways For cable shield connections there are four options with advantages and disadvantages 1 Shield grounded at both ends Good r f shielding but susceptible to ground loop currents that can be VERY large up to at least 100 A in bad cases 2 Shield grounded at both end with large area parallel bonding wire Good at r f and now the ground current flows mainly through the bonding wire but the intense magnetic field that may result is not good news The bonding wire size needs to be for example 10 mm 2 3 Shield grounded at one end only No ground current but not good at radio frequencies for which the cable is more than 1 8 wavelength long R F interference may actually be worse than for an unshielded cable 4 Shield grounded at the sending end and grounded through a capacitor may be two in parallel for effectiveness from about 100 kHz up to 1 GHz and beyond at the receiving end Good at r f if the capacitor type and positioning are correctly designed and no low frequency ground current One capacitor needs to be of the type with an integral spark gap so that it is not damaged b
63. e of grounding from the hub to the console Make it big Wire the power supply to the console Now cable other console items back to the hub NO OTHER COMPLETE ground connection allowed between hub and any other terminal point Open the shield for the sake of unformity at the terminal end for every piece of shielded cable leaving each shielded cable grounded at the hub end Your single piece of grouding is what keeps it all safe and silent Spoke 2 From the hub run AC to perhaps a free standing tape machine Ground it back to the hub As above run signal cables to the hub grounding the shields at the hub only Spoke 3 From the hub run AC to perhaps a rack in another studio in your plant This new rack becomes a hub for the world it lives in and it has ground wires emanating from it to new terminal points Spokes 4 through 400 As above NEVER NEVER NEVER Here it is here is what keeps it all honest and hum free NEVER take a shortcut and run a cable directly from one terminal point to another ALWAYS run such cabling back up the hubs spokes to the main hub and then down the appropriate spoke to the desired terminal point tapping into hub grounds all along the way How to test that you don t have ground loops Buy a digital clamp on current meter There should be NO current on any ground wire None If you can measure current flow on a ground wire then fix it you either have a circular path or else a faulty piece of equipment
64. e safe from shock hazard because the metal housing was not connected to either wire of the line cord called floating case One of the problems with appliances and equipment which have a floating metal case is that a shock hazard exists if the case comes into contact with the hot wire This so called fault condition may happen in many ways with some of the more common causes being a pinched line cord failure of installation systems or movement of components due to shock or vibration which will cause the hot wire terminal to touch the case Naturally if for any reason the case does become live then a person touching it may be shocked if he is grounded If this hot chassis is connected to another chassis or instrument by a typical shielded cord then that chassis or instrument will become hot also The entire purpose of the present three wire system is to provide a separate ground path which will effectively eliminate any possibility of shock If the live wire touches the grounde metal case the ground connection in the case causes that the situation becomes a showrt circuit as drawn in picture below Service Entrance Panelboard Receptacle This short circuit situation causes very high current surge to flow in the circuit which will cause the distribution panel fuse to blow almost immediatly The cureent in short circuit situation can be pretty high because of the low resistance of the mains distribution wiring The integrity of the
65. e strong magnetic fiels inside them so typically those motors also cause a noticable magnetic field arount the motor If your equipments are near some powerful electric motors you might have quite strong magnetic fields near your equipments Remeber also that fans used in air conditioning and in many equipments can generate problematic magnetic fields so it is a good idea to keep yout equipment away from those Radio interference interference Radio interference can cause serious noise problems to the audio system which is not properly shielded The most typical noises are all kinds of interference noises and the transimmission is heard in the audio system Some strong radio transmitters and industrial systems which use radio frequency signals can sometimes be modulated with mains frequency humming for example because of poor power supply If this kind of modulated radio frequency signal enters to your equipments it can cause mains hummign like interference which is very hard to get rid of Main voltage quality problems If mains voltage is not nice sine wave then it contains harmonics which can usually more easily enter to the circuit than 50 Hz mains Typical sources for this kind of power quality problems are high frequency interference caused by dimmers Computer power supplies and fluorescent lighting can cause harmonics to the power and thus interference to sensitive equipments Some cheapest UPS equipments put out vety low quality main voltage and
66. ed poer is When the power is balanced the mains cable has less electric field around them so they should induce less noise to nearby audio cables Those clames are partially true partially quite nonsense If you placed an unscreened cable next to a balanced power cable would expect that less noise hum would be picked up as the hum is capacitively coupled If you placed a screened cable next to a balanced power cable quite little difference would result if any The capacitively coupled signal is now intercepted nearly completely by the screen Practically only the magnetically coupled component will reach the screened signal wire s Magnetic field around the cable will be practically the same whether the mains cable is balanced or not as there is still the same mains current flowing up one wire amp back down the other Balanced power can solve the ground leakage problems caused mostly by computers and baddly designed audio equipments mostly guitar amplifiers When the leakage current is redicud to none using balanced power there is less noise in the ground wire If you have a chassis leakage problem balanced power will radically reduce your noise floor If you don t it won t help in your system If your noise is all hissy white noise from noisy electronics balanced power won t do a thing If your noise is mostly hum from power supply leakage on bad equipment especially old guitar amps it can do an amazing job If it s hum from ground loops it
67. ed together Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Methods for breaking ground loop Fort check that you have made the cabling between equipments properly Proper audio cable connection methods are essential in getting humm free system Rane technical note Sound System Interconnection is a very good source for information how the audio wiring between equipments should be connected This is a well worth to read article Breaking of ground loop can be done in many ways some which are better and some are less good Dangerous method break the mains ground connections Logically you could think you could eliminate ground loops by disconnecting the power cord ground pins on all your gear Some people might try to break the ground connection by cutting the grounding pin in the connector using cheater plug cutting the ground wire in equipment taping over the grounding connector etc Do not do this Removing the ground connection isn t right It is against electrical safety regulations and potentially very dangerous Removing ground connection can defeat the actions of your noise filter or spike protectors inside the equipments If the ground connection is cut then a fault in the isulation inside equipment will cause dangerous voltages to the equipment case instead of burning a fuse Removing the ground connection from the equi
68. em may become such that you will reach the maximum gain travel of a fader at your source device before obtaining expected power within your amplifiers Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message How does balanced power help to solve ground loop humming Using balanced power solves ground loop problems because it takes it s ground from one source hence no potential difference You can do this yourself simply by taking all power from one spot If your equipments leak to the ground then balanced power might be helpful How does balanced power work Balanced power systems have been most commonly used with the 120V mains power used in USA In normal wiring there is one neutral wire which is always at almost ground potential and other wire which carries the 12V AC voltage There is also a separate safety ground wire In balanced power there is two out of phase 60V lines rather than normal 120V and neutral The voltage difference between those out of phase 60V lines is 120V so the equipments will get full 120V between their power input pins The balanced power is generated from normal AC voltage by using an isolation transformer with centre tapped 120V output and the centre tap of the output is grounded That expensive power balancing equipment is just a 1 1 mains power isolation transformer with a center tap to ground so that you ha
69. enced the video signal causing degradation of the displayed signal Video hum is usually observed as bars rolling vertically through the video image video hum may also cause video distortion or even tearing of the picture in severe cases Video hum may be a problem in any system where video sources and display devices are connected to different A C power sources with varying grounding potentials Typically the humming can be seen as slowly vertically moving horizonal bars in normal TV video signals The same kind of bars can be also seen in computer screen but typically they are not as visible because bars are moving so fast that you see them as some strange flashing in screen The picture below is a real world example of the effects of a ground loop and what it causes a a video picture received from the cable TV network wS org AWA Ad you can see that video signal has strong hummign bars and other interference in it Those have entered the cable TV signal because of ground loops in the system Ground loops in the video systems can have following effects e Hum Bars The mains frequency 50 Hz or 60 Hz can cause stationaly or moving horizonal humming bar to appear on the video signal as shown on the picture above If you have light dimmers nearby those humming bars can easily become quite severe and easily visible e RF Interference Herring bone interference on video line is caused by a ground loop that includes your coax shield acting
70. end post message Ground loop isolation in data networks and interconnections Isolating serial data lines When you have two computers in different rooms connected together using long RS 232 wiring you can face ground loop problems Isolating RS 232 line communications is harder than those audio or antenna connections The best solution to solve those ground loop problem is to buy a commercial equipment which is designed for this kind of purposes There are RS 232 isolators current loop converters and short distance modems which can do the job B amp B Electronics has a very good data sheet collection including schematics of many products availabla on thei web site They have also very good RS 422 485 and Current Loop application notes available on their technical library Ethernet networks and ground loops Ground loops in Ethernet networks can cause network not to operate properly and other annoying ground loop problems Thick Ethernet The thick coaxial media system was the first media system specified in the original Ethernet standard of 1980 Today most sites use twisted pair media for connections to the desktop Thick coaxial segments are still sometimes installed as a backbone segment for interconnecting Ethernet hubs since thick coaxial media provides a low cost cable with good electrical shielding that can carry signals relatively long distances between hubs An Ethernet interface is attached to a thick Ethernet segment
71. end of antenna cable can be grounded to the common ground with the mains ground somewhere quite far away When there are multiple ground paths they are virtually never at the same potential and therefore some current will flow through your equipment grounds often causing the hum you are experiencing Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Why professional sound systems suffer from ground loop humming Good and bad balanced connections Balanced interconnection systems used in professional audio world are naturally very good at rejecting noise problems The shield grounded on both ends of the cable to equipment cases provides a very good shields agains RF interference and electric fields The blaanced narure of the signals will very effectively eliminate the effect of small potential differences between the audio equipments The twisted narure of the wires is good at reducing the effect of noise from the magnetic field Because those design choises a balanced audio interconnection should be quite much free of any ground loop problems when the whole system is done using balanced inteconnections And if there is need to connect anything unbalanced to such system those should be connected using DI boxes and isolation transformers This should provide a hum free operation for equipments Unfortunately in real life the situation is not so
72. er frequencies to be heard first this is perceived as barky brittle High quality audio transformers cover whole audio band with good response but those are quite expensive Depending the application you might have to do some weighting against the price of the transformer and the sound quality Whenever possible an input transformer should be used at the destination end of an interconnect cable Input transformers offer much better Common Mode and Radio Frequency Rejection than is possible with output transformers Audio isolation transformer product information There are ready made circuits available from shops selling car audio stuff ground loops are usually problem also in car environment If you live in USA take a look in Radio Shack s catalog on car electronics or check the Radio Shack Product Support pages which have specifications of Ground LP Isolator 270 0054 which cost about 15US Might not be the highest quality solution though If you are looking for very good sound quality you might want to invest to some better quality and much mor eexpensive audio transformers For more professional product check JK Audio Pureformer Stereo Isolation Transformer Those products seem to be quite suitable for solving ground loop problems in consumer audio systems but have not tested them myself Europeans should take a look at their nearest dealer which carriers Monacor products because Monacor s new catalogue lists FGA 40 Best Nr
73. ere are lots of other interference sources which can cause humming and other kinds of noise An earth loop will typically inject a 50Hz ot 60Hz hum into the signal cables There can be also exist other harmonic frequencies in ground loop soiation but practically always there is that 50 Hz or 60 Hz strongly around if you have a 100Hz or 120Hz hum which often has a hard edge to the sound without that lower frequency 50Hz or 60Hz aroud you should definately check also other sources of interference Possible causes for this kind of only higher frequency interference is something wrong in the wiring of the power supply or some noise source in the electrical power system which causes that harmonic noise light dimmer for example lam getting a lot of hum and hiss from my system Is there a quick way to tell if the amplifier is making the noise or is it a problem with my system The fastest way to tell if the amplifier is the cause of the noise is to disconnect the input cables from the amplifier If the noise is still there it may be amplifier if it s gone it s a source device inducing noise into the amplifier If after removing the input connectors from the amplifier you find the noise still present it will then be necessary to determine if the noise is coming from the AC line This further isolation may be helpful Try relocating the amplifier using a different AC service if the same level of noise is present the amplifier is likely to be the cau
74. esk then use balanced connection between your mixing desk and the power amplifier and use ground lift to isolate audio ground in the cable the ground lift should be done in the amplifier end if you can t use balanced connection and ground lift then use isolation transformer in that audio line If your system has also video and or computer equipments then give them a separate power feed Use audio isolation transformers in all audio connections between your computer video system and your mixing desk computers and video equipments typically have unbalanced audio connections so isolation transformer is the only proper way to get rid of humming problem Keep some spare audio isolation transformers always available Audio isolation transformers are very powerful tools for solving unexpected humming problems when you connect some extra equipments to your system When you have some extran isolation transformers always available the problems can soleved easily ad effectively whenever they pop up Keep transformers and power distribution panels away form your audio equipments Audio equipments and wiring can very easily pick up humming from magnetic fields So avoid putting any sources of such magnetic interefrence near your system This applies to power transformers video monitors computer monitors electric motors fluorescent lights and any mains wirign which carry large currents Do not keep your cables coiled Coiled cables for a coil which will e
75. fault current flowing in the earth wiring will cause the voltage on that wiring to rise relative to true earth potential This could cause a shock to someone touching for instance the case of a faulty washing machine and a water tap at the same time In order to minimise this risk an equipotential zone is created by connecting the services to the main earthing point Such services are metal pipes gas water etc central heating metallic ventilation trunking exposed parts of building structure lighting conductor and any other metallic service The equipotential bonding reduces the voltage difference which could exist between the metalwork of these services if an earth fault occurred to any one of them How the ground is wired to electrical outlets The best way would be to run all the grounds separately back to a single block of copper at the central grounding bar Unfortunately this is often difficult to achieve in practice The practical way is to arrange your grounds as a strict tree structure with equipment only connecting to the leaves of the tree For ground wire routing the electrical installation regulations worldwide generally state that the ground wires should be routed on the same route than the mains curren carrying wires going to the same outlet or distribution panel This is the most often used practice Usually the safety ground is a separate yellow green wire in the cable and sometimes it is a separate wire in the same cable bundle
76. flowing but exposes this audio line to other kind of problems if one of the equipments is not connected to electrical grounding then the equipment don t have any common gound which then not to work as expected To avoid this kind of problems and still limiting the current passing in cable shield wire to value which does not cause problems an scheme called ground lift is introduced Ground lift places a resistor usually around 100 ohm between the equipment ground and cable shield This resitor limits the current passing in the ground loop situation but still provides quite good ground connection This system is unfortunately quite sensitive to radio interference so the 100 ohm resistor is usually shunted with small capacitor usually 4pF to 10 nF which makes the impedance to be low at radio freqwncies but does not let too much 50 Hz current flowing Before trying to use ground lift circuit is is best to check that everything is otherwise wired correctly It is stupid to use ground lift trick to fix other problems in the system because ground lift does has it s own problems A good document how to do the audio wiring correctly is Rane Note 110 Sound System Interconnection Ground lift in balanced connections Full ground lift circuits for balanced XLR connector 1 not connected 1 This is the most basic ground lift circuit which works nicely when all equipments are grounded and have balanced inputs outputs Because the cable shield is cut
77. free connections but well designed balanced connection avoid problems in very many cases Infortunately there are many equipments where the balanced connections are not designed well so they do not perform as well as you woudl expect them to do Grounding of inputs and outputs The grounding of audio cables have Grounding in balanced audio connections It is absurd that you cannot go out and buy pro audio equipment from several different manufacturers buy standard off the shelf cable assemblies come home hook it all up and have it work hum and noise free Use only balanced lines because they were develloped to provide good isolation against external interfences Tie the shield to the chassis at the point it enters the chassis and at both ends of the cable Standard XLR cables come with their shields tied to pin 1 at each end the shells are not tied nor need be this means equipment using 3 pin XLR type connectors must tie pin 1 to the chassis usually called chassis ground not the audio signal ground as is most common If the grounding od XLR pin 1 is done correctly in the equipments the currents running in the cable shield easily cause humming inside the equipment electronics This has lead to a situation that not using signal ground is a common practice in pro audio practice This is not a good solution to the problem Design rules used in professional audio equipment design Audio frequency groundloop problems are typically in the low
78. from reg to traces from logic load drivers to supply The common mistake is to daisy chain the ground by having the ground of the high current item seek it s current path through the ground of the logic This causes ground spikes on the logic and thus logic errors due to bad voltage levels at the logic chips Physical separation is to prevent electromagnetic coupling of course Even getting the grounds proper won t help if you couple the magnetic field back into the logic traces Always image traces to be resistors Thick ones are small resistance and thin ones are large The objective in laying out the board is to encourage the large currents to take the path back to their own source without getting onto the other grounds Separating current paths in this way can make a micro run right along side of a vicious current driver and not have logic problems in most cases The cases in which it usually doesn t work is when the signal being sent to the driver is analog instead of digital You re going to get some amount of ground differiental with the separate ground paths and so the analog signal will reflect this differance in the signal voltage relative to ground Current loop coupling of the signal to the driver could solve a really bad problem of ground differientals but have never used that technique If your going to go to that extreme then you may as well isolate them altogether If your signal is digital you can clean it up abit by having a sch
79. g is often at somewhat different potentia there will automatically be a potential difference between any wiring run between the two buildings Potential differences can be in some cases power faults lightning can be dangerously high and the current flowing in wire shield can be dangerously high do not recommend any direct galvanic connection using shielded cable between different buildings unless you absolutely know that it is safe do do so Generally the connections between different buildings should be galvanically isolated like for example telephone connections the line itself is not grounded on the building where it enters and they should be protected agains fault conditions overvoltage spikes excessive currents If you can get connection using fiber optic cable recommend using it instead of copper One of the key advantages to fiber optic cable over copper cable is immunity to ground problems and overvoltages Since fiber is glass there is no metal contact and therefore no ground problem Unfortunately to convert to fiber means usually buying an extra box for each output and each input a significant added expense Sources This article is based on The Cherry Juice Issues Online MAY CHERRY JUICE 1999 article GROUNDING and it is updated and made more accurate with my own knowledge and experiences Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion post message
80. gh the N conductor all the way to the transformer star point This system has become very popular in new installations in Europe and has been a standard in hospitals for a long time e IT The transformer is not erthed at all The star point floats Mostly used in heavy and process industry where continued operation even if there is an earth fault is required The more common european voltages in these systems are 500 V and 690 V In this case housing of the objects are connected to local grouns e TT Transformer and objects have separate grounds Common in US Three phase in Europe In Europe most use 230 400V where the 230V can be found between any of the 3 phases and neutral and the 400V can be found between two of the three phases Phase difference between phases is 120 degrees Three phase power is normally available in at least Finland Sweden and Germany being used for ovens electric stoves large motors and dryers Three phase power is also typically available in places where large sound and light systems are used around stages etc Typically there are 4 wires routed to every house for 3 phase feed Those are typically them are labeled R S and T the fourth being ground The phase shift between R and S are 120 deg the same phase shift exists between S and T and between T and R The voltage difference between the live phases is 400 V the voltage difference between any live phase and ground is around 235 V The usual household power ou
81. ghtened with screws every 5 10 cm so that they make good contact For both input and output use use connectors isolated from the enclosure but connect the connector ground terminal through a capacitor 1 10 nF with as short wire as possible The capacitor will have a low impedance at RF but 100 k 1Mohm impedance at hum frequencies and their harmonics thus adding very little hum This approach is recommended for all unbalanced connectors RCA 6 3 mm jack 3 5 mm jack BNC etc If you are using balanced connections with XLR connectors wire the pin 1 ground directly to the case do not connect it to the analogue signal star ground points For extra protection add ferrite beads to the wires inside equipment Ferrite beads with a few turns of wire mounted close to the socket into both the signal and ground terminals of the connector will have an RF impedance of several hundred ohms but still practically no effect at audio frequencies For adding effectively of this on input circuits add a small 1OOpF 1nF chip capacitor after the ferrite beads from the signal wire to the ground with 1000 ohm signal source impedance this capacitor could be up to 1 nF thus the corner frequency of 160 kHz Do not use this kind of capacitor on the output circuits since this can cause stability problems to some op amps Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post
82. ground wire and the ground potentials of different electrical power outlets are never equal The leakege current can also cause other type of problems In some situations there are ground fault detect interrupter GFCI circuits in use the leakage current caused by many equipments together can make the GFCI to cut the current Typically GFCI circuits are designed to cut current when there is 30 mA or more difference in currents flowing in live and neutral wires the difference of those current must flow to ground Some GFCI circuit can cut the mains feed even at 15 mA leakage current which may mean that if you connect many computer equipments each of them having 0 5 to 2 mA of leakage to GFCI protected power outlet you can cause the GFCI to cut the power feed Ground wire resistance In europe it is not important how much ohms the grounding is but the maximum current before the unit switches off is important So a grounding of 230 volts and a safety of 24 volts We say it must be less then 30 mA in our body So for 16 amps and 24 volts it is 1 5 ohms This means that the maximum voltage on the case is 24 volts even when all current is flowing thru the grounding wire In places where even this 24V is considered very dangerous for example in hospitals the ground resistance must be made lower to make sure that there is never dangrous voltage present in the case For example in Finland the grounding resistance for medical room outles must be less than 0 2 ohm
83. h can exist if power is taken from multiple power outlets If the distance and electrical code permits is is a good idea to run a power extension cords from your single power feed points to all subsystems connected to your audio system instead of using the local power sources Wire all audio equipments which you connect to mixer to same phase Use dedicated power feed for your audio system Wire all sound sources musical instruments effects and your mixing desk to same grounded dedicated audio power feed Do not connect any other equipments than audio equipments to this power feed This saves you from many humming problems It is a good idea to mark clearly which extension cords are part of your audio power feed so that you don t accidentally connect any other equipments to them it is good idea to tape over all power outlets from this audio feed which are not used by your audio system so nobody will accidentally plug any other equipments to your audio power Especially avoid plugging fluorescent lights lighting dimmers computers and video equioments like video projectors and TVs to your audio power feed Use balanced connections everywhere you can Balanced connections are much less sensitive to to pick up interferences and humming If you still get himming with basic balanced wiring there are much more to do to avoid it than with unbalaced connections Most professional audio devices are connected via balanced cables to minimize pickup of stra
84. h very large ground loop signals and has very large bandwidth with very little loss This type of anti humming transformer also provides DC continuity between the input and output leads which is a good thing transformer does not stop ground loop current flowing the amout of current is lower bause the added indictance but the transformer reduces the current cancel the effect of ground loop current Good one can reduce the ground loop effect up to 40 50 aB Hum isolation transformers are effective solutions for hummign problems The downside of them is that they are somehow bulky devices because of the large core needed to do the job The boxes have seen have been packed in metal case have weighted at least one kilogram Hum isolation transformers are typically stand alone passive boxes which are added to video system when problems are encountered Video isolation transformers There are special wideband isolation transformer which can isolate video signals but not without problems The design of a high bandwidth transformer which can go to very low frequencies is very hard You have to always make some compromises on low and high frequency responses highest components of composite video cna be attenuated even few dB All real isolation transformers have one serious drawback which can t be avoided they can t pass the DC level through So any system that relies on the video having any particular DC reference will not function properly There are many
85. he host building Majority of today s networks are still attached via a copper based medium This copper wire can be the path for distruptive and potentially dangerous current and voltage events Typical effect of power related problems are from intermittent reboots or lockups to spark producing power supply damage Network interface cards serial ports parallel ports and modems are are all prime targets for destructive power events Govering standards in USA In the opening page of the National Electric Code NEC states that the purpose of the Code is the practical safeguarding of persons and property from the hazards arising from the use of electricity The Code fusther states that the Code contains provision considered necessary for safety Compliance with will result in an installation free from hazards but not necessarily efficent convient or adequate for good service The Institute of Electrical and Electronics Engineers IEEE has published I EEE Standard 1100 1992 I EEE Recommended Practice for powering and Grounding Sensitive Electronic Equipment The main purpose of the standard is to present recommended engineering principles and practices for powering and grounding sensitive electronic equipment The standard attempts to provide a consensus about what specific installation paractices should be used to afford electronic equipment maximum availability In all areas the IEEE specifications are more stringent than those contained
86. he order of 1 amp rather than 0 1 A or 10 A Even a very small induced voltage can cause a very large current in a ground conductor loop because the resistance and inductance are very low These currents can indeed be tens of amps Current induction can be caused for example by cables carrying high currents and from transformers What those grounding currents and voltage differences can do Small voltage differences just cause noise to be added to the signals This can cause humming noise to audio interference bars to video signals and transmission errors to computer networks Higher currents can cause more serious problems like sparking in connections damages equipment and burned wiring My own experience on th field is limited to sparking connectors heating cables and damaged computer serial port cards have read about burned signal cables and smoking computers because of the ground differentials and large currents caused by them So be warned about this potential problem and do not do any stupid installations Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Cable shield connections and groundloops There are sometimes lots of talk about how the cable shields should connected whn the equipments are interconnected Some arguments say that to avoid ground loops is a good idea to connect the cable shield only at one end to avoid larg
87. he same system are receiving its power from a different ground than other components or the ground potential between two pieces of equipment is not identical Ground loop is a common problem when connecting multiple audio visual system components together there is a good change of making a nasty ground loops Ground loops commonly cause humming noise to audio signals and interference bars to picture Ground loop makes the system sensitive to pick up interference from mains wiring which can lead to erratic operation of the quipments or even damages to the equipments Some articles claim that wiring and grounding problems account for up to 80 percent of all power quality related problems related with sensitive electronic equipments like audio video systems The audio video and power industries have each designed their systems and equipment independently As a result there s a degree of incompatibility Usually which is pwefectly adequate in power distribution and operation safety sense is not good enough for AV systems Ground loop interference problem is a consequence of this Always when operating with grounding issues remember that there is no absolute ground There is a certain amount of resistance to electrical current between all grounding points This resistance can change with humidity temperature connected equipment and many other variables No matter how small the resistance can always allow an electrical voltage to exist across it when there
88. hen designing the electrical distribution More information on that is available from Equitech articles Power Management in the Studio Audio Wiring and Grounding 1996 National Electrical Code Technical Support Bulletin and Installing a Technical Grounding System Those articles provide you understanding how to make good grounding system for studio Do not try to modify your electrical wiring yourself When you know what needs to be done call professionals to do the job properly you might need a special consultant to do the plans for modifications because standard electricians don t usually know all the special requirements audio studio has When you have proper groundung system in your studio then you can start doing the the audio wiring in a right way You can easily easily make your system very sensitive to power system noise if you do not do the wiring properly Rane application note Sound System Interconnections gives you good undertanding how the audio connections should be done The problem is that in many cases you don t have possiblity to change the electrical distrubution system already in the place because it will come hard to do and expensive Then you have to live with what you get and try to solve those problems with suitable isolation devices Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Example systems with and without gr
89. hile others have a common ground You can use the former type to break a CATV ground loop but not the latter So be sure to buy models which have no galvanic connection between 75 ohm input and 300 ohm output so there is isolation between input and output because some models only do impedance matching but galvanic no isolation they are useless in this project If you use an ohmmeter between the input and output you will find that there is a very low resistance between all the terminals if there is no isolation and open circuit if the balun transformet provides galvanic isolation The circuit is easy to build Just take two of those 75 to 300 ohm antenna transformers and connect their 300 ohm sides together Now you have antenna isolator you need 75 Ohm __ 300 Ohm 75 Ohm This circuit has been suggested by Paul Grohe grohe galaxy nsc com who suggested that suitable transformers are available from Radio Shack Radio Shack cat s 15 1140 and 15 1253 or MCM 33 050 and 33 010 LiveDV magazine suggests using Radio Shack 15 1140 and 15 1523 antenna transformers wired together in their Soundings Getting Wired tutorial January 1996 According some comments I have recieved some people have pointed out that the not all Radio Shack 75 300 baluns are not isolating so the above circuit might not work as epected don t have access to those component from Radio Shack so I can t check what is the real situation have received mixed mess
90. ignal path as well Unground that and if the signal gets through at all you will have the world s noisiest circuit as the other path what was the shield will be established through some other ground path through other equipment Some notes on using ground lifts Disconnecting the screen in balanced audio cable will break the ground loop and possibly eliminate hum But a word of warning before disconnecting the screen If you are running equipment from two or more separate power receptacles especially if they are widely separated and the building wiring is old or not up to spec there may be residual 50 or 60 cycle voltages present between the two alleged ground connections These will be small of the order of millivolts unless something is seriously wrong with the building system but they may be large in terms of audio signals and can do a lot of damage if fed into a high gain audio input So it is important to try the effect of ground lift at low gain first Ground lift for unbalanced connections Situations where two grounded equipments with unbalanced connections are connections have ground loop related humming problems and no other solution helps then you can try to use ground lift Ground lifting in inbalanced connections works only efectivily when both of the equipments are properly grounded to same point In some cases the humming problem may becomes worse if ground lift is used So ground lift in unbalanced connections is not a foolproof me
91. ijo Laine Radioamat rin kasikirja EU Harrastekirjat 1978 1980 page 164 have not been able to locate the book to check the circuit but the circuit in one ready made isolator had very similar circuit On the picture above you see the whole J A A Junction h iri adapteri adapter from The picture below is close up picture of the details inside the antenna isolator adapter It had three turns of thin wire in promary and secondary wrapped around small ferrite core The wiring inside the isolator is very similar to the audio isolator circuit the only difference is that now connectors are antenna connectors and the transformer is the one designed for antenna signals described above The thin wires between the transformer and the coaxial cable are kept minimum to avoid the adapter to pick up interference If you live in Finland you can buy this type of isolation adapter from under name J A A Junction h iri adapteri televisioon It costed 43 mk when last checked the price about 9 US dollars For more ideas how to fight against ground loop caused by cable TV connection check the article by at web magazine reviewed an antenna wire ground loop isolator product SO read the if you are looking for an isolation device suitable for antenna network which is used in USA Simple two capacitor isolator This circuit is a simple isolator for TV and Radio antenna connection This circuit passes radio frequency signals nicely but does no
92. immunity to RF interference For the circuit design start with a continuous ground plane Unfortunately this ground plane solution is a good solution if only a relatively small dynamic range 20 dB for digital 60 dB for video is required This means that ground plane approach is usable for many video circuits digital circuits and not very demanding audio applications However high quality audio systems should be designed with 100 120 dB dynamic range thus with 1 V signal levels any unwanted signals should be below 1 10 uV With various AC and DC currents flowing in the circuit sooner or later they are going to end up into the ground plane So there is a risk of several microvolt AC potential differences accross the ground plane If the circuit topology is bad this AC voltage e g hum is directly added to the signal In a preamp you also have to consider any leakage current flowing from the signal source through the preamp ground to the power amp Grounding toplogy does have very much effect how this currect affects circut operation One good idea for building a very high quality audio equipment is to keep the traditional star grounding topology inside the equipment and prevent any RF from entering the enclosure By keeping the RF out of the main circuit board the LF grounding can be more freely done according to audio requirements To kepe the RF out the equipment enclosure should be fully metallic and any removable panels should be ti
93. is any current flowing between those grounding points and there is some current flowing almost always Audio frequency groundloop problems are typically in the low millivolt range so it does not have to be much interference in grounding system to cause problems in audio systems Remeber that there is no absolute ground There is a certain amount of resistance to electrical current between all grounding points This resistance can change with humidity temperature connected equipment and many other variables No matter how small the resistance can always allow an electrical voltage to exist across it The ground wires between wall sockets and power company transformers are not perfect conductors and neither is the shield of your coaxial video cable If they were ground loops would not be a problem Effects of ground loop in video pictures are in the form of a black shadow bar across the screen or as tearing in the top corner of a picture This is caused by different earth potentials in a system General topics e Why grounding is used in electrical wiring e Basics of groundloops e Cable shield connections and groundloops e Electrical wiring in buildings e Examples of different AV system with and without ground loop problems e How the signal cable grounding is done in typical AV equipments e Mains connectors e Naming Electricity System Earthing Arrangements e Solving typical home AV system ground loop problems e Other than ground loop rel
94. l work is going to rise to something near to phase voltage This sound horrific but is actually not dangerous provided that all earthed metal work is nicely bonded and there are no unbonded earthed objects around that are better earths than your earth spike How the ground connections are made in the main distribution board The three phase power power comes from power company using just four wires L1 L2 L3 and PEN protective earth and neutral L1 L2 and L3 are just connected to the power bars in the main distribution panel The PEN wire is connected to the PE protective earth bar which is connected to the central grounding bar Neutral bar is connected to the PE bar in the main distribution panel and nowhere else in the building which has 5 wire 3 phase wiring Nain distribution bus Ll Le Lo NM PE From Power company PEN z bea oz Le L3 Lightning protection Antenna wiring Telephone Telecommunicatlon equipments Hater pipe Gounding Flumbi m electrodes 3 Steel structures im building The central grounding bar works as the central point for whole building grounding system and every grounded system in the building is connected to it The central grounding bar is just a metal bar which connected the grounding wires from the mains power telephone equipments antenna wiring lightning protectors metal plumbing water pipes building steel structures and building grounding electrodes together As mentioned elsewhere a
95. lbox Etc this site is for the electrician Car sound systems and groundloops o Ground Loops and Autosound Systems Where all this information comes from Most of the information comes from my personal personal knowledge on the field have had experience on designing building using maintaining and faultfinding many audio video and computer network systems have also designed electronics devices for audio video and telecommunication applications When I have found stange problems on those systems have tried to make a good investigation what is the cause of the problem and what are the sensible ways to solve the problem Various books magazine articles and technical documents from many web sites have been also been very useful when have put this web document together If you have some comments on this page mail them to me to tomi engdahl iki fi Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Why grounding is used Terminology In Britain people have earth and in Northern America they have ground They are exactly th esame thing only different terms are used in different countries Purposes of Grounding Grounding system has three main purposes Overvoltage protection Lightning line surges or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical dist
96. lets that any equipments connected to different electrical outlets and interconnected would work very erratically you would propably cause many equipment damages Computer sustems are generally much more sensitive to the ground potential differences than ground to neutral differences The bottom line is that separate ground and neutral wire is a good thing for many problems It solves more problems that what it potentially causes And in wery rare situations where separate ground and neutral wires cause some problems in those same situations a wiring with connon neutral ground wire would have caused much more but different kind of problems in form of ground potential differences When taking account situation where computers are interconnected networked a good stable ground potential for aal equipment is much more important than very small neutral to ground potential Separate ground and neutral wires is a good method to keep the outlet grounds at same potential which is very important in networked computer systems Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Audio signal grounding in audio equipments Grounding in consumer audio is somewhat fragile because there is no overall plan Each piece of equipment takes a slightly different approach As long as there are only a few units involved there are few if any problems Once the system gr
97. lt like those cheapest universal adaptors and can cause lots of magnetic fields around them It is not advisable to put any sensitive signal wires or equipments near those wall transformers because they can cause serious humming problems Look around and leave adequate space between the gear with transformers inside of them Magnetic fields induced from other wires Hign current carrying mains wiring can cause quite strong magnetic fields around the cable If you run an audio cable near high current mains wiring it can easily pick up humming It is a good idea to keep at least 0 5 meter distance between high current mains wiring and your audio cabling If the audio cable must cross a mains cable then make this crossing at exactly 90 degree angle so the mains cable magnetic field will not be coupled to audio cable The interference coupled from mains wiring can become especially noticable if there are some problematic loads like fluorescent lighting light dimmers or lots of computers connected to the mains wiring Magnetic fields from distribution panels Main poer distribution panels have high current carrying wires relays and contactors in them and they can cause quite storng magnetif fields around then It is not advisable to put any computer monitors or audio equipments near them Few meters clearance from mains distribution panel is usually enough to stop any magnetic interference Magnetic fields from electrical motors Electrical motors us
98. mall filter such as a ferrite bead depending on the application and frequencies of interest Make sure the decoupler for the DVDD is located close to the pin with the bead not much further away The digital input lines should be close to each other and connect to the nearby digital IC Underneath these lines the analogue and digital ground planes should CONNECT The reason for this is to keep the radiating loop area of the digital current path to a minimum If you don t do this every time a digital edge occurs the pulse will either flow around rather a large path or get injected into the IC s analogue section depending on your implementation If your analogue side voltage needs to be very stable it needs its own regulator Look for low noise regulators such as the ancient LM723 Other designs may find the digital supply regulation adequate and so just use an inductive filter to remove the necessary frequencies Why some circuits have separate analogue and digital grounds Separating analogue and digital ground generally has to do with return currents and ground noise Even though we think of GROUND as having zero impendence it is a wire like anything else Even ground planes have some impendence and so currents flowing through these grounds cause voltage drops in the planes If we have a circuit that is operating on a senative analog voltage levels or frequencies we might not want these unexpected voltage drops occuring in the circuit The are
99. message Other noise and hum sources than groundloops There are also other sources of noise which can cause humming to audio systems than groundloops If you have done all the countermeasures against groundloops and still have the problems or your problems seems not be caused by groundloops look at the possibility of other sources of noise as described in this document RFI issues Audio cables can act as affective antennas for RF energy Preamplifiers and other audio input devices vary widely in their tolerance of RF signals In audio system where there has been done lots to avoind ground loop problems cable shields float at one end The downside is that this makes each cable act as an effective whip antenna If the cable length and ambient RF frequencies are just right Murphy s law will anttend to this the whip antenna becomes tuned and can produce very high RF voltges at it s floating or ungrounded end and that RF will then capacitively couple to audio signal wires inside the cable shield This RF voltage can be reduced by terminating the floating end of the cable at RF frequencies through a resies network which consists of reries connected 51 ohm resistor and 10 nF ceramic capacitor This network terminates the line at frequencues above 300 kHz but looks open at audio frequencies so avoids forming ground loop EMI isssues Hum and noise can also enter the audio signal path magnetically Basic physics tells that any conductor
100. midt trigger on the driver side of the loop with it s ground relative to the high current load This can provide a volt or more of tolerance in the ground differance If you get the currents going right you will see less problems with the logic side but you might see more problems with the driver because it s signal from the logic is corrupted by lifting of the ground potential because of the high currents When you have reduced this effect by minimizing the high current ground ohmage to the point where you cann t minimize it any more AND you have included schimdt buffering then it s time to admit defeat and galvanically isolate the two circuits When you have power electronics and some microelectronics on the same circuit the layout of the current loops is critical This also applies to situations where you have microelectronics and audio circuit on the same board What are the problem with treating both digital and analog grounds as the same ground source Your digital circuit noise can get to your analogue signal path if you don t use separate grounding systems for digital and alalogue parts those are interconnected only in one place Digital grounds are invariably noisier than analog grounds because of the switching noise generated in digital chips when they change state For large current transients PCB trace inductances causes voltage drops between various ground points on the board aka ground bounce Ground bounce translates into varying
101. millivolt range As a general design rule true professional equipment designed for the real world of Pro Audio should not have its mains chassis ground and electronics ground permanently and directly connected It should either be totally isolated switchable or have the chassis and electronic ground connected via a soft coupling resistive capacitive network Signal balancing Good balancing of the signal is absolutely necessary for the balanced inputs to work as espected Balancing means that the inputs and outpus use different signals but that s not all Balancing also means that the cables are impedance balanced both wires in the pair see the same impedance The impedance balancing is absolutely necessary for reliable operation in real world situations If the impedances are not properly balanced the equipment might give good CMRR figures on typical test bench measuring setup but perform quite poorly on real world situations In the sending end the ba ancing is easy to use J ust match the output impedances of the output amplifier stages by using same size output resistor for both inverted and non inverted outputs For ba anced inputs you must select a differential input circuit which really shows the same impedance to both inverting and non inverting inputs Quite many basic differential amplifier schematics show different imepdance values to those input So be careful in the design process and analyze the input impedances carefully Floating t
102. ming bars especially if combined with differential video inputs back porch black level clamp system does not help in fighting against higher frequency noise which might be injected to the video system through the ground loop Active video isolators Video Isolator passes a video signal from its input to its output with no electrical connection and is able to provide complete isolation for the video signal passing through it Having the Video Isolator in the video signal path makes it possible to have Standard Safety earthing of all equipment with no associated earth loop problems In the studio feeds between different buildings are no longer a problem and it is no longer necessary to run technical earth to non critical locations such as viewing rooms Electro optical isolators convert video signal voltage to blinking LED and other part of the circuit receives that light and convert it to back video signal voltage This method guarantees very good isolation complete galvanic isolation but has typically bandwidth and linearity problems Poor bandwidth will result in fuzzy images and poor linearity will result in an inability to produce the same gain for all signal levels most noticeable in gray scale patters Anti hum video transformers Anti hum video transformers are not real transformers they are common mode chokes Anti hum transformers work as a series inductor offering a series impedance to the circulating earth currents thus effectively
103. n hum free Avoid connections to other grounds than your system ground There are other things than the power connections which can me an unwanted grounding connection to your audio system Audio connectors which have metal shell which is in contact with the cable shield can cause unwanted grounding if they touch any grounded metal in the building or some other grounded equipment Same applies also to microphones and snake cable connection boxes So if there is change thet your exposed audio wiring ground can touch any building ground then put some insulation between your wiring and that ground Avoid putting equipment racks over any metallic parts in the floor because it is possible that they are grounded for some reason If you have to place equipments on such place then put some kind of carpet between the metal parts in the floor and your equipment rack to provide necessary isolation Use correct gain structure in your system By using the correct signal levels throughout the system will minimize the humming noise and distortion Gain controls in PA power amplifier be typically set between half way and fully up Amplifier gain controls set at a lower position require input signals to be set to a higher level to obtain suitable power levels Particularly with unbalanced input lines the hotter your signal is at the input of an amplifier the more noise propogation you will have into your amplifiers If you have set the amplifier gain set too low your syst
104. nced operation the signal wires should be well impedance balanced and the shield of the cable should connect to the chassis ground the the point of entry Balanced and unbalanced interconnections Balanced and unbalanced systems are not designed to interface together directly In nowadays system there is unfortuanately many times need to interface balanced and unbalanced equipments to each other This kind of interfacing is always very possible source of causing unwanted humming entering to the system The most proper way to do balanced to umbalanced interconnection is to use an transformer isolation in the interconnections This gives you the most reliable results In some cases just a special cable or adaptor will do the job but in this case you have to be very careful what you are doing to avoid himming to enter the system Unbalanced interconnections Unbalanced interconnections common in home audio should be avoided in professional sound systems for many reasons An unbalanced system uses only two wires one for signal and one for ground which arrangement has an inherent problem called common impedance coupling If two different circuits share the same conductor or wire a current flowing in either circuit will produce a voltage drop across the wire and that voltage drop will become summed to the signal in the cable Since the cable shield is effectively connecting the grounds of the devices together it carries a current derived from the powe
105. nces much lower than 1 mV can cause serious noise problems with unbalanced circuits If you have unblanced connections would advice you to use audio isolation transformer instead of ground lift when you are solving problems with nonbalanced audio connections Audio Wiring and Grounding article from Equitech web site provides more information how ground lift is wired and how it affects the audio system performance Wires and connectors article at Multimedia Bluffer Guides You can easily test the effectiveness of ground lift in your system urn the volume down disconnect the shield at one end and slowly bring the volume back up It s easy if you ve got phono connectors just pull the plug partway out so the pin makes a connection but the outer shell doesn t Be warned If other grounds aren t good enough or mose of the equipment are not grounded at all this will cause an even worse hum If the PC is not properly grounded this kind of experimenting can even cause damages to audio equipments Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Audio isolators Isolation transformer for audio lines Audio isolation solves groundloop problem If you want to do the ground loop elimination in audio path you have to cut the galvanic connection but pass the whole audio range The simplest and most common way to do the isolation is use audio transfo
106. ncy spectrum without much distortion is very hard to produce so there are not many of them on the market Some of the isolation transformers are only designed for CCTV application where more signal distortion is accepted than in broadcast industry The choke humbugging transformer is primarily used in Broadcast TV because it passes the DC component of the signal It is used in studio and in remote ENG The isolation transformer is primarily used in CCTV security manufacturing avionics display etc Differential video amplifiers Differential amplifier approach uses an operational Amplifier Operational Amplifiers only amplify the difference between the two input lines This method eliminates common mode noise between the incoming signals by making A B C as only the difference between A amp B are amplified Operational amplifiers is maintain wide bandwidth signals throughout your system while eliminating ground loop problems that are caused by power and video Diffeerential video amplifier inputs are used in some video equipments typically some video projectors and video distribution amplifiers to fight against ground loop problems Differential video amplifiers have a limitation on their input voltage range which gives some limitations how much common mode signal those circuits can tolerate If the ground potential difference is more than few volts then operational amplifier based isolators don t work effectively Too high voltage difference c
107. nded practices ains power isolation in laboratories is mainly done for safety reasons not for fighting against ground loop problems The mains powered electronics devices which are being repaired are connected to mains power through isolation transformer to make it safer to test them A general recommended paractice for electronics device repair shops in Finland is to use at least two mains isolation transformers in their repair environent The first one is an isolation transformer whcih isolated all the test equipments like oscolloscope from the mains ground and the other one is the one used for isolating the equipment which is being tested or repaired This arrangement is very good on both safety and noise reasons Sometimes isolation transformers are also used to fight agains noise problems but generally they are used for safety reasons in electronics laboratories Mains isolation transformer does not always help in groundloop problems It is sometimes suggested that an isolation transformer might be used to solve the ground loop problem It is true that somethimes a mains isolation transformer does help but not always The reson that mains isolation transformer will not always work is that there is quite a variety of mains isoltaion transformers designed for different used Those mains isolation transformers all isolate the main live ant neutral wires but vary what they do ti the ground connections Some transformers cut the ground connecti
108. ne common point and when two grounding points cannot be avoided one side must isolate the signal and grounds from the other Usually ground loops are an after the fact type of problem in which the end user blames the installer the installer blames the manufacturer and actually nobody is at fault Neither the manufacturer nor the installer can usually predict where a loop will occur Only after the system is installed can it be determined if a problem will exist Ground loop problems can be corrected and avoided It is important for the dealer isntallee and the end user to be aware that this problem can occur It is a good idea to design the system to avoid most obvious source of this kind of problems and then be prepared still to face some problems when starting to use the system A ground loop problem may occur at several points in the system and each occurrence of the problem must be corrected individually Why grounding is so important Earthing of electrical systems is required for a number of reasons principally to ensure the safety of people near the system and to prevent damage to the system itself in the event of a fault The function of the protective conductor or earth is to provide a low resistance path for fault current so that the circuit protective devices operate rapidly to disconnect the supply The NEC National Electrical Code defines a ground as a conducting connection whether intentional or accidental between an electric
109. nimize microphone hum pickup e Use low impedance microphones 150 6000 ohms All modern recording equipments and mixers are designed to work with low impedance microphones e Use microphones with balanced outputs three pin XLR connectors Thus kind of microphones pick up less hum than unbalanced microphones Routinely check microphone cables to make sure that the shield is connected at both ends e Check that the screw near the XLR connector on the microphone is securely screwed in place inside microphone handle Do not connect the ground on XLR connectors to the shell of the connector because ground loop hum may occur if a grounded shell touches a metallic surface e Do not ground microphone juction boxes or snake boxes except through the cable shield Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Ground lift The current which flows in the ground loop flows through audio cable shield In balanced connections the current flowing in the shield should not effect the signal in the cable or this signal connections in equipments If the equipments are well designed cable shield grounding is done in the right way then small amounts of currents do not cause any problems In practice equipments are not that well designed and even very small current can induce humming to the system If you cut the audio cable shield the current will stops
110. nnected to the coil end marked as coil start you will get a nice isolator If you for some reason connect the wires in one side of the transformer in the wring way your transformer will cause a 180 degree phase shift to your audio signal If some of the signals in your audio system will get this kind of phase shift and some other will not you will face all kinds of sound quality prolems If you have this kind of system it is best to test that the audio isolation transformer will not cause unitended phase shift to the signal The tansformer used for this should have a flat frequency response over whole audio frequency range should have high enough impedance at lowest frequecies and should not cause noticable distortion If the impedance drops on low frequencies this can cause attenuation of the lowest frequencies if the transformer is connected to the equipment which have a very high output impedance This kind of isoltion transformer circuit should be best connected on the receiving end equipment input end of the cable to get best performance If the cable is not very long not many meters in practice it does not matter to which end of the cable this transformer isolation circuit is connected Isolation for balanced lines For balanced lines equipped with XLR connectors the audio signals are transported between signal pins 2 and 3 So the isolation transformer should be wired so that the primary is wire between input XLR pins 2 and 3 and the seconda
111. o system A problem with audible noise coming from your audio system when other electronic components fridge water cooler ect could be the result of of a contaminated ground neutral conductor in your A C wiring and a ground loop in uour audio system This can happen when certain type of devices come on Typically their power supplies are non linear and throw garbage back onto the neutral and or ground conductors Usually line conditioners or UPS devices will not do anything to help solve this problem Common Causes for Computer System Problems Many times when a user thinks that his system is bad or has gone bad the fault is electrical or magnetic in nature Monitor problems are very often caused by nearby magnetic fields neutral wire harmonics or conducted transmitted electrical noise Intermittent lockups of computers are very often the caused by a Ground Loop an electrical phenomena that sometimes manifests itself when a system and it s peripherals are improperly plugged into different electrical circuits Many don t even know if their wall outlet is properly wired and grounded an absolute necessity for a computer and peripheral to operate reliably and safely Have you ruled out Ground Loops in your computer system Ground loops can cause problems to LAN connections if not properly wired A ground loop caused by RS 232 connection to other computer can cause computer lockups When ground loop is not a problem Ground loop does not cause
112. o system Most people have their surround sound receiver connected to a home entertainment center with at least a TV and cable If this is the case try disconnecting the cable If your stereo system has also a receiver which is connected to wall antenna plug then remove it also because the receiver antenna connection can also be a source of humming If removing antenna cable helps to get rid of humming then get an antenna isolator to all your antenna connections or an audio isolator to the audio cable between your computer and the amplifier PC based DVD systems PC is becoming a more and more popular signal source for a home AV system Nowadays when many new PCs are equipped with DVD drives and display cards with TV outputs so increasing number of people have started to connect their PCs to their home theater systems If you are using one ground for your PC system and a different one for your cableTV service then you most likely have Cable TV ground loop This can be witnessed as an audible hum through your speakers or vertical black bars on a video display There are two remedies to correct this problem The first is to use the same ground for both the Cable TV and A V system Unfortunately chanign the grounding of those you well need an electricial and a cable TV installation people Better grounding practices usually reduce the problem but quite often does not solve it completely The second and usually more viable option is to install high
113. o wires about 1 2 twists per cm is enough e Next you need a small transformer core suitable for UHF frequencies used a donut shaped ferrite core Try looking in an old TV or radio Wrap the twisted wire a few turns around the core One wire is the primary winding the other the secondary so it helps to color code the wires e Make the leads between the coaxial antenna plugs and the core as short as possible e You re making a transformer i e if you have a red and a blue wire connect the blue ends to one antenna plug and the red wire to the other plug not two colors on 1 plug For tv frequency signals such a simple transformer using a suitable core is almost perfect Do not tru to use other types of transformers because your circuit would not work then and they would cause annoyning interference to other TVs connected to same antenna network and in worst case you get cable TV people huntung for you because you messed with their cable network Td have seen another transformer circuit posted in the usenet Kari Hautanen wrote an article to sfnet harrastus elektroniikka newsgroup about antenna isolator The article says that you can built a suitable transformer using following method Primary and secondary are three turns of 0 2 mm Cu wire wrapped around small magenta coloured toroidal ferrite core Seems quite simple but the article did not mention the exact core size It mentions the source of the circuit to be a book Osmo A Wiio Re
114. of system it is essential to keep the the ground potential difference very low in the whole network area Every cabling rack in the distribution points must be grounded to the main grounding bar using a separate ground wire The electrical system ground must be also very good and at the same potential as the central grounding bar It is essential to keep the active elements HUBs LAN switches routers at exactly the same potential as the rack cabinet The resistance from any grounding point to the central grounding bar must not me more than 1 ohms and the voltage differece must be less than one volt The resistance between the workstatio mains power gound in the network cable ground must be less than 2 ohms In order to keep the grounding resistance low the grounding cables must be thick enough In undhielded twisted pair cabling the ground potenatial differences are not as critical as in shielded cabling but it still a good idea to keep the ground diffeences minumum to guarantee reliable network operaration Especially the grounding of the equipment racks and the active network equipments must be good Sources e Tony DeSpirito Networking Equipment And Downtime Caught In The Middle Electronics Design April 1 1997 pages 42 48 e Harri Kosonen LAN vianhaku osa 1 LAN mittarit ja ty kalut Prosessori 8 1998 page 32 Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a fri
115. oils magnetically there is no physical contact Thus the ground loop is broken Adding isolation transformer to each audio line is usually expensive and can make the sound quality somewhat worse than straight wire In the data world they avoid the problem altogether by using unshielded twisted pairs UTP This kind of wires are isolated from one or both of the ends of the connection This has proved to be a wholly acceptable solution and works well in practice Most of the modern office LAN cable wirings are nowadays done using unshielded twisted pair wiring and rest of them most often using shielded twisted pair wiring However for the audio and videoworld unshielded cables are not an option for any serious high quality signal transmission There are some adapters available to transfer audio and video using unshielded twisted pair wiring but those adapters are generally only suitable for not demanding dapplications like security cameras CCTV and similar applications where the absolutely best signal quality need not be preserved In any case going from normal video or audio connections to unshielded cable needs special converters which cost money and there is no guarantee that such converters will solve the initial grounding caused noise problems they are just designed to be wiring media converters not groundloop problem stoppers Analog audio and video designers do not have an option of using unshielded twisted pair wiring as general media for
116. old cenral radio systems amplifiers Those amplifers had a transformer isolated balanced audio input with impedance of around 1 kohm took the high quality input transformer from the preamplifier board and tried how well they would work in my applications The text on the top of the transformer indicated that those transformers were 1000 1000 ohm audio transformers The measurements showed that those transformers perform better than those telephone transformer took a project box and pair of XLR connectors to make a nice set of audio isolation balancing transformers for professional audio system keep those boxes with the audio wiring set and use them as problem solvers if there is some humming problem in the system which can t be easily solved in other ways Notes on selecting audio transformer If you want the best sound quality not much sound degration you must select a good audio transformer Any transformer of the proper ratio will give you a high impedance input but not any transformer will sound good Cheap transformers add distortion mostly at low frequencies and it s not the good kind of distortion They also tend to have poor high frequency response Makign good audio transformers is not easy Lower impedance transformer are generally easilier that higher impedance High Z primary is difficult to wind because the capacitance between windings starts to become a big issue with that many turns And that kills your high end There was
117. on ground and then find that there is a substantial amount of digital noise getting into the analog circuitry Then the entire board design must be redone Sometimes separate grounds are needed and sometimes they re not Star ground or metal case ar ground plane approach for analogue signal systems Star grounding and using equipment metal chassis as a common have both heir benefits and disadvanges when implementing then in equipments Audio amplifiers are are fairly sensitive to grounding schemes in terms of hum noise and rf pickup Star grounding inside is the best method for sighting against hummign and other noise problems ecexpt RF noise FOr preventing RF noise entering your system it would be best to use metal case for your equipment and connect the connector and wiring shields ground connector directly to the case in the point where the connector enters the case Star grounding as it is s very goof methodf for wiring analogue equipments But when considering high frequency RF circuits it is absolutely the wrong way to 90 because at radio frequencies wire is no longer just a wire it is effectively an inductor which causes that the star grounding scheme which works very well for lof frequencies does not work on RF The method of having RCA jacks insulated from the chassis and run the RCA grounds to the star ground is not recommended practice nowadays Ground them to the chassis this will maintain a continuous ground and supply the best
118. on to mains ground some other doesen t For example international office product safety regulations including IEC 950 and UL 1950 require that an isolation transformer is only allowed to isolate the hot and neutral wires the grounding wire must be passed straight through Since the computer circuits including data communication circuits are connected to the grounding wire and not the neutral wire the isolation transformer or any power conditioner or UPS with an isolation transformer has absolutely no affect on computer grounding problems For laboratory use there is available special isolation transformers which also isolate the ground connection at least in Finland This tranformer provides complete isolation of live and neutral wires The output can be non grounded electrical output because the tranformer provides adequate isolation Remeber that you are generally allowed to connect only one equipment to this kind of safety isolation transformer If you connect more that one equipments to safety isolation transformer you can create a potential hazard This kind of transformer is good laboratory environment but it might not considered safe or not meeting the electric code outside laboratory Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Design tips for balanced audio connections Balanced connections does not automatically guarantee hum
119. onnection must be low enough to ensure that sufficient current can flow through the protective device so that it disconnects the supply quickly lt 0 4 second and that voltage on the earth connection does not rise more than 50V Measuring the resistance of an earth electrode is not easy and should be left to professionals Safety if the neutral in the feeding is cut How safe or unsafe MEN or PME is depends on the rules which cover its application and the record of the supply utility in avoiding neutrals going open circuit The key word in the titles is MULTIPLE The exact situation will vary dramatically depending on where the break in the neutral occurs If it is just outside the substation then the neutral conductor will be replaced by all of the multiple earths in parallel and providing the load is balanced over the three phases the voltage disturbance will not be too serious When the supply company neutral goes open the neutral return is via the earth stake Soil types here range from sand to loam to clay to rock so the ground stake can range from a good to a very poor earth The voltage from each active to the neutral will depend on the loads on each phase and the ground resistance The worse the balancing of your load over the three phases the worse the voltage disturbance will be If we assume that the earthing spike has a resistance of 100 ohm it is pretty clear that your equipment is not going to work but your neutral and earthed meta
120. orld shielded data cables are often attached to both the transmitting box and the receiving box In video circuits likewise the ground is connected at both the source and the destination In audio circuits as well shields are attached at both ends of each cable there are few special excpetions to those rules but they are quite rare Where the problems come When the video and audio cables are wired between the equipments in the same rack cabinet there is not problems to be expected because all the equipments are tightly grounded together But problems can be expected as audio video ordata cable could be attached between two pieces of equipment in separate rooms separate floors or even separate buildings If the ground connection is good at the both of the ends of the cable and there is any voltage difference between those two grouding points where the equioments on the ends of the cables are connected significant voltage current travel down the shields of the cables This current flowing on the cable shields can induce humming noise to the signals inside the cable and inside the equipments connected to the cable You can see up to many volts of voltege on between the cable ends and up to amperes of current flowing on the shield which should only have micro volts or millivolts of noise Even in buildings with excellent ground systems the distances run can be so great that the natural resistance of the copper wire and metallic conduit materi
121. ou have to use a separated conductor for grounding and for neutral General information There are multiple reasons why modern electrical wiring is done so that there are separate wires for neutral and ground Two most important reasons are the following 1 Safety When there are separate wires for neutral and ground it is much less likely that a problem in electrical wiring causes a dangerous situation which will cause electrical shock or fire If the ground and neutral were the same conductor the cutting only the neutral wire for example by accident would cause the grounded metal case of the equipment to be on mains potential just because there is only live connected to equipment and that voltage can go through the equipment to the cut neutral cable and from there to equipment case When ground and neutral are separate then cut neutral causes only the equipment to stop working and no dangerous situation If ground gets cut by accident there is no danger caused before some equipment gets damaged So when there is separate wires for neutral and ground a singe wire fault cut or short circuit to other wire on any wire going to outlet does not cause immediate danger to the user of the equipment e Live shorted to ground or neutral fuse blows immediatly When fuse is blown then the dangers of electricity are gone e Neutral shorted to ground No immediate danger to use just nasty ground loop problems start to occur If there is GFCI or other
122. ound loop problems Examples of hum free systems without ground connection e Typical home stereo system where all components have ungrounded two pin mains connectors If the system has radio it uses the built in antenna or short piece of wire as antenna Examples of hum free systems with one ground connection e Typical home stereo system where all components have ungrounded two pin mains connectors The radio receiver is connected to the antenna connector in the wall e Typical home stereo system where all components have ungrounded two pin mains connectors The stereo system is connected to PC soundcard PC has grounded powwr connector e Typical home theatre system where all components have ungrounded two pin mains connector The ground ground connection is formed through TV and VCR which are connected cable TV feed e Stereo system is mostly built using components which have ungrounded power connectors One system component has grounded power connector Examples of systems with multiple ground connections but are usually hum free e Small home studio system which consists of grounded and ungrounded equipments which are located near each other All equipments are powered from one power outlet using multiple output grounded exptension power cord The system has lots og ground loops but they are very small and they don t have any current flowing in them unless there is strong changung magnetic field near the system e Typical home the
123. oundloop AES EBU interface uses the well known symmetrical connections with transformer isolation and an output impedance of 110 ohm So an AES EBU connection on the professional equipmet should not cause any groundloop problems when connected properly S PDIF connection also known as IEC60958 was also originally designed to be transformer isolated at the transmitting end So theoretically ground loops should be impossible as each coaxial S P DIF output should be equipped with an insulating transformer in order to avoid ground loop problems But in reality the sitation is not so good because in some cases because in some equipments the S PDIF output are not isolated from the rest of the circuitry Reasons for S PDIF problems In reality many coaxial S P DIF inputs and outputs of soundcards and such devices lack such transformers Maybe those products are so cost sensitive that the manufactuers have to cut corners in this way And even ifthe coaxial S P DIF output of an audio component is equipped with a transfomer hat doesn t mean that the output is isolated because in some equipments the ground of the S PDIF output connector RCA connector is still permanetly connected to the same ground as all the audio connectors instead of correctly left floating Usually the absense of isolation in S PDIF connection is not a problem in normal use but can be a problem among with those audio experts who want the best sound quality without humming Usually the
124. ows beyond a certain point the lack of a grounding plan catches up with the consumer and there is hum or worse The exact point where trouble begins depends on the specific units involved and the local power and cable TV system wiring Ideally you want the audio system grounded at a single point The grounds of the input and output connectors in typical audio equipment are typically wired to common ground in the equipment That common ground is typically connected to equipment case If the equipment has a grounded power connector then the case ground is connected to mains grounding connector If the equipment does not have the gounded power connector that ground is not connected to mains ground case is floating That is tyhe typical case in home audio equipments and also in many professional semiprofessional equipments Many commercial amps uses balanced inputs for hum reduction but that is not available in home audio equipments With home equipments the grounding situation gets worse for audio when equipments with grounded plugs are added to the system as the ground potential can vary through various circuits in your home This differing ground level will be impressed on the low level signals as common mode hum Usually the the real trouble maker in your system is the connection to the cable TV system The antenna connector shield is grounded typically in the equipment to same point as all the audio inputs equipment case but the other
125. p problems are one of the most common noise problems in audio systems Typical indication of the ground loop problem is audible 50 Hz or 60 Hz depends on mains voltage frequency used in your country noise in sound Most common situation where you meet ground loop problems are when your system includes equipment connected to earthed elecric outlet and antenna network or equipments connected to different grounded outlets around the room Everything connected to a single mains earth which is usually connected to all the earth pins in all the power sockets in one room Then antenna network is also grounded to same grounding point This would normally be okay as the grounding is only connected to each other in a star like fashion from a central earth wire leading to the real Earth via a grounding cable or metal pipe earth cables run through your power cables into the equipment Once you take into account that some of your equipment is linked with shielded cable you are quite likely to face some problems Currents could quite possibly run from one piece of equipment into the earth cable into another piece of equipment then back to the first piece via a shielded audio cable That wire loop can also pick up interference from nearby magnetic fields and radio transmitters The result is that the unwanted signal will be amplified until it is audible and clearly undesireable Even voltage differences lower than 1 mV can cause annoying humming sound on your audi
126. pments which have it is dangerous against electronic safety regulations and you risk damaging your equipment Running without a power ground will not automatically electrocute you but will make this much more propable if something goes wrong in your system NEVER use a three wire to two wire adapter on ANY piece of audio gear where a human can POSSIBLY come into contact with it You re asking for a nice 120v signal thru someone s body Yes it MIGHT eliminate the hum but there s a MUCH safer way to do the same thing Is a GFCI a substitution for ground conductor Ground fault interrupterscan be used as replacement for ground connections in three prong receptables according NEC The NEC requires that three prong receptacles without ground that are protected by GFCI must be labelled as such The NEC section 210 7 d and CEC section 26 700 9 are quite explicit that GFCIs are a legal substitute for a grounded outlet in an existing installation where there is no ground available in the outlet box But your local codes may vary Because the NEC talks only about existing installations without ground it seems that you can t use GFCI as ground fault problem solver because your system already have grounding and GFCI is a substition for grounding in installation where there is no ground conductor Transformer isolation of whole studio system You can isolate your system completely from the power company with a special transformer But if you
127. power outlets Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message How the signal cable grounding is done in typical AV equipments Grounding of case The equipments which have metal case have typically grounded power connectors In this case the metal enclosure is grounded to the ground of mains input There are some equipments with metal cases and power connector which is not grounded In those cases the the metal case is floating not connected to ground This arrangement is possible and safe if everything inside the equipment is double insulated Most modern Hifi equipments belong to this category Grounding of audio connectors The unbalanced audio inputs and outputs have theur ground side of the connector wire to audio ground which is typically connected to metal case of the equipment because the connector are typically mounted on metal case without isolation between case and connector In those cases the audio ground gets connected to mains input ground if the equipment has a grounded power connector in it This is the de facto industry standard to do the signal wire grounding and you have to live with it If the connectors are balanced then the connector grounds are typically connected to equipment central grounding point which is connected to mains ground professional audio equipments are typically grounded Video input
128. r line as well as the audio signal current A receiving cannot tell the difference between signal and hum and will amplify both if they are present If you have a humming problem with an unbalanced connection the choice is to somehow reduce the problem is to reduce the interchassis current We could eliminate it by simply breaking the chassis to chassis shield connection This is usually best done using an audio isolation transformer fitted to the line Simply just cutting the audio cable ground wire will not stop the effects of voltage differences between equipments On the other hand cutting the mains cable ground wire connection is potentially dangerous and against electrical safety code Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Advice on setting up hum free safe PA system This text is based on my personal experiences with PA systems RaneNote 110 and the advice given in Concert Sound and Lighting Systems book written by John Vasey second edition published 1993 by Focal Press Following those simple rules give you will avoid almost all causes of humming problems and you will save many hours for more creative work in your system setup Use single power feed everywhere you can If your system power requirements allow take power only from one electrical power outlet This will avoid the ground potential difference problem whic
129. r than with single phase distribution especially when the load is well balanced The power comes from the power company through 4 current carrying wires 3 phase wires and neutral wire If the current is exactly matched in all phases there is no current flowing in neutral wire The neutral wire is connected to the building ground in the central mains distribution panel where is the building main grounding bar power source From the main central distributibution panel there goes 5 wires to the subpanels 4 current carrying wires are 3 phase wires and neutral wires Safety ground is a spearate wire which also goes to the central grounding bar like neutral wire The difference of neutral and safety gound wires is that neutral wire does carry current in normal operation the difference of currents taken from each phase but safety ground does not carry any current in normal operations This separation guarantees that in normal operation the whole safety ground wire is in building ground potential This 5 wire wiring system is basically good and it is used in most buildings and places where ground loops are expected to be a problem All distribution of 3 phase voltage inside of building should be done using 5 wire system to avoid grounding potential difference problems Distribution of 1 phase power should be done using 3 wire system The safety ground wires should be interconnected in star or tree like fashion Three phase distribution in Europe
130. r to accompany but kept separate from the line and neutral conductors throughout the distribution All metal boxes should be connected to the earth What are the wire colors used in wiring House wiring colors used in USA Green body color Grounding Conductor White body color Grounded Conductor Neutral ANY other Body Color Figure that it s HOT Wiring colors used in equipment cables GREEN with YELLOW stripes Ground BLUE Neutral BROWN Live Typical colors used in house wiring in Europe Information of this is from regulations in use in Finland GREEN with YELLOW stripes Ground BLUE Neutral BROWN or BLACK Live Grounding Green or green yellow means that it s there to tie all of the stray metal parts together so that hopefully none of them can get to where they ll make a hazard A far better term for this wire is that it is the Bonding conductor Grounding wire should NEVER be asked to carry current Do not thrust the color coding unless you know under which standard the wiring is done There some some other color codes also in use Inside of any electronic equipment it is dangerous to trust any color codes unless you know which Standard that unit was built under House wiring problems Problematic old wiring The most problematic are those builing which are wired using 4 wire 3 phase wiring where neutral and ground share the same conductor at some places of wiring This is a bad thing because in this situation there will be
131. ransformer inputs and outputs are also a good way to do the impedance balancing Floating input and output will be automatically balanced if a good audio transformer is used Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Ground loops and equipment design Ground loops are not only a problem in connections between equipments When you design electronics circuits you should always avoid causing unnecessary ground loop because they cause many annoying problems A typical problem when the grounding is not done properly is that the electrical noise from the noisy parts of the circuit gets to the parts of the circuit which should be free of noise Here is some guidelines for designing grounding systems used in equipments System part interconnections When you have two circuits that are tied together electrically but one of them is high current then you should direct the ground and power paths to feed them separately You want the current of the driver to stay on the driver side and the current of the logic to stay on it s own side The thin trace inbetween is still needed because this is not galvantic isolation e gt lt e jm eee lt lt lt lt physical CURRENT POWER FOR REGULATOR LOGIC separation gt gt gt gt DRIVER DRIVERS e gt ground lt e iat as ai un nn thick thin x traces traces very thick
132. re going to go to the trouble of doing this you might as well consider rewiring your studio with good power system which has proper start grounding The use only professional equipments with balanced audio input and outputs and do the wiring correctly If you stil face problems you can consider using balanced power system to power your equipments Solving the ground loop hum problem using the right ground loop isolator is the safe effective way to eliminate unwanted hums at an affordable price Typically ground loop problems can be solved with audio isolation transformers connected to the audio line There are also commercial audio distribution amplifiers which provide this isolation Regardless of what type of ground loop isolation method is used remember never remove the ground prong on the power cable This may work as a temporary solution but personal safety should not be compromised If you can t find the ground loop and don t want to use isolation transformer try tempting the circuit with an even better ground Heavy gauge wire has very little electrical resistance so less current is likely to flow through the shield Get some heavy gauge wire and run lengths of it from your computer s chassis to each other chassis On audio equipment there s usually a screw marked for this purpose You should hear the hum go down as soon as you make the connection If heavy duty ground connections don t stop the hum you ll have to use suitable isola
133. remely important and is a major safety and signal issue These simple rules apply to ALL cabling including CATV Video AC and signal One exception is the ethernet Ground the computer LAN one end preferably to the same point as your audio system and make sure that the thin ethernet connector metal parts do not touch any parts of computer case there are nice plastic isolation cases available for them would recommend to use 10 Base T ethernet which used twisted pair wiring because it does not need any grounding and does not cause ground loops in any case What are isolated ground receptables NOTE The following description describes isolated ground as defined in USA wiring system In other countries isolated ground can mean different things for example real ground but not connected to the power ground bar Many new buildings in USA are equipped with Isolated ground receptacles These are normally recognizable because they are bright orange and have a triangle marked on the face Basically these receptacles have a separate green wire equipment ground and the wire goes back directly to the circuit breaker panel without being connected to anything else Isolated ground receptacles are installed in the hope that electrical noise generated in the building or by other pieces of equipment will not disturb the operation of delicate computer equipment plugged into them As far as what the NEC allows an isolated ground is a grounding conne
134. ribution system wires Grounding provides an alternative path around the electrical system of your home or workplace minimizes damage from such occurances Voltage stabilization There are many sources of electricity Every transformer can be considered a separate source If there were not a common reference point for all these voltage sources it would be extremely difficult to calculate their relationships to each other The earth is the most omnipresent conductive surface and so it was adopted in the very beginnings of electrical deistirution systems as a nearly universal standard for all electric systems Current path in order to facilitate the operation of overcurrent devices This purpose of grounding is the most important one to understand Grounding system provides certain level of safety to humans and property in case of equipment damages Grounding operation in electrical distribution network The main reason why grounding is used in electrical distribution network is the safety when all metallic parts in electrical equipments are grounded then if the insulation inside the equipments fails there are no dangerous voltages present in the equipment case Then the live wire touches the grounded case then the circuit is effectively shorted and fuse will immediatly blow When the fuse is blown then the dangerous voltages are away The safety is the primary function of grounding Grounding systems are designed so that they do provide the necessary
135. rmer which is ment for audio use Usually when you install an audio galvanic isolatio any type to almost any place in the audio cable connection is solves the ground loop caused humming problem nicely Possible isolation components The most suitable component for audio line galvanic isolation is audio transformer It is very compact completely passive and widely available For audio signal isolation transformers are the way to go and they have been used for this application in audio studios successfully for test of years In audio studios commonly used technique very traditional is to balance the lines between the systems using audio transformers which do the balancing and galvanic isolation While optoisolators can be used to isolate grounds they have insufficient linearity and dynamic range for analog audio Optoisolators have also the problem that circuit using them will always need some external poer source to operate do not recommend using optisolators for any high quality audio isolation application Transformer use Cheapest transformers for audio use have some problems on the sound quality typically distorted bass response and attenuating in high frequency response Basically a poor transformer slows down upper frequencies and allow the low frequencies to pass first creating what we perceive as a fat warm tone Inadequate frequency response on the low end rolloff at like 20Hz causes low frequencies to be slowed allowing the upp
136. ry is wired between output XLR pins 2 and 3 The grounding pin 1 of the output XLR connector can be wired to metal case of the isolator but do not connect the input XLR connector pin 1 to anything LINE OUT PLT The transformer to be used in the circuit above should be 600 600 ohm audio transformer which can handle the signal levels you are about to transfer through the isolator wihtout causing too much distortion or other problems not very low signal level microphone transformer for line signals etc The transformer which is used should have very flat frequency response over the whole audio frequency range 20Hz 20kHz and even more This kind of isoltion transformer circuit should be best connected on the receiving end equipment input end of the cable to get best performance If the cable is not very long not many meters in practice it does not matter to which end of the cable this transformer isolation circuit is connected ensen Transformers has a good application note T 11SSP 6M 600 Ohm Line Isolation Application which deascribes how to built a very nice isolation transformer for 600 ohm balanced audio lines Other simpler design is described at J T 11 DM Bbasic Hum Stopper Transformer isolation box Both of the designs use more components than my simple deisgn but are expected to perform better under stron RF fields Circuits I have built Circuit using telephone line transformers built my first isolatiors using two high qu
137. s Video inputs are unbalanced connectors Their ground is typically connected to equipment metal case and video circuitry ground of the equipment If the equipment has a grounded power connector then those video inputs get grounded to mains ground Antenna connectors The most commonly in recievers and VCRs then ground of the antenna input is connected to equipment metal case This means that if an ungrounded equipment is connecte to grounded antenna network the equipment gets grounded through the antenna cable index back site search acronyms discussion mail to a friend post message Mains connections 3 phase distribution The most common way toi distribute high power to building is 3 phase system That 3 phases system has advantages that it saves wiring copper and is very suitable for driving powerful electric motors The wiring is designed so that it need that the power takem from each phase should be about equal This is done by connecting all high power loads to all three phases and distributing all smaller loads eventually to those three phases Three phase power has three hot wires 120 degrees out of phase with each other These are usually used for large motors because it is more efficient provides a bit more starting torque and because the motors are simpler and hence cheaper The 3 phase wiring is usually used in electrical distribution because the power can be carried with a little bit less coppe
138. s to be considered safe The above is the objective and all the crap around it is just to make it difficult Ground means something connected to the surrounding and it must be less then x ohms measured with AC and the wire must handle the short circuit current present in the circuit without overheating Sources e Frequently Asked Questions on Electrical Wiring by Chris Lewis and Steven Bellovin e Grounding article from CodeCheck com e Shock Hazard and Grounding by Jack Sondermeyer from Peavey web document which is no longer available Other useful grounding links e Why Ground from Q amp A Electrical from CodeCheck com e The shocking story of grounding e Two Modern Power Quality Issues Harmonics amp Grounding from Copper Building Wire home page e Residential Wiring and Grounding Guidelines from Power Clinic e The Hows and Whys of Isolated Grounding e United States Practices to Protect People and Equipment Against Lightning from Power Quality magazine Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Ground loop basics What is ground loop A ground loop occurs when there is more than one ground connection path between two pieces of equipment The duplicate ground paths form the equivalent of a loop antenna which very efficiently picks up interference currents Lead resistance transforms these
139. safety functions Grounding also have other functions in some applications but the safety should not be compromised in any case Grounding is quite often used to provide common ground reference potential for all equipments but the existing building grounding systems might not provide good enough ground potential for all equipments which might lead to ground potential difference and ground loop problems which are common problems in computer networks and audio video systems How electric shock happens The hot wire is at 120 volts or 230 volts depends on the mains voltage used in your country and the other wire is neutral or ground If a person were to touch the neutral wire only no shock would result simply because there is no voltage on it If he were to touch the hot wire only again nothing would happen to him unless some other part of his body were to become grounded A person is considered to be grounded if he comes in contact with a water pipe metal conduit the neutral or ground wire or stands barefoot on a concrete floor In other words neither wire is a shock hazard unless a person is grounded and then only the hot is a potential shock hazard Of course if a person were to touch both wires at the same time he would be shocked simply because his body is completing connection between hot and ground wires Metal case safety Back in the early days equipment and appliances fitted with the two wire power plug were readily accepted to b
140. se If the noise is lower the AC service may be the cause Magnetic fields from transformers can cause humming Mains transformers typically cause an AC magnetic field around them This magnetic field can be copled to wiring electronics or signal transformers and cause humming Typically audio electronics are designed so that the magnetic felds caused by the mains transformer are not coupled to the sensitive elctronics in the equipment but the magnetic fields from other equipments can be coupled to the electronics If you have many equipments which have transformers inside them stacked together then you have a risk that the magnetic field form other equipment s transformers can cause hummign to the other equipments The normal aluminium case does not provide much protection against low frequency magnetic fields and only steel case can shield agains magnetic fields Some power transformers in powerful equipments like amplifier are leaking a pretty heavy magnetic field This has something to do with it being cheaply constructed without good core material and something to do with the design configuration Leaving a couple blank spaces between the equipment with that leaky power transformer and anything else might help You can also try moving things around so the units that are least suceptable to hum pickup are closest to humming source Many equipments nowadays use small wallwarts which you plut go wall socket Those transformers are usually chapely bui
141. se distribution which uses a 5 wire system In the 5 wire system there are 3 hot wires 1 neutral wire and 1 grounding wire The common 3 wire receptacle uses only one of the 3 hot wires This 5 wire wiring system is basically good and it is used in most buildings and places where ground loops are expected to be a problem power source This three phase power system is called THREE PHASE STAR FOUR WIRE EARTHED NEUTRAL system This is the most common way used in European wiring systems and used almost everywhere in Finland but note that three phase distribution circuits come in several flavours There is a distinct difference between those in the US and those in Europe They are classified as follows e TN Transformer star point earthed Protective Earth and Neutral share the ground conductor PEN and are separated at the fuse panel This circuit is also referred to as TN C C for common PE and N In UK this is called TN C S i e combined in supply and separate in the installation and it is also referred to as Protective Muliple Earthing PME as the PEN supply conductor is grounded at regular intervals along the supply e TN S As above but PE and N are brought separatley all the way from the earthed transformer and never allowed to get into contact with each other elsewhere The idea is that PE shall never carry any current it shall consequently not carry any potential and is supposed to be very clean All return currents go throu
142. sformers e Anna Valley Electronics TYPE 2000 ISOLATOR four separately isolated inputs suitable also for computer signals e Brick Distribution Amplifiers with differential input from Video Accessory Corporation e Deerfield Lab wideband isolation transformers e ES 3230 decoupling video transformers e GLI250 Ground Loop Isolator 250 MHz ground loop isolator for workstation video signals from Extron Electronics e Humbug video isolator from Tecton provides 600V isolation e Inline Inc IN2062 IN2063 RGBHV RGB Hum Suppressors e IN2062 IN2063 RGBHV RGB Passive Hum Suppressors from Inline Inc e Jensen Transformers company which makes video isolation tranformers for example so Max VB 1RR and VB 1BB e North Hills Signal Processing Video Isolation Transformers and Humbucking Transformers e Steven amp Billington Limited Video Isolation Transformer e Telecommnect Ground Loop Transformer e Video Hum Stoppers Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Networked computer equipments and ground loops Power related problems were the number one cause of computer downtime according studies condicted by Contingency Planning Research and Stratus Computer 1994 Many of the power related problems can be traced to the most basic element of the computer network The wiring and grounding of t
143. shielded cable and balanced connection is very effective way to fight against magnetic noise A cable type callsed star quad improves magnetic noise resistance of the cable by effectively averaging the gmanetic pickup of four conductors the downside of this cable is higher price harder connection to connectors and higher cable capacitance than normal shielded thisted pair cables Even when you are using twisted pair cables all parts of your system are not completerly shielded against magnetically picked noise Every part of the signal chain where the cable condictors are not twisted can still pick up magnetic interference A mated pair of XLR connectors leaves many centimeters 3 5 centimeters of signal conductors untwisted and is very vulnerable to magnetic pickup It woudl be bad idea to lay pair of such connectors near any strong magnetic field like on top of power amplifier or audio equipment mains power supply Wires are not the only components in audio system which can pick up magnetic fields Any audio transformer can also pick up magnetic noise good ones less porer ones more If your audio system used audio isolation transformers for audio signal isolation it si a very good idea to keep those away from magnetic noise sources Tomi Engdahl lt Tomi Engdahl iki fi gt
144. solated use special cable assemblies to solve the humming problems Use unbalanced cables for short distances Any unbalanced cable must be kept under few meters in length Cable lengths longer than this will amplify all the nasty side effects of unbalanced circuitry s ground loops Keep your audio cables away from power wires and transformers Power wires generate magnetic field around them and this can cause humming to the audio cables Especially avoid placing your audio cables near you main power feeding cables and cables which are connected to lighting system the dimmers cause very fast current changes to cables which induce easily humming to audio cables Keep the audio cables at least half meter away from power cables If the audio cables must cross power cable then they must cross them at axactly 90 degree angle to keep the hum coupling minimum Isolate ground in all wires which go to equipment connected to separate power feed If you must connect equipments which are powered from other power source than your mixing desk then you must make sure that they don t cause ground loop problem Safest choice is to use audio isolation transformer in every connection you need to equipments connected outside your dedicated audio power feed For balanced connections also ground lift in audio wire is an acceptable way to isolate audio grounding between different system If your power amplifiers are connected to different power feed than your mixing d
145. t They Really Are ground loops are a mystery to many people Using Grounding to Control EMI grounding issues in general and for medical equipments describes ground loops well What is a ground loop Electrical mains wiring grounding issues Grounding mutipart article on electrical system grounding issues with view to safety and noise issues three part article in the end of Cherryland Amateur Radio Club online magazine Cherry Juice read part 1 part 2 and part 3 Grounding and Wiring for Electronic Equipment general installation on grounding practices in electrical distribution systems Ground Resistance Principles Testing Techniques amp Applications Isolated Grounding a technique often used with sensitive electronic equipment in USA to reduce common mode noise Testing grounding conductors and grounding electrodes The Hows and Whys of Isolated Grounding in isolated grounding receptacle grounding terminals are electrically insulated from the receptacle mounting insulating the receptacle grounding circuit from the metallic conduit grounding system when the receptacle is installed in a metal outlet box to reduce noise interference Two Modern Power Quality Issues Harmonics amp Grounding Audio and video systems installations 2 A Clean Audio Installation Guide by Benchmark Media Systems Balanced Line Technology technical description of audio connections used in professional audio systems Groun
146. t from plastic back between the RCA jack s ground shield and the receptacle Another solution is cut the cable ground connection inside the jack If you are in buiness of modifying a cable to include groundlift option would recommend adding a small capcitor to the place where you cut the cable to reduce the possibility of the ground lifted cable to pick up RF interference Using ground lift circuits Ground lift circuit would reduce possibilities of audible ground loops A truly covers all bases piece of equipment would have a switch to activate or deactivate the ground lift To test if your equipment has ground lift insert a balanced TRS or XLR cable into the equipment and measure the resistance between the shield contact of the exposed connector and the casing of the equipment or the earth pin of the mains cable of the equipment using a multimeter If there s a 1000hm to 5000hm resistance your equipment is ground lifted Ground lift is quite effective in balanced audio connections but is much less useful in unbalanced connections which is the connection type used in almost all consumer audio equipments You might try this ground lift scheme with this connection type but the results would be much worse Even when you can limit the shield connector current to values which do not cause problems there is still the ground potential difference between equipments which gets amplified and you get still some 50 Hz noise Even ground potential differere
147. t pass significantly 50 Hz signals so the ground loop is eliminated The circuit can be easily built into antenna connector or to a small box would recommend to use small metal box where you connect one of the antenna connectors to the metal box and isolate other connector from box Metal box allows mechanically strong contruction and provides good shielding against radio interference The capacitors in the circuit should be rated at least 250VAC 400V DC to make sure that the adapter with stands situation when antenna network ot television radio is floating at mains live potential C1 l nF Le l nF CLECE 2304 There is one disadvantage of this the circuit breaks the continuous shielding of the antenna cable which makes you antenna cable pick up radio interference more easily for example radio interference picked by ground loop itself Usually this is no big problem but if you notice severe interference then you might have to stop using this isolator The beast place tu put this isolator to keep possibility of interference minimun is just between TV receiver and antenna cable going to wall This capacitor isolator scheme might feel quite strange at the first sight but it actually works and cuts the ground loop because it provides high impedance to low frequencies 50 or 60 Hz mains frequency but has low impedance at the RF frequencies that are used at cable for TV channels To eliminate the hum you must insert a high impedance at 60
148. t your computer sound card to a stereo receiver which is connected to wall antenna plug The computer is connected to grounded power outlet which causes that the sound card audio ground is connected to mains ground The receivers gets connected to antenna ground because it is wired to the antenna plug in the wall The mains ground and antenna are tied together ar at least should have somewhere else in the house Unfortunately there is all kinds of electricla interference which can be coupled to those grounding wires and cause small potential differences between the ground on the antenna outlet and your mains outlet The small potential difference causes small current flowing through the equipments and cables which causes hummign to them antenna 4 lt 222 receiver Computer plug Ei audio cable If you want to get rid of this annoying humming problem then first remove the antenna connection of your receiver If removing antenna cable helps to get rid of humming then get an antenna isolator to the antenna connection of your receiver or an audio isolator to the audio cable between your computer and the receiver Typical computer audio problem case have my computer soundcard connectoed to my HiFi system connected my TV to my AV receiver and get very loud buzzing even if the TV is off Same also happens if connect my VCR to the AV receiver decided to go through the routine ground loop
149. television For lightning protection any antenna masts should be grounded here as well Ground connection points from the telephone system controller security alarm panel audio equipment and other electronics gear should be connected to this ground buss All distribution of 3 phase voltage inside of building should be done using 5 wire system Distribution of 1 phase power should be done using 3 wire system The safety ground wires should be interconnected in star or tree like fashion For more information check Residential Wiring and Grounding Guidelines from Power Clinic If possible all electronics and computer equipment should have a separate isolated electrical subpanel with isolated ground receptacles provided at all locations remote from the main Isolated ground means that the ground wiring is otherwise isolated form all other wiring except that it is connected to the main grounding bar for one single point This practice will ensure that all electronic equipment grounds are at the exact same electrical potential and avoid the minute differences in grounds that cause ground loops These differences are reflected in signal carrying conductors or shields between the components and may be amplified to audible or visible levels Components that cannot have equal potential grounds should have signals that are isolated from each other This can be expensive and difficult to achieve It is much easier to prevent the problems in the first place w
150. the cable this arrangement makes the cable more prone to pick up radio frequency interference This kind of ground lift circuits are built in to some equipments can be activated using switch and they are available as ready made products like GLX GROUND LIFTER and similar The shield of the cable is conneted to pin 1 only in one end of the cable It s more common to tie the shield at the sending end and lift it at the receiving end Either way will work but tying the shield at the sending end has some advantages for reducing crosstalk Partial ground lift with RFI filtering for balanced XLR connectors 10 nF L I 1 I 1 100 ohm 2 2 Bm 3 This ground lift connection does not fully cut the gound carrying cable shield but icreases the resistance so much that the currents which would flow in the shield in typical ground loop situation are limited to so low values that they have no effect in system performance Because the ground is not completely cut then the circuit also works also when ungrounded consumer equipments with RCA gt XLR adapters are connected to the system The capacitor makes sure that the cable shield appears to be continuous to the radio frequency signals radio frequency interference protection provided by shield is not lost This circuit is quite universal and I have used this circuit for succesfully solving some balanced circuit ground loop problems Telescoping shield cables In the au
151. the center pins with one 10 nF capacitor and use the connectors mounting nuts to connect a second 10 nF capacitor between the bodies making sure that the connectors don t touch You can then wrap the center with tape or put heat shrinking plastic tubing on it This construction is a little flimsy but it won t get any stress and the leads will be shorter than if you used a plastic box to mount the connectors thus reducing the possibility of picking up RF interference When constructiong the circuit remeber to keep all the component leads very short remeber that you are dealign with very high frequency RF signals which can easily radiate out of circuit on even wuite short wires and those wires can pick up interference as well or use a very small plastic box for the whole circuit Transformer isolator using two baluns There is an alternative approach to antenna isolation problem use transformer as in audio lines The problem is to how to make a good transformer for antenna signals If the transformer causes impedance mismaches this can cause signal reflections which disturb you and maybe your neighbours also One way to do it is to use readily availabe 75 ohm to 300 ohm transformers called baluns or matching transformers used when connecting old televisions with 300 ohm antenna input to modern antenna network with 75 ohm connectors Those units are readily available from TV shops Notice that some 300 75 baluns are true isolated transformers w
152. the gate unless the sound has a signal level which is higher than the set threshold value If the problematic hum source is some instrument and the hum is very faint a noise gate can make less annoying When you set the noise gate threshold so that the gate does not pass any signal when there is no signal from the instrument then the hum is not added to the main mix When the instrument is played a very weak humming is quite hard to notice Commercial products for audio line ground loop elimination e ES034 Ground loop isolator isolation transformer for car audio from Scosche Industries e FGA 40 Ground Isolator is 1 1 audio isolation transformer with 10 kohm impedance from Monacor Best Nr 06 4370 e Ground LP Isolator 270 0054 from Radio Shack designed for car audio Equipment to remove hummign already in signal e N Hummer 1a AC Line Noise Eliminator from Stro Lion Technologies e SN 700 Noise Hum Eliminator a single ended realtime noise eliminator which tries to eliminate huming noise form audio lines made by Roland index back site search acronyms discussion mail to a friend post message Reducing Microphone Hum Microphones and microphone cables are espefially sensitive to hum picpup because of the great amplification needed for microphone level signals few millivolts The hummign can be caused to microphone signals because of ground loops and because of induced noise Here are some tips to mi
153. the wire which causes 0 1V voltage difference between those two equipemt grounding points Signal Interconnection line Signal 0 1V Grounded Equipments Safety Ground Wire AC voltage caused by Resistance 0 1 ohm current in ground wire 1 A current flowing Because there is voltage difference between the ewuipments the signal in the interconnection wire sees that difference added to signal This canbe heard as humming noise on the wire because the AC current cause the voltage difference of those ground potentials to be also AC voltage This is one reason for this 50 Hz or 60 Hz noise you hear in the audio signal or see in video signal as annoying horizonal bars Another problem is the current flowing in the signal cable grounding wire This current passes though the cable and through the equipment Of the way the curren parsses is not weel designed this can cause lots noise to the equipment or other kind of problems like computer lockups Lots of designers count on ground being ground and do not optimize their design to eliminate their sensitivity to ground noise If you are a product desiger remeber to take care that ground loop current does not cause problems in your equipment by designing proper grounding scheme inside the equipment Why ground loop is a problem Ground loop is a common problem when connecting multiple audio visual system components together there is a good change of making a nasty ground loops Ground loo
154. thod and it should be only used as temporary solution Here is a typical ground lift circuit for unbalanced connections Ground not connected Ground Try this circuit only if you know that both equipments are properly grounded If the equipments are properly grounded this circuit will cause enormous amounts of humming and potentially damage the input amplifier of the receiving equipment because of the flowing stray currents on the ungrounded equipment The best solution for solving unblanced connection ground loops is using audio line isolation transformer Note on using the circuit Because this circuit cuts the shield of the audio cable this greatly reduces the RF shielding which the continuos cable shielding normally provides If you are using the circuit above be sure that there are no severe RF interference sources like mobile phones or communication radios near your audio system The RF shielding of the circuit can be made better by using the circuit aboe which provides cable shield continuity to RF signals but works as ground lift for audio frequencies If you happen to use RCA connectors in audio connections you can try if this ground lift helps if you partially remove the RCA connectors so that the center pin touches the jack but the outer ground does not connect the jack side If this solved the problem then you can do the ground lift circuit In RCA connectors you can do the ground lift by inserting a rolled up paper strip or plastic cu
155. tlet connection uses one phase and ground Three phase is usally used only on some permanetly wired high power loads typically ovens and electric stoves in normal household A typical rating for mains fuse in typical household in Finland which has three phase power is 3x25A 25A per phase If three phase connector is avaible some heavy equipments in places where heavy machinery is used then the most common one available is 3x16A connection Other possibilities for power distribution Some smaller electrical installations small houses only use one phase feed In those cases the power company only brings one of the three phases to the house In those cases the wiring from power company is implemented using two wires neutral ground and phase The frequency in USA is 60 Hz and nominal voltage in USA is defined in the following manner e 120 volts is the voltage at the transformer e 115 volts is the voltage at the panel voltage drop losses in the cable from the transformer to the panel e 110 volts is the voltage at the receptacle voltage drop losses in the cable from the panel to the receptacle So if the outlest are very lightly loaded you will get nearly 120V and if wiring hevily loaded the voltage drops to around 110V In Europe the frequency is 50 Hz and voltage on the outlet is nowadays is 230V the real voltage typically is between 220V and 240V In USA the domestical service has typically 3 wires 2 hots and a neutral The voltage
156. to balanced power articles should give you a good overview of the balanced power systems Remember that most of those articles are written by the manufacturers of balanced power systems e Audio noise and AC systems revisited e Lifting the Grounding Enigma e Power management in studio There are other alternatives than balanced power If you are looking to quiet down a studio you have also other alternatives than just go straight to balanced power system Usually the ground loop induced humming problems can be solved with carefully designed audio and mains wiring Taking the power for all equipments from single source usually keeps the humming problems away if the equipments are properly designed connected together in the right way Try a good common isolation transformer if you are trying to solve power line borne problems And good quality 1 1 audio isolation transformer in problematic audio lines will always help you to get rid of humming and noise Some on line UPS equipments provide galvanic isolation and good mains power noise reductions UPS also provides you some safety against high voltage spikes and power interruptions Be prepared to buy a good UPS with sinewave output because if the UPS output is not good sinewave you can get noise problems because of bad power that the UPS gives out Stay away from the cheapest computer UPSes The problem with these is that they have a lot of line harmonics on them and they can make noise problems
157. tor in that audio line Direct DI boxes as ground loop problem solvers Direct boxes are devices that convert unbalanced instrument level or line level outputs into balanced microphone level inputs They are used heavily in large arena size sound reinforcement systems where the keyboards etc are located far away from the mixer Impedance differences between the keyboard and mixer prohibit one from running cables directly out of the bass amp of keyboard and to the mixer To use the Direct Box one takes the guitar amp s output it usually has one on the back and using a 1 4 patch cable plug the other end into the direct box input Make sure that the switch if it has one labeled Speaker Instrument is on Instrument Plug a normal XLR cable into the output end and the other into your cabling which goes to the mixer If the system is grounded at bothe ends and ground potentials start flowing you ll get a ground loop Ground loops can be identified by a low hum 60Hz in the US and 50 Hz in Europe through the sound system First place to check direct box Direct box usually has a switch labeled Ground Lift for solving this type of problem The ground lift switch will lift the ground safely and the hum should stop If the switch isn t there use a special ground lift cable on the XLR cable Do not by any means disconnect the grounding pin of the AC cord How to use noise gate to reduce hum Noise gate does not let any sound through
158. ts in one room so this trick can avoid many problems If this doesn t work call in an electrician to make sure that your buildings earth actually works at all you could be risking your life otherwise Tips for building well working systems As with any project planning can have adirect effect on the results Before you start setting everything up you should decide where your equipment will be placed Now determine where to run the cables For initial testing connect all of your components and run your cables across the floor out in the open Once you are satisfied with the way everything is setup make sure everything is working properly ou are now ready to permanently install the system and run the cables Run the cables in the predetermined locations being aware of electrical and coax anteenna wiring Do not run your audio cables parrallel to these types of cables because they tend usually be quite strong noise sources for audio cables When making connections use the established color coding system for consumer electronics White is left Red is Right and yellow is video When running cables thru walls make sure you use cable types approved for permanent installation have found that it is essential to keep a flashlight handy and work with a second person You should keep in mind that properly installing and setting up your equipment is just as important as selecting it Spend a little time planning your system and installation will save time
159. tted directly to the source and the receiving end must be protperly terminated for reliable operation The reason for this is that the transformer input and output impedances are not exactly 75 ohm Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Grounding and Rack Installations General practices In the data and broadcast world virtually all equipment is mounted in upright metal cabinets or racks By doing so it is easy to establish safety ground and mechanically stable construction When all equipments are mounted on rack cabinets which have grounded with a large wire running to a central ground point it is easy to establish safety ground Second and most likely conduit running in and out of therack will be the mains power cord Virtuallyall professional audio and video equipments have a grounded three pin inUSA power cord That the gounding connection in power plug is connected inside that piece of equipment to the metal box or chassis of the equipment thus grounding the box and reducing the possibility of shock hazard to the user There are also other ground circuits going into and out of the equipments and equipment rack If shielded signal cables are used for input or output as almost always is the shield of the cable is grounded to the metal box of that piece of equipment where the cable is connected Generally in the data w
160. ve two legs of AC which are 180 out of phase with respect to one another with respect to ground so that your ground currents cancel out The important fact not noted is that the center tap is also situated as a the center of the output voltage swing That s the key in a balanced power system Balanced power is not high tech stuff Power transformers don t need to be wideband they don t need to have extremely low distortion and they don t need to work on a wide variety of different voltages with extreme linearity On the other hand they do need to be able to work into a wide variety of loads The transformers used in balanced power units are specially would toroid transformers The windings have to match perfectly or the balanced aspect of the power doesn t work How is the balanced power claimed to help The manufacturers of balanced power systems claims that balanced power solves all ground loop problems in audio and video systems Typical claims are also that you get much better noise margin If you have chassis leakage problems it can be a miracle If you don t it doesn t do any better than any other isolation transformer haven t had the need to use balanced power but in theory it solves similar problems in a similar manner that a balanced audio signal does namely noise cancellation Not to blindly be relied on to fix everything or to be a substitute for careful troubleshooting The typical claim made by the the salesman of balanc
161. voltage level bounce on signal lines For digital lines this isn t a problem unless you cross a logic threshold For analog it s just plain noise to be added to your signals How to eliminate this problem why the suggestion of keeping analog and digital grounds separate is made by having them separate on the IC so use separate grounds Two completely separate supplies allows switching currents to be speced and optimized for at the regulator and to have analog supply optimized to be nice and quiet Filtering and bypassing can help to short out some ground bounce currents And if you connect the analogue and digital grounds together do it only in one single well designed place If you are building an analogue to digital converter circuit then you have to be very careful in keeping the analogue and digital grounds separare or otherwise you will not get the resolution you expect to get because of the noise The AGND and DGND pins should connect to the analogue ground preferably with it flooded under the whole IC package If you don t do this noise on the DGND pin fom the digital supply will get injected into the analogue section inside the IC Decouplers should be placed close to the AVDD pins analogue supply which connect to the analogue supply plane In order to stop noise being introduced to the analogue plane OR being injected into the analogue section of the chip from the DVDD pin the DVDD pin should be connected to the analogue supply plane via a s
162. with an external MAU The MAU provides an electrical connection to the thick Ethernet coax and transfers signals between the Ethernet interface and the network segment The MAU is powered from the Ethernet interface but all signal lines coming to the MAU are electrically isolated in the ethernet card The standard notes that the thick coax segment should be grounded at one point for electrical safety reasons There must only be one grounding point to avoid disrupting the Ethernet signals carried by the cable All other metal parts on the cable should be insulated or carefully routed and fastened in place with plastic cable ties to avoid accidentally touching an electrical ground If the components and cables conencted to MAY are properly isolated from nearly grounded metal parts the system is ground loop problem free Thin Ethernet Thin Ethernet 10Base 2 uses coaxial cable which goes from computer to another That cable should be grounded from one end for safety resons That cable is electrically isolated from the computers at the ethernet card The cable shield be accidentally and easily get in contact with the matal case of the computer if the metal connectors in the cable touch the matal case of the computer To avoid this kind of problems it is a good idea to use connectors which have plastick isolation over them or install a platic isolation around them Make sure that the you don t have any metal connectors or broken cable shields connectors tou
163. won t do anything or anything more than plugging all your equipments to one extension cord Balanced power is a particular tool to solve a particular problem Because balanced power uses isolation transformer this can help to stop some interferences from mains power to enter you audio equipment power system But simple transformer does not usually do much help on this either Tips on buying balanced power systems Sometimes balanced power helps sometimes it doesn t and it s nearly impossible to predict The only advice can offer is to buy from a dealer who will let you return it But if you re having a hum problem try to fix it by studying out your system grounds first Equipment that is designed built and connected correctly shouldn t need a balanced power source to make basic problems go away You probably can t do anything about the equipment design or construction some people modify internal wiring to correct a manufacturing deficiency but you can by isolation procedures examine your grounding and shielding to make sure you haven t created a problem Who makes balanced power systems e Equitech is the pioneer of the ba anced power systems e Electronic Specialits makes isolation transformers and power conditioners for many different applications e Furman makes cheaper balanced power systems e PowerPRO 20 is a balanced power product by Cinepro Where I can find more information on balanced power systems The following links
164. worse for that reason Tomi Engdahl lt Tomi Engdahl iki fi gt index back site search acronyms discussion mail to a friend post message Ground loops and audio racks The quipments connected to metal audio racks will get connected to each other through the metal rack This can lead th ground loop problems if the wiring is not done carefully If you face this type of problems do not use insulating tape or other non conducting materials to cure the problem That could end up being very dangerous Instead think of a redesign How to construct rack system Assuming that this rack is the hub of your plant then proceed as follows It s called hub and spoke grounding Begin with an empty rack standing in the middle of the floor First bring AC to the rack allowing for expansion Buy one or two five foot pieces of wire mold with recepticles spaced every four inches Bond the green wire from the recepticles to the rack so that the rack is at the same electrical potential as the earth ground for the AC You can add more racks and wiremold strips as needed until you have adequate rack space Bolt all racks together until there is NO question that they are electrically just one piece of metal Mount the power supply for the console in this rack Mount all outboard equiopment in the rack View the rack as a hub for ALL business at your plant Start substituting the word hub for rack Spoke 1 Run a single piec
165. y electrical noise Consumer audio devices use unbalanced cables and are very prone to picking up noise especially at low signal levels from devices such as microphones Balanced circuits have an inherent ability to only pass audio signals and reject unwanted noise Balanced refers to the fact that there are two symmetrical signal lines and one ground while unbalanced uses just one signal line in reference to ground Normally XLR connectors are used in most balanced devices while unbalanced consumer gear normally use mini plug or RCA connectors Do not ground the XLR connector shells The recommended practice in professional audio community is not to ground the shells of XLR connectors The reason is XLR shell can come easily in contact with metal railings or somethign else which is grounded to somewhere else than your audio system If your shells are not grounded nothing harmful will happen But if you have for some reason grounded the XLR connector shell to audio ground you will get hummign to your system because all kind of ground paths loops and sorting yout those can drive you crazy It is best to leave the sells not connected so you don t add a new intermittent problems to your audio systems Transformer isolate all unbalanced connections If you have a mixed balanced and unbalanced system do yourself a favor and use isolation transformers in every connection between balanced and unbalanced system When unbalanced lines cannot be transformer i
166. y new buildings in USA are equipped with Isolated ground receptacles These are normally recognizable because they are bright orange and have a triangle marked on the face Basically these receptacles have a separate green wire equipment ground and the wire goes back directly to the circuit breaker panel without being connected to anything else Isolated ground receptacles are installed in the hope that electrical noise generated in the building or by other pieces of equipment will not disturb the operation of delicate computer equipment plugged into them The black hot wire goes to the brass or copper screw which is connected to the right smaller slot The white neutral wire goes to the silver or chrome screw which is connected to the left larger slot The bare wire ground goes to the green screw for the separate ground path These connections should always be made by a qualified electrician IEC connector IEC connector is a standard international mains connector used in equipments like computers printers fax machines and many other grounded quipments which have removable power cord The same connector is used in both 120V and 230V equipments The connector can handle voltages up to 250V and current up to 10A SCHUKO Finland Sweden Germany and many other European countries use a SCHUKO mains connector CEE 7 7 in grounded equipments The connector provides two pins for carrying live and neutral wires current up to 16 A
167. y transient high voltage spikes that may be induced on to the shield What wiring practices are used in practice The professional lighting and sound industries generally favour solution 4 based on practical experience of what works and is reliable There are also ground both ends people in sound industries who remain unconvinced of this and use option 1 Video industry generally favours option 1 When considering the wiring for other application you need to consider following things e What are the chances of large earth currents e What are the chances of excessive emission from cables whose screens are not earthed at low frequencies at both ends index back site search acronyms discussion mail to a friend post message What s the problem in grounding systems used in buildings NOTE This documents tries to give you general information about electrical wiring inside building This documents is only written to give a general understanding of some of the most common electrical wiring systems This document is not ment to be an accurate description of all wiring systems Don t do any electrical work based on information provided here Leave the work to professionals who know all this and the local regulations Building grounding In the construction of most commercial buildings one ground is usually run throughout the building to keep the impedance as low as possible Low impedance in the ground is needed

Ground loop problems and how to get rid of them

Contents

Download Pdf Manuals

Related Search

Related Contents