Instruction Manual 207
Contents
1. a a AEE S a EE EESE R 19 7 0 APPENDICES Appendix A Introduction to Balanced and Unbalanced Wiring 20 Appendix B Dealing With Ground and HUM ssssnnsssssnnusssnnnnsssrinnssrrrirssrrrrrssrrrursrrrrresrrrrrerrrreren 21 Appendix C 23 Appendix D Standard Cable Wiring 24 Aphex Systems Ltd Model 207 Page 3 e 0 1 0 Controls and Indicators with Quick Setup POWER ON When the unit is turned on audio is not passed through to the output for a few moments while the tube warms up During the warm up time the power indicator is yellow When the power indicator turns green the audio will pass through to the output This protects you from heavy turn on thumps MICROPHONES You can use any type of balanced low impedance microphone from dynamics to ribbons to condens ers The 207 supplies a very clean and stable 48V phantom voltage source suitable for even the most expensive microphones Phantom voltage is sepa rately selectable on or off for each channel at the front panel OUTPUTS The two outputs can be used at the same time They are not fully isolated from each other however To unbalance the XLR output simply use pin 2 high and pin 1 ground leaving pin 3 either grounded or floating You may ground the ring of the phone jack as will happen when you plug in a2. Ol Solution Delivery Series Two Ce T U B E Ano lns TRUMEMNT P R EAMmMPLIER Instruction Manual P N 999 4160 Revision 1 Released 01 01 2002 Manufactured by Aphex Systems Ltd 11068 Randall St Sun Valley CA 91352 USA APHEX S Y S TEM S amp S Copyright 2002 Aphex Systems Ltd All rights reserved Produced by Donn Werrbach Creation tool Adobe InDesign 1 5 Printed by Stuart F Cooper Co Los Angeles I INSTRUCTION MAnNnuA L A MESSAGE FROM THE PRESIDENT Dear Aphex Customer We are pleased to present the Model 207 Tube Microphone and Instrument Preamplifier as part of our Solu tion Delivery Series Extensive and unique features combined with high performance and wrapped in an attrac tive package make this preamplifier an essential piece of gear for anyone serious about creating high quality audio As with all our products we are extremely proud of the ingenuity of design and the manufacturing quality of the Model 207 We love to hear from you our customers about your experiences with any of our products Our customer support is unmatched in the industry so please do not hesitate to contact us Sincerely Marvin Caesar Safety Declarations TO PREVENT FIRE OR SHOCK HAZARD DO NOT EXPOSE THIS DEVICE TO RAIN OR MOISTURE DO NOT REMOVE THE COVER NO USER SERVICEABLE PARTS INSIDE SHOCK HAZARD REFER SERVICING TO QUALIFIED PERSONNEL ONLY DO NOT OPEN ATTENTION A
3. INIWNYLSNI Z IH Las BTS WOOYdVSsH LNdLNO LAdLNO 3 1 1 3 13441 Yala DNILVYJdO IND MOT ngpr WIL 1 INdLNO a LAdNI DIN Be dyd HDLIMSOLNY 4 Yad 38 NIV 313855 4 Vay 7 ANI LNOW OV LYISNI NdN YIMOd JNOHd SUL Y 1 31385514 A8v 5 WVYI VIQ ADOT Gala Id IS G lt Aphex Systems Ltd Model 207 Page 8 TWO CHANNEL TUBE MC PREAMPLIFIER CI P 3 0 Installation amp Interfacing 3 1 INSTALLATION The Model 207 occupies a single rack space 45mm or 1 3 4 inches of a standard EIA equipment rack When rack mounting use appropriate cushioned rack screws Never restrict air flow through the device s fan or vents When installing the units into a rack distribute the units evenly Otherwise hazardous conditions may be created by an uneven weight distribution Connect the unit only to a properly rated supply circuit Reliable earthing grounding of rack mounted equipment should be maintained Try not to position the 204 directly above devices that generate excessive heat such as power amplifiers unless adequately ventilated or near equipment with heavy transformer hum fields CHANNEL 1 OPERATING Pint GND Pin 2 Tip HI Ring 3 2 REAR PANEL VIEW MIC INPUT CHANNEL 2 PROTECTED UNDER US PATENT OPERATING 5 450 038 APHEX AND MICLIM AR
4. That may eliminate the equalizer and any other processing provided there but it may neverthe less be an excellent solution You will be able to have tracks that sound incredibly alive and dimensional not needing much additional processing anyway REPLACING CONSOLE S MIC PREAMPS Ch1 Line l Dop 0000 Output Input O OOO 0000 20000 0000 0000 0000 0000 0000 0000 Ch2 _ Hne Output Input Console When driving a console s insert jack you may need to build or obtain a special insert cable usually in the form of a Y cable That is because the insert jacks of low cost consoles are usually 1 4 stereo phone jacks that carry send and return as unbalanced lines using tip and ring similar to the Model 207 5 insert jack You should consult your console s manual for instructions on connecting outboard equipment to the insert jack The 207 s output can easily adapt to driving an unbalanced insert You simply set the oper ating level switch to whichever setting is closer to the insert s operating level It will usually be 10dBV for home studio mixers and 4dBu for fully professional studio desks 4 5 BYPASSING THE CONSOLE ALTOGETHER When you are laying down tracks why even involve your mixing console Maybe you had to do that to Aphex Systems Ltd Model 207 TWO CHANNEL TUBE M
5. You will need to locate a metal screw that solidly binds to the metal chassis of the gear You may even need to drill a hole through the chassis and install a screw yourself Equipment in rack shelves can have their chassis grounded to the metal rack frame by a heavy wire and the frame itself can act as a brute force ground You just have to try everything you can think of Usually a combination of all these methods will be needed to completely clean up a badly humming audio system Balance Out the Audio Remember balanced lines are inherently hum free If you can balance out your unbalanced equipment you will be able to stop the hum Pseudo Balancing You will find in Appendix D an interconnecting method called Pseudo Balanced This works when connecting an unbalanced output to a balanced input This breaks up the ground loop by requiring the shield to be grounded only at one end For best results always ground the shield only at the receiving end Level Interface Units Aphex manufactures the Model 124 Level Interface box which is designed to electronically convert two unbalanced inputs and outputs into two balanced inputs and outputs and at the same time translate the 10dBV IHF unbalanced levels to the pro 4dBu balanced levels This cost effectively gives your non professional unbalanced equipment a fully profes sional I O equal to the world s best pro audio gear Seriously consider putting one of these on each unbalanced pi
6. fits afforded by the Model 207 Figure 4 5 X Y TECHNIQUE Figure 4 7 BINAURAL MIC Example Neumann KU 100 Cardioid Mid Bi Directional Sides Figure 4 6 M S TECHNIQUE Page 16 Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER J P 5 0 Warranty amp Service 5 1 Limited Warranty PERIOD One year from date of purchase SCOPE All defects in workmanship and materials The following are not covered a Voltage conversions b Units on which the serial number has been defaced modified or removed c Damage or deterioration 1 Resulting from installation and or removal of the unit 2 Resulting from accident misuse abuse neglect unauthorized product modification or failure to follow instructions contained in the User s Manual 3 Resulting from repair or attempted repair by anyone not authorized by Aphex Systems 4 Occurring from shipping claims must be presented to shipper WHO IS PROTECTED This warranty will be enforceable by the original purchaser and by any subsequent owner s during the warranty period so long as a copy of the original Bill of Sale is submitted whenever warranty service is required WHAT WE WILL PAY FOR We will pay for all labor and material expenses for covered items We will pay return shipping charges if the repairs are covered by the warranty LIMITATION OF WARRANTY No warranty is made either expressed or implied as to the merchantability and fitness for an
7. Levels Shield grounded at receiving end only Positives Stops ground loops and reduces noise Negatives None Ti t Standard store bought cable Shield is grounded at both ends Positives Both ends are interchangeable Negatives May cause ground loops through shield contacts BETTER Custom cable Shield is grounded at receiving end only Positives Stops ground loops and reduces noise Negatives Should be oriented so lifted shield is at sending end No Connect lt XLR to 1 4 TRS Phone Balanced Cables From an Output Female XLR To an Input Stereo Phone Plug No Connect Stops Ground Loops From an Output Stereo Phone Plug SSD ae To an Input Male XLR No Connect Stops Ground Loops Aphex Systems Ltd Model 207 Page 25 I INSTRUCTION MAnNnuUA L Appendices PART 2 BALANCED OUT to UNBALANCED IN Voltage Balanced Outputs Used on the 207 It was mentioned that there are several types of bal anced output stages in use today The following dia grams show you how to properly unbalance each type of output If you follow these instructions you should have no problems SIMPLIFIED SCHEMATIC Unbalancing loses half the output level You lose 6dB of gain Female XLR Don t Ground or Connect Pin 3 Transformer Balanced Outputs Mono Phone Plug Kees SIMPLIFIED SCHEMATIC Unbalancing loses
8. brings us all of its warmth and clarity while remaining directly linked to its solid state support unit There are no transformers or high voltage supplies yet the strength of the output signal is more than powerful enough to drive any practical load to full professional levels with ease Because of the unique capabilities of the RPA circuit we were able to mix the mic and instrument signals directly to the tube without any interaction The result is exceptionally high perfor mance 2 4 UNPACKING AND INSPECTION Your Aphex product was carefully inspected and pack aged at the factory prior to shipment The carton and its internal packing materials are designed to protect the unit from most rough handling than can occur during transport and handling However you should thoroughly inspect the carton and its contents for signs of physical damage before attempting to use this device It is your responsibility to immediately report any damage to your dealer or the freight com pany so that a damage claim can be appropriately filed Shipping claims are always the responsibility of the consignee that s you We also encourage you to save all of the original packing materials in the event that this unit should ever have to be returned to the dealer or factory for repair Page 7 INSTRUCTION MANUF L Introduction NMOHS ISNNVHD YALA JOYLNOD dINW3ud NATON 133 NTIN 1 3 0 1 NPA
9. conductors What makes a system unbalanced is when one of the wires is formed into a tube that wraps around the other conductor without touching it such that the outer conductor can be said to shield the inner conductor This describes all of the coaxial cable used for video cable TV and radio as well as most of the high fidelity audio cables 144 744 Figure 1 Balanced Line Model Figure 2 Unbalanced Line Model Balancing If both conductors are identical insulated wires that are twisted together then they form a balanced line This describes telephone lines microphone cables and most professional audio cables Typical balanced cables include an additional shield wrap around the twisted pair but this is not strictly required for bal anced lines to work properly Many people because they have more experience with unbalanced wiring think that balanced is con fusing Believe it or not balanced lines are really easier to understand than unbalanced There is no grounding issue with balanced and the way It works is perfectly natural and simple Balancing naturally rejects hum and noise and eliminates all sorts of com plications in interfacing Balanced transmission works something like this Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER CI P Appendices Your balanced input stage looks at the two wires and detects only the potential voltage difference between them Anything that is the
10. console However it will overload a mic input If you turn down the 207 s gain to reduce its output low enough to stop overloading the mic input of your mixer then your large console gain amplifies the basic noise floor of the 207 That will result in a very poor signal to noise ratio Always use the most gain possible in the 207 and adjust your mixer s fader or line input gain to accept it and never feed a mic input from a 207 CHANNEL 2 OUTPUT HEADROOM GAIN PHANTOM POLARITY LOW MicLim i E 23y mM AD ISEAN yR _ m INSTRUMENT INPUT JACK MicLim LIMITING LED ERN Input impedance is 1 megohm to Switches on the Shows when MicLim is r i eee working Screwdriver adjustable works properly accept 99 of all music MicLim operating OPERATING instrument pickups It is not designed mode Use is always LEVEL to receive extremely high impedance recommended GAIN non powered piezo pickups how off mainly for Adjusts the microphone pre ever esting amplifier and instrument gain Aphex Systems Ltd Model 207 Page 5 2 0 Introduction 2 1 WHAT DISTINGUISHES THE MODEL 207 There are certainly a lot of mic preamps available in the world It seems that every audio equipment company has at least one model to offer A study of currently available products shows that a large per centage use similar cir
11. least make sure all equipment is powered together off the same distribution panel circuit same circuit breaker Appendix B Dealing With Grounds and Hum Ground Loops Many people equate this term with hum and that s just about the bottom line of it If you have a ground sensitive system like unbalanced audio equipment for example then hum will result from ground cur rents that flow from the ac power system It is some times very difficult to isolate and stop ground currents between unbalanced equipment but it is quite easy to clean up balanced gear That s why pro gear is always balanced The cost of balancing is that of more expensive connectors cable and electronics but the cost is worth it when you depend on your audio quality That s why the Model 207 is equipped with a fully balanced I O Now that we ve sold you on only using really expensive pro gear lets show you how to get away with the really cheap stuff At least from the standpoint of killing ground hum A ground loop is an ac current that has become routed through your audio ground system The cur rent comes mainly from ground potential differences that exist between different wall outlets that return to opposite phases at the power distribution panel Secondarily however many pieces of equipment con tain line filters and transformers that leak a small amount of ac power into the chassis and ground return You may once have had the experience of getting za
12. mono style phone plug The XLR output will still remain balanced The output impedance of the XLR jack is low enough to optimally drive loads of 600 ohms and higher It is designed to interface with fully professional balanced gear The phone jack output impedance is signifi cantly higher but meets the requirements for driving typical semi pro prosumer balanced and unbal 1 INSTRUCTION MANUA LL anced equipment INSERT JACK This allows you to insert any kind of line level equip ment into the signal path between the 207 s front end preamps mic and instrument and tube output stage The operating level at this jack is in the vicinity of IHF level 10dBV You should set up your inserted outboard gear for 10dBV I O sensitivity All Aphex processors can be readily set to operate at this level HEADROOM METER As the level approaches OdB you run out of head room and the output will go into clipping unless MicLim is turned on There is a span of 27dB indi cated so you can watch your signal level for safety and convenience When MicLim is on the peak level will be held to about 3dB under clip for over level inputs rising as much as 20dB beyond the normal overload point INSTRUMENT INPUT This input is available at the front panel through a quarter inch phone jack The input impedance is 1 megohms to match all coil type pickups and all pow ered pickups Fully passive piezo pickups
13. same on the two wires for all practical purposes as seen measuring from ground is called a common mode signal and is cancelled out by the differential amplifier Figure 1 illustrates how the hum is induced into both wires equally and therefore is cancelled out Since the balanced line has wires that are twisted together each wire tends to pick up the same amount of induction from external sources Induction will create no significant voltage difference between the wires hence the noise or hum will not be picked up by the differential input stage It can be seen that the signal generator driving the twisted pair will cause a difference between the wires and that signal will be readily picked up by the dif ferential input stage One of the beauties of the bal anced line is that it is completely independent from ground Nothing is connected to ground at all nor does it care about ground Nevertheless most pro fessional cable has an overall shield wrap that is intended to be connected somehow to ground You may well ask why and the answer is less than glo rious Simply nothing is perfect not even balanced cable Under some circumstances the shield can over come extreme interference problems that can t be adequately rejected by the twisted pair alone Things like 2 way radios television transmitters and light dimmers can induce very heavy interference that may be reduced by shielding You are going to find virtu ally all balanc
14. will work but may not deliver full tone High impedance unbal anced microphones will usually work extremely well with this input When a plug is inserted the mic input Is inoperative CHANNEL 1 PHANTOM POLARITY LOW CUT MicLim 08000 a TING _ TWO rUSeSelkt mic FS POWER INDICATOR Glows yellow during the standby start delay to allow for the tube s warmup time Turns green when unit is ready to operate Light is off when the unit Is switched off PHANTOM Switches the 48V phantom power to the microphone jack on or off Page 4 PAD Inserts 20dB of loss at mic and instru ment inputs allow ing for excessively high levels POLARITY Inverts the relative polarity phase of the mic and instru ment inputs LOW CUT Aphex Systems Ltd Model 207 Switches on the 70Hz Low Cut filter Affects mic and instrument inputs OUTPUT TRIM TWO CHANNEL TUBE MC PREAMPLIFIER CI P OPERATING LEVEL This adapts the model 207 s internal dynamic range to match either professional balanced equipment or semi professional unbalanced equipment at the output It controls both output jacks Both jacks supply the same output level Set this switch to match the requirements of your system OPERATION If you are untamiliar with the use of microphone pre amplifiers then we recommend reading this manual for detailed instructions Ev
15. 1 consuming 3mA the drop is 003 X 3405 10 22 volts That means the voltage actu ally appearing on pins 2 and 3 is 48 10 22 37 78 volts That is why if you use a voltmeter to check phantom power while the mic is plugged in you will always see something less than 48 volts This is not a Page 12 fault with the mic preamp Plugging and Unplugging a microphone when phan tom power is switched on can sometimes be danger ous Some microphones can be damaged by power inrush Good practice calls for switching off the phan tom power before changing or inserting a micro phone Wait ling enough to hear the mic go silent before unplugging You should be aware of the shock hazard with the phantom power system Long open mic cables that are disconnected from the preamp while phantom is on can hold a d c charge for long periods of time sometimes days They will act as a storage capacitor and you can get shocked most rudely by holding the XLR plug and touching the pins inside Also beware of microphone patch bays that may carry phantom voltage Don t hold the patch cord by the metal parts only the plastic shell 4 3 2 USING THE POLARITY SWITCH There will be times when you need to reverse the polarity phase of a mic signal Vocalists monitoring themselves on headphones will hear a different sound when the phase is reversed for example The reversed phase may sound fuller and more truthful That is because there is a cancellation o
16. C PREAMPLIFIER CI P Using the 207 be able to use console s the mic preamps but with the 207 you can go direct to tape or disk and elimi nate an entire layer of electronics Usually effects and equalization are best added later during mixing Simply driving your recording electronics directly from the 207 gives you the best initial sound tracks pos sible Most studio recording sessions lay down 1 to 4 tracks at a time session by session until the needed tracks have all been created If you have one or two Model 207 s you would have enough outboard pre amps to handle most recording sessions The main trick is to set the preamp gains low enough to prevent overload then record straight through without riding gain This gives you natural levels to work with later In mixdown you can compress tracks and ride gain all you want With MicLim you can run all of the recording levels higher using higher mic gains and not worry about overload When MicLim acts It is fast and smooth Most of the time you won t notice it work You will truly appreciate having hot clean and quiet tracks at mixdown You will be amazed at the quality you can achieve and how easily it comes to you with great initial tracks You will find yourself messing around with EQ and compression far less because the sound won t need all that fixing Whatever artistic or production effects you want to use will work better and be easier to accomplish 4 6 U
17. E REGISTERED TRADEMARKS OF Qi inpu ute AA 66 QZ Qi APH EX VALLEY MODEL 207 2 CHANNEL TUBE MICROPHONE PREAMP APHEX SYSTEMS LTD MADE IN U S A ni 8 GND Pin 2 Tip HI Pin3 Ring amp EN60950 100 240V 0 12 0 05 50 60Hz 3 3 AC LINE CONNECTION Use only a power cord that carries approvals for use in your location The 207 s internal power supply is designed to operate from all nominal power sources from 100 to 240 volts a c at 50 60Hz without requiring the user to change any settings In case of failure do not attempt to change the internal fuse because it will never blow unless the power supply fails catasrophically The power supply will need to be serviced by a com petent service technician in such a case 3 4 MIC INPUT CONNECTIONS 3 5 INSTRUMENT INPUTS The MICROPHONE input connectors are located on the rear panel They are the standard XLR 3F type Use only properly wired balanced mic cables The INSTRUMENT inputs are located on the front panel providing a high input impedance of 1 meg ohms The instrument jack accepts standard 1 4 phone plug music instrument cords 6 guitar cords This input is also suitable for high impedance micro phones having cables with 1 4 phone plugs The do it yourselfer can refer to appendix D for numerous examples of proper cable and plug wiring PROPER MICROPHONE CABLE WIRING Female XLR Male XLR 3 6 INSERT JACK The Model 207 allows you to i
18. FIN D VITER DES CHOCS LECTRIQUES N ENLEVEZ PAS LE COUVERCLE IL N Y A AUCUNE AVIS RISAIE DE PIEC S D ENTRETIEN L INT RIEUR R F REZ LES NE PAS OUVIR R PARACIONES UNE PERSONNE QUALIF E CAUTION For protection against electric shock do not remove the cover No user serviceable parts inside WARNING This equipment has been tested and found to comply with the limits for a Class A digital device pursuant to Part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the operating guide may cause interference to radio communica tions Operation of this equipment in a residential area is likely to cause interference in which case the user will be required to correct the interference at his own expense The user is cautioned that changes and modifications made to the equipment without approval of the manufacturer could void the user s authority to operate this equipment It is suggested that the user use only shielded and grounded cables to ensure compliance with FCC Rules Conforms to standards UL60950 and EN60950 Page 2 Aphex Systems Ltd Model 207 US Liste 59887 Copyright 2001 by Aphex Systems LTD All rights reserved All Aphex products are trademark
19. However shorting the 1 4 phone will not affect the XLR You may safely plug a mono style TS 1 4 phone plug into the phone jack and take an unbalanced output The diagram shown below explains the electrical rela tionship of the two output jacks If you intend to take an unbalanced output from the XLR jack you must not ground either pin 2 or 3 Simply take from pin 2 and use pin 1 for ground Leave pin 3 unconnected gt ae Refer to Appendix C D for more information on the proper wiring of balanced and unbalanced lines 3 8 OPERATING LEVEL SWITCH Between the input and output jack is located the Operating Level switch This sets the nominal oper ating level for both output jacks simultaneously to either 10dBV or 4dBu You should select the posi tion that most closely matches your receiving equip ment In the event that you are not familiar with the operating levels of the equipment in your system you should consult your manuals In general most entry level home studio equipment operates at 10dBV as it is assumed that the user will likely intermix home hi fi equipment such as cassette decks and CD play ers Most professional recording gear and live sound equipment operates at 4dBu 3 9 OUTPUT TRIM In addition to the OPERATING LEVEL switch on the back panel there is a front panel trim for precise output level matching The OUTPUT TRIM is recessed to stay out of your way and can be adjusted with a small s
20. M GOUT tales 11 4 3 Using the Microphone INPUT seseris a 12 4 3 psen nanne aner EaR EEEE EEA 12 E 12 15 15 SS SIO 13 4 4 Replacing Your Console s Mic Preamps 14 the GONsOre 7 EE 15 4 6 Using the 207 for Stereo Recordings 15 ccie nanni adea EE EENE 15 PO Fey TOC WMS cise 15 WS VOCS sarap 15 4GA 16 MO 16 5 0 WARRANTY AND SERVICE MV penini E aren hte aE n trae sate EEE ei r E date denied oddone 17 vain E AEE EE EEE ons 17 6 0 SPECIFICATIONS SO e EA RTS aR EEES TEENS 18 0 2 Architectural
21. Noise Pickup Mono TS Phone Plug cL Not Used Stereo TRS Phone Plug Sill Male XLR Mono TS Phone Plug Not Used Corsa yo Ground Shield This End Only Stereo Plug To 207 Insert Jack Ground Shield This End Only To 207 Insert Jack Ground Shield This End Only Aphex Systems Ltd Model 207 Page 27 TWO CHANNEL TUBE MC PREAMPLIFIER 7 Patent Notice This product is protected under one or more of the following Aphex patents 4 578 648 4 633 501 4 843 626 4 939 471 5 115 471 5 5 334 947 5 227 000 5 422 602 5 424 488 5 450 034 5 463 695 5 483 600 5 485 077 5 612 612 5 737 432 5 848 167 5 896 458 5 098 995 5 930 374 Aphex Systems Ltd Model 207 Page 28
22. SING THE 207 FOR STEREO RECORDINGS Stereo recordists will find the Model 207 perfect for their work The low noise and highly detailed open sound of the 207 delivers breathtaking results All expert recordists know the techniques we re about to show you However others may find them interesting to learn about SPACED PAIR TECHNIQUE About the most obvious technique is using two microphones spaced apart some distance and pointed directly at the sound source The spacing between mics and distance from the source depends on the width of the sound platform you want to include With spaced pairs there will be a phase difference between the two mic outputs This can cause can cellation of certain frequencies An accepted com promise is called the 3 1 Principle According to this Aphex Systems Ltd Model 207 principle you should place the microphones 3 times as far apart as their distance to the front of the sound source With such a wide separation of the mics omnidirectional types are called for Otherwise you might exclude the whole center of the sound stage from adequate coverage X Y TECHNIQUE Also called a COINCIDENTAL PAIR this technique employs two cardioid pattern microphones The grills of each microphone should be placed as close together as possible without touching Each micro phone should be positioned at right angles to each other Use the intersection of this 90 angle as a sight and aim toward the middle o
23. ally have a higher output level than passives but not always Passive pickups couple directly through the instrument cord to the music amplifier or preamp Magnetic pickups are exclusively associated with steel stringed instruments like basses and guitars These pickups are wound with coils of wire that generate an output voltage when the strings interfere with a magnetic field set up by an internal permanent magnet Acoustic instruments that don t use steel strings are usually amplified from piezoelectric pickups placed on the instrument where vibrations will twist or bend the piezo crystal to generate a voltage output 90 of all piezos in use are amplified but passive pickups are available Passive piezos cannot usually be connected directly to a music amplifier with good results The sound will be very thin and weak They require a special input stage that provides extra gain and an extremely high impedance like 10 megohms or more Magnetic passive pickups and most active pickups piezo and otherwise are most suited to a 1 megohm impedance at the amplifier input Since Aphex Systems Ltd Model 207 CHANNEL 7 INSTRUMENT GAIN INPUT anean Ow CUT Metin 3 q a wre PHANTOM POLARITY PAD L 000 we wanted to design the Model 207 to meet the widest requirements we gave it a 1 megohm input impedance Therefore we cannot recommend it for any type of passive piezoelectric pickup That said let
24. crewdriver blade The range of adjustment is O to 12dB First set the OPERATING LEVEL switch to the appropriate position Next using a loud input or an oscillator drive the OUTPUT HEADROOM meter to ZERO Set the OUTPUT TRIM to just barely drive your equipment to its maximum input level If you are in doubt about how to do this simply set the OUTPUT TRIM fully clockwise and rely on the OPER ATING LEVEL switch to get you close enough OUTPUT JACK SCHEMATIC with OPERATING LEVEL SWITCH OUTPUT PAD 10dBV 4dBu Page 10 604Q Sleeve Tip 1 4 PHONE JACK XLR JACK Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER CI P 4 0 Using the 207 FRONT PANEL VIEW CHANNEL 1 INS TRUMENT INPUT PHANTOM POLARITY Pau Low cur Mick n 4 Two TURE ME erie 4 1 SPLIT INDEPENDENT PREAMP SECTIONS The Model 207 is a two channel unit It contains two separate independent preamplitier channels Each channel operates as a mic preamp or an instrument preamp Plugging into the instrument jack automati cally disables the mic input and substitutes the instru ment input 4 2 USING THE INSTRUMENT INPUT This input is designed to work with most standard instrument pickups both active and passive Active pickups have an amplifier built into or attached to the instrument or instrument strap These are identi fied by running on a battery Active pickups gener
25. cuits based on one or two pop ular commercial i c chips The basic design has been done by the chip maker and the chips do a compe tent job We could have brought out such a me too design but it Is important to Aphex that we offer products that are more than just competent They must also be different and better That is why we did not introduce our first mic preamp until we invented something that would make all the differ ence That invention turned out to be a new and unique way to use a vacuum tube in a circuit that yields the clear and detailed tube sound yet has none of the limitations of conventional tube circuitry like short life noise heat and low bandwidth That invention is called the Reflected Plate Amplifier RPA and was granted U S Patent 5 450 038 We introduced our first microphone preamplifier incorporating the RPA the Model 107 in 1996 and It soon became one of the most popular mic preamps in the world People appreciated the difference it made in the quality of their work Tens of thousands of 2 channel units were sold More recently we came up with another invention pertaining to mic preamps We had the idea that if we could build a mic preamp that not only sounded great but also had a way to automatically prevent input overloading over a significant dynamic range above normal clipping then we would have another innovative hit on our hands Many months of research went into inventing a method t
26. dard mic cable fall into a class called phantom powered mics The power is called phantom because it rides the mic cable invisibly without inter fering with the audio signal carried on the same wires 48 V D C SUPPLY Figure 4 1 Phantom Powering The industry standard phantom power source is posi tive 48 volts d c supplied to pins 2 and 3 through precision low noise 6 81KQ resistors You may note from spec sheets that many mics rated for phantom power actually run at something less than 48 volts For example the Audio Technica AT3031 small dia phragm condenser mic is rated for 11 to 50 volts at 3 milliamps On the other hand the Neumann TLM193 spec sheet states only that the supply voltage should be 48 4 volts and the current consumption is not stated Don t let these specifications confuse you They all run perfectly well off the standard phantom power source described above For the technically interested here s why The 6 81KQ resistors mentioned are shown in figure 4 1 below Since the power to the microphone is car ried equally a requirement carefully observed by all mic manufacturers on pins 2 and 3 it is like power ing the mic through a single series resistance equal to the two resistors in parallel which is a resistance of half or 3 405KQ A voltage drop will occur across the series resistance equal to the microphone s current consumption times the series resistance In the case of the AT303
27. distortion is so natural The very slight tube distortion of the Model 207 comprises typically less than 0 02 of second order harmonics at average levels What is even more interesting is that this curve follows the tube s law as regards level and furthermore it responds to certain very subtle dynamic space charge effects known only in tube amplifiers Thus the sound with an RPA can have a large and open feeling that is very natural and transparent 2 3 WHAT ELSE IS SO SPECIAL It may sound trite but everything else about the Model 207 is special When we designed its circuitry and decided upon its features we took into consider ation a very wide range of factors We blocked in the things that our marketing experts wanted but then made sure that every circuit and feature could work in harmony Some things were discarded by engineering because they would have compromised the sound Once we had the Model 207 very well defined we went to work at embodying the circuits cleanly and cleverly using some great ideas from the Model 107 but redesigning most of it from scratch through computer modeling and simulation and finally through actual physical prototypes and lis tening sessions There are no databook or textbook preamplifier circuits in the 207 It s all Aphex That being said let us point out just a few of the things that are special about the Model 207 Then as you read more of this manual you will gain apprecia tion
28. ece of gear you use Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER CI P Avoid Transformers The use of balancing transformers is an option but you will invariably lose audio quality due to trans former limitations Try everything else first Appendix C Proper Wiring Techniques A true balanced line should be used wherever your equipment allows Use twisted pair shielded cable For unbalanced wiring you should use high grade low capacitance shielded wire for best results If you have an unbalanced output but have a balanced input the pseudo balanced configuration may help deal with ground loop hum This method and others are illustrated in Table 2 CONNECTOR WIRING STANDARDS The 3 pin XLR 1 4 63 5 mm TS mono phone and the 1 4 63 5 mm TRS stereo phone are the most commonly used line level connectors in pro audio Less common is the use of the RCA phono jack which is essentially a consumer type connector The XLR and the TRS are three conductor and are used for balanced connections The TS and the RCA are two conductor and are used for unbalanced connections In addition to the three main contacts on an XLR there is also a grounding lug contact This lug is con nected to the connector s case shell In all Aphex products audio ground and chassis ground are one and the same Aphex products that use XLR con nectors tie Pin to the XLR case automatically There fore it is
29. ed cables include a shield so you need to deal with it even if it is not actually needed That subject will be addressed a little later Unbalancing Unbalanced wiring works a little differently Figure 2 shows the basic plan In this case the wires are not twisted they are coaxial The unbalanced input stage is somewhat like the balanced input stage because amplifies a difference signal but this time it is the dif ference between two non symmetrical conductors To make things even less symmetrical the outer con ductor is connected to ground at both ends The principle is that the outer shield conductor shields the inner conductor from induced noises This can only work well if the cable is relatively short and the ground at each end of the cable is somewhat Aphex Systems Ltd Model 207 equal i e there is no grounding difference that can cause current to flow through the shield con ductor Grounding difference is a serious problem in studios because often the equipment grounds are connected to power outlet grounds and there can be a significant difference of ac voltage between alter nating wall outlet grounds For this reason unbal anced systems can sometimes never be made hum free and just changing one piece of equipment in a studio can cause hum to appear somewhere else When you are using unbalanced gear it is a very good procedure to power all your equipment from one large power isolation transformer At the very
30. ed lines as high imped ance The fact is however that both balanced and unbalanced lines are operated at low impedance in modern practice owing to the fact that all output stages have become low impedance A few excep tions might be outputs from passive mixers instru ment pickups electric guitars and some keyboard synthesizers It is generally ideal to drive any audio line from a low impedance and receive into a high impedance Generally a minimum 1 10 ratio is possible This is called bridging This has become modern practice and all balanced inputs are normally running 10K ohms or higher impedance Because of these developments it is now no longer as critical to consider impedance when dealing with interfac ing pro line level equipment impedance matching is mostly a requirement of the past A word on impedance and interfacing adapters If you are connecting between two line level devices and they have different connectors example 1 4 phone to XLR or vice versa you do not need to use an impedance matching transformer With very few exceptions you are strictly dealing with a difference in connector types and should only use hard wired adapters or cables for this situation APPENDIX D Standard Cable Wiring In relation to 1 4 phone jacks you may see the terms TS and TRS as abbreviations Here is a what Page 24 Standard Wiring Convention Balanced Ground Shield Earth Screen Pos
31. en experts will find some of the unique features of the 207 well worth a little extra study Y CABLE See Appendix D INSERT Q OPERATING 9 aa Do O Quick Setup Standard Hookup to Rear Panel ONE CHANNEL SHOWN Source Passive or Phantom Powered Use high quality balanced mic cables MIC INPUT CHANNEL 1 OUTPUTS Pin 1 Sleeve GND Pin 2 Tip HI Pin 3 Ring Select the correct OPERATING LEVEL to most closely match your receiving equipment s input sensitivity IN To Inputs of OUTPUT HEADROOM METER Indicates the available headroom in decibels below clipping At OdB the output level reaches the maximum level available at all outputs depending upon the Output Trim and Operat ing Level settings Line Level Processor i e Compressor EQ Line Level Devices DO NOT Connect to Mic Level Inputs Use balanced or unbalanced cables as needed Consult Appendix D for wiring options Why You Shouldn t Connect a 207 s Output to a Mic Level Input The bottom line you will get a lot of noise and possibly a lot of distortion The Model 207 is designed to generate a line level output from a mic level input It optimizes the signal to noise ratio by giving you a strong signal far above the preamplifier s basic self noise level This strong output signal can be up to 65dB higher than the mic signal It is perfect in level for a standard line input of a mixer or
32. even to the extent of compromis ing sound quality Even the inordinately expensive world class studio desks place a compromise on the mic preamps they build in Good preamps require a lot of circuitry that just won t fit inside Let s not forget too that a really great mic preamp requires Its own Ingenious circuitry and design It is not surpris ing that of all the parts of a mixing desk it is mainly the mic preamps that ever get replaced No matter how noble the intent there is one dilemma that can thwart you in successfully bypassing the mic pre of some consoles You must become aware of this problem in order to deal with it We have been instructing you to connect the Model 207 to the LINE inputs of your console or other equipment and NEVER connect it to a mic input The problem is that when connecting your 207 to your console s line inputs you may actually be connecting to mic Page 14 INSTRUCTION MANUA LL inputs and not knowing it That is because many consoles simply put a heavy pad in front of the mic pre input to make a line input out of it The whole microphone preamplifier circuit is still in line and car rying your signal You have to suffer the sonic limi tations of the console s mic preamps and that may mask out the benefits of using the 207 There is a solution if your console has pre fader inserts You can plug the output of your 207 into the console s insert jack bypassing the channel s whole front end
33. f frequencies within the ear when the external sound from the headphone mixes with the sound directly conducted to the ear Flipping the phase can make the effect less notice able Distance to Mic2 Distance to Mic1 LLG Sound Cancelled Figure 4 2 Phase Cancellation Effect Another time when phase reversing can be helpful is in mixing multiple microphones that are within each Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER P Using the 207 other s coverage areas The crosstalk between mics may come through different delays due to the dif fering distances from the sound These sounds may tend to cancel out in the mix You may get a nasal or hollow effect when all mics are on Changing the polarity of one or more mics will often clear up the problem It is always worth the time to experiment with mic polarity 4 3 3 USING THE PAD An input pad is nothing more than a resistive attenuator that drops the level coming from the input jack Its purpose Is to give you a way of prevent ing overload of the preamp when incoming signals become excessive Another purpose is to change the preamp s mic input into a line input In the 207 we provided a pad of 20dB That means when the pad is on the net gain of the preamp is 20dB lower than normal You will almost never need the pad unless you are working a live concert or other very loud venue If you have brought the GAIN all t
34. f the sound source see illustration on subsequent page The microphones should be of the same make and model An advantage of this technique is better rejection of back side room noises that include the audience and slap back or echo The X Y technique is often used to record noisy live events M S TECHNIQUE Another popular stereo micing technique is referred to as the Middle Side technique This method com bines two microphones of different response patterns positioned along the same horizontal plane One is a cardioid mic which 5 aimed directly at the front center of the orchestra The second microphone has a figure eight pattern positioned so that the axis of the lobes are lateral facing left and right An elec tronic matrix circuit processes both microphones and provides Left and Right channel outputs This method vectorially extracts the left and right channels trom the sum and difference signals the middle cardioid and side figure 8 patterns Generally M S is practiced with specially built micro phones that are sold with the M S processor The mic preamps are normally integral to the processor How ever certain M S processors allow you to use exter nal mic preamplifiers so you could introduce a Model 207 When doing so just be sure to set the gains of the two channels reasonably close and do not change them during the recording With M S recording the stereo separation will change if either the middle or side
35. for many other special aspects of this product First let s look at the front end Other preamps even those costing many times more pass the mic signal through switch contacts to enact the pad and polar ity features This eventually leads to contact distortion creeping into the sound because switch contacts will eventually oxidize and in the very least need to be operated frequently to keep themselves clean That is a big problem especially for fixed installations where it is impossible to exercise all the switches regularly daily We used expensive d c operated sealed bifurcated gold contact relays to switch these functions These relays never oxidize and can remain stationary for many years without contact distortion Next let s look at the low cut filter It is a second order active filter that is designed for musicality Aphex Systems Ltd Model 207 not just rumble cutting We very slightly peaked the response at 120Hz by about 1dB so there will be a natural phase compensation effect in the important low mid bass region helping regain a greater sense of bass presence That benefit is immediately appar ent to experienced mic preamp users We received so much praise for this type of filter in the Model 107 that we kept it for the 207 Just one more mention Let s look at the RPA tube output stage Here we merge a real operating vacuum tube into the world of semiconductors The tube serves as the main gain element and
36. gain should be changed BINAURAL TECHNIQUE Page 15 C I INSTRUCTION MANUAL Using the 207 This attempts to record sound like the ears hear it using two closely spaced microphones either worn on a person s head near the ears or located inside of Distance X a dummy head with simulated ear canals It attempts to capture sound waves with the refractions that occur naturally due to the shape of the head These days binaural microphones are commercially avail able that come with a matched dummy head How ever many incredible recordings have been made with e 3X two small identical omnidirectional mics mounted to eyeglass frames Figure 4 4 SPACED PAIR 3 to 1 TECHNIQUE For those recordists that do much of their work in binaural the Model 207 is perfect Its low noise and clear open sonic quality generate recordings that are incredibly realistic and beautiful catching all the nuances and details FURTHER READING There are more microphone techniques than we can cover in this manual Many reference books exist that go into great detail Here are a few Modern Record ing Techniques by Huber and Runstein Sound K Reinforcement Handbook by Gary Davis and Ralph Jones and Introduction Professional Recording L Techniques by Bruce Bartlett If you are one who enjoys the challenge of recording we believe you will aaa Cardioid Mics truly appreciate the outstanding performance bene
37. he way down and you still have an excessive output level then switch on the pad You can then readjust the gain as desired 4 3 4 USING LOW CUT In the practical world mics pick up all sorts of unwanted low frequencies such as hand noise wind rumble or lectern thumps We designed into the 207 a very effective way of cutting out these low fre quencies while maintaining a sense of normal low end response Switching on the LOW CUT FILTER rolls off all frequencies below 70Hz at 12dB per octave but places a slight compensation around 120Hz to improve the low end phase distortion and percep tion of remaining bass We first offered this cutoff shape with our Model 107 tube mic preamp and it received tremendous acclaim from vocalists and recordists alike So not wanting to waste a good thing we carried it forward to the Model 207 Use the LOW CUT filter whenever you need it How ever please try going without if whenever possible Even though it is outstanding as a rumble fixer you will notice it s presence We suggest as a matter of good practice that you always try isolating the mic trom unwanted vibrations instead of summarily switching in the LOW CUT filter Aphex Systems Ltd Model 207 Figure 4 3 LO CUT Response ee a ee I Ul UW oO UW I I Response dB gt YA AA 100 2K Frequency Hz I N N Ul Wu 4 3 5 USING MicLim MicLim works bes
38. ip Ring 10dBV 316mVRMS Between front end and Tube Output Stage Refer To Sections 3 amp 4 rating and connectorization meet governing standards where units are sold Power Consumption maximum 12 watts 10dBV Same Same Same Same Same 8 to 53dB minus OUTPUT TRIM loss Same Same Same Same infinity to 38dB minus OUTPUT TRIM loss Same Same Same Same 10 7 8dBu Unloaded 6 75dBV Unloaded 01 12dB Same Same Same Same Same Same Same Same Same Same Dimensions 19 W x 1 75 H x 8 25 overall depth 482 6mm W x 445mm H x 209 6mm overall depth depth behind front panel 7 5 190 5mm Net Weight Rack mounted 6lbs 2 73kg Shipping Weight 9lbs 4 1kg All specifications are subject to change without notice Page 18 Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER CI P Specifications 6 2 ARCHITECTURAL SPECIFICATIONS Basic Description A two channel electronic preamplifier for microphones and instruments comprising a transformerless balanced microphone input and a high impedance unbalanced Instrument input for each of the two channels The pre amplifier shall comprise a Reflected Plate Amplifier tube type transformerless output stage The preamplifier shall further comprise an operating level switch to select between nominal output levels of 4dBu and 10dBV The two preamplifier channels shall be operable independently There shall be tw
39. itive Signal High Hot Negative Signal Reference Return Low Common Standard Wiring Convention Unbalanced Positive Signal Ground Shield Signal Reference Return that means TS refers to the Tip Sleeve or mono 2 conductor type and TRS refers to Tip Ring Sleeve or stereo 3 conductor type 1 4 phone connectors This applies to jacks female connectors and plugs male connectors Note We recommend using only conventional 1 4 phone plugs with the Model 207 and with all other audio equipment Professional patch bay cords using brass PJO55 telephone type plugs are designed only for patch bays and will not make proper contact with standard 1 4 phone jacks The following instructions show all the different ways you will probably ever need to hook up your 207 as well as any other equipment you may own You will see that connecting balanced outputs to balanced inputs is ultimately simple and the same cable will work for all flavors of output stages Connecting a balanced output to an unbalanced input requires a little more knowledge and care You should refer to your equipment manuals and determine the type of balanced output stage that is provided then use the correct transition cable as depicted in this section Improper transition cables can cause crosstalk hum and distortion problems within your system TYPES OF BALANCED OUTPUTS Believe it or not there are at least 5 types of bal anced o
40. no output level You retain full gain Ground Pin 3 Directly to Pin 1 Impedance Balanced Outputs Alternatively Carry Pin 3 Through Twisted Pair Cable and Ground at Other End Female XLR Mono Phone Plug SIMPLIFIED SCHEMATIC ENOG E Unbalancing loses no output level You retain full gain Female XLR Pin 3 Doesn t Matter OK Grounded or Not Grounded Mono Phone Plug Servo Balanced Outputs SIMPLIFIED SCHEMATIC Unbalancing loses no output level You retain full gain Ground Pin 3 Directly to Pin 1 Female XLR Do Not Carry Pin 3 Through Cable and Ground at Other End Mono Phone Plug ENGGA E V Page 26 Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER CI 7 PART 3 UNBALANCED to UNBALANCED Standard Cable Guitar Cord Mono TS Phone Plug Mono TS Phone Plug Mia PART 4 UNBALANCED OUT to BALANCED IN Standard Method Mono TS Phone Plug Stereo TRS Phone Plug Sal Guitar cord of Part 3 above usualy works just as well ot Male XLR Mono TS Phone Plug PART 5 Y INSERT CABLES Male XLR To Equipment Input Female XLR 26 From Equipment Output 3 1 Don t Connect Pin 3 Mono TS Phone Plug To Equipment Input C_ irae Ground Shield This End oa From Equipment Output C irae Mono TS Phone Plug Appendices Enhanced Method Pseudo Balanced Advantage Reduced Hum and
41. not necessary to use the XLR case ground lug This also makes possible the use of XLR ground drop adapters see Note 3 TABLE 1 The wiring convention shown is now stan dardized in 17 countries including the USA Please note that any equipment that still uses Pin 3 as posi tive on XLR connectors is not adhering to the stan dard THE PIN 1 DILEMMA AND HOW IT AFFECTS CABLE SHIELD CONNECTIONS The three main contacts on an XLR or TRS and the accepted wiring assignments shown above are Aphex Systems Ltd Model 207 Appendices only part of the picture The standard for terminat ing ground is Pin 1 Sleeve But which ground It could be connected to audio signal ground or chassis ground depending on the method of grounding used by the equipment manufacturer In all Aphex prod ucts audio ground and chassis ground are one and the same at all I O jacks This is just good common sense engineering practice which is what you would expect from us course Unfortunately many products are designed so that the noisy currents from the shield drain into signal ground instead of chassis ground This practice creates a real hum and noise problem for end users The appropriate overall grounding scheme of an audio system would be a lot easier to predict without this problem The standard balanced line wiring recommendation from Aphex Engineering is this In the majority of cases maximum noise rejection occurs when the shield is connected
42. nsert additional signal processing between the mic preamp s front end stage CAUTION Beware that 48 volt PHANTOM POWER and the tube output stage This is clearly shown in may be applied to either or both of the micro phone inputs creating a potential shock hazard Standard practice dictates shutting off the phan tom power before plugging or unplugging micro phones Wait at least 10 seconds for the voltage to fall sufficiently This is not only for safety but for protection of sensitive microphones against power inrush Aphex Systems Ltd Model 207 the 207 s block diagram at left The interconnect is unbalanced by way of a stereo TRS I O jack on the rear panel You will need a conventional Y cable to interface with external equipment Such cables are available commercially Make sure you have the cor rect cable tip is send ring is receive and sleeve is ground Check the following chart Page 9 INSTRUCTION MANUA LL Installation amp Interfacing TABLE 3 1 INSERT Y CABLE PINOUTS Tip SEND Ring RETURN Sleeve GND 3 7 OUTPUT CONNECTORS The output connectors are located on the rear panel There are two output connectors per channel one 1 4 TRS phone type and one XLR 3M type They may both be used at the same time to feed separate equipment Both jacks run at the same output level but are not fully isolated from each other Shorting out the XLR will take down the 1 4 phone
43. o achieve this goal When we succeeded we called it MicLim Later we introduced the Aphex Model 1788 Remote Con trolled Mic Preamp including the MicLim feature Months of trials proved it to be extremely useful in live sound reinforcement applications Additional testing showed it is also useful in recording When we next introduced our very high end Aphex Thermionics Model 1100 Thermionic Mic Preamp we included the MicLim feature and it has received high acclaim among some of the world s top sound engineers Meanwhile our Model 107 remained a solid product Page 6 INSTRUCTION MANUA L in the marketplace because of its low cost high per formance and value However after enjoying many years of sales we thought we owed it to the world to update the Model 107 with the new things we have learned and developed since its inception Hence the 207 was born Production of the Model 107 was dis continued In addition to improving on the Model 107 the Model 207 is a whole new product We transported the front end and RPA components that characterize the sound of the 107 but we completely revised our thinking about every other detail We added the MicLim feature and a professional quality instru ment input We even added a processing insert jack so you can insert EQ gating or compression after preamplification but before the tube output stage In this way you always get the sonic benefits of the tube We created a
44. o industry standard output jacks per channel an XLR 3 pin male and a 1 4 TRS phone jack Additional specifications are stated below Microphone Input The input jack shall be a standard XLR tupe 3 pin female The input impedance shall be nominally 2000 ohms All normally operated controls for the mic input shall be placed on the front panel The mic preamp shall com prise the following features 1 Selectable 48VDC Phantom Power 2 Selectable Polarity 3 Selectable 20dB Pad 4 Selectable 70Hz 12dB Octave Low Cut Filter 5 Selectable Peak Limiter 6 Continuous Gain Control The selectable peak limiter shall be a type that limits the mic signal before any amplification to prevent input overload The input stage shall be transformerless and actively balanced The preamplified microphone signal shall be sent through an INSERT jack to the output stage to facilitate the use of outboard signal processing Instrument Input The input jack shall comprise a 1 4 phone jack The input impedance shall be 1 megohms The input stage shall comprise a low noise JFET integrated circuit amplifier Insert Jack A 1 4 TRS phone jack shall be provided at the rear panel for inserting outboard signal processing for the microphone input only The insert jack shall comprise an unbalanced send and an unbalanced return that oper ate at nominal 10dBV levels The point of insertion shall be between the microphone preamplifier and the tube output stage Ph
45. ow it may be apparent that if you deliberately Page 13 e 0 Using the 207 increase the preamp gain until peaks frequently drive MicLim to limiting you could obtain a very dense output level by bringing the average signal so much closer to the peak ceiling Although it is certainly pos sible to operate MicLim in that fashion and often the effect will be desirable we recommend the use of restraint MicLim was designed to be fast and unobtrusive for protection against accidental over loading especially with voices You may find the fast speed of this limiter too aggressive for general pur pose effect limiting Your favorite studio compressor limiters can still be put to good use If you re not sure about whether to use MicLim just use it If you never need it then it won t have any effect at all But when that big ass peak comes along Bam You re saved 4 4 REPLACING YOUR CONSOLE S MIC PREAMPS The most basic application for the 207 is to provide an upgrade over the microphone preamplifiers in your mixing console We are not insinuating that your console s preamps are no good just that the Model 207 is better If you did not know that you probably would not have bought your 207 Consoles are built for functionality at a target price point Lower priced equipment may have a huge array of facilities rivaling more expensive equipment However everything inside is designed as cheaply as humanly possible
46. pped by touching two pieces of gear at the same Page 21 e 0 6 0 Appendices time That illustrated the ground loop effect straight through you No matter what you do you may not be able to prevent some of your equipment from generating ground currents The most likely cul prits are digital products because they use switching power supplies that require heavy line filters to pre vent conducted EMI from going out of the box Fil ters so employed very often take the ground leakage current right up to the UL safety limits Although it won t kill you that is a lot of ground loop current for audio cables to handle There are basically three ways to attack the problem of a ground loop First is to eliminate it from its source and the second is to re route it through another path The third is to balance out your unbal anced audio interfaces Identify the Sources A good way to identify grounding problems is to use a multimeter to check the ac voltage between the chassis of your various gear when no audio cables are hooked up and all gear is plugged in and switched on Just start touching the two probes to the metal chassis of different pieces of gear Ideally you should always see zero volts Warning You may see as much as the whole line voltage between two different chas sis It does happen This voltage between chassis will be responsible for your ground loop problems If you find there is more than about 1 volt between eq
47. rmal operating signal level follows the IHF Institute of High Fidelity standard of 10dBV or 0 316 volts 316mV RMS Converting to dBu dimensions this works out to be the same as 7 7 9dBu There is therefore a difference of 11 79dB between pro and consumer operating levels Grounding There is the notion that some king of earthly ground exists out there that sinks all the noise and acts as some kind of a shield You see wires connected to ground rods and water pipes that are supposed to get a good ground This is not a correct interpreta tion of grounding from an audio standpoint Proper grounding of equipment and wiring is important and you will gain a better understanding of that as you read along Balanced vs Unbalanced Every audio signal is connected through a circuit The circuit must contain two conductors to create a com plete return path In other words a signal voltage Is conducted to a piece of equipment by injecting a cur rent into a wire That current has flow though to the destination through the wire and return back to the source through another wire Since audio is an alter nating voltage swinging through negative and posi tive polarity the current through the two conductors changes direction each alternate half cycle Which Page 20 INSTRUCTION MANUA L wire is the source and which is the return alternates accordingly In this regard balanced and unbalanced lines are the same They both need two
48. s look at this input a little further The INSTRUMENT Jack is located on the front panel where it can be accessed by musicians most easily The front end of this preamp is a low noise FET amplifier stage so you should notice this preamp is unusually quiet However because of the high impedance nature of an instrument pickup the noise level of the INSTRU MENT preamp will be higher than the mic preamp for the same amounts of gain taken This is a law of physics and not a design fault help mitigate the noise problem when the INSTRUMENT is not going to be used we designed a way to defeat the INSTRU MENT input and its associated noise TIP You will reduce the INSTRUMENT preamp noise by running the volume on the instrument higher and running the 207 s GAIN lower 4 3 USING THE MICROPHONE INPUT The Model 207 is perfect for all types of microphones either powered or not We encourage you to try every mic you own with the 207 Many features of the 207 are standard with all pro fessional preamps polarity pad etc Some fea tures are unique and we hope you will fully exploit them All controls for the MIC preamp are on the front panel You won t have to reach around back for the phantom power switch or pad Please read the rest of this section to pick up any tips we may have for you 4 3 1 USING PHANTOM POWER Active microphones that take power through the Page 11 INSTRUCTION MANUA L e 0 Using the 207 stan
49. s or registered trademarks of Aphex Systems LTD Other brand and product names are trademarks or registered trademarks of their respective holders TWO CHANNEL TUBE MNC PREAMPLIFIER CI P Table of Contents 1 0 CONTROLS 5 4 2 0 INTRODUCTION 2 1 What Distinguishes the Model 207 scceencosnccsetaiaes aa ee EE 6 2 2 What Does the UDE AdO ras eia oE n A A EAE EEEE SE 6 2 3 What ISS EE 7 PAC AE E EE 7 BP e AD OID centres 8 3 0 INSTALLATION AND INTERFACING OW WINS eI A ets le singe aged aia tae uae adeasaee 9 32 Rear Panel VIEW etter 9 Do R 9 JA Eae 9 een cron Ren rec meer ter nee ee 9 9 ys ESE E A aah oes T A TE 10 R NESEN 10 E 10 4 0 USING 207 4 1 Split Independent Preamp 11 AD Using the NSAR
50. send it to Aphex Systems Ltd 11068 Randall Street Sun Valley CA 91352 PH 818 767 2929 FAX 818 767 2641 Aphex Systems Ltd Model 207 Page 17 6 0 Specifications 6 1 GENERAL SPECIFICATIONS OPERATING LEVEL Switch Setting MIC INPUT Connector Type Balanced Maximum Level CMRR Nominal Preamp Gain INSTRUMENT INPUT Connector Type Input Z Maximum Level Nominal Preamp Gain OUTPUT Connector Type Output Z Balanced Output Z Unbalanced Nominal Level Maximum Level Output Trim AUDIO Frequency Response EIN Crosstalk THD Tube Type INSERT Connector Type Send Return Nominal Operating Level Point of Insertion SYSTEM FUNCTIONS OTHER SPECIFICATIONS Power requirements Unit is electrically supplied through an agency approved IEC type datachable primary power cord The voltage INSTRUCTION MANUAL 4dBu XLR 3F Transformerless NPN active balanced 2KQ nominal OdBu Greater than 70dB 60Hz 20 to 65dB minus OUTPUT TRIM loss 1 4 Phone Jack Unbalanced JFET Amplifier 1OVRMS infinity to 65dB minus OUTPUT TRIM loss XLR 3M and TRS 1 4 phone jack Impedance Balanced may be used unbalanced XLR 66Q TRS 1200Q XLR 33Q TRS 600Q 4dBu 21dBu Unloaded O to 12dB 0 0 5dB 30Hz 30KHz 129dBu Input Shorted 10Hz 22kHz 794 or better 10Hz 22kHz 11dBfs lt 0 18 12AT7 ECC81 Dual Triode 1 4 TRS Phone Jack T
51. t on microphones having an impedance of 50 ohms or higher That includes just about every powered and passive microphone in exis tence Additionally the use of phantom power in no way inhibits the performance of MicLim All you have to do is turn MicLim on and it will instantly become armed Nothing will happen how ever until an audio peak approaches clipping then the limiter will act on the microphone signal to pre vent the peak from reaching the clip point When ever the limiter hits a peak the red LIMITING light will flash There are no special rules about making MicLim work for you The concept is simple run the preamp gain at a point where the peaks indicated on the Headroom Meter only reach the MicLim threshold infrequently or unexpectedly The great advantage of operating in this manner is to keep the audio signal far above the noise but fearing no distortion should the sound level suddenly increase Recording this way can give you an uncanny sense of dimension because the background will have no audible noise even at high monitoring levels For those who will send this 207 s output to a digital audio workstation the greatest benefit is maximizing the use of the quan tum dynamic range The closer to the top you digi tize a signal the more digital resolution you get You lose 1 bit of digital for every 6dB under maximum so keeping the signal up to the top guarantees the best digital audio By n
52. to the input ground only espe cially in locations with high levels of RFI That means the sending end shield should be left disconnected However if you already have cables with the shield connected at both ends go ahead and try them out If you are connecting a fairly simple audio system it may be fine as is A word on optional shield connections Connect ing the cable shield of a balanced line at both ends creates unnecessary ground loops which may carry noise and hum currents that can be amplified Con necting the shield only at the sending end instead of the receiving end may exaggerate common mode noises at the receiving input stage It can actually increase RFI and noise more than having no shield at all Because of the Pin Dilemma mentioned above you may be forced in some situations to experiment with how the cable shield is connected to ground to eliminate a pesky hum or radio interfer ence problem It might be good to try XLR ground drop adapters see Note 3 as a method of trying these conflicting methods out and being able to change easily if necessary IMPEDANCE Regardless of inaccuracies it has become more or less standard over the years to refer to balanced lines as Page 23 Appendices INSTRUCTION MANUA L TABLE 1 BALANCED amp UNBALANCED CONNECTOR WIRING STANDARDS 3 Pin XLR 1 4 TRS Phone Pin 2 Tip Pin 3 1 4 TS Phone RCA Sleeve Shell low impedance and unbalanc
53. totally new and attractive style for the chassis and panel that makes it look as great as it performs With the Model 207 you are getting exclusive Aphex design advantages and legendary sonic quality at a very modest price We hope you enjoy using it for many years to come 2 2 WHAT DOES THE TUBE ADD The Model 207 uses a discrete solid state transfor merless front end carefully crafted for extremely low noise and high common mode rejection It runs with out feedback making it nearly ideal as an input stage never reflecting any feedback current back out to the microphone Certainly the input stage has a mea surable distortion level but it is very low and does not impart any appreciable tonality The tonality for which our tube preamplifiers are famous is due exclu sively to the tube Our unique and stable RPA tube circuit retains the tube s transconductance and grid characteristics while at the same time creating a much more efficient amplifier stage that runs on low power supply volt ages We designed the RPA in the Model 207 to deliver a specific tube distortion curve that subtly voices the preamp If you have been using the Model 207 or its predecessor the Model 107 then you know what that means The preamp is character ized by most users as very transparent and detailed but not colored The beauty of tubes is that their Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER CI P Introduction
54. uipment grounds you should start looking for a remedy Commonize the Power Try plugging all of your equipment into the same outlet strip Get one that has enough outlets in one strip or string more than one together Of course you need to make sure you don t overload the one ac cir cuit your strip is plugged into If the load is too great for one circuit use a second or third circuit that is tapped off the same 120 volt phase in your distribu tion panel That means all outlets should be on odd or even numbered circuit breakers That s because as you go down the column the circuit breakers tap into alternating legs of your incoming electric power Be sure you re always on the same leg You can tell you re on the same leg by measuring the ac voltage between the hot slots of the different outlets you ve chosen It should be very low or zero That will remedy 50 percent of the cases Page 22 INSTRUCTION MANUA LL Check the Cord Polarity For products that have 2 wire power cords try revers ing one of the power cords in the socket That may reduce the ground current generated by the internal electronics of the offending gear Redirect Ground Loops Sometimes it just comes down to brute force ground ing That means providing such heavy low resistance ground current paths that little current is left to flow through your audio grounds You can try adding heavy gauge for example 12 gauge copper wire from chassis to chassis
55. utput stages in use today They may be placed into two main classes transformer balanced and Aphex Systems Ltd Model 207 TWO CHANNEL TUBE MC PREAMPLIFIER CI P transformerless balanced usually called active bal anced Transformer balanced outputs are becoming outdated because of their high cost and their sonic limitations However they can still be found on a lot of older equipment Within the transformerless class there are several types of circuits that are used by different manufac turers These different types of output circuits all look just about alike to any balanced line but they act dif ferently when driving an unbalanced line You need to observe the proper cable wiring for each type of output circuit We strongly recommend that you refer to your various equipment manuals to find out what is used in each case before hooking up to unbalanced lines When connecting a balanced output to a balanced input however you don t need to know what kind of balanced output you are dealing with Simply treat it generically PART 1 BALANCED OUT to BALANCED IN 1 4 TRS Phone to 1 4 TRS Phone Balanced Cables Appendices XLR to XLR Female OK for Microphones Standard store bought cable Shield grounded at both ends Positives Good for microphones Negatives May cause ground loops through the shield grounds used to connect equipment together Female No Connect Preferred for Line
56. y particular pur pose Any and all warranties are limited to the duration of the warranty stated above EXCLUSION OF CERTAIN DAMAGES Aphex Systems liability for any defective unit is limited to the repair or replacement of said unit at our option and shall not include damages of any other kind whether incidental consequential or otherwise Some States do not allow limitations on how long an implied warranty lasts and or do not allow the exclusion or limitation of incidental or consequential damages so the above limitations and exclusions may not apply to you This warranty gives you specific legal rights and you may also have other rights which vary from State to State 5 2 SERVICE INFORMATION If it becomes necessary to return this unit for repair you must first contact Aphex Systems Ltd for a Return Authorization RMA number which will need to be included with your shipment for proper identification If available repack this unit in its original carton and packing material Otherwise pack the equipment in a strong carton containing at least 2 inches of padding on all sides Be sure the unit cannot shift around inside the carton Include a letter explaining the symptoms and or defect s Be sure to reference the RMA number in your letter and mark the RMA number on the outside of the carton If you believe the problem should be covered under the terms of the warranty you must also include proof of purchase Insure your shipment and
57. ysical Properties The device shall be packaged in an all metal chassis measuring 19 482 23mm wide 1 75 44 42mm high with an overall depth of 8 25 210mm Depth behind the front panel shall be approximately 8 203mm The device shall have a net weight of approximately 6lbs 2 73kg and is capable of mounting in a standard electronic equipment rack Power The unit shall have a self contained power supply operating from the ac line Primary voltage connectorization and agency listings shall be appropriate to meet local requirements Aphex Systems Ltd Model 207 Page 19 7 0 Appendices Appendix A Balanced and Unbalanced Lines and Operating Levels Interfacing all types of equipment with balanced and unbalanced lines and can sometimes be trouble some First you have to somehow connect balanced to unbalanced and then you have to deal with dif ferent levels This tutorial will teach you about the principles of balanced and unbalanced lines wiring standards and how to effectively interface them Standards Professional audio equipment usually comes equipped with inputs and outputs that are balanced using 3 pin XLR connectors and sometimes 1 4 inch phone jacks as well This equipment most often is designed to operate at 4dBu a professional industry stan dard That translates to a magnitude of 1 23 volts RMS Root Mean Squared Consumer gear has unbalanced I O as standard usu ally on RCA Jacks The no
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