OWNERS MANUAL
Contents
1. Input Impedance 20kOhms Balanced Voltage Gain ST600 32dB ST400 30dB ST 1000 4 34dB Hum and Noise Better than 100dB referred to maximum output Output DC Offset 50mV maximum Output Rise Time Less than 3 microseconds Protection Over temperature if the unit should exceed its rated temperature thermal sensors shut down the amplifier until a safe working temperature is reached Inputs Have radio frequency filters V x limiting circuits keep output devices within safe operating limits Current Requirements 240V ST600 8 Amps ST400 6 Amps ST1000 10 Amps Minimum Load Impedance Stereo mode 4Q per channel nominal Bridge mode 8Q nominal Dimensions ST4 6 Front Panel 482mm x 88mm 19 x 3 5 2U ST100i Front Panel 482mm x 1 32mm 19 x 5 25 3U Front To Back 427mm 16 5 including rear mounting support x 83mm13 25 high Weight Boxed Unboxed ST600 20 Kg 18 Kg ST400 20 Kg 18 Kg ST1000 23 Kg 21 Kg 6 2 Stereo Specifications Both channels driven continuous average power at 1 KHz 0 1 distortion ST400 40 400Watts 80Q 260Watts ST600 40 600Watts 8Q 400Watts ST1000 4Q 1000Watts 80Q 680Watts 6 3 Mono Specifications Continuous average power at 1 KHz 0 1 distortion ST400 80 800Watts ST600 8Q 1200Watts ST1000 8Q 2000Watts2. amplifiers Loss of power at a concert is never welcome but lack of thought can turn a power loss into an abandoned performance It is good practice to familiarise yourself with the location of the hall fuse box and to ensure that the local hall manager has instructions that in the event of a loss of power it should not be reset without an all clear from the sound crew 5 4 Stereo mode In stereo mode STi Series amplifiers work as two separate mono amplifiers housed in a single chassis with separate inputs outputs and controls To operate as a stereo two channel mono amplifier the mode switch on the rear panel must be in the left position 3 7 and the speakers wired appropriately 4 13 5 5 Mono Parallel Mode In mono parallel mode STi Series amplifiers work as two separate mono amplifiers fed with the same signal but with separate level control of each output For the amplifier to work in parallel mono mode a signal cable must be connected between the two channel signal inputs 4 10 4 11 The speaker connections remain the same as in stereo mode 4 13 5 4 5 6 Mono Bridged Mode In bridged mode the STi Series amplifier utilises both channels as a single mono block This is achieved by inverting the phase of channel B to produce output voltages twice as high as those available from a single channel This higher output voltage is delivered into a single load It must be remembered that in bridged mode the minimum load impeda
3. gt GUDIo d STi SERIES OWNERS MANUAL CONTENTS 1 INTRODUCTION 1 1 Tuz 1 3 1 4 1 5 1 6 1 7 Introduction Serial Number Warning Caution Attention Loudspeaker Warning Smoke Warning 2 FRONT PANEL Zui 22 Z2 2 4 22 2 0 On Off Power Indication Bridge Level Peak Indicators Cooling vent 3 REAR PANEL 3 1 J2 3 3 3 4 2 3 3 6 3 7 AC Input Fuse Signal Output Ground Switch Cooling Fan Signal Input Bridge Switch 4 INSTALLATION 4 1 4 2 4 3 4 4 Unpacking Mounting Cooling Requirements Cable Looms 4 5 4 6 4 7 4 8 4 9 4 10 4 11 4 12 4 13 4 14 4 15 4 16 Power Requirements Voltage Selection AC wiring Balancing Option Balanced Signal A Description Input Connections Balanced Input Connections Unbalanced Speaker Wi re Output Connections Signal Matching Cable Routing Grounding 5 OPERATION 5 1 oe 5 3 5 4 ores 5 6 Def 5 8 PowerUp Power Down Power Loss Stereo Mode Mono Parallel Mode Mono Bridged Mode Protection Cleaning 6 PERFORMANCE amp SPECIFICATIONS 6 1 6 2 6 3 General Specifications Stereo Specifications Bridged Mono Specitications 1 INTRODUCTION 1 1 Introduction The STi Series of amplifiers from C Audio consists of three models ST400i ST600i and ST1000 incorporating considerable knowledge and expertise accumulated over many years involvement in the art of Amplifier design and manufacture Mod
4. it inside the rack and increasing the risk of thermal overload In addition to keeping the amplifier cool the fans will also draw dust and dirt into the amplifier casing which may remain there If this dust is allowed to build up inside the amplifier it will reduce the effectiveness of the heatsinks and the amplifier may produce lower than normal output levels see 5 7 To reduce dust intake into the rack air vents in the rear of the rack should have dust filters which are periodically cleaned In certain environments the dust level will be much higher than is normal e g in discotheques which have smoke machines located near the amplifiers Some smoke oils deposit a corrosive residue which over time attacks the component leads and Printed Circuit traces Care should be taken not to use such smoke oils In the presence of these amplliers damage caused in this way will not be covered by the warranty In such circumstances steps should be taken to locate the amplifiers as far away from a potential dust source as is practical and this must be borne in mind when considering service intervals 4 4 Cable Looms When the amplifiers are housed in a rack the input and output connections are usually terminated on a connecting panel Typically when multiples of amplifiers are housed in a rack the panel may be configured with multipin input connectors which will have a variety of signal sources usually being outputs from a crossover frequency dividing netwo
5. may potentially damage a speaker After waiting for a couple of seconds turn the level controls clockwise Normally these controls will be in the full on position i e all the way to the right However it may be that to balance your speaker components you require less level to one unit than another The level controls may be safely used for this purpose When switching on a whole rack of amplifiers they should be individually switched on one at a time The practice of leaving all amplifiers in a rack switched on and powering up the whole rack by connecting it to the A C is dangerous and likely to blow the mains fuse of the supply to the rack As aforementioned power amplifiers are subject to high current transients when switched on switching on a number of amplifiers simultaneously i e as described above will possibly cause a current surge greater than the mains supply is capable of delivering resulting in a mains fuse blowing 5 2 Power Down When you have finished using the amplifier first turn the level controls anticlockwise all the way off then move the power on switch to the UP off position The green LED should fade out For safety it is advisable to disconnect the AC power feed before going any further If you always follow this strict procedure the amplifier will be ready for you next time you need it Technical Note The STi series amplifiers incorporate a thermistor controlled soft start circuit to reduce the inrush cu
6. mixer Wherever possible the amplifier level controls should be near maximum and the level controlled by the mixer master faders Alwavs keep an eye on the mixer meters to ensure you are not overdriving the mixer Never operate the amplifier with less than the rated load impedance This will not result in increased pow er but due to the amplifiers output protection is likely to result in premature clipping and damage to the loudspeakers 1 7 Smoke Warning Glycol based smoke machine fluids i e most of them deposit a residue which is a conductive solvent and attacks some metals especially copper In addition to spoiling the paint finish of your amplifier such deposits if allowed to accumulate will attack component leads and Printed Circuit Board traces The best course of defence against this potential problem is to ensure that sources of smoke are located well away from the fan intakes Damage caused to amplifiers by smoke residue can be costly to repair and is explicitly excluded from the normal warranty cover 2 FRONT PANEL CONTROLS 2 1 On Off This switch powers up the amplifier The amplifier is ON when the switch is switched to the right see 5 1 2 2 Power Indication The green power LED is a visual indicator that will light up when the unit is connected to the mains and switched on 2 3 Bridge The yellow bridge LED is a visual indicator that will light up when the amplifier is being used in bridge mono mode see
7. outputs to electronic signal processing equipment there is no standard pin wiring On XLRs pin 1 is usually ground but pin 2 can be phase or anti phase Accordingly when setting about wiring a balanced system care must be taken with each piece of equipment connected in the signal chain 4 10 Input Connections Balanced Signal input to the STi Series is via male and female XLR connectors which are linked The signal cable should be of good quality with an overall shield to reduce hum and noise For balanced operation the pin wiring is Pin ground connects to the cable shield Pin 2 signal phase Pin 3 signal anti phase 4 11 Input Connections Unbalanced If using the input unbalanced the pin wiring is Pin not connected see note Pin 2 signal phase Pin 3 ground cable shield Note When using the input with an unbalanced source some of the benefits of a truly balanced system can be achieved by connecting the signal in a quasi balanced configuration In this configuration a two core plus screen cable is used connected at the amplifier end as per a BALANCED input 4 0 At the signal source end of the cable the pin 3 core of the cable must be connected to the cable screen In some manufacturers equipment this correction will be made internally check user manuals enabling a pin to pin cable to be used Otherwise the connection must be made inside the connector at the signal s
8. 11 3 7 Bridge Switch The STi series may be configured to Bridge Mode enabling the total power of both channels to be summed into one load e g 1200 watts in the ST600 For normal stereo operation the switch remains in the left position labelled stereo moving the switch to the right selects bridged mono operation Caution Never operate this switch when the amplifier is switched on Never power up the amplifier after moving the switch without resetting the speaker connections see 5 6 Never use in bridge mode with a load of less than 8Q nominal Failure to observe these requirements may result in permanent damage to the amplifier or speakers connected to it and will invalidate the warranty 4 INSTALLATION 4 1 Unpacking Before this unit left the factory it went through an exhaustive test procedure and was carefully inspected before packing to ensure flawless appearance Before powering the unit up carefully inspect the outer carton for any signs of rough handling or physical damage When you unpack the carton do not damage it as it should be stored safely with all the internal packing materials in case the amplifier needs to be returned to a dealer for service After unpacking the unit carefully inspect it for any signs of physical damage In the event that any damage is discovered do not power the unit up but immediately contact your Dealer who will advise you on an appropriate course of action and submit a written claim to cover the da
9. ains or output wiring When there are multiple units in a rack it is preferable to tie all input cables to the amplifiers together and to tie all mains leads to the amplifiers together maintaining of course maximum separation between mains and input cables 4 16 Grounding Normally the ground switch should remain in the normal left position In this position the audio ground of the signal is tied to the chassis of the amplifier which is tied to the AC ground When you are installing your amplifiers however it is possible that the interconnection of the various units e g mixing console equalisers Crossovers amplifiers may result in a ground loop A ground loop as such is not necessarily undesirable but it often results in a hum on the output of the amplifier which is unwanted Such hum is often caused by poor cabling see 4 15 When testing the amplifier in the system at the end of installation if excessive hum is present and the cabling has been checked as per 4 5 move the ground switch to the right position which isolates the AC ground from the audio ground This may be done with the amplifier switched on and the speakers connected without any adverse effects If the hum reduces the switch may be left in the ground lift mode If it does not move the switch back to its normal position and examine other pieces of equipment in the signal chain Most of them should also be fitted with ground lift switches and by a process of tria
10. ern power amplifiers are sophisticated pieces of electronic engineering capable of producing extremely high power levels They must be handled with respect and correctly installed if they are to provide you with many years of reliable service They are potentially extremely dangerous if abused misused or incorrectly installed Please take a little time to study this STi Series manual in order that you can get the best service from the amplifier 1 2 Serial Number Every STi Series amplifier has an individual serial number which is marked on the rear of the unit Make a separate note of this number somewhere safe where you can refer to it You may need to know this number on an occasion when the amplifier is not to hand e g if it is stolen or has been sent away for repair or the rear is not easily accessible 1 3 Warning The STi amplifier must be earthed via the earth connection in a three core mains cable supplied see 4 7 To prevent the danger of electric shock or fire hazard do not expose the unit to rain or moisture If the unit should come into contact with moisture for any reason disconnect it from the mains supply and leave it in a suitable place to dry out 1 4 Caution All controls needed for the safe operation of this amplifier are accessible from the outside of the casing There are no user serviceable parts inside the unit Never remove the service covers with the unit connected to the mains supply In the event of a failure re
11. fer to your Dealer Unauthorised servicing or tampering with the circuitry may be dangerous and invalidates your warranty 1 5 Attention The STi Series has been designed to be rack mounted in any standard 19 equipment rack or in fixed installations stack mounted on its base If this amplifier is to be used in a mobile application it must be properly mounted in a suitable equipment rack with front and rear support C Audio will not be responsible for any damage electronic or mechanical sustained due to a failure to rack mount in a mobile application or insufficient support in the rack housing Failure to comply with this will invalidate the warranty Please read section four concerning installation which details the correct procedures for mounting the STi Series 1 6 Loudspeaker Warning The single most common cause of loudspeaker damage is due to amplifier clipping This may be due to driving the power amplifier itself into clip or by sending a clipped signal to the amplifier Never operate the amplifier with the red 5 peak LED s flashing more than occasionally Also beware of sending a clipped signal to the amplifier Owing to the amplifiers wide bandwidth and high slew rate such signals will be reproduced with extreme accuracy and loudspeaker damage will almost certainly result If you are operating your system with the mixer faders near maximum and the amplifier level controls below half way you are in danger of clipping the
12. g clockwise until it clicks The speakon plug will now be safely secured 4 14 Signal matching The STi Series input sensitivity is 4dBu OVU or 1 2vRMS The input impedance is 20k Q for all models For the amplifier to achieve its full rated output gain it is important that the input signal is matched Different types of pre amplifier e q mixing console disco mixer etc have different output levels If the signal is too low the amplifier will not meet its rated output and if the signal is too high the signal will be clipped distorted at maximum gain See 1 6 If you are unsure consult your dealer 4 15 Cable Routing The majority of hum and noise problems are caused by poor cabling This may take the form of badly made XLR connections most often a missing screen termination inadequately screened cable or poor cable routing In the event that hum at the output of the amplifier is experienced first check that the input connectors and cable are correctly wired Check that the cable used is of good quality with an effective screen and preferably twisted inner cores If all is well check the routing of the input cables The input cables to the two channels should run together to the source equipment The cables should be tied together with lacing cord or plastic cable ties or better still be twisted together which will tend to cancel any hum induced into the cable screen Ensure that input cables are not in close proximity to any m
13. l and error it is usually possible to achieve the required result Another possible source of hum is poor cabling inside the rack see 4 4 5 OPERATION 5 1 Power Up Plug in all signal input and output cables to and from the amplifier If the amplifier is being used in a PA system then all the cables in the system should be connected including all the signals from the mixing console i e the outputs via a multicore Ensure that the amplifier power switch is in the OFF position up Ensure that both amplifier level controls are turned fully anti clockwise to the OFF nil gain position Connect the AC cable from the amplifier or rack to the mains feed If the amplifier is being used in a PA system it is normal to switch on the mixing console and the crossover before the amplifiers Ensure that the console master gain controls are fully down or muted Ensure that the crossover gain controls are fully down or muted Switch the amplifier on by moving the switch to the DOWN position Observe that the green power LED comes on The STi Series features a relay on each speaker output This disconnects the load i e speakers automatically from the output of the amplifier when the amplifier is switched off When the amplifier is next powered up the load remains disconnected for approximately two seconds and is then automatically reconnected This is because high power amplifiers are subject to high current transients when switched on which
14. mages 4 2 Mounting If the amplifier is to be permanently installed it may be stacked on its base and multiple units may be piled up one above the other However it is always advisable to mount the amplifier in a suitable 19 rack and if the amplifier is to be used in any mobile application then it must be properly installed in a rack The variation and range of different racks and flightcases is enormous Although they are all designed to accomplish the same basic objective some are of much stronger quality than others It is important to ensure that the rack you use is suitable for its application Most of the world s large touring sound companies mount their amplifiers into housing racks of wood or metal which are then mounted in foam lined flightcases or wooden cases to provide maximum protection The housing rack must have racking rails at the front and rear for bolting the unit to so that it can be evenly supported all round Racks for multiple units are normally designed with wheels to facilitate easier moving around Generally speaking the rack should be designed such that when it is in use and in transit the rack is off its wheels so that it cannot move This generally also means that when the amp is static the amplifiers are resting on the floor of the rack or on the amplifier below them thus reducing the stress on the racking strip and bolts This is especially important when a rack is in a truck and may be liable to be bounced arou
15. nce has to be doubled e g Mathematically Power Voltage2 Resistance Impedance Stereo Bridged Mode Mode Output Voltage 50V lOOV Load 4Q 8Q Power 625 Watts 1250 Watts Bridge mode is usually employed when very high output levels are required to drive a specialist speaker enclosure which has a very high power handling Operating amplifiers and systems in bridged mode requires extra care because of the higher voltage levels on the speaker lines It is also worth remembering that in the event of a failure more of the system may be lost than when it is being used in the conventional stereo manner To operate the amplifier in bridged mode the following procedure should be followed Disconnect tile amplifier from the AC Remove speaker wires if already fitted Switch the mode switch to the right 2 3 3 7 Residue connect the speaker cables as described 4 13 after checking that the total speaker load is not less than 8Q Connect a signal input cable to channel A only If there is a parallel signal link cable between channels A and B this must be removed Check that the power switch is in the off position Check that both level controls are at minimum fully anti clockwise Residue connect the AC Switch the power switch to on Check the power LED comes on Check that the yellow bridge LED is on Turn the channel A left control pot level control clockwise when trying this application out for the first time it is advisable to turn the le
16. nd in transit It is also imperative to ensure that the rack rails are securely fastened to the rack itself to prevent them tearing loose in the event of an accident When mounting multiple units into a rack it is good practice to mount the heaviest items at the bottom and the lightest at the top In this way the rack is more stable with a lower centre of gravity for easier handling The rack should have rear access even if all connections to the amplifiers are via the front of the unit as it may be necessary to gain access from time to time e g to lift a ground switch or check a connection 4 3 Cooling requirements It is essential that air can circulate freely around the amplifier to keep it cool The rear fan will draw air into the amplifier case forcing it over the large transverse heatsink in order to keep the power devices cool and exhaust through the front vent The front and rear of the unit must not be obstructed in any way to prevent this If the unit is mounted in a rack care must be taken that the rack is sufficiently open at the front and back to allow a sufficient flow of air through the rack If the air flow is restricted in any way a separate fan should be mounted on the back to draw air inside the rack Similarly the front of the rack must not be obstructed for example some racks in fixed installations utilise perspex front doors to prevent tampering These must not be used as they would restrict the exhaust of the air trapping
17. ops which produce hum The use of the ground lift switch 3 4 4 16 may be of assistance but care should be taken to ensure that the AC cables are in an optimum position before this is tried 4 5 Power Requirements The current requirements of the STi Series are as follows 220 240V 100 110 V ST400 6 amp 12 amp ST600 8 amp 18 amp ST1000 lO amp 20 amp Accordingly when multiple units are mounted in a rack and share a common AC feed care must be taken to ensure that the AC connector is of sufficiently high current capacity otherwise the connector may overheat with the risk of fire and or breakdown 4 6 Voltage selection Before use the amplifier must be set to the local operating voltage This is normally set at the factory for the country the unit is to be used in i e 100 110 120 220 or 240V Check that the amplifier is set to the right voltage by checking the markings on the rear panel and the markings on the carton The amplifier should only be used when set to the appropriate local voltage and operated from an AC mains of 10 of the selected line voltage Failure to comply with these regulations may lower the performance of the amplifier 4 7 AC Wiring This unit must be connected to a three wire grounded outlet at the appropriate voltage see 4 6 Where required a mating AC cable plug type CEE22 V is supplied with each STi Series amplifier Should you need to wire your own mating connector it is essential to note that
18. ource end of the cable 4 12 Speaker Wire Any signal chain is only as strong as its weakest link The importance of the speaker cable quality and diameter is frequently overlooked There are several factors which dictate the type of cable you should use e q the length of the cable run the signal type going down the cable the output power of the amplifier Generally speaking the lower the frequency the longer the distance and the higher the output the thicker the speaker cable must be If the cable is too thin signal output will be lost most noticeably with bass frequencies and the system damping factor will be reduced If you are unsure about the type of cable you should use consult your local dealer for advice Many loudspeaker enclosure manufacturers stipulate the appropriate cable for their speakers in their literature 4 13 Output Connections Speakon Connection to the speakon sockets can only be made with a speakon plug The positive phase output should be connected to Pin 1 of the Speakon plug The negative non phase output should be connected to Pin 1 of the speakon plug For bridged mono operation the output should be taken between channel A pin positive and channel B Pin 1 positive This needs two speakon plugs with one wire taken from each To activate the output push the speakon plug into place and turn it clock wise until it clicks into place To lock the plug in place turn the locking ring on the speakon plu
19. plifier has been set to operate on 220 240V 100 110 120V ST400 T10 amp 20mm T20 amp 32mrn ST600 T10 amp 20mm T20 amp 32mrn ST1000 T10 amp 20mm T20 amp 32mrn It is essential that if the fuse should need to be replaced for any reason only one of the correct type and rating are used The correct fuse allows the STi Amplifier to deliver its full power without danger A fuse of a lower value than specified will be likely to blow again when the amplifier is required to deliver its full rated output whilst a fuse of a higher value will not protect the unit Never attempt to bypass the fuse as this can result in serious damage and will invalidate your warranty 3 3 Signal Output There are two Speakon connectors When connecting speaker cables it is most important that correct phase polarity is observed 4 13 otherwise your speaker system s performance will be reduced 3 4 Ground Switch This switch is used to lift the audio ground from the AC ground For its use see section 4 16 3 5 Cooling Fan A cooling fan is mounted inside the chassis behind the chrome fanguard to ensure the cool running of the amplifier 2 6 and 4 3 It is important that nothing obstructs the airflow to the fan at any time 3 6 Signal Input Input to the amplifier is via two male or female XLR connectors Although the inputs are balanced provision has been made for them to be used unbalanced if required without the need for adapters see 4 8 4 9 4 10 4
20. rk in a PA system or various monitor outputs from the mixing console in a studio application The connection panel will thus normally have a number of input and output connectors together with an AC input and cables from these connectors will connect with each amplifier It is important that the appropriate type of cable is used and that care is taken with the way in which the cables are routed round the rack and tied together Poor cabling may result in reduced performance amplifier failure unreliability and increased hum To reduce these possibilities all cables should be loomed together with cables performing similar functions but not with other cables For example if a rack is housing six STi Series amplifiers there will be 12 signal cables connecting the amplifiers to the connector panel These 12 cables should utilise screened pair cable and they should be tied together in a bundle using plastic cable ties or lacing cord and also tied to the rear rack rails so they cannot move around inside the rack If signal cables are left free and not tied a magnetic hum field may be created and the possibility of them causing hum through ground loops is increased The back panel of the ST Series has been laid out such that all signal input cables can be loomed together up one side of the rack and all speaker outputs can be loomed up the other side Similarly all AC cables should be carefully loomed and positioned as these too may also cause ground lo
21. rrent At switch on the resistance of the thermistor is high but rapidly drops to a very low value thus giving control over the inrush current If however the amplifier is turned off and back on rapidly the thermistor may not have had time to return to its high resistance state resulting in possible failure of the chassis fuse or even the 13 amp mains plug fuse It is therefore recommended that after switching off the unit it not be turned on for at least 30 seconds 5 3 Power Loss If power to the amplifiers or the whole system is lost for any reason whilst in use the following precautions should be observed Mute the signal source outputs e g mixing console and pull the master level faders all the way down When power is lost there is a natural tendency to push the faders up further to try and see if this will bring the sound back Should this happen unexpectedly and the amplifiers regain power they will suddenly go to full power after the relays release the outputs and this is likely to blow your speakers Turn the amplifier level controls down and switch the amplifiers off If multiple amplifiers are being used and the power should come back on unexpectedly without the amplifiers being turned off the AC surge may add to your problems by blowing a mains fuse generally in the most inaccessible place When the power has been restored follow the normal power up procedure ensuring the console is powered and muted before switching on the
22. section 5 5 2 4 Level The two black rotary level potentiometers individually control the input signal to each of the amplifier s channels When turned fully clockwise they allow the amplifiers maximum gain to be utilised 2 5 Peak Indicators The two red peak indicators show when each channel is about to clip see 1 6 2 6 Cooling Vent All high power amplifiers produce considerable heat as a by product of power output Keeping an amplifier cool is essential to its performance and long life The cooling system of the ST Series employs a fan mounted on the rear of the amplifier chassis which draws air through the amplifier and exhausts through the vent in the front panel It is important to ensure that this vent is never blocked see 3 5 and 4 3 3 REAR PANEL 3 1 AC Input On amplifiers set to 220 240V mains is connected to the amplifier via the IEC 10 amp Euro connector A mating mains connector also rated at 10 amps is supplied with the amplifier The voltage 220 240V is set by removing the fuse cover and re inserting it with the appropriate voltage uppermost On amplifiers set to operate at 100 110 120V mains is connected to the amplifier via a fixed mains cable This cable is rated at 20 amps with the voltage internally set at the factory 3 2 Fuse A mains fuse is fitted to protect the amplifier The fuse is of the anti surge type The rating of this fuse varies depending on the amplifier model and what voltage the am
23. t unbalanced uses only two wires Until comparatively recently signals could only be balanced using large low impedance matching transformers However these have a number of inherent limitations sometimes introducing colouration into the sound limiting the frequency bandwidth adding weight and are expensive Modern technology has now produced a more reliable cost effective and technically superior system electronic balancing where the signal is balanced by a small electronic circuit The advantage of a balanced signal is that it can reduce noise and reject interference particularly where long cable runs are used such as might be the case in a PA system where the mixing console is in the auditorium and its outputs are fed through equalisers and crossovers to the amplifiers at the stage For a balanced system to be fully effective it is essential that the complete signal chain from source to amplifier is balanced Thus it is imperative to ascertain whether the equipment in the signal chain has the option to be wired balanced and how it has been previously wired A balanced signal uses three wires one for ground one for signal phase and one for signal anti phase When cabling a system it is important that phase polarity is carefully observed throughout the signal chain This is harder than it sounds however because although the XLR and 1 4 stereo TRS Tipring sleeve are almost universally used as the signal connector for inputs and
24. the earth pin is the central one in the connector The AC cable supplied is colour coded according to the European standard which Brown Live Blue Neutral Green Yellow Earth Ground Where a fixed mains lead is fitted the colour coding is to the American standard which is Black Live White Neutral Green Earth Ground The cable supplied has bare wires at the other end for terminating in an appropriate plug When wiring up the terminating plug it is essential that the earth wire is connected and that the supply feeder has a good earth connection A poor earth connection may result in the amplifier chassis not being grounded thus increasing the risk of electric shock If a number of amplifiers are connected via an AC distribution board and extension cable care must be taken to ensure that the cable is of a heavy enough current capacity The longer the cable the heavier the gauge required for safety and to prevent loss in the cable It will also be necessary to ensure that the mains outlet is of sufficient amperage for the load see also 4 4 4 8 Balancing Option The STi Series will accept both balanced and unbalanced inputs It is important to determine which signal type you will be using This is governed by the signal output from the devices preceding the amplifier in the signal chain 4 9 Balanced Signal A Description A low impedance signal can be balanced or unbalanced A balanced signal is a three wire system whils
25. vel to half power only and then feed audio into the amplifier to ensure everything is working When you are satisfied that it is turn the audio source down in level and turn the amplifier level up then proceed in the usual way In bridge mode the channel B level contro has no function Powering down should follow the normal procedure 5 7 Protection The STi Series has a number of internal electronic protection Circuits to prevent damage occurring to the amplifier or the speakers If the working temperature of the amplifier rises above 90 C the amplifier will automatically shut down The principle causes of over temperature can be i the air vents are blocked ii poor air circulation in the rack or housing lil the fan has failed vi incorrect load impedance v output cable short To remedy the above see 2 6 3 5 4 3 When the temperature inside the amplifier drops below the safety threshold it will come on again automatically Since this could result in speaker damage it is advisable to reduce the level controls by 50 until the amplifier has started working again Be aware if an amplifier has shut down once through overheating it is likely to do it again thus a thorough checking of the air cooling system and the output cables should be made at the first opportunity 5 8 Cleaning 6 SPECIFICATIONS AND PERFORMANCE 6 1 General Specifications Total Harmonic Distortion Less than 0 1 from 5Hz 50KHz Typically less than 0 03
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