User Manual
Contents
1. the compressor stage Note that the gain reduction indicated is a measure of the degree of compression and does not include any gain make up applied The gain reduction scale is printed beneath the meters and also applies to both channels SPECIFICATIONS Balanced Line Input Electronically balanced unbalanced compatible with input impedance greater than 5Kohm Gain range 20dB to 20dB Nominal input level 4dBu Maximum input level 26dBu 3 pin female XLR connector Unbalanced Input Input impedance greater than 5Kohm Gain range 20dB to 20dB Nominal input levels 10dBu Maximum input level 12dBu 2 pole 0 25 jack socket Auxiliary Input Compressor Switchable for high or low gain plus 40dB gain variation Maximum input level 18dBu 2 pole 0 25 jack socket Threshold 20dBu to 20dBu Attack 0 5msec or 20msec Release 40msec or 2 seconds Ratio 1 1 5 to 1 30 Gain Make Up 0 to 20dB Stereo Operation Ganged Threshold Attack Release and Ratio controls Linked control voltages Bargraph Meters Switchable to output level or compression 0dB 4dBu Outputs Electronically balanced unbalanced compatible Output impedance 47 ohms Maximum level 26dBu 3 pin male XLR connector Unbalanced Outputs Output impedance 47 ohms Maximum level 18dBu into 10Kohms 2 pole 0 25 jack socket Frequency Response 10Hz to 40KHz 0 1dB Noise 82dBu 22Hz 22KHz Dynamic R2. to operate the equipment OPERATION Front Panel The front panel controls are identified in fig 2 Input Gain A line level signal should already be at about the correct operating level but this may be checked by bypassing the compressor i e turning off the COMP IN switch and monitoring the level on the bargraph meter The INPUT GAIN should be adjusted until the OdB LED is illuminated on music of normal loudness with the red LEDs illuminating occasionally on higher volume peaks The front panel auxiliary input sockets may be switched between high level signals LO GAIN suitable for active guitars and keyboards and low level signals HI GAIN suitable for microphones pick ups or passive guitars and are also controlled by the input gain control Compressor Operation A compressor functions by reducing the gain of the signal when it exceeds a certain level or threshold The amount of gain reduction may be fairly gentle through to limiting where the signal is clamped at the threshold level The amount of gain reduction is determined by the ratio control which is calibrated as a ratio of the output to input signals The gain of the signal is reduced by a voltage controlled circuit Variable time constants are applied to the control voltage to adjust the rate at which the gain is reduced called the attack time and the rate at which unity gain is restored after the signal returns to below the threshold referred
3. T L Audio INDIGO SERIES User Manual C 2021 VALVE COMPRESSOR Tony Larking Professional Sales Limited Letchworth England Tel 01462 490600 International 44 1462 490600 Fax 01462 490700 International 44 1462 490700 INTRODUCTION The T L Audio Indigo Series combines classic valve techniques with low noise solid state circuitry to produce audio processing units offering very high quality signal paths with comprehensive control facilities and the unique valve sound The C 2021 is a two channel valve compressor It may be operated as two independent mono channels or as a full stereo compressor with ganging of controls and combined control voltages All parameters of the compressor are variable and a bargraph meter may be used to display output level or gain reduction The block diagram of the unit is shown in fig 1 Each channel has three input sources a balanced line level input via an XLR connector an unbalanced line level input via a jack socket and an instrument input also on an unbalanced jack socket but located on the front panel where it provides a convenient means of patching a guitar or keyboard directly into the compressor All three inputs may be used simultaneously The gain of the input stages is controlled by a centre detented control calibrated for OdB nominal gain from the line input sources at the centre and providing 20dB of variation The instrument input has a sensitivity switch associated with it to ma
4. ange 108dB Sidechain Insertion Points Unbalanced switched 3 pin jack socket tip send ring return Nominal level 2dBu Output impedance 47 ohms Return input impedance 10Kohms Power Requirements Rear panel selectable for 220 240V 50Hz or 110 120V 60Hz operation Rear panel fuse 20mm 1 AT 250V Power consumption 30VA typical Detachable 3 pin IEC connector mating connector and cable supplied Front panel On Off switch with green LED Dimensions 19 rack mounting 1U high 483mm wide x 44mm high x 250mm deep Weight 4Kg The above specifications are subject to change without notice SERVICE Should the compressor require service it must be taken or posted to an authorised dealer Please retain the original packing for possible future use and ensure the unit is suitably protected during transit The manufacturer cannot accept responsibility for damage caused during transportation The compressor is supported by a limited warranty for a period of one year from the date of purchase During this period any faults due to defective materials or workmanship will be repaired free of charge The warranty excludes damage caused by deliberate or accidental misuse operation on the incorrect mains voltage or without the correct type and value of fuse fitted It is the user s responsibility to ensure fitness for purpose in any particular application The warranty is limited to the original purchase price
5. ar of the unit The pin connections are Sleeve Ground II Tip Send Ring Return The insertion point is unbalanced and operates at a nominal level of 2dBu If used as an additional send only e g as a send to a tape machine or monitor mixing desk the Tip and Ring should be wired together to preserve the signal path through the insertion point When used in this manner the send will be post compressor Balanced Outputs The output is via a balanced 3 pin male XLR connector The mating connector should be wired as follows Pin 1 Ground screen Pin 2 Signal Phase or hot Pin 3 Signal Non Phase or cold Unbalanced Outputs An unbalanced line output is provided for each channel on a 0 25 mono jack socket Tip Signal Phase or hot Screen Ground Ventilation The unit generates a small amount of heat internally This heat should be allowed to dissipate by convection through the grills in the side panels and top cover which must not be obstructed Do not locate the unit where it will be subject to external heating for example in the hot air flow from a power amplifier or on a radiator The compressor may be free standing or mounted in a standard 19 rack Rear Panel The rear panel connectors are identified in fig 3 Make sure that all settings mains and audio connections have been made as described above before attempting
6. ections Audio Inputs Each channel has a female 3 pin XLR connector suitable for balanced or unbalanced line sources at a nominal level of 4dBu The mating connector should be appropriately wired as follows for balanced or unbalanced operation Balanced inputs Pin 1 Ground screen Pin 2 Signal Phase also known as or hot Pin 3 Signal Non Phase or cold Unbalanced inputs Pin 1 Ground screen Pin 2 Signal Phase or hot Pin 3 Signal Ground When using unbalanced signals the signal ground may be obtained by linking pins 1 and 3 in the mating XLR connector If this connection is not made a loss in level may result Unbalanced Line Inputs An unbalanced line level input at a nominal level of 10dBu is also provided for each channel on a 0 25 mono jack socket The mating plugs should be wired as follows Tip Signal Phase or hot Screen Ground Auxiliary Inputs A 2 pin mono jack plug is required which should be wired as follows Tip Signal Phase or hot Screen Ground The auxiliary input is suitable for direct connection of instruments including guitars and keyboards Good quality screened cable should be used particularly for microphone or low level sources to prevent hum or noise pickup Insertion Points The insertion points are interfaced via a 3 pin 0 25 switched jack socket on the re
7. ependently for each channel However operation of the STEREO LINK switch will cause the compressor to be set for full stereo operation where the Threshold Attack Release and Ratio controls for channel A control both channels The input gain and gain make up controls remain separate to allow relative input output gain balance adjustment In stereo mode the control voltages are also linked ensuring that the same amount of gain reduction is applied to both channels even if one signal is below the threshold This ensures that the stereo image is preserved Bargraph Meters The compressor is equipped with twin LED bargraph meters These meters normally monitor the audio output from the unit and are calibrated for nominal level of 4dBu at the balanced output OdB Similarly 0dB on the meters also corresponds to 10dBu at the unbalanced output The reference point may be internally adjusted by your dealer if required The output level scale is printed between the two bargraphs and applies to both channels The meters may be switched to indicate the amount of compression applied to the signal by operating the GAIN RED N switch If the signal is below the threshold the meters will not illuminate i e no gain reduction is occurring As the signal passes through the threshold the 0dB LED will illuminate indicating that gain reduction has started For further increases in input level the meter will indicate the gain reduction occurring at
8. itch left or right with a small screwdriver until the desired voltage is displayed The mains fuse required is 20mm anti surge 1AT rated at 250V If it ever necessary to replace the fuse only the same type and rating must be used The power consumption of the equipment is 30VA Warning attempted operation on the wrong voltage setting or with an incorrect fuse will invalidate the warranty Audio Operating Level The compressor is equipped with inputs and outputs suitable for connection to a wide variety of other audio equipment Generally the balanced XLR connections will be required for interfacing to other professional equipment where the operating level line up level or nominal level will be 4dBu or about 1 2V rms The unbalanced jack connectors are generally intended for interfacing to semi professional equipment and have an operating level of 10dBu or about 225mV rms The compressor may be used to change between operating levels for example by connecting the unbalanced output of a semi pro mixing console to the compressor s unbalanced input and taking the balanced output of the compressor to the balanced input of a tape machine at 4dBu All inputs and outputs of the compressor may be used simultaneously if required Balanced interconnection is always preferable to obtain the best headroom and noise rejection but can only be used if the other equipment in the chain e g the mixing console also has provision for balanced conn
9. of the equipment and excludes any consequential damage or loss Please retain proof of purchase and record the following details Serial Number ceceeeeee
10. pression applied Please read this manual fully before installing or operating the Compressor PRECAUTIONS The T L Audio C 2021 Compressor requires very little installation but like all electrical equipment care must be taken to ensure reliable safe operation The following points should always be observed All mains wiring should be installed and checked by a qualified electrician Ensure the correct operating voltage is selected on the rear panel before connecting to the mains supply Never operate the unit with any cover removed Do not expose to rain or moisture as this may present an electric shock hazard Replace the fuse with the correct type and rating only Warning This equipment must be earthed INSTALLATION AC Mains Supply The unit is fitted with an internationally approved 3 pin IEC connector A mating socket with power cord is provided with the unit wired as follows Brown Live Blue Neutral Green Yellow Earth Ground All mains wiring should be performed by a qualified electrician with all power switched off and the earth connection must be used Before connecting the unit to the supply check that the voltage selector switch on the rear panel is correctly set The unit may be set for 115V accepting voltages in the range 110V to 120V 60Hz AC or to 230V for voltages in the range 220V to 240V 50Hz AC Adjustment to the operating voltage should be made by sliding the selector sw
11. ssor is fast enough to reduce the gain of a 1KHz signal in less than half a cycle effectively preventing an overload of any following equipment which has limited headroom such as a digital processor tape machine or transmitter The release time is switchable to 40msec or approximately 2 seconds Adjustment of the attack and release times allows unobtrusive compression to be applied to virtually any audio signal but should very short transients occur the time constants become signal dependant generally reduced to prevent a slow release leaving a hole in the signal after the transient Also a fast release setting will be extended by a slow attack setting Due to this automatic modification of the time constants the controls are simply calibrated fast and slow Ratio The ratio may be varied from 1 1 5 very gentle compression to 1 30 near limiting The compressor normally operates with a soft knee i e the compression is gradually introduced as the signal passes the threshold in which case the ratio refers to the compression eventually obtained Gain Make Up Up to 20dB of gain make up may be applied to retain the subjective loudness of the signal Bypass The Compressor In switch allows the processing to be bypassed for comparison of the compressed signal with any gain make up that has been applied with the original signal Stereo Operation In normal 2 channel operation the controls operate ind
12. tch the gain to a low level pickup e g a passive guitar or microphone or a higher output source such as a keyboard or active guitar followed by the 40dB variation of the input gain control After the input stages the signal is fed to the valve compressor core and the sidechain processing The sidechain also monitors the output of the compression stage and generates a control signal which varies the attenuation of the compressor The sidechain processing includes fully variable control of the compressor threshold and ratio plus switched fast and slow time constants for attack and release Frequency dependant compression for example de essing may be achieved by placing an equaliser into the sidechain insertion point The channel B sidechain controls normally operate independently but the comprehensive stereo mode offered by the C 2021 allows the channel A controls to be used for both channels A and B ensuring accurate tracking and easy adjustment of the parameters Stereo mode also combines the compressor cell control signals which always applies the same amount of gain reduction to both channels thereby preserving the stereo image Independent gain make up controls are provide to retain the subjective loudness of a compressed signal Each channel has a balanced line level output on an XLR socket and an unbalanced output on a jack socket Twin LED bargraph meters are provided which may be switched to monitor the output signal level or com
13. to as the release time The effect of compression is to limit the dynamic range of a signal It may be used to keep a variable output from a bass guitar for example at an even level or to add punch to vocals drums guitar or a complete mix Whist the subjective sound quality can be improved by compression the overall signal level may be reduced A gain make up control at the output of the compressor stage allows the signal level to be brought back to the same loudness as the uncompressed signal Frequency selective compression may be obtained by inserting an equaliser into the sidechain signal from which the control voltage is generated Boosting a range of frequencies will have the effect of lowering the compressor threshold at those frequencies i e making the compressor more sensitive Note that the equalisation is not applied to the audio output but is used to modify the control sidechain A common use of sidechain equalisation is de essing to reduce sibilance on vocals Suitable equalisers which can be inserted into the sidechain are the TL Audio Indigo Series 2011 or 2012 valve equalisers which match the 2021 in audio levels and styling Threshold The 2021 compressor has a variable threshold set by a rotary control calibrated from 20dBu to 20dBu resulting in increased compression as the control is rotated clockwise Attack and Release The attack time is switchable to 0 5msec or 20msec At 0 5msec attack the compre
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