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The Technical Stuff

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A bias level is applied to the diodes by the Compression Ratio pushbutton switches. This controls the
threshold of limiting, and is adjusted for the correct value as determined by the currently selected
compression ratio selection. R55 controls the compressor’s attack time

by regulating how fast C22 is

charged. Likewise, R56 determines the compressor’s release time by controlling the rate at which
C22 discharges. The output of this stage is then applied to the gate of the FET in the gain reduction
circuit, which in turn controls the gain in the manner previously described.

Power Supply

One feature in the 6176 circuit not found in the original 1176 is the addition of a MOSFET regulated
power supply, which has the effect of improving bass response as well as significantly reducing the
noise floor.

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Summary of Contents for 6176

Page 1: ...Model 6176 Channel Strip Universal Audio Part Number 65 00053 Universal Audio Inc Customer Service Tech Support 1 877 MY AUDIO Business Sales Marketing 1 866 440 1176 www uaudio com ...

Page 2: ...ges in connection with the furnishing performance or use of this material Copyright 2009 Universal Audio Inc All rights reserved This manual and any associated software artwork product designs and design concepts are subject to copyright protection No part of this document may be reproduced in any form without prior written permission of Universal Audio Inc Trademarks 6176 1176LN 2 1176 LA 610 LA ...

Page 3: ...that highly recognizable blackface 1176LN sound Most of us at Universal Audio are musicians and or recording engineers We love the recording process and we really get inspired when tracks are beautifully recorded Our design goal for the 6176 was to build an integrated mic preamp compressor that we would be delighted to use ourselves one that would capture the original character of the 610 and 1176...

Page 4: ...asp the plug body when connecting or disconnecting it 7 Grounding of the Plug This unit is equipped with a 3 wire grounding type plug a plug having a third grounding pin This plug willonly fit into a grounding type power outlet This is a safety feature If you are unable to insert the plug into the outlet contact your electrician to replace your obsolete outlet Do not defeat the purpose of the grou...

Page 5: ...l Putnam Jr iii Important Safety Instructions iv Two Page Two Minute Guide To Getting Started 1 Front Panel 3 Rear Panel 9 Interconnections 10 Insider s Secrets 11 The Technical Stuff 18 Glossary of Terms 35 Recall Sheet 39 Specifications 40 Additional Resources Product Registration Warranty Service Support 41 ...

Page 6: ... point or channel input connect only the Compressor line output Step 3 Set the Polarity switch on the left side of the front panel to its down position ensuring that the output signal will be in phase with the input signal If using a microphone set the Pad switch on the left side of the front panel and the Phantom Power switch in the center of the front panel to their down positions so that the pa...

Page 7: ...side of the front panel Begin by setting the Input and Output knobs to approximately 5 12 o clock position for unity gain Then set the Ratio to 1 or alternatively turn the Attack knob past its fully counterclockwise position so that it clicks In this mode a compression ratio of 1 1 signal passes through the limiter compressor section thus adding color but with no gain reduction Compare the differe...

Page 8: ...UT connection see 7 on page 9 The impedance for the Mic input can be set to 500 ohms or 2 0K ohms Switching between these two positions while listening to a connected microphone may reveal a different tonal quality and or gain difference Typically a microphone preamplifier should have input impedance roughly equal to about 10 times the microphone output impedance For example if your microphone has...

Page 9: ...d on loud instruments 4 Polarity Determines the polarity of the 6176 s Preamp LINE OUTPUT see 5 on page 9 When IN ø is selected the signal is in phase and pin 2 is hot positive When OUT ø is selected the signal is out of phase and pin 3 is hot positive Polarity reversal may be useful in cases where more than one microphone is utilized in recording a source 5 Hi Z Input Connect high impedance signa...

Page 10: ...out phantom power 12 Power Turns the 6176 power on or off When powered on the purple LED immediately above this switch is lit 13 Join Split This switch allows separate use of the preamp section and the limiter compressor section When the switch is in the SPLIT down position each side of the 6176 acts as a separate device each with its own separate rear panel in out connections see 1 and 2 on page ...

Page 11: ... 9 17 Input Determines the level of the signal entering the limiter compressor section as well as the threshold Higher settings will therefore result in increased amounts of limiting or compression Turning the Attack knob all the way fully counterclockwise position past the point where it clicks has the same effect as setting the Ratio switch to the 1 position where signal passes through the limit...

Page 12: ...he 6176 Ratio control allows seven different modes of operation BP Bypass This position automatically routes the preamp output directly to the limiter compressor output thus completely removing its associated tone from the signal This feature is provided so you can quickly remove the limiter compressor section from the signal path altogether without having to physically move cables 1 Selects a 1 1...

Page 13: ...6176 by using this mode Engineers typically use All mode on drums or on ambience or room mics It can also be used to dirty up a bass or guitar sound or for putting vocals in your face In order to set a specific amount of limiting or compression on the 6176 begin by turning the Output knob to unity gain approximately 5 and the Input knob to its fully counterclockwise 0 position Set the Ratio as des...

Page 14: ...ay slow blow fuse for operation at 115 V or a 200 mA time delay slow blow fuse for operation at 230 V 5 Preamp LINE OUTPUT A balanced XLR connector carrying the line level output signal of the 6176 preamp section Note that Pin 2 is positive when the front panel Polarity toggle switch is down IN ø Pin 3 is positive when the front panel Polarity switch is up OUT ø see 4 on page 4 6 Preamp LINE INPUT...

Page 15: ...preamp Gain Impedance and Filter controls as well as the various limiter compressor controls to achieve the optimum sound for your signal source If you are using the 6176 in JOIN mode begin by setting the limiter compressor Input and Output controls to approximately 5 for unity gain When operating in JOIN mode the rear panel Preamp LINE OUT and the Limiter Compressor LINE IN jacks are automaticall...

Page 16: ...ereo mic preamp favored by many engineers for vocal recording In his December 2001 review for MIX magazine Michael Cooper raved about the 2 610 s abilities in this regard writing The 2 610 is the richest fattest and sweetest mic preamp I ve ever heard on vocals Bigger than life and possessing astounding depth the sound made all other mic preamps I ve used sound somewhat 2 D by comparison The botto...

Page 17: ...trong belted out rock vocals And reviewer Trevor Curwen writing for The Mix in August 2000 reported that When recording vocals the 1176 LN was used with a low ratio resulting in a very natural smooth sound and even performance being captured Strapping the compressor across the vocal when mixing and adding just a little more squeeze gave it the presence it needed to sit consistently in the mix with...

Page 18: ...ll known industry golden ear Allen Sides Goo Goo Dolls Green Day I mult the left and right drum overheads and bring them back on the console then insert a pair of 1176s in All button mode into a pair of the mults That puts the unit into overdrive creating a very impressive sound Engineer Andy Johns employs a similar technique What you do is you run your room mics through a couple of 1176s just so ...

Page 19: ...rfect for country lead guitar fills Even if you don t want to compress a signal the use of 1 1 mode in the limiter compressor section allows the 6176 to act as a tone box adding both solid state amplification and tube overdrive that can make an electric guitar sound positively monstrous Andy Johns remembers using a pair of vintage 1176s on Jimmy Page s guitar on the song Black Dog for the multi pl...

Page 20: ...a thick and creamy tube coloration with loads of sustain Recording a five string Fender bass with active pickups I switched the impedance to 47 kohm The gain setting was different but I used the same limiter settings matching levels using the PRE meter switch position to get the same amount of compression In general I put the bass sound somewhere between a pristine direct sound and a miked bass am...

Page 21: ...per as well One of its features is ultra fast attack and release times and used correctly or incorrectly depending on the way you look at it you can use it to add distortion to any otherwise pristine audio track Running most sources through a distortion device can cause the signal to lose some of its definition as you increase the effect Also distortion devices tend to add a significant amount of ...

Page 22: ...for EQ Throughout the years engineers have variously referred to this characteristic sound as edge growl present and urgent Generally speaking the higher the Input level the more these descriptive terms come into play The 6176 has a similar sonic footprint though with improved bass response You ll find that its operation is most transparent when doing gain reduction of 4 dB or less This will serve...

Page 23: ...r consoles are commonplace today the 610 was quite a breakthrough at the time While the 610 was designed for practical reasons it was its sound that made it popular with the recording artists who frequented Putnam s studios in the 1960s The unique character of its microphone preamplifier in particular made it a favorite of legendary engineers like Bruce Botnick Bones Howe Lee Hershberg and Bruce S...

Page 24: ...limiter compressor section of the 6176 is based upon the 1176LN a device first released forty years ago and still prized to this very day by audio professionals the world over Designed by Bill Putnam Sr original founder of Universal Audio its circuit evolved from the popular 175 and 176 vacuum tube limiters combined with the latest solid state amplification circuitry derived from the company s suc...

Page 25: ...l update the model H simply marked a return to a silver faceplate and the addition of a blue UREI logo The companies that Bill Putnam Sr started Universal Audio Studio Electronics and UREI built products that are still in regular use decades after their development In 1999 Putnam s sons Bill Jr and James Putnam re launched Universal Audio In 2000 the company released its first product a faithful r...

Page 26: ...mplify signals by as much as 1000 Accomplishing musical sounding compression is no simple task either and a number of different circuits have been developed through the years to attain that goal One of the most unique of these designs is the one Bill Putnam Sr created for the original 1176 limiter compressor upon which the 6176 limiter compressor is based The naturally edgy sound of the 1176 came ...

Page 27: ...t peak levels causing distortion While many of today s digital recording media approach or even exceed 120 dB of available dynamic range quiet passages of recorded music can still be lost in the ambient noise floor of the listening area which in an average home is 35 to 45 dB Despite the increased dynamic range compression is especially important when recording digitally for two reasons One it hel...

Page 28: ...t A ratio of 1 1 therefore means that for every 1 dB of increase in input level there is a corresponding 1 dB increase in output level in other words there is no compression being applied A ratio of 4 1 however means that any time there is an increase of 4 decibels in the loudness of the input signal there will only be a 1 dB increase in output signal A ratio of 8 1 means that even when there is a...

Page 29: ...hich most affect how tight or how open the sound will be after gain reduction The attack time describes the amount of time it takes the limiter compressor circuitry to react to and reduce the gain of the incoming signal usually given in thousandths of a second milliseconds or even millionths of a second microseconds A fast attack kicks in almost immediately and catches transient signals of very br...

Page 30: ...ll four ratio buttons on an original 1176 are pushed in simultaneously In ALL mode distortion increases radically due to a lag time on the attack of initial transients a phenomenon which might be described as a reverse look ahead The ratio goes to somewhere between 12 1 and 20 1 and the bias points change all over the circuit thus changing the attack and release times as well The unique and consta...

Page 31: ...ed by active basses and guitars while the 2 2M ohms setting is more suitable for instruments with passive pickup systems Since a particular instrument s output impedance may actually be somewhere between the active and passive levels feel free to experiment to achieve the best sound at the desired level Again changing the input impedance will not harm your instrument or the 6176 Phantom Power Most...

Page 32: ... hole on the front panel between the Input and Output knobs The procedure for adjusting the meter is as follows 1 Power on the 6176 and allow it to warm up for five minutes 2 Set the Meter switch to the GR Gain Reduction position 3 Set the Input control fully off turn the knob fully counterclockwise 4 Use a small screwdriver to slowly adjust the GR Zero Set trim pot so that the meter reads 0 dB Wa...

Page 33: ...nected in a stereo configuration the fastest attack time is doubled that is it becomes 40 microseconds instead of 20 microseconds Use the following procedure to calibrate the 1176SA stereo adapter 1 Remove the signals from both 6176 units 2 Disable the gain reduction on each limiter set both Attack controls fully counterclockwise 3 Connect the 1176 SA to both 6176s This requires two RCA style cabl...

Page 34: ...wer transformer located at rear center of the 6176 and it can be identified by its wire colors Black Blue White and Orange Move the connector to location H8 for 230V operation or location H6 for 115V operation NOTE When changing operating voltage the fuse value must be changed as well Make sure the 6176 is properly set for the voltage in your area before applying AC power to the unit Failure to do...

Page 35: ...gn and performance is critical to the sound of the device This transformer was distinguished by the fact that it used several additional sets of windings to provide feedback a practice widely used in the tube amplifiers of the era which made it an integral component in the operation of the output amplifier Putnam spent a great deal of time perfecting the design of this tricky transformer and caref...

Page 36: ...ustable input level is used to control the amount of compression This input circuit was used in Revisions A F With Revision G a differential op amp input instead of the attenuator transformer input stage was used Gain Reduction Stage Figure 3 Gain Reduction Stage As shown in Figure 3 gain reduction is achieved by a Field Effect Transistor FET which is used as a variable resistor In the 1176 the FE...

Page 37: ... circuit samples the signal level after the gain reduction LN Circuitry The LN circuit which appeared in revisions C and later was designed to reduce the distortion that the FET introduced in the gain reduction stage FETs are inherently nonlinear devices and any non linear device will introduce signal distortion The LN circuitry was designed to ensure that the FET stayed as much within a linear re...

Page 38: ...rol Circuit Figure 5 Gain Reduction Control Circuit As shown in Figure 5 this circuit controls the amount of compression as well as the attack and release times of the limiter The input to this circuit is taken from the output of the preamplifier section just before the volume control potentiometer R23 The compression ratio push button switches determine the level of the signal which is sent to th...

Page 39: ...r s attack time by regulating how fast C22 is charged Likewise R56 determines the compressor s release time by controlling the rate at which C22 discharges The output of this stage is then applied to the gate of the FET in the gain reduction circuit which in turn controls the gain in the manner previously described Power Supply One feature in the 6176 circuit not found in the original 1176 is the ...

Page 40: ...specially unpleasant sound Compression The process of automatically reducing the level of peaks in an audio signal so that the overall dynamic range that is the difference between the loudest sections and the softest ones is reduced or compressed Compression is sometimes described as gain reduction or peak reduction Compression ratio A term that describes the amount of increase required in the inc...

Page 41: ...t or boosted FET An acronym for Field Effect Transistor a type of solid state semiconductor Gain reduction A synonym for compression or limiting Hi Z Short for High Impedance The 6176 s Hi Z input allows direct connection of an instrument such as electric guitar or bass via a standard unbalanced jack High shelving filter An equalizer circuit that cuts or boosts signal above a specified frequency a...

Page 42: ...plifier s output signal is reversed in phase and then mixed with the input signal This serves to partially cancel the input signal thus reducing gain A benefit of negative feedback is that it both flattens and extends frequency response as well as reducing overall distortion Noise floor Unwanted random sound noise added by an electronic device Patch bay A passive central routing station for audio ...

Page 43: ...176 threshold is determined by the setting of the Input and Ratio controls Transformer An electronic component consisting of two or more coils of wire wound on a common core of magnetically permeable material Audio transformers operate on audible signal and are designed to step voltages up and down and to send signal between microphones and line level devices such as mixing consoles recorders and ...

Page 44: ...Recall Sheet _____________________________________________________________ 39 ...

Page 45: ...ectable 15k ohms or 600 Output Load Impedance 600 floating Frequency Response 20 Hz to 20 kHz 1 dB Gain 40 dB 1 dB Distortion 0 5 T H D from 50 Hz 15 kHz with limiting at 1 1 seconds release setting Output of 22 dBm with no greater than 0 5 T H D Signal to Noise Ratio 75 dB Attack Time Adjustable from 20 to 800 milliseconds Release Time Adjustable from 50 milliseconds to 1 1 seconds Stereo Interco...

Page 46: ...do if you re having trouble with your device is to check for any loose or faulty external cables bad patchbay connections grounding trouble from a power strip and all inputs outputs mic line Hi Z etc If your problem persists call tech support at 877 MY UAUDIO or send an email to hardwaresupport uaudio com and we will help you troubleshoot your system Canadian and overseas customers should contact ...

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