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Model LA-2A

Leveling Amplifier

Universal Audio, Inc.

www.uaudio.com

PO Box 3818

Santa Cruz, CA 95063-3818

Summary of Contents for LA-2A

Page 1: ...Model LA 2A Leveling Amplifier Universal Audio Inc www uaudio com PO Box 3818 Santa Cruz CA 95063 3818 ...

Page 2: ...preceded it the electro luminescent light source provided the fast attack necessary for broadcast applications Additionally the cadmium sulfide photo cells provided a very natural two stage release which resulted in a compression characteristic more transparent than the other compressors of its day To this day the LA 2A delivers a trademark sound treasured by engineers worldwide Here at Universal ...

Page 3: ...r 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 will only 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 grounding type plug 8 Carts and Stands...

Page 4: ...rranties of merchantability and fitness for a particular purpose Universal Audio Inc shall not be liable for errors contained herein or direct indirect special incidental or consequential damages in connection with the furnishing performance or use of this material Copyright 2000 Universal Audio Inc All rights reserved This manual and any associated software artwork product designs and design conc...

Page 5: ...Switch 3 Calibration 4 Meter Zero Adjust 4 Side Chain Pre Emphasis R37 4 Stereo Balance Adjust R3 4 Theory of Operation 5 Compressor Basics 5 Gain Reduction Circuit 8 Side Chain Circuit 11 Output Circuit 11 Metering Circuit 11 Appendix 12 Creative Classics The 1176 Solid State Limiting Amplifier and the LA 2A Leveling Amplifier 12 The LA 2A 12 Developing the 1176 13 More Than a Vintage Fad Classic...

Page 6: ...nal 16dBm peaks Input Level 16 dBm maximum Very fast attack time Release Time approximately 0 06 seconds for 50 release 0 5 to 5 seconds for complete release depending upon the amount of previous reduction Input Impedance 600 ohms balanced Output Impedance 600 ohms balanced Panel Size 19 x 5 Depth Behind Panel 7 Panel Controls Gain Output level Peak Reduction and Meter Selector Switch Meter dB Gai...

Page 7: ...onnect Ground 7 to the cable shield Peak Reduction Control Operation of the LA 2A is very straightforward There are only two controls that one must deal with The first is the Peak Reduction control This control should be set so that the compressor exhibits the desired amount of compression This control should be set independently of the Gain Control Gain Control This control does not affect the co...

Page 8: ...0 dB settings The middle setting is for gain reduction and the meter reads the amount of compression in dB Limit Compress Switch The Limit Compress Switch changes the characteristics of the compressor IO curve When in the Compress position the curve is more gentle and presents a low compression ratio A higher compression ratio results when the switch is set to the Limit position ...

Page 9: ...ly more sensitive to the higher frequencies Stereo Balance Adjust R3 For stereo operation two LA 2A units are interconnected in order to achieve the same amount of gain reduction from each of the two units to maintain stereo imaging In order to accomplish this terminals 6 from each unit should be connected together Additionally their grounds terminal 7 should be connected together The interconnect...

Page 10: ... Level dB Compression Expansion Perfect amplifier Figure 1 Input output characteristics of a compressor an expander and a perfect amplifier In contrast to an amplifier whose job is to present a constant gain a compressor varies its gain in response to the level of the input signal Large input signals result in less gain thus reducing or compressing the dynamic range of the signal Referring again t...

Page 11: ... input level is increased by 10 dB while the output level only increases 5 dB This would be a compression ratio of 2 1 Lower ratios such as 2 1 result in more gentle compression Note that a compression ratio of 1 1 is no compression at all Typically compressors let you choose a threshold This is the point at which gain reduction starts to take place When an audio signal is below this threshold the...

Page 12: ... A TH O D E FO LLO W ER 1 2 B H 7 PRE EM PH A SIS V O LTA G E A M PLIFIER 1 2 A X7 A ELEC TRO LU M IN ESC EN T D RIV ER 6 A Q 5 O U TPU T TRA N SFO RM ER O U TPU T N EG A TIV E FEED B A C K G A IN C O N TRO L PEA K RED U C TIO N C O N TRO L STEREO IN TERC O N N EC TIO N Figure 3 Block diagram of the LA 2A compressor ...

Page 13: ...of the input signal In order to do this the compressor must first have some method of determining the level of the signal and must then be able to use this to control the gain There are many different schemes to accomplish these tasks In the case of the LA 2A both of these functions are performed by the T4 which is an electro optical element A T4 is comprised of an electro luminescent EL panel and...

Page 14: ...hematic of the LA 2A input and gain reduction circuit The T4 electro optical device is the heart of the compressor and its gain reduction characteristics Its unique characteristics affect the overall sound and character of the LA 2A In addition to the compression curve the combination of the EL panel and the photo cell determine the attack and release characteristics of the LA 2A This is one of th...

Page 15: ...characteristic is critical to the sound of the unit The amount of compression as well as the compression threshold is controlled by the Peak Reduction potentiometer This potentiometer controls the gain of the side chain circuit The greater the gain of this circuit the lower the threshold and the greater the amount of compression will be Many modern limiters and compressors allow for the direct adj...

Page 16: ...ponse Subsequent to the filter a 6AQ5 provides the signal necessary to drive the electro luminescent panel EL panels were often used for night lights and hence are usually designed to be driven with 120 volts 60 Hz AC They were not designed for audio and applying the wide bandwidth signals that arise in audio applications results in a shortened lifetime of the part Output Circuit Figure 7 Schemati...

Page 17: ...with the fader of a console it keeps the volume up during softer sections and brings it down when the signal gets louder The dynamic processing that occurs at ratios below 10 or 12 to one is generally referred to as compression above that it s known as limiting Modern day compressors offer a great degree of programmability and flexibility while older devices such as the 1176 and the LA 2A are more...

Page 18: ...former whose design and performance is critical Its primary function is to convert the unbalanced nature of the 1176 circuit to a balanced line output and to provide the proper impedance matching to drive the line impedance of 600 ohms These two jobs are accomplished by the primary and secondary windings whose turns ratio defines the impedance ratio This transformer is critical due to the fact tha...

Page 19: ...s to the sound of equipment The owner of Ocean Way Studios in Los Angeles and Nashville he s also a speaker designer and engineer who is especially respected for his work with live musicians including orchestra and string dates Among his recent credits are work with the Goo Goo Dolls Alanis Morissette and Green Day Sides brings his different perspectives into play when he talks about using the 117...

Page 20: ...everything but I d have to say I ve used an1176 on everything at one time or another They have an equalizer kind of effect adding a coloration that s bright and clear Not only do they give you a little more impact from the compression they also sort of clear things up maybe a little bottom end gets squeezed out or maybe they are just sort of excitingly solid state or whatever they are The big thin...

Page 21: ...ss and presence of a sound they give it an energy It seems like when I m mixing I end up using an 1176 on the vocals every time And if I want to compress a room sound I ll take a mono room mic put an 1176 across it and push in all the buttons Bruce Swedein Bruce Swedien is a master engineer who needs no introduction He also is a die hard 1176 fan I have two silverface 1176LNs in my rack that Bill ...

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