Model LA-3A AUDIO LEVELER Universal Audio Manual Number 65-1301 Revision 1.
IMPORTANT SAFETY INSTRUCTIONS Before using this unit, be sure to carefully read the applicable items of these operating instructions and the safety suggestions. Afterwards keep them handy for future reference. Take special care to follow the warnings indicated on the unit, as well as in the operating instructions. 1. 2. 3. 4. 5. 6. 7. Water and Moisture - Do not use the unit near any source of water or in excessively moist environments.
THE LA-3A AUDIO LEVELER Thank you for purchasing the LA-3A Audio Leveler. The LA-3A is a solid-state version of Universal Audio’s vacuum tube based Teletronrix LA-2A, and was designed by Brad Plunkett. In it’s day, the LA-3A was considered an improvement over the LA-2A because it eliminated “noisy tubes” and maintenance issues. Today, both products are revered for their smooth and musical control of audio levels. Engineers choose the LA-2A or LA-3A based on the different sonic character each one offers.
TABLE OF CONTENTS LA-3A SPECIFICATIONS 3 LA-3A FRONT PANEL 4 LA-3A REAR CHASSIS 5 STEREO OPERATION 7 WHAT COMPRESSORS DO 9 Peak Reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Gain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Meter Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Meter Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Limit/Compress Switch. . . . . . . . . . . . . . . . .
COMPRESSOR THEORY OF OPERATION 12 HISTORICAL NOTES 16 RECALL SHEET 19 Compressor Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . 12 The T4 Cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Side-Chain Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 The 610 Preamp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Classic Compressors. . . . . . . . . . . . . . . . . . . . . . . . . . 17 The 1176 LN. . . . . . . . . . . . . . . . . . . . .
LA-3A SPECIFICATIONS Balanced Line Input Impedance. . . . . . . . Max. Input Level. . . . . . . . . . . . . . . . . . . . Internal Output Impedance. . . . . . . . . . . . Maximum Output Level. . . . . . . . . . . . . . . Internal Output Impedance. . . . . . . . . . . . Recommended Minimum Load. . . . . . . . . Frequency Response. . . . . . . . . . . . . . . . . Maximum Gain. . . . . . . . . . . . . . . . . . . . . Noise Floor. . . . . . . . . . . . . . . . . . . . . . . . . Distortion. . . . . . . . . . . .
LA-3A OPERATING INSTRUCTIONS The LA-3A is a solid state compressor that automatically reduces the level of loud signals in order to maintain a more consistent volume level, void of loud peaks that can cause unwanted clipping and associated distortion. For the remainder of this manual, the more common term “compressor” will be used instead of “leveling amplifier” or “audio leveler”.
function is determined using the two-position switch below the GAIN knob to the left of the meter. When OUTPUT is selected, a meter reading of 0 corresponds to an output level of +4 dBm at the LA-3A output. In the GR mode the meter will move from 0 to negative numbers on the left side. The meter will indicate relative levels of gain reduction during loud signal passages. Typically, the PEAK REDUCTION control is adjusted to read between -3 and -5 on the meter.
50/30 dB Gain Switch The 50/30 dB GAIN switch is an input pad to prevent high output devices from overdriving the input transformer of the LA-3A. Setting the switch to the 30dB position will attenuate the incoming signal by 20dB. For studio use, the normal setting is down (30dB) when not using the MOD function. See MOD Switch below for more info. MOD Gain Switch The MOD (modification) GAIN switch improves the signal to noise ratio of a “stock” LA-3A.
• When changing operating voltage, the fuse value must be changed as well. • Make sure the LA-3A is properly set for the voltage in your area before applying AC power to unit! Input/Output Terminal Strip The terminal strip provides screw connections for INPUT, OUTPUT, STEREO balance and CHASSIS GROUND. The strip can be used instead of the XLR connections. In addition, you can use the XLR OUTPUT as well as the terminal strip output to “split” the output signal and feed two separate devices.
Stereo Setup / Calibration 1. Set the STEREO ADJ control to full Clockwise. 2. Set the PEAK REDUCTION knob to 0. 3. Set the GR / OUTPUT switch to OUTPUT. 4. Connect a signal generator to the inputs of both LA-3A units. 400 to 1000 Hz recommended. Set the signal generator output level to produce a typical level for your application. 5. Adjust the GAIN control on each unit so the outputs are equal at O dB on each unit. External meters can be used to view output level as well. 6.
WHAT COMPRESSORS DO There are four main reasons to use a compressor: 1. Prevent loud transients or volume bursts from overdriving a recording device or sound system. These loud burst can completely destroy a digital recording by creating terrible sounding distortion. Constant overdriving of a PA system can cause subtle, but ear fatiguing distortion as well. 2. Smooth out wide variations in volume creating a more controlled sound.
Compressing Vocals The LA-3A is very popular for vocals. First of all, like many pieces of “vintage” gear the LA-3A has a unique “sonic signature” produced by the audio path transformers and discrete amplifier components. This, coupled with the attack and release character, produces great results that bring vocals forward. Bass Guitar The LA-3A is also very popular for Bass.
Dual Unit The LA-3A shipping carton contains all the necessary brackets and hardware required for standard 19” rack mount. Bracket and hardware locations are shown below Instructions 1. Set the two LA-3As next to each other as pictured. Remove the 4 screws on the top cover on the left unit (as shown in the FRONT VIEW drawing below). 2. Remove the 4 screws on the top cover on the right unit (as shown in the FRONT VIEW drawing below). 3.
COMPRESSOR THEORY OF OPERATION Compressor Basics Before we dig in to a description of the compressor circuit, it is useful to examine the general characteristics of compressors and review some terminology. The chart below depicts the input/output characteristics of a compressor, an expander and a perfect amplifier. When operated within its specified range, an amplifier provides a constant amount of gain regardless of the level of the input signal.
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 to the line marked “compression” in Figure 4, we see that an input level of -30 dB results in an output level of -20 dB, indicating a gain of 10 dB.
The T4 Cell D I A G R A M OF THE T4 ELECTRO-OPTICAL CELL The cell T4 is comprised of an electro-luminescent (EL) panel and a photoelectric cell housed in a light proof box or can. The EL panel is essentially a night-light. As you would expect, the larger the signal that is applied to it, the brighter the light that is generated. This light shines upon the photoelectric cell.
milliseconds) to approximately half of its off resistance. The remainder of its release can take place over as much as several seconds. The next aspect is the “memory” of the cell. This results in two important aspects of the character of the LA3A. The amount of time it takes for the cell to recover after the light is removed depends on how long light had been shining on it and how bright the light.
HISTORICAL NOTES N AT “ K I NG” COLE WITH BILL PUTNAM SR. Bill Putnam Sr. was awarded the 2000 Technical Grammy for his multiple contributions to the recording industry. He was highly regarded as a recording engineer, studio designer/operator and inventor. Putnam was considered a favorite of musical icons including Frank Sinatra, Nat King Cole, Ray Charles, Duke Ellington, Ella Fitzgerald and many, many more.
The 610 Preamp The 2-610 was inspired by the Putnam-designed 610 console built in 1960 for his United Recording facility at 6050 Sunset Boulevard in Hollywood (now Ocean Way). As was the case with most of Putnam’s innovations, the 610 was the pragmatic upshot of a recurring problem in the studio: how to fix a console without interrupting a session. The traditional console of the time was a one-piece control surface with all components connected via patch cords.
Universal Audio 175 and 176 vacuum tube limiters, the 1176LN retained the proven qualities of these industry leaders, and set the standard for all limiters to follow. It was Bill Putnam himself who, in 1966, was responsible for the initial design of the 1176. Its circuit was rooted in the 1108 preamplifier, which was also designed by Putnam. As is evident from entries and schematics in his design notebook, he experimented with the recently developed Field Effect Transistor (F.E.T.
GR GR GAIN GAIN SANTA CRUZ, CALIFORNIA ON UNIVERSAL AUDIO, INC. POWER SANTA CRUZ, CALIFORNIA ON PEAK REDUCTION UNIVERSAL AUDIO, INC. POWER GR GR GAIN GAIN OUTPUT OUTPUT SANTA CRUZ, CALIFORNIA UNIVERSAL AUDIO, INC. POWER SANTA CRUZ, CALIFORNIA ON PEAK REDUCTION UNIVERSAL AUDIO, INC. ON PEAK REDUCTION POWER 330 Encinal Street • Santa Cruz CA • 95060-2101 • www.uaudio.
