Related Manuals for Universal Audio LA-2A
Summary of Contents for Universal Audio LA-2A
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Page 1: Leveling Amplifier
Model LA-2A Leveling Amplifier Universal Audio, Inc. www.uaudio.com PO Box 3818 Santa Cruz, CA 95063-3818... -
Page 2: Teletronix La-2A By Universal Audio
To this day the LA-2A delivers a trademark sound treasured by engineers worldwide. Here at Universal Audio, we have gone to great lengths to recreate the LA-2A with complete authenticity. It’s been no small feat to locate obscure parts, put quality control programs in place that didn’t exist 30 years ago and find personnel capable of the... -
Page 3: Important Safety Instructions
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 itself, as well as in the operating instructions. Water and Moisture –... - Page 4 Universal Audio LA-2A Leveling Amplifier. The information contained in this manual is subject to change without notice. Universal Audio, Inc. makes no warranties of any kind with regard to this manual, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.
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Page 5: Table Of Contents
Table of Contents Teletronix LA-2A by Universal Audio................... ii Specifications ........................1 Operation of the LA-2A .......................2 Input and Output Connections................2 Peak Reduction Control ..................2 Gain Control ....................... 2 VU Meter Operation.................... 3 Limit / Compress Switch..................3 Calibration ...........................4 Meter Zero Adjust .................... -
Page 6: Specifications
Specifications Gain Reduction: up to 40 dB Distortion: less than 0.35% total harmonics at +10 dBm, and less than 0.75% total harmonics at +16 dBm output Response: +/- 0.1 dB, 30 cycles to 15 kilocycles Noise: 75 dB below +10 dBm output level Gain: 40 +/- 1dB Output Level: +10dBm nominal, +16dBm peaks Input Level: +16 dBm maximum... -
Page 7: Operation Of The La-2A
Operation of the LA-2A Input and Output Connections Input and Output connections are made using standard XLR style connectors. Terminal strips are also provided. Output Input 10 9 8 5 4 3 2 1 6AQ5 A-24 Power Transformer HA-100X 12AX7 12BH7 12AX7 Output connections... -
Page 8: Vu Meter Operation
VU Meter Operation The VU Meter is used for both output level monitoring and gain reduction monitoring. When used to monitor the output level, the user may choose either +4 dB or +10 dB settings. The middle setting is for gain reduction, and the meter reads the amount of compression in dB. -
Page 9: Calibration
Calibration Meter Zero Adjust The zero-adjust of the meter is set by the screw-adjust potentiometer located next to the Limit / Compress Switch. To adjust this, put the meter into Gain Reduction mode. Make sure that there is no signal present. Loosen the locking nut and use a screwdriver to adjust this potentiometer until the meter reads zero. -
Page 10: Theory Of Operation
Theory of Operation Compressor Basics Before we dig in to a description of the LA-2A circuit, it is useful to examine the general characteristics of compressors and review some terminology. Figure 1 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. - Page 11 As an aside, an expander is a device which increases the dynamic range of a signal. For example, a 10dB change in the input signal might result in a 20 dB change in the output signal, thus “expanding” the dynamic range. There are several other terms related to compression that can be demonstrated by referring to Figure 2.
- Page 12 Figure 3 - Block diagram of the LA-2A compressor.
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Page 13: Gain Reduction Circuit
LA-2A Block Diagram A functional block diagram of the LA-2A is provided in Figure 3. A brief overview of the operation will be provided here. The input transformer provides isolation and impedance matching. After this the signal is fed into both the side-chain circuit and the gain reduction circuit. - Page 14 stage. To see why this is true, we can look at the extreme cases. If the resistance is extremely high (this is the case when there is a small input signal and the light is off) then the photo-cell does not affect the circuit and there is no gain reduction. The second case we can look at is when there is a large signal present.
- Page 15 The next important aspect is that of the release of the compressor. This is determined almost entirely by the characteristics of the photo-cell. The LA-2A uses cadmium-sulfide photo-cells. The first important aspect of the cell is its “two-stage decay”. After the light is removed from the cell, it releases quickly (40-80 milliseconds) to approximately half of its off resistance.
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Page 16: Side-Chain Circuit
Side-Chain Circuit The previously described gain reduction circuit is controlled by the control voltage which is supplied by the side-chain circuit. The LA-2A is a feed-back style compressor. This is due to the fact that the signal that is used to drive the side-chain circuit is affected by the gain reduced signal. -
Page 17: Appendix
previously, the gain reduction is controlled by the photo-cell in the T4 el-op. In order to track the operation of this cell and determine the gain reduction, a second photo-cell is also illuminated by the same EL panel. This photo-cell is hand-selected to match the gain reduction photocell and hence gives an accurate indication of the amount of compression. -
Page 18: Developing The 1176
legendary Bill Putnam's company, Studio Electronics Corp shortly before he changed the company’s name to UREI®. Three different versions of the LA-2A were produced under the auspices of these different companies before production was discontinued around 1969. Developing the 1176 It was Bill Putnam himself who, in 1966, was responsible for the initial design of the 1176. - Page 19 currently mixing, I'm using both an 1176 and an LA2 on his voice, which is not unusual for "The 1176 absolutely adds a bright character to a sound, and you can set the attack so it's got a nice bite to it. I usually use them on four to one, with quite a lot of gain reduction. I like how variable the attack and release is;...
- Page 20 Ken Kessie Mixer Ken Kessie (En Vogue, Tony! Toni! Tone!, Celine Dion) is known for being experimental. "Seems like everybody knows the basic tricks for he 1176," he says, "But here are two that might be lesser known. If you turn the attack knob fully counterclockwise until it clicks, the 1176 eases to be a compressor and acts only as an amplifier.
- Page 21 inconsistent piece to piece than the 1176s, because of the tubes and the difference in fatigue of the tubes. "My big mentors were Andy Johns and Lee DeCarlo and Ron Nevision because they were all Record Plant guys. I learned how to make a rock and roll record from them. Although over the years it's become my own thing, my style still tends to be that Record Plant style, U87s, 1176s, LA-2As, 47 F.E.T.s...it's what I like."...
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