UAD Powered Plug-Ins Manual - 155 - Chapter 15: LA-2A
Teletronix LA-2A Leveling Amplifier
Background Audio professionals passionate about their compressors revere the LA-2A.
The original was immediately acknowledged for its natural compression char-
acteristics. A unique electro-optical attenuator system allows instantaneous
gain reduction with no increase in harmonic distortion – an accomplishment
at the time, still appreciated today.
The LA-2A is known for adding warmth (such as for vocals, guitar, or synths)
and fatness (such as for drums or bass) to signals.
LA-2A Signal
Flow
A functional block diagram of the LA-2A Leveling Amplifier is provided in
Figure 50. The input transformer provides isolation and impedance matching.
After this the signal is fed into both the side-chain circuit and the gain reduc-
tion circuit. The side-chain is comprised of a voltage amplifier, a pre-emphasis
filter, and a driver stage that provides the voltage necessary to drive the elec-
troluminescent panel. This signal controls the gain of the compressor. After the
gain reduction circuit, the signal is sent through an Output Gain control and
a two-stage output amplifier, followed by the output transformer.
Figure 50. LA-2A signal flow
Input
Transformer
Voltage
Amplifier
Voltage
Amplifier
Optical
Attenuator
Cathode
Follower
Output
Transformer
Pre-
Emphasis
Electro
Luminescent
Driver
Input
Output
Stereo
Interconnection
Trim
Gain
Negative
Feedback
Peak
Reduction
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