Inova manual Schematic diagram of the LA-2A side-chain circuit

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. 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 LA-2A. 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. In the case of the LA-2A this results in behavior where the release time is slower if the unit has either been in compression for a while, or the amount of compression is large. This signal dependent release 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 adjustment of the threshold. Other units such as the 1176LN use a fixed threshold and provide an input level control, which adjusts the signal level before it is applied to the compression circuit. In contrast, the LA-2A, while also having a fixed threshold, does not control the input level, but rather controls the amount of side chain gain applied to the input signal.

 

 

 

 

 

 

 

PO W ER

 

 

STEREO

 

 

 

O U TPU T

 

 

 

SU PPLY

 

IN PU T

PA RA LLEL

 

 

 

 

 

 

 

 

 

 

ATTEN U A TO R

 

 

 

 

 

 

 

 

 

D RIVE-A M PLIFIER

 

 

 

 

 

 

 

 

 

R34

 

R37

1 Meg

 

 

 

 

 

 

C 1 1

 

LIM

 

C12

R33

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R30

 

V 4

 

 

 

 

 

 

 

 

4 7K

 

 

 

 

 

 

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V3 A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R3

STEREO

 

R32

 

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1 2A X7 A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 6 - Schematic diagram of the LA-2A side-chain circuit.

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Contents Model LA-2A Leveling Amplifier Teletronix LA-2A by Universal Audio Important Safety Instructions Copyright LA-2AUser’s GuideTable of Contents Specifications Peak Reduction Control Operation of the LA-2AInput and Output Connections Barrier Strip ConnectionsVU Meter Operation Limit / Compress SwitchSide-Chain Pre-Emphasis R37 Meter Zero AdjustStereo Balance Adjust R3 CalibrationCompressor Basics Theory of OperationCompression region DB of compression Compression knee Block diagram of the LA-2A compressor Gain Reduction Circuit Diagram of the T4 electro-optical cellSchematic of the LA-2A input and gain reduction circuit Schematic diagram of the LA-2A side-chain circuit Side-Chain Circuit Output CircuitMetering Circuit LA-2A AppendixDeveloping Mike ShipleyMurray Allen Allen SidesJim Scott Ken KessieBruce Swedein Mike Clink

LA-2A specifications

The Inova LA-2A is a sophisticated optical compressor renowned for its classic design and exceptional sound quality. Hailing from the lineage of legendary optical compressors, the LA-2A combines vintage warmth with modern reliability, making it a staple in professional recording studios globally.

One of the main features of the LA-2A is its opto-electronic gain reduction circuit, which utilizes a light-dependent resistor (LDR) and a sealed optical element to achieve compression. This unique mechanism provides a smooth and transparent compression, allowing the audio signal to maintain its natural dynamics while controlling peaks effectively. The optical design contributes to a musical response, widely regarded as one of its defining characteristics.

The LA-2A also features a simple and intuitive interface. It includes essential controls such as Peak Reduction, which adjusts the level of gain reduction, and Make-Up Gain, which compensates for any lost level after compression. The device typically has two modes: the Compress mode for moderate compression and the Limit mode for more aggressive limiting. This flexibility makes it suitable for a variety of audio sources, from vocals to instruments.

Another noteworthy characteristic is its true tube circuitry. The LA-2A employs a vacuum tube in its audio path, contributing to its warm tonal character. This tube coloration enhances the richness of audio signals, making the device particularly popular for vocals and bass, where presence and depth are paramount.

Additionally, the build quality of the LA-2A is exceptional. The chassis is constructed from durable materials, ensuring longevity and reliability in demanding studio environments. Its vintage aesthetic features analog VU meters, adding to its charm while providing visual feedback of the gain reduction.

Inova has modernized the LA-2A with contemporary features while preserving its classic sound. Enhanced technologies such as improved signal-to-noise ratio and updated component designs ensure that the LA-2A remains competitive in today's digital landscape.

Ultimately, the Inova LA-2A is a beautifully crafted compressor that delivers a unique sonic signature. It combines vintage appeal with modern functionality, making it an essential tool for audio engineers and music producers seeking to achieve professional-grade mixes. Its smooth compression characteristics, intuitive controls, and durable design are testaments to its lasting legacy in the world of audio processing.
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