Model 312A Voltage Controlled Amplifier Electronic Gain Control Module (VCA)

The Model 312A voltage controlled amplifier is a high-performance voltage controlled amplifier or electronic gain control (VCA-EGC) designed for audio or instrumentation applications where low distortion, low noise, low control-voltage feedthrough and exceptional gain control characteristics are of primary importance. The 312A approaches immeasurably small intermodulation and total harmonic distortion independent of gain, input or output levels. The 312A has been designed using precision matched pair discrete SMD component technology, resulting in outstanding performance, high reliability, temperature stability and wide dynamic range. It is pinned out for industry compatibility.

The gain versus control voltage characteristics of the 312A are an exponential function (20db/volt) allowing the designer to easily and accurately program the gain in decibels. The all discrete VCA core boasts a gain-bandwidth product of better than 50Mhz, resulting in full audio bandwidth at 60dB of gain without slew rate distortion error.

The Model 312A can be shunt jumper configured to be a current in-current out, voltage in-current out device, voltage in-voltage out or current in-voltage out device. Additionally, the gain control input of the Model 312A can be shunt jumper configured to allow either positive or negative (inverting or non-inverting) gain control voltage to control the device.

The Model 312A VCA-EGC module can be utilized in voltage controlled automation consoles, filters, gates, compressors, oscillators, test instrumentation, radio AGCs and any other signal modifier circuits where voltage controlled amplification is required.

The appearance of the first modular VCAs in the late 1960s and early 1970s accelerated the field of fader automation and dynamics control. While the performance of early VCAs is lacking by today’s standard specifications, many of the early SSL, Quad-8, Harrison, Sony and MCI consoles, as well as a whole herd of rack mounted compressor limiters by dbx and the like built during that era are still in operation. When a channel fails, most operators will need to repair the channel strip or VCA module rather than replace the entire console.

The Sonic Imagery Labs Model 312A VCA is a footprint-compatible upgrade to these early VCAs. In most cases, upgrading to the Sonic Imagery Labs Model 312A VCA is simply a matter of altering the components surrounding the old VCA to those of the recommended schematic for the newer higher performance Model 312A VCA module.

Features:

• Ultra Low Total Harmonic Distortion, <0.005 THD+N @ 1kHz
• Ultra Low Noise <4.4nV/rtHz typical @0db Av
• Wide Dynamic Range >100dB typical
• Wide Gain Range
• Simplified Standard Retro/Upgrade Footprint
• Operates over ±12V to ±16V supply rails
• Low Control-Voltage Feedthrough
• I-In, I-Out or V-In, V-Out Selectable Operation
• Selectable Gain Control Operation (pos/neg)
• Particular emphasis on audio performance
• Designed, assembled and produced in the USA
• 3 Year Warranty

Applications:

• Voltage Controlled Faders and Panners
• Voltage Controlled Filters and Equalizers
• Gates and Expanders
• Compressors and Limiters
• Voltage Controlled Oscillators
• Automatic Gain Control (AGC)

Specifications and Datasheet:
Model 312A VCA EGC Datasheet and Specifications PDF
Model 312A VCA EGC Application Note AN-14
Model 312A VCA Digital Gain Application Note AN-15
Model 312A VCA Upgrading Vintage Consoles & Compressors Application Note AN-16