Classic VCA

Discrete core voltage controlled amplifier module

The 6HP wide Oakley Classic VCA is a new version of Oakley's first Eurorack module. This is a voltage controlled amplifier module inspired in part by a classic vintage design, the ARP4019 sub-module which was used on the wooden case ARP2600P semi-modular synthesiser. The design has a fully discrete core but uses op-amps for input summing and the output drivers.

Two signal inputs are provided, one DC coupled and the other AC coupled. The former allows audio and low frequency signals to be processed. While the latter has a inbuilt high pass filter so that it can be only used to process alternating frequencies. Both inputs can be used simultaneously and each one features an input level control.

Two control voltage (CV) inputs are provided. CV1 can be operated in either exponential or linear mode, determined by the position of the switch on the front panel. CV2 is linear and is provided with a standard attenuator pot that can control the sensitivity of the input.

CV1 features a reversible attenuator. When the pot is turned right of its central position, the pot acts as a normal attenuator; increasing the sensitivity of the CV input. Left of centre, the pot will act in inverting mode and the CV will be tipped upside down so that increasing positive voltages will decrease the gain of the VCA.

When no input jack is inserted into either CV input socket, the CV pot of that input becomes a gain control. This allows that pot to be used as a simple volume control. With no jack inserted into the CV2 input and the CV2 pot is set high it allows the CV1 input to turn the VCA off.

This newer version of the Classic VCA has two outputs. Out A is the standard output of the VCA. Out B, gives you the difference signal between the sum of the two audio inputs and the final output of the VCA. This is a sort of anti-output; when the Out A output signal goes up in level this output goes lower. You can use it as a ring modulator (with either CV pot set to max) or in conjunction with Out A as a simple voltage controlled pan.

A single +5V CV input with its associating pot turned up full with produce unity gain (0dB) through the VCA.

http://www.oakleysound.com/CVCA-e.htm