Doepfer Module A-130 Linear VCA.

You are looking at the Doepfer Module A-130 Linear VCA. 

The Module A -130 and provides voltage-controlled amplification. 

The amount of amplification is determined by the sum of the voltages at the two inputs CV1 and CV2, and the control voltage generated by the manual Gain control. By means of the Gain control the VCA can be opened manually without external control voltage.

The control voltage range for CV1 and CV2 is about 0...+5V to obtain an amplification in the range 0...1.

CV2 is additionally equipped with an attenuator. This enables to adjust the level of the control voltage (e.g., when the maximum value of the control voltage is clearly higher than +5V).

The VCA has two audio inputs, each equipped with an attenuator (kind of a miniature mixer). 

The sum of both audio signals is processed by the VCA according to the applied control voltages and the position of the Gain control. 

The audio output is also equipped with an attenuator to adjust the output level to the particular requirements. 

The Model  A-130 is equipped with the high-end VCA circuits SSM2164/V2164.