Module A-133-2 can be used for a lot of applications: as a simple VCA, or a voltage controlled polarizer/attuverter, or a voltage controlled inverter up to a DC coupled ring modulator. In principle the module contains two special voltage controlled amplifiers (VCAs) that allow both positive and negative amplification.

The overall amplification is defined by the sum of the voltage generated by the Man control, the external control voltage CV and the position of the CV control which works as an attenuator for the external control voltage. Without external CV the amplification is +1 when the Man control is fully CW. In the center position the amplification is zero and fully CCW it's -1 (i.e. the incoming signal is inverted). By means of the external control voltage CV the manually adjusted amplification can be modulated.  CV can be both positive or negative (i.e. bipolar) to obtain positive or negative amplification values controlled by the external CV.
In addition the CV signal can be modulated via the modulation control input Mod by means of another control voltage. The Mod socket is normalled to +5V, i.e. a constant positive voltage is used as modulation CV provided that no plug is inserted into the Mod socket. The control voltage range for this socket is bipolar and can be adjusted to the user's requirements by means of a trimming potentiometer. The factory setting is -5V...+5V (i.e. -5V no modulation, 0V about 50% modulation, +5V full modulation).
The current amplification is displayed by a dual color LED. It's not a signal display but indicates the amplification (yellow = positive amplification, red = negative amplification)

Application examples:

• voltage controlled amplifier (VCA) with pure positive overall amplification (Man + CV)
• voltage controlled inverter with pure negative overall amplification (Man + CV)
• voltage controlled polarizer/attenuverter overall amplification changing between positive and negative (Man + CV)
• DC coupled ring modulator with offset feature, the "classical" ring modulator corresponds to Man=0 and symmetrical audio signals for In and CV
• additional effects by means of the modulation feature of the CV signal (using the Mod input)

Additional technical information:

• input voltage range: about 14Vpp (-7 V ... +7 V), with signals beyond these values clipping/distortion occurs
• maximum attenuation of each VCA: about -60dB, i.e. even at the center position of control Man, which corresponds to the "theoretical" amplificication value zero, the input signal appears with -60dB attenuation at the output
• The following document shows the positions and functions of the trimming potentiometers of the module: A133_2_trimming_potentiometers.pdf