Doepfer A-135-3 Voltage Controlled Stereo Mixer

Voltage Controlled Stereo Mixer

A-135-3 is a is a voltage controlled stereo mixer with four inputs. Behind a front panel with 8 HP only eight linear VCAs (voltage controlled amplifiers) and the mixer based on the VCAs are available.

Controls, Inputs and Functions of each input:

• Level (manual control of the VCA amplification), small rubberized knob (L1...L4)
• Control voltage input with associated attenuator (CV 1...4), for the full VCA control range about 0...+5V control voltage are required (attenuator fully clockwise), for higher control voltages the attenuator is used, the attenuators are without knobs, just plastic shafts with white marker
• Signal Input left/right (InL 1...4 / InR 1...4)
• The signal inputs are not equipped with an attenuator. But the VCAs can process all signals up to 15Vpp / -7.5...+7.5V without clipping. In case of higher levels an external attenuator is required (e.g. A-183-1).

The sum of the left and right signals appear at the sockets Out L and Out R. The maximal amplification is about 0.5 to avoid clipping at the mixer outputs (otherwise the outputs may distort with 15Vpp signals at each signal input and full amplifications). If another maximal amplification (e.g. 1) is required two resistors have to be replaced.

All inputs and outputs are DC coupled. Consequently the module can be used to process both audio and control voltages.

Additional technical specification for each VCA (based on the specifications of the VCA circuits CEM3360/AS3360 used in the module):

• Crosstalk between two channels: better than - 80dB
• Signal attenuation at 0V CV: better than -80dB
• Total harmonic distortion: typ. 1%
• Control voltage feedthrough: max. 15mV