doepfer a-135-3 voltage controlled stereo mixer price : $179.00

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. e.g. for max. amplification 1 the two 47k resistors r27 and r31 have to be replaced by 100k. the positions of the resistors are shown in the document. all inputs and outputs are dc coupled and the signal processing is non-inverting. consequently the module can be used to process both audio and control voltages.

it's possible to combine two or modules to enable the mixing of more that 4 stereo signals. in this case one of the modules is configured as "master" and all others as "slaves". details are available in the technical document.

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

the following document shows the positions and functions of the jumpers of the module.

this module has a maximum current draw of 40ma. it requires 89 te/hp worth of space to fit in a eurorack frame.