Synthasystem Voltage Processor/Mixer

classic steiner synthasystem module reproduced in euro format 

PCBs courtesy of david ingebretsen's faithful reproduction of the original schemtics

aluminum euro panel by clarke robinson, 14hp

This module mixes and can also invert incoming signals. There are 3 sets of paired inputs and 2 outputs, three passive attenuators, and the ability to add a fixed DC offset to the signals on the third set of paired inputs. This is a very useful module because it can mix audio as well as control voltages and can provide inverted and non-inverted versions of the input signal(s).

Quoting from the Synthasystem Manual:

The Voltage Processor is a six input mixer with two outputs. Three of the inputs run through input level pots and the other three have a fixed gain.

DC voltages and or AC signals can be mixed (summed) together and taken out of the output jacks.

The Voltage Processor has two outputs A and B. A consists of 4 output jacks in parallel and output B consists of two output jacks in parallel.

Any signal, no matter what input is used, will appear in output A and B simultaneously but their phase relationship depends upon what inputs are used. When AC signals from separate sources are mixed and taken out of an output it is not, in most cases, important as to what their phase relationships are because a waveform will sound the same whether or not it is inverted. Therefore the polarity markings above the inputs can be disregarded.

When using the voltage processors to mix DC control voltages it is important however to understand how each input treats the input voltage.

The first two inputs are marked A+ B-. This means that a positive DC voltage fed into any of these two inputs will drive output A positive and output B negative in equal amounts simultaneously. This could for example drive two oscillators in perfect contrary motion. One of these two inputs marked VR1 is fed through an input level pot which can turn the input signal to zero. The other input is set at a fixed level.

The next two inputs marked A- B+ do just the opposite of the first two inputs. A positive voltage fed into any of these two inputs will drive output A negative and B positive. One of these is marked VR2 and goes through an input level pot. The other input is set at a fixed level.

The last two inputs marked A+ B+ mean that a positive voltage fed into any of these two inputs will drive both outputs A and B in a positive direction. One input marked VR3 goes through an input level pot. The other input is set at a fixed level. A front panel voltage pot can also be turned on with a switch to feed in a voltage which also drives both outputs A and B in the same direction simultaneously. All oscillators being driven can be shifted or tuned up or down in pitch exactly the same amount by turning this pot.

Inputs/Outputs:

This module has 3 sets of paired inputs. One input of each pair goes through a passive attenuator. Each pair is labeled with reference as to how its signal appears at the A or B output.

A+ B- : The signal at these input jacks will appear non-inverted at output A and inverted at output B.
A- B+ : The signal at these input jacks will appear inverted at output A and non-inverted at output B.
A+ B+: The signal at these input jacks will appear non-inverted at output A and B.