This module is a variation on the standard two-inverting-stage op-amp DC Mixer. It has provision for an offset pot, four DC mixer inputs, processor style inputs, with both inverting and non-invering outputs, though the inverting output cannot be used with the processor function.

It will work on either +/- 12 volts or +/-15 volts without modification.

A little on how it works:

The schematic for one half of the dual voltage processor. Both sections are identical.

The circuit is a standard two-inverting-stage op-amp DC Mixer. The processor works by feeding the signal to the two summing nodes, both of which are at 0V (virtual grounds). With a processor input pot in the center of it's travel, the signal is fed equally to both inverting stages. The output of the first stage, being an inversion of the input signal, cancels out the signal being fed directly into the second stage. By adjusting the pot to either side, either the inverting or the non-inverting is increased with respect to the other, the difference being buffered by the second stage and fed to the output.