The mh31 – VC Modulator is a Ring Modulator of different cast.

Contrary to other common Circuits the mixing of Frequencies is realized by using Operational Amplifiers. The result differs audible, soundwise from other Ring Modulators and one must not expect classical functions of a Ring Modulator.
Here we come into noisy and dirty terrain. Moreover the module is DC-coupled, so it is usable for control voltages, too..

The module offers one VCA for each signal input, including a initial amplification control and a control voltage input with attenuator. Do you drive the CV input with another audio signal you can dial in even a third signal. The incomin carrier signal switches the sum of both incoming signals (carrier and modulator). The result gets mixed with the kind of rectified carrier signal.