The MM315 Balanced Modulator is a ring modulator with surprising clarity and precision that belies its "vintage" character, enabling it to do double duty as a high-quality VCA with handy utilities (patchbay and attenuators) as a bonus.
For the uninitiated, ring modulation differs from a standard VCA by allowing negative multiplication of signals as well as positive. It was used in many classic synths and electronic music studios to allow the generation of clangorous metallic tones (not to mention Daleks and Cybermen!) from two simple input waveforms of differing frequencies. For this reason it could be thought of as the "East Coast Wavefolder".
The MC1496 modulation chip from the late 1960s has passed into legend and is still popular today, however the original AR315 was about the only use of its more sophisticated, much better-performing, analogue computing grade sibling the MC1595L, which is now out of production. We have sourced new-old-stock examples of this chip for the MM315.
The result is an excellent ring modulator which has very low distortion and does not "lose tone" as amplification is increased, unlike MC1496 based circuits. Indeed, it can easily serve as a good quality conventional output VCA if paired with an envelope generator that outputs zero volts when idle.
The two outputs (MOD1 and MOD2) are identical and are independently connected to the output signal via 1k protection resistors. There is also a bonus 4-way patchbay and two 100k passive linear attenuators.