Available as an assembled Module and as a DIY project.
No info about availability.
Four channel mixer with a twist
The MultiMix module is a mixer of which the first three inputs have each an independant level control. Each level control can be set so that the gain of the input is anything from -1.1 to +1.1. This means that not only can inputs be added together, but can subtract as well. With each input knob set to its middle position, then none or very little of the input signal will reach the output. Mixers with attenuverters controlling the inputs are very useful for controlling audio and CVs. One excellent application is to use the MultiMix with a VCA to create a very flexible ring modulator. The Multimix also features a fourth input that is summed with the final mixed output. This can be used to cascade several Multimixes together to form much larger mixers.
The module features a clever combination of four output sockets to achieve a variety of uses. Two mix outputs are available: One is MIX OUT and this is simply the four inputs added together - the first three inputs being added according to the levels set by the pots. The second main output is OUT3/MIX. This is exactly the same as MIX OUT until you start connecting jack plugs to either OUT1 and/or OUT2.
Inserting a jack into OUT1 and the IN1 signal will be removed from the OUT3/MIX socket. It will, however, still be present at the MIX OUT socket. The OUT1 socket gives you only that pot controlled version of the signal going into IN1. As before the pot will control the level and phase of the signal. You can thus use this pot to attenuate, or invert, CV or audio signals independently of what is happening on the other three inputs. Inputs 2 and 3 also behave likewise. They can be treated as independent reversible attenuator channels or be treated as level controls on a mixer. It all depends on how those output sockets are used.
The module also features two output level LEDs. These monitor the signal level at the MIX OUT socket. The 5V one lights when the signal exceeds +/-5V. The peak one lights when the output signal is getting near clipping, ie. around +/-11V.
These merchants probably sell this module. Huh?