The Befaco A*B+C V4 DIY Kit is the self-build version of a 6HP Eurorack module that Befaco calls a voltage-controlled voltage processor. It has two identical channels for audio and control voltages. It suits modular users who are comfortable with a through-hole soldering project and want a flexible processing utility in a small amount of rack space.
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Two channels of A × B + C: each channel multiplies input A by input B, then adds a third signal at C
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DC coupled: handles slow modulation and static voltages as well as audio
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Normalled inputs: B and C default to 5V when unpatched, so a channel can work as an attenuator or offset source without extra cables
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Signal LEDs: two red LEDs over Out 1 and two green LEDs over Out 2 show the signal level
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Compact: 6HP wide and 35 mm deep including the power connector
With audio, the multiply stage gives four-quadrant amplitude modulation for ring-mod tones. The module can also act as a linear VCA, a signal mixer, a 2x gain stage, a phase inverter or a plain attenuator. With control voltages it works as a voltage-controlled attenuator, CV mixer, inverter, VCA or DC generator. That range makes it a general-purpose module for scaling, offsetting, combining and gating modulation, or for shaping and mixing audio.
The build uses two boards, a main board and a control board. You solder them together and join them with M2 screws and spacers. The panel has four B100K potentiometers, four 3-position slide switches and one 2-position switch. Befaco's assembly guide asks even experienced builders to read every step before starting, and points first-time builders to its introductory how-to material. Befaco also sells a ready-built version of the module.