Random*Source (Serge Modular) VC Resonant EQ – Eurorack 10-Band Voltage Controlled Resonant Equalizer

Up for sale is a Random*Source VC Resonant EQ, the voltage-controlled Eurorack version of the legendary Serge Resonant Equalizer, built under license from Serge Tcherepnin.

This is a 10-band filterbank designed specifically for electronic sound synthesis and processing, producing formant-like peaks and valleys rather than a flat, "graphic EQ" response. Unlike most equalizers, most of the bands are spaced a Major 7th apart instead of in octaves, which keeps the bands from all resonating together — giving it a much more musical, unpredictable character than a standard EQ.

What sets the VC version apart is full CV control over every one of the 10 bands, each with its own attenuverter so you can decide exactly how positively or negatively an incoming CV affects that band. Push any band past the 3 o'clock position and it starts to self-resonate, simulating the natural formants of acoustic instruments — patch in an LFO or envelope and you get shifting, vowel-like sweeps that no ordinary filter can do. There's also a built-in 2-channel input mixer so you can blend or overdrive multiple sources before they hit the filter, plus a Feedback section (with phase switch) for pushing the whole thing into chaotic, near-oscillating territory.

Outputs include two Comb outputs (odd/even band sums) and two Main outputs (mix of all bands), giving you a lot of routing flexibility for parallel processing or stereo-ish patches.

This is one of the most distinctive-sounding filter modules in Eurorack — equally at home shaping drums, adding formant character to oscillators, or being used as a sound source in its own right through self-feedback and resonance.