Befaco BF-22

The Befaco BF-22 is a two-channel Eurorack filter based on the Sallen-Key design of the early Korg MS-20. It is for patchers who want that dirty, screaming MS-20 character in a modular system. Befaco notes that it also reproduces the original's noise floor, so it suits players who value grit over a pristine signal path. This listing is the assembled version.

• Two Sallen-Key filters, each switchable between 12 dB low-pass and 6 dB high-pass
• Two cutoff CV inputs per channel: one with an attenuverter, one with a fixed 1V/oct response
• CV-controllable resonance, slightly more pronounced than on the original MS-20
• Link switch that routes filter A's output into filter B for series patching
• Input level that matters: how hard you drive the input changes the filter's response considerably

Each channel has an HP/LP switch, cutoff and resonance knobs, an audio input and output, a resonance CV input and two cutoff CV inputs. The first cutoff input's attenuverter does nothing at centre, applies full CV fully clockwise and inverted CV fully anticlockwise. The second input is set to 1V/oct, so the filter can follow a pitch sequence. For the strongest resonance with the least noise, the manual suggests turning resonance up until just before the LEDs start to flash.

The Link switch is where the module becomes more than two separate filters. With Link engaged, filter A feeds filter B and B's own input is disconnected. Set A to high-pass and B to low-pass for the classic MS-20 signal path. Set both to the same mode for a steeper slope, or overlap them for a band-pass response. Filter A's output stays available while linked, so you can tap the intermediate signal too. With Link off, the two channels run in parallel as independent filters for separate voices or stereo processing.

The module is 17 HP wide, has a heat-treated aluminium front panel, and runs on either ±12V or ±15V supplies without modification. It is designed in Barcelona, where the assembled units are built.