Befaco BF-22 VCF
Dual MS-20 Sallen-Key filter with dirty character
17 HP Eurorack module
The BF-22 is a dual Sallen-Key voltage-controlled filter inspired by the early Korg MS-20, offering two independent hi/low-pass filter sections that can be linked in series. It carries the character of the original MS-20 filter — warm, dirty, and capable of aggressive screaming resonance — with added attenuverters for CV control and selectable 6/12 dB slopes.
Features
- Dual independent Sallen-Key filter sections (A and B)
- Inspired by the early Korg MS-20 filter circuit
- Selectable high-pass or low-pass response per filter
- 6/12 dB per octave slope selection
- Cut-off CV attenuverters for bipolar CV control
- Volt/Oct tracking on cut-off CV input across 4 octaves
- CV inputs for both cut-off and resonance per filter
- LINK switch connects Filter A output to Filter B input for series operation
- Eurorack compatible, also runs on +/-15V without modification
- Banana or mini-jack connector versions available
- MS-20 character: warm, dirty, and aggressively resonant sound
Controls & Jacks (21)
- Filter A Cut-off — Manual cut-off frequency control for Filter A
- Filter B Cut-off — Manual cut-off frequency control for Filter B
- Filter A Resonance — Manual resonance control for Filter A
- Filter B Resonance — Manual resonance control for Filter B
- Filter A LP/HP Switch (6A) — Selects low-pass or high-pass response for Filter A
- Filter A Cut-off CV Attenuverter (3A) — Bipolar attenuverter for Filter A cut-off CV input
- Filter B LP/HP Switch (6B) — Selects low-pass or high-pass response for Filter B
- Filter B Cut-off CV Attenuverter (3B) — Bipolar attenuverter for Filter B cut-off CV input
- Filter A CV RES (7A) — CV input for Filter A resonance
- Filter A Cut-off CV Input Attenuated (4A) — Attenuverted CV input for Filter A cut-off
- Filter A Cut-off CV Input V/Oct (5A) — V/Oct cut-off CV input for Filter A
- Filter B CV RES (7B) — CV input for Filter B resonance
- Filter B Cut-off CV Input Attenuated (4B) — Attenuverted CV input for Filter B cut-off
- Filter B Cut-off CV Input V/Oct (5B) — V/Oct cut-off CV input for Filter B
- Filter A IN VOL (8A) — Audio input volume for Filter A
- Filter B IN VOL (8B) — Audio input volume for Filter B
- Link Switch (11) — Routes Filter A output internally to Filter B input
- Filter A Audio Input (9A) — Audio input for Filter A
- Filter A Audio Output (10A) — Audio output from Filter A
- Filter B Audio Input (9B) — Audio input for Filter B
- Filter B Audio Output (10B) — Audio output from Filter B
How-To Guides
- Classic MS-20 Band-Pass Patch
- Resonant Low-Pass Sweep
- Inverted CV Cut-off Modulation
- Parallel Dual Filter Processing
- Self-Oscillating Sine Wave
- Resonance Swept by Envelope
- High-Pass as DC Blocker and Low Rumble Remover
- LFO Wobble Filter Effect
- Dual Send-Return Parallel Processing
Explore the interactive BF-22 VCF panel on BleepDex — tap any control to learn what it does.
