Mutant Cure VCF








  • Vactrol based voltage controlled filter.
  • LP topology is Sallen-Key.
  • HP topology is mutant-ish Sallen-Key.
  • 24dB and 12dB outputs.
  • MODE input switches between LP and HP modes. If some voltage is presented at this input, then it switches mode to opposite choisen with the switch.
  • two dual vactrols inside.


  • 36 mA +12V
  • 36 mA -12V
  • 0 mA 5V
  • 26 mm deep
  • 10HP



PCB - 2mm thickness, gold platted, black mask. $25

Two panels - 10HP front & back. Anodized alu, black print. $25

SMD parts + soldering. $10

Shipping per set: $5 - only boards, $8 - boards+panels.


TOTAL for complete set with shipping: $68


Paypal: info(at)


Assembled module $290 + $10 shipping.


MUFFWIGGLER forum thread


















This is a replacemet for The Mutant VCF designed by Scott Stites. Old page about the Mutant VCF is here: The Mutant VCF sounds very good but I was not statisfied how resonance is implemented there. Also there are some things I don't very like - FET based switches, too many buffers, etc. So I decided to re-design it with my rules. I returned to the beginning and started with a clean state. The aim was to make vactrol based 24 dB/oct multimode VC filter.

At first I made Sallen-Key LP filter. Were no problem here. It sounds very nice, resonance and selfoscillation are perfect. It oscillates clean sine at full frequency range, only at maximum resonance. Watch and listen to the waveforms in the video below.

Sallen-Key LP filter topology and first prototype:




HP mode.


Sallen-Key HP filter topology:

As you can see plots are OK, but is not easy to make HP switchable from LP - too many switching points. Also using dual vactrols is impossible because resistors are connected in series there, but in Sallen-Key HP they are separated.



Sallen-Key LP and mirrored HP filters simulation plots:




I decided to make HP mode in similar way as Scott Stites made in the Mutant VCF. It allowed to have acceptable number of switching points and to use dual vactrols. But this is completely different filter with different response, not just mirrored LP. I was forced to use another capacitor C3 instead of C2 to have the same as LP cutoff and selfoscillation frequency. But anyway with existing capacitors values HP mode oscillates 2 semitones higher than LP. HP mode oscillates stable at full range, selfoscillation happens only at maximum resonance. But it oscillates quiter than LP and the wave is distorted, it sounds normal nevertheless. Also this mutant-ish HP mode adds a bit of harmonic content at cutoff frequency, but this is not bad, sounds cool. Watch and listen to the waveforms in the video below.


Mutant-ish HP topology:



L-1 Mutant Cure VCF simulation plots LP and HP:



I built a prototype but made many errors there, so was forced to heavy modify it :-)



Mode switching.


I used electronic switches for switching modes. They work from SPDT mechanical switch at the frontpanel or from CV. Some voltage applied to MODE input switches the filter in mode opposite chosen with mechanical switch, gate type signal is ok.


L-1 Mutant Cure VCF video shows the waveforms:





I tried to make soundsamples so simply and understandable as possible. Just basic patches. Only L-1 modules used. Waves from a pair of L-1 Basic VCO into the filter, then into L-1 2-ch VC Stereo Mixer, filter cutoff and mixer level are modulated from L-1 VC ADSR. Sequenced from MIDI. I tweak attack & decay and filter knobs when playing.








Sample 1 - saw + saw, LP mode. Sample 2 - saw + saw, HP mode. Sample 3 - triangle + saw, LP mode. Sample 4 - saw + saw, LP mode, level is modulated in the L-1 Tube VCA 2П2П.


Direct links to 16/44.1 FLAC files:



More 'Sample 3'. Two remixes. Earlier versions really.:







Direct links to 16/44.1 FLAC files:






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