High pass / Low pass VCF loosely based on the later, OTA, Korg MS20 VCF. The module is one single filter with two inputs that can be used simultaneously. In phase and out of phase outputs allow interesting feedback loops. Feed the inputs with VCA modules for best results.

MA20 front panel
Two audio inputs.
  • HP IN
  • LP IN
  • Patch the same signal to both inputs for bandpass-like response.
Two FM inputs
  • FM 1 with a Push/Pull potentiometer to attenuate and/or invert the CV signal
  • FM 2 is unattenuated
Resonance control pot that ranges from 0 to self oscillation. This is highly dependent on the input signal level(s).
The module is built and trimmed for:
Various pcb headers to easily normallize two MA20 modules together.
MU format (will fit in and STG cabinets and rack frames)
Built with love and care in Chicago using high quality parts including:

The module is based on the Korg MS20 (later OTA model) VCF circuitry. However, the MA20 VCF implements various changes and enhancements to the original circuit so it should not be taken as an exact clone. A few differences:

Simultaneous HP and LP inputs
Allows for a range of effects. Some subtle. Some pretty weird.

+ OUT and - OUT
These can be patched in interesting ways. They can also be fed back into the HP or LP input. You can't hurt anything so go nuts.

A VCA (or two) for best results
Patch VCA(s) in front of the inputs.

The PEAK response is dependent on the input levels present at the HP IN and LP IN jacks. With PEAK turned full up CW the filter will oscillate. As the signal levels at the HP and/or LP input increases the oscillation will interact with the signal. At a certain point the oscillation will stop and you get overdriven sounds. Patching a VCA in front of the HP or LP input gives you full control of the input drive and allows you to modulate these input levels. You can also use an attenuator or mixer instead of the VCA but you will lose the VC capabilities. Check the sound samples and patch diagrams below for examples of this and others using VCAs.

Click here to download the PDF user guide.

Price: $210.00 + shipping
Email me with your address for a total with shipping.

Sound Samples

All samples are recorded straight to the soundcard. No effects, no EQ, no processing, nothing.

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