L-1 Mutant Vactrol VCF
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MUTANT VACTROL VCF – VC vactrol based multimode filter.
This module is based on Scott Stites Mutant Vactrol Filter. Thanks to Scott for kindly allowing L-1 to use the design!
Scott Stites site:: http://www.birthofasynth.com/Scott_Stites/Pages/mutant_main.html
Power consumption: V+ 30mA, V- 26mA.
Extract from Scott Stites Mutant Vactrol Filter page:
The Mutant Filter is so named because at its heart is the Sallen-Key structure of two Buchla Low Pass Gates (actually “not” as it turns out) with the embellishments of an expo current sink and a resonance clipper similar to that found in the Korg MS-20 filter. It is not a clone or an adapation – it’s more of a mutation, an almagm metasticized from disparate elements. The result is a filter that can be sublime, organic, raucous or downright mean. At times it can be sublimly organic in its raucous mean-ness. Its sounds are legion, and the samples on this page are just a taste of the beauty and weirdness that can be wrought from it.
Before proceeding further, here is a composition using only the filter in various modes. It’s a nice glimpse of the filter in actual use as opposed to the rather dry expository samples that follow. There’s some organically sublime mean raucousness in there…somewhere.
THE MUTANT FILTER IN DETAIL
The resonance limiter was taken from Rene Schmitz’s ‘Late MS-20 Filter’ design. I used regular signal diodes instead of the green LED’s of Rene’s design mainly because I couldn’t find any green LED’s around here at the time I was putting it on breadboard. Green LED”s would work just fine. The expo control is taken directly from Rene’s 4069 VCO design.
I have an added switch which allows the lower half of the resonance signal to be clipped. Surprisingly, this is the tamer resonance mode (and sounds quite pleasing). When the resonance is not clipped, the filter will more freely self-oscillate and render some of the wilder MS-20 like resonance tones.
The Mutant Filter has six modes of operation:
|Mode 1||12 dB low pass with resonance tapped from the 24 dB low pass point.|
|Mode 2||24 dB low pass.|
|Mode 3||12 dB High Pass with resonance tapped from the 12 dB band pass point.|
|Mode 4||12 dB Band Pass.|
|Mode 5||12 dB High Pass with resonance tapped from the 24 dB high pass point.|
|Mode 6||24 dB High Pass.|
The modes are selected by setting a toggle switch to one of three positions and setting another toggle ‘Tap’ switch to either tap 1 or tap 2.
MODES 1 AND 2
3Two sections (just the Low Pass structure) wired in series allow a 24 dB response for Low Pass filtering. The resonance in this mode is clipped and inverted as it’s fed back to the input. When the mode switch is set to the LP position, the 12 dB low pass response is present on the output when the tap switch is in position 1. The 24 dB low pass response is available when the tap switch is in position 2. Note that the resonance is always tapped from the 24 dB output.
MODES 3 AND 4
Modes 3 and 4 configure the first section of the filter to a 12 dB high pass filter and the second section of the filter to a 12 dB low pass filter. The resonance in this mode is clipped and fed back to the input non-inverted. When the mode switch is set to the BP position, the 12 dB high pass response with resonance tapped from the band pass output is present on the output when the tap switch is in position 1. The 12 dB band pass response is available at when the tap switch is in position 2.
MODES 5 AND 6
Modes 5 and 6 configure both sections of the filter to the 12 dB high pass configuration. The resonance in this mode is clipped and fed back to the input non-inverted. When the mode switch is set to the HP position, the 12 dB high pass response with resonance tapped from the 24 dB high pass output is present on the output when the tap switch is in position 1. The 24 dB high pass response is available at when the tap switch is in position 2.