[sdiy] What would be THE best, most versatile VCF available on DIY community ?

David G Dixon dixon at mail.ubc.ca
Tue May 29 02:58:27 CEST 2012


I've got a couple of filter designs of my own that I think are pretty
versatile, and for which I sell handmade PCBs.  Both filters are based on
the SSM2164 chip (although I actually use the Coolaudio V2164 chip, which is
available for less than $4 from a number of vendors, and is thankfullly not
obsolete).

The 2164 Korgasmatron III is a MS-20-inspired dual VCF which has up to three
signal inputs to each filter.  Each input can be assigned separately to any
one of six filter modes with rotary switches: 12dB LP, 6dB LP, BP, 6dB HP,
12dB HP, and notch.  The filters can be operated in series or in parallel.
PCBs are $35.

The 2164 4P LPF is a cascaded 4P with a couple of twists.  It's got separate
gain cells after every filter stage, which gives resonance without
sacrificing the signal (which happens in all conventional cascaded 4P
filters unless something else is done, like the MOTM 440 "bass boost").
This has the added advantage of passing the sine waves at self-oscillation
at equal amplitude.  This feature can be switched off to give the
conventional single gain cell configuration if a more classic sound is
desired.  It also has an extra capacitor on every filter stage which is 100
times larger and can be switched in to make the filter a dedicated
quadrature LFO which is stable to very low frequencies.  There are eight
outputs, each at 45 degrees phase shift from the last.  The board is set up
so you can easily tap out the input, the feedback signal, and four selected
outputs to a multimode expander.  With these, just about any filter mode
imaginable can be obtained by summing the various signals at different gain
ratios.  I've figured out the gain ratios for 30 distinct modes, but
hundreds of additional "in-between" modes are also possible.  I haven't
built the expander, so YMMV.  PCBs are $40.

Email privately if you are interested.




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