Korg35 style VCF
This is a Korg35 style VCF. The Korg35 was found, for example, in the Korg MS10 and in the early Korg MS20. It's a great sounding filter with a rather typical Korg MS-style growling and screaming resonance. The early MS20 had two Korg35s, one for the High pass and one for the Low pass, instead of building two VCFs I added a switch on the input to select Low pass or High pass filter mode.
Unfortunately there are no building instructions for this module, but at least you'll find the schematic, some photos, and some comments.
The finished module.
Here's a test of the low pass filter output.
Here's a test of the high pass filter output.
That's it! Have fun and make nice filter sweeps!