It started life as the SVF design (based on the J. Haible discrete 2040 gain cell) which Scott Stites posted over at electro-music in April. 

I'd been wanting to work with another filter for a while and this one looked interesting, so I started playing with it. I lopped off the audio input section and grafted on the CP3 mixer (moar transistors!). It's definitely interesting! A very thick, rich-sounding filter with a lot of different personalities depending on how hard you drive the inputs.