Whiteface is based on the legendary ARP4023 VCF module often found in the “whiteface” ARP Odyssey Mk1.
I’ve engineered out the rare parts and the need for matched transistors for the CV input section by using a Roland-inspired circuit there instead, no change to the vibe though!
The audio path remains pure ARP, with one exception – built as specified on the schematic, the resonance would clip in a way which is neither musical or desirable when set too high. I’ve come across a couple of other versions which have this ‘don’t turn it up past 8’ trait, but I went further and engineered that out – a single resistor value change. In Whiteface, the resonance is usable and musical over the entire range!
As we’re bringing part of a hardwired synth to modular, it’s also necessary to buffer the output. I’ve used an inverting buffer, which also adds a bit of gain to bring it up to modular levels. A nice side effect of the inverting buffer is that if you mix the input signal with the filter output, and find the sweet spot, you can do highpass filtering too!