A Diode Ladder VCF
Å voltage controlled lowpass diode ladder filter. Cutoff and Res master knobs. Control voltage inputs for both Cutoff and Res, with attenuators. Selectable resonance gain compensation mode so the volume stays relatively flat as resonance increases. Selectable keyboard tracking mode and it self oscillates, so the filter can be played. Has a soft-clipping overdrive circuit on the front-end, plus adjustable input attenuation. Has a HP-like mode that works by subtracting the LP signal from the input - there's a front-panel pot to help tune this.
Tiny demo and snapshots here:
Inspiration taken from: http://www.timstinchcombe.co.uk/index.php?pge=diode
https://www.instructables.com/Diode-Ladder-VCF-With-NO-PCB/
https://www.haraldswerk.de/Filter/NGF_Ladder/NGF_Ladder.html