This is a multimode VCF based on a design by Electric Druid (ED). It uses pole mixing to achieve multiple filter behaviors.
Changes from ED design include
- Resistor value changes
- Added AC coupling capacitor on input signal to resonance compensation mixer.
- Added op amp buffers and pulldown resistors on LP1–4 after AC coupling capacitors.
- Added second inverting stage on input. Reduced first stage gain to 0.51 and increased output stage gain by the same factor.
- Changed BP resistors for unity gain at peak.
- Changed 7th mix to {1, 2, 2, 0, 0} notch.
- 7th and 8th mix have enough resistor footprints to implement any desired mix.
- Multiplexer replaced with rotary switch.
- Added header for expansion.