dual ladder VCF proto-type

Listen with good headphones or speakers - lots of bottom end!
This circuit is still quite rough and I haven't settled on all the component values yet. It uses dual opto-coupler ICs - LED to transistor - to form two ladder VCFs. One is a diode ladder similar to the EMS design, the other is similar to the TB-303 transistor ladder, with many parts left off.
The diode ladder gets the audio input and the LEDs transfer the audio over to the transistor ladder, so both VCFs run in parallel but can be tweaked individually. The PCB version will have individual freq CV inputs and a 'both' CV input.
The outputs will be available separately plus a mixed output and possibly a difference output; only allowing the parts that are different between the two signals. It goes without saying the mixed output simply blows chunks!