MS-20 external pitch-to-CV

[garcho]

Could and would anyone be so kind as to give me some tips on where to look for information regarding the block I've highlighted on the schematic below? Is it a somewhat standard circuit block? It's part of a pitch-to-control-voltage converter, for the Korg MS-20. Thanks y'all!


click to enlarge

[anotherjim]

Thanks, I feel like my brain has been squeezed out and put back inside out after trying to understand that!
PWM I think, with that entire 4069 squaring it up before filtering to DC. What happens between that and the first 2 LM339 comparators, I can't tell for sure -  some kind of timer (Saw!? Tri?) that's reset at the input frequency...

This calls for strong beer!

[robthequiet]

Is it something you are fixing or using for some actual box, or just studying it in the academic sense? Without simulating this it's hard to be specific, but it does resemble as anotherjim says some kind of comparator/rectifier, with the twin diodes and the hysterical opamp pair before the buffers.  I found a video on what it does at https://youtu.be/Dxl_ZQezVAw. Not trivial!

Edit: Found a nice circuit library Here

[Processaurus]

Be aware the MS 20 uses an unusual standard for the pitch CV, the rest of the analog synth world uses 1 volt/oct, but Korg used Hz/volt. It would need further circuitry to interface with other, non korg analog synths.