Elektor Octave up circuit 1979

[Steben]

The text is in dutch... sorry for that. Yet the cricuit speaks for itself.

[bool]

My first instinct upon seeing the schema was how useful would be to squeeze a fet-based "sustainer" within the first opamp and how to squeeze-in some sort of filtering within the last opamp nfb.

[Mark Hammer]

I built one back in the day, and was none too impressed.  Mind you, I knew much less about what it takes to get robust audible octave-doubling back then.  Still, it is very close to the Craig Anderton design, which I feel offers a little more flexibility.

https://www.diystompboxes.com/smfforum/index.php?topic=20937.0