This is the simple circuit:
And after I'd got it working on a breadboard Nick made some suggestions:
Nick wrote: ↑Mon Nov 07, 2022 8:47 pmI would suggest trying with better metal film or carbon resistors, maybe tackman. Also try a simple 9v battery (or two if its split rail) I don't trust that SMPS and certainly don't if you have made a dummy split rail. Also if that ceramic cap in the feedback path? of so, replace with a polystyrene. Most ceramic (not so much C0G) introduce a shocking amount of distortion. Also need power rail decoupling, electrolytic and ceramic.