All-discrete ring mod based on the one half of the Buchla 111 circuit. Note: original 111 was a dual; this PCB is for a single ring modulator, so you would need two for a clone project. Adapted from PCB design by vtl5c3.
* Based on examining an original module, Apetechnology identified a possible error in the schematic. R27/R78 are labeled 680 on schematic, but found to be 680k in an actual module. A test build/comparison showed little if any audible difference, but I'll change the legend on the next run of PCBs. Meanwhile, this is the resistor in question: