I’ve now breadboarded a full voice of the WSG (3 oscillators) as well as the filter. Not everything behaves quite the way I expected… but it’s all right, I guess, except that the output is very very quiet — nearly inaudible. It’s better if I increase the value of R10 (a lot). Odd. It’s quiet at both the input and output of the filter, so if there’s a problem it’s upstream of the filter, but I can’t think why both audio oscillators would be too quiet.
(Oh, and the Pignose hum — wasn’t the Pignose, it was the cable.)
Update: Actually now that I think about it, the input to the filter is further upstream than I was thinking, and that may be fine. So maybe there’s something wrong in the filter.