Been working on getting this circuit to work for awhile. Graham, I don't know if you remember this, but I emailed you about six or seven months ago having trouble building the first module. Never ended up getting it to work, set it aside for quite awhile. Lately, got the itch again. I tried breadboarding it up based on the strip board layout given...still no dice. I pretty much gave up and for the past week have been looking at alternatives (SSM2044? Space and power aren't a concern for the project I have in mind...)
Then, tonight, I stumbled on this thread and, encouraged by the success of others, decided to give it one last whirl. I decided to breadboard the Q&D circuit by itself to rule out the possibility of bad components... Success! Everything sounds all distorted to hell without any attenuation of the Casio's output, and I started to pick up a radio station(...?), but the important thing is that I was getting audio through the circuit and a clear cutoff/resonance response. Hot diggity!
So tomorrow I think I'll add back the input resistors/capacitors and work on a stripboard layout that isn't quite so crowded. no offense Graham, but that thing is freakin' tiny! It's pretty incredible that you got it to fit inside the SK case, but I plan on making mine external anyway. If I'm successful, I'll be sure to post my layout here so folks who don't need a tiny board don't have to.
Cheers! I owe you a few beers when this is complete, graham!