I finally got this thing going last night... tons of work and it's a complicated little beast!! But while I had this circuit working for a short time, I swapped out a transistor and now I have some SLOW motorboating going on... that gets faster if I adjust certain parameters. I'm realizing there is probably some controlled feedback in this circuit, but not sure how to affect that equation, if it's the value or efficacy of the coupling... (decoupling?!) or the relative gain of the transistors. I used a ton of replacement transistors as the originals weren't available... but the transistors described in the schematic weren't even the ones in the unit! So I know there is room for a little FUDGE.... I realize there are tons of reasons this could happen, but I'm restoring an old CRUMAR ORCHESTRATOR synth... and some of the transistors were bad, so I ordered some new ones, though the BC style transistors weren't available and the ones in the thing were different than the ones in the schematic. I'll show you the particular part of the schematic I'm dealing with. I'm wondering if the decoupling and or coupling caps in this would even be suspect, or am I just dealing with a controlled feedback circuit that I need to balance with high or lower gain transistors? Also I'm struggling a little with the schematic and the polarities of the transistors in the circuit...it took me DAYS to get this far and I could kick myself, as I had the thing working last night, but it wasn't quite the way I remembered it sounding, so I moved a few around... lol... I will never do THAT again! I've been inside this thing every day for a week now... fixed everything in there, but this "brass" setting, is a separate synth circuit that is basically discrete from the other functions and sounds. And it's the coolest, of course!
Pics of the circuit here.
https://ia801401.us.archive.org/21/...3-pm/Screen Shot 2021-07-31 at 5.57.43 PM.png
https://ia801401.us.archive.org/21/...3-pm/Screen Shot 2021-07-31 at 5.57.57 PM.png
https://archive.org/details/screen-...3-pm/Screen Shot 2021-07-31 at 5.58.16 PM.png
Pics of the circuit here.
https://ia801401.us.archive.org/21/...3-pm/Screen Shot 2021-07-31 at 5.57.43 PM.png
https://ia801401.us.archive.org/21/...3-pm/Screen Shot 2021-07-31 at 5.57.57 PM.png
https://archive.org/details/screen-...3-pm/Screen Shot 2021-07-31 at 5.58.16 PM.png