Buchla 160 Noise

In the original schematic, there is a connection missing (the red question mark)	The early production PCB I had was missing this. Check for continuity between the right end of R31 and the left end of R32. If they're NOT connected, you will need the jumper (yellow wire).

The actual noise comes from the avalanche noise generated from the reverse base-emitter voltage on Q1. Not every transistor will work here - many will give "crackles and pops" more than a nice even "hiss". You should use a socket for Q1 (IC socket pins) so it can be selected. I just soldered one in with the idea that if it wasn't suitable, I could de-solder it and try again (transistors are cheap these days). Of course the first one wasn't that great, so I de-soldered it and put in a socket. After trying about a dozen other transistors without any luck, I put the original transistor in the socket. Apparently the heat damage from de-soldering it did the trick - success!

If you have a 194 Band Pass Filters module, put the white noise output into it and listen to the different outputs. If they all have equal level outputs, you're probably good. A variable bandpass filter sweep is a good test also.