[sdiy] The Korg MS-20 VCO core is oscillating!

[lanterma at ece.gatech.edu]

My students and I were able to get the MS-20 VCO core going on the breadbaord; thanks to the many people who offered advice.

The problem, was, uhm, err... well... there's this diode, D4:

http://www.korganalogue.net/korgms/images/service/ms20/circ1.gif

It turns out it the circuit works much better if you have it the correct direction. ;)

*Aaron hangs head in shame*

I checked over their wiring around the CA3083 transistors multiple times, *including* looking at the diode, and somehow just never saw it until just recently, and I went "hey, is this diode going the right way?"

It's like my brain interpolates what it expects to see and doesn't see what's there. I have that problem when proofreading all the time, especially if I'm proofreading something I just wrote; I have the same problem with equations I've just written on the board.

(We're having trouble getting it to oscillate at low frequencies, but I think that's now just a matter of tweaking the current source.)

- Aaron