November 3, 2008

292C secrets

I cracked open my first 292c repair last night. I found some interesting things during this repair. First, there are some parts in the actual 292c that are not on the schematic. I probably found the most confusing way to draw this, but I just added it on top of the schematic in red. the cap around IC7 is going from inverting input to output, even though my artwork may look misleading. I'm not sure what the point of that resistor/cap kludge in the middle is. My guess is to roll off the highs (around 24k) a little bit in gate mode only. This makes me wonder why nobody has complained about oscillations in all this cloning that has been going on. Check out the hacked solution to solve the lower gain on the second channel. I don't think that's factory.

Second, the channels don't match! Well, the first one on the left has an error, so that doesn't count, but the second one doesn't have a 100p around IC7 at all!?

I love Buchla repairs, they are like an archeological dig.


VICMOD said...

today I hear the robins sing
today the thrush is in the wind
today who knows what tomorrow will bring TODAY

just got a buchla 200e and loving it :-)
would like to see how much an original 200 VCO goes for.

Resse P. Dubin said...

Glad to see the original schematic as well as the presence of the 3/2 vactrols, before I go off on my own clones.

Keep up the excellent work. This is my new favorite site.