Been a bit busy with the mundane part of life (you know family, work, that sort of stuff) so Forbin has been somewhat neglected but I have been trundling along with a few bits and pieces. This is our old favourite the Buchla 258 VCO clone... I have been doing a bit more work and have made a second PCB for the wave shaping section only. I have also taken some aspects of a Cat Girl design and worked it into the Waveshaping control along with some buffering and amplification of the output waveforms to boost them to +-5V so they are in line with the other VCO's in the Choir. This picture is to try and help out
ericcoleridge with the FET placement. Good plan to write on the board the GDS of the pins just to make sure! It is a bit odd and confusing, you can see the squarewave board mirrored on the right (got the press and peel printed back to front yet again....) There has been some discussion about the pots used and I have used 100K's BUT my waveshape control input has an extra summer and buffer... I will draw up what I have done and try and get it up here soon. It does allow me better control of the wave shape as I was finding that most of my control was up at one end of the travel (more so with the squarewave than the sawtooth).
1 comment:
Hello,
i just wanted to say thanks for putting these photos up- i just built a sawtooth version & it was very helpful to refer to your photos. Initially i put my 2220 in the wrong way, but on turning it around it fired up nicely! I'm also getting low output amplitude, so i'd be curious to see how you resolved the problem. I used modern transistors, but NOS carbon comp resistors where possible for authentic vintage tone ;)
I also used 10 turn pots for +/- & FM amount, they really open up the sound a lot!
cheers from Tasmania!
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