[sdiy] Octave Cat woes

[rob hukin]

Hi All,

Has anyone here successfully managed to get an early (pre-SRM) Cat working with a MIDI/CV converter? I have two in for repair, both now fixed and happy to drive each other using the series patch (CV/Gate) connections. However, when connected to a MIDI/CV converter (tried Kenton Pro 2 and Synhouse MIDIJack), the ADSR generator behave strangely - full sustain and no decay - and the Gated Repeat function doesn't work. The schematics are at http://www.overacker.com/cattune.htm, if you're interested.

I've looked at this for far too many hours now, trying to work out what's happening. I don't think the gate signal is the problem - the internal gate signals look the same using the keyboard or MIDI/CV.  I'm wondering whether it has something to do with the Trigger Generator, which seems to generate a trig pulse from changes in the CV, possibly taking advantage of CV droop between key strokes (when you repeat the same note) and changes in CV when another key is hit. I must confess I don't really understand how or why this circuit works. Enlightenment much appreciated!

Note to CAT repairers - 4016B's won't work properly in the envelope generator. I think 4016A's were used originally, though they don't seem to be readily available now (lower R_on) - 4066's work fine.

thanks,
rob.