It does sound like you have an issue around one op-amp.
Try soldering a 47pf capacitor between pins 1 and 2, and another between
pins 6 and 7 of the op-amp that is giving trouble. You may have a stray
capacitance issue with all those long wires. If that solves it, do the same
to the other op-amps too as a preventative measure.
Also, look for bad solder joints around the IC, or a wrong resistor value.
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
Try soldering a 47pf capacitor between pins 1 and 2, and another between
pins 6 and 7 of the op-amp that is giving trouble. You may have a stray
capacitance issue with all those long wires. If that solves it, do the same
to the other op-amps too as a preventative measure.
Also, look for bad solder joints around the IC, or a wrong resistor value.
>--- In cgs_synth@yahoogroups.com, frank death <maldoroar@...> wrote:_______________________________________________________________________
>>
>> Have you wired the connections to the potentiometer (for pitch) the
>wrong way round? I haven't built this circuit but from a few circuit
>bending things ive done i learnt that wiring a potentiometer the wrong
>way can cause pitch to go up when you turn anti-clockwise.
>> Of course i could be totally wrong as well.
>>
>I would assume that if I'd wired the 8 pots in that row back-to front,
>then zero pitch would have been at full clockwise rotation, rising as
>I rotate the pot counterclockwise. IE the other way round to what the
>pots in the other rows are doing. I haven't stuck a meter on it, but
>it appears that rows A, C and D are putting out from 0v (pot fully
>counterclockwise) to I think 5v (pot fully clockwise) whereas row B is
>putting out 0v (pot fully counterclockwise) to -5v (pot fully
>clockwise), so the pots on row B aren't reversed, they're acting
>differently.
>
>IIRC each opamp in an 072 inverts the signal going through it (maybe
>someone more knowledgeable than I could confirm/deny this) so maybe
>something's causing one of the opamps to not work properly? Casting
>about a bit here TBH.
>
>Otherwise, as mentioned, it works great. I left it running all night
>last night to burn it in, no other problems evident. I took some
>photos of the completed piece, and uploaded them to my flickr account:
>
>http://www.flickr.com/photos/16804034@N00/2618961254/
>http://www.flickr.com/photos/16804034@N00/2618138477/
>http://www.flickr.com/photos/16804034@N00/2618139529/
>http://www.flickr.com/photos/16804034@N00/2618140773/
>
>I'll upload the .fpd file to the files section when I'm on my work
>computer. A couple of notes - wiring everything off board was
>necessary because of where I wanted the panel to go in my synthesizer,
>and because it's a frac-rack panel, and there's not enough height in
>that panel format. It is a COMPLETE pain in the ass though, and I
>STRONGLY recommend attaching the pots to the boards, as per Ken's
>instructions, and using a larger panel size. There are 18 wires per
>step, plus a further 8 wires to solder in if you do it my way, which =
>152 wires! Worth it, though.
>
>
>------------------------------------
>
>The CGS Modular Synth home page: http://www.cgs.synth.net/
>Yahoo! Groups Links
>
>
>
>
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>