Cgs synth

> I recently completed an 8-step version of the sequencer/programme r.
> There were three problems with it when I first tested it, two of which
> I located - a solder whisker joining two of the board buses and a dry
> joint on a resistor. The third one is stumping me.
> Row 2 of the sequencer, when the pots are at zero, and the CV out is
> connected to a VCO CV in, the VCO puts out the same pitch as the other
> three rows do when they're at zero. However, when you rotate the pot
> clockwise, the pitch goes down instead of up! On row 1,3 and 4 the
> pitch goes up as expected. Having examined the schemo, I figure the
> problem must be located with some build error either on row S, or on
> the tl072 that is at the output of row 2, however having carefully
> examined the boards, I can't find what I've done wrong! Any
> suggestions? I tried replacing the 072, and resoldered the 2 smd caps
> on the back of it, no effect.
> I'm very pleased with this piece otherwise, it's great, many thanks Ken.
>

>
> Have you wired the connections to the potentiometer (for pitch) the

> Of course i could be totally wrong as well.
>

>--- 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
>
>
>
>

On Sat, Jun 28, 2008 at 5:35 PM, <sasami@...> wrote:

> 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.
>
>
> >--- In cgs_synth@yahoogroups.com <cgs_synth%40yahoogroups.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@... <sasami%40hotkey.net.au>
> Modular Synth PCBs for sale <http://www.cgs.synth.net/>
> Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>
>
>



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---------------------
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[Non-text portions of this message have been removed]

--- In cgs_synth@yahoogroups.com, sasami@... wrote:
>
> 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.
>