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I apologize if this is posted twice - I have a difficult time with Yahoo groups sometimes and finding recent posts. Posting again because it doesn't seem to have made it through.
Ok, I'm building this now and am confused. I think Ken has his schematic wrong for the CV section:
http://www.cgs. synth.net/ modules/pic/ schem_cgs49_ twf.gif
This schematic shows the CV "+" inputs summing into the non-inverting input, pin 3, and the CV "-" input going into the inverting input, pin 2. If you look at the traces on the board this is reversed: The single "CV-" input goes to pin 3, the non-inverting input, and the summed "+" CV inputs go to the inverting input, pin 2, with the 2K2 resistor in the negative feedback loop between the output and pin 2.
So, correct me if I'm wrong, please, but I'm going to venture that this mod will not work as suggested then, right, because we can't throw another input onto the non-inverting input of the TL072, can we? If, as suggested, I add a wire, through a 200K resistor, to the intersection of the 100K input resistor for the CV- input and the 2K2 pull-down resistor, ultimately feed into into the non-inverting input summed along with the "CV-" input, this won't work, will it? Am I off? The way I've understood op-amps is to sum/mix multiple inputs into an op-amp this has to happen via input resistors which sum into the inverting input, with the non-inverting input tied to ground.
So, does this mean we either have to sacrifice the CV Invert switch or not have the spread functionality?
--- In ModularSynthPanels@ yahoogroups. com, "joshdaigleusa" <taviny@...> wrote:
>
> Thanks again!
>
> --- In ModularSynthPanels@ yahoogroups. com, Scott Deyo <contact@> wrote:
> >
> > Each through a resistor.
> >
> > Scott Deyo
> > contact@
> > The Bridechamber
> > www.bridechamber. com
> > Jealous Edison Record Kompany
> > www.jealousedison. com
> >
> >
> >
> >
> > On Feb 12, 2010, at 3:32 PM, joshdaigleusa wrote:
> >
> > > So should each of those 2 junctions go through a 200K resistor (in
> > > other words 2 resistors or 1 resistor with 2 wires connected to the
> > > other end)?
> > >
> > > Thanks!
> > >
> > > --- In ModularSynthPanels@ yahoogroups. com, Scott Deyo <contact@>
> > > wrote:
> > > >
> > > > Jack to left lug of pot
> > > > Middle lug via 200k resistor (haven't tested this yet, but should
> > > be a
> > > > good value) to two places:
> > > > CVSN of Filter B
> > > > Junction of Junction of 100k and 2k2 resistors that go to pin 2 of
> > > > Filter A CV inputs op-amp
> > > > Right lug to ground
> > > >
> > > > So, the effect should be, putting 5V in, with pot turned all the way
> > > > up, Filter A should go down around 2V5-worth of frequency, and
> > > Filter
> > > > B should go up an equal amount.
> > > >
> > > > Scott Deyo
> > > > contact@
> > > > The Bridechamber
> > > > www.bridechamber. com
> > > > Jealous Edison Record Kompany
> > > > www.jealousedison. com
> > > >
> > > >
> > > >
> > > >
> > > > On Feb 11, 2010, at 5:14 PM, joshdaigleusa wrote:
> > > >
> > > > > How is the spread CV on the bridechamber panel for the CGS CMOS
> > > VCF
> > > > > pansl wired up? I don't see anything on the CGS site and tried
> > > to do
> > > > > some searching here but couldn't turn up anything.
> > > > >
> > > > > Thanks!
> > > > >
> > > > >
> > > > >
> > > >
> > >
> > >
> > >
> >
>