Cgs synth

I've built two of these VCO's and on both of them i had to lower the gain so
that the SAW would not hit the voltage rails. I changed the 330k resistor in
the feedback loop of the tl072. Change it to a lower value. It should not
take much like maybe a 250k or something. I can't remember exactly what i
used.
Josh

On 3/8/06, c10h14no2i <c10h14no2i@...> wrote:
>
> I did check both resistors.. I even replaced them with what you have
> specified in the schemo's.
>
> When I test using the AC output from the VCO, I get +5/-15 volts.
> When I test w/ the DC output from the VCO the bottom of the wave
> starts at about +10 volts, and goes up to where I guess its clipping.
> I dont understand why there is such a difference between the ac and dc
> outputs. (does that give you any clues?)
>
> Then I dont understand why the square output is centered on 0, when it
> is getting its input from the saw, which is messed up.
>
> Also, I tested the output of the ca3140, and its a perfect saw
> centered on 0
>
> That sure narrows down where the trouble could be coming form.
> BUT, I have gone through, checked every component around the tl072,
> and heated each solder point to make sure its good. Still have the
> same problem. I know the circuit works, so Ive got to be missing
> something... I just can't find it!
> Is it possible that something is wrong w/ the tl074? Can an IC kind
> of work, or are they just good or bad? (unfortunately I built this
> module before I learned the value of ic sockets)
>
> Thanks again.
>
>
> --- In cgs_synth@yahoogroups.com, sasami@... wrote:
> >
> > The 240k is the offset resistor. it sounds like the resistor you have in
> > there is too small, perhaps not a 270k at all.
> >
> > Ken
> >
> > >Sorry for the basic question, but which are the offset resistors? The
> > >ones around the tl072 that outputs to the saw out?
> > >
> > >If so, I should mention I am using a 270k instead of the 240k, and a
> > >560k instead of the 330k, which is what the elby instructions said to
> > >do. I think everything else is per the schematics.
> > >
> > >
> > >--- In cgs_synth@yahoogroups.com, sasami@ wrote:
> > >>
> > >> Usually caused by the signal hitting a power rail and running out of
> > >> anywhere to go. It's what i'd expect to find if an offset resistor
> > >was not
> > >> soldered in propperly (or the wrong value), or some other voltage
> > >> determining part. The name givven to this is "clipping".
> > >>
> > >> Ken
> > >>
> > >> >I got a working scope today, and the saw out of the VCO is very
> > >> >strange. Rather than /|/|/|/| it goes -\-\-\-\. That is the
> best I
> > >> >can do, but the 1st example should be a normal saw, and the 2nd
> > >> >example, whats going on is that it goes straight up, has a flat
> top,
> > >> >then slopes down. I tested my paia VCO and the shapes are fine,
> so Im
> > >> >sure Im using the scope correctly.
> > >> >Any idea what could be causing this?
> > >> >
> > >> >Thanks,
> > >> >Scott
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >The CGS Modular Synth home page: http://www.cgs.synth.net/
> > >> >
> > >> >Yahoo! Groups Links
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >
> > >>
> _______________________________________________________________________
> > >> Ken Stone sasami@ or sasami@
> > >> Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/<http://www.blaze.net.au/%7Esasami/synth/>
> >
> > >> Australian Miniature Horses & Ponies
> <http://www.blaze.net.au/~sasami/ <http://www.blaze.net.au/%7Esasami/>>
> > >>
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >The CGS Modular Synth home page: http://www.cgs.synth.net/
> > >
> > >Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > _______________________________________________________________________
> > Ken Stone sasami@... or sasami@...
> > Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/<http://www.blaze.net.au/%7Esasami/synth/>
> >
> > Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/<http://www.blaze.net.au/%7Esasami/>
> >
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