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.
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/>
> >> Australian Miniature Horses & Ponies
<http://www.blaze.net.au/~sasami/>
> >>
> >
> >
> >
> >
> >
> >
> >
> >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/>
> Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>