Is the 200K to go from the input to ground and the 600K to be in the
feedback loop? Could I just be destroying the opamp?
I'm glad to know I've stumped someone besides myself...
Chub
feedback loop? Could I just be destroying the opamp?
I'm glad to know I've stumped someone besides myself...
Chub
--- In cgs_synth@yahoogroups.com, sasami@h... wrote:
> All I can say is you have me stumped! I've not heard anythng like
this
> before, and I've sold dozens of these.
>
> Ken
>
> >Now I'm getting someplace!
> >
> >I've got a perfect sawtooth up to the pin 2 of the saw output
> >opamp. 15 volts DC at pin 1. I disconnected the 330R resistor,
> >expecting to see zero vdc at pin 7. Measured about 10vdc
instead!
> >+15 vdc at pin 8 and -15vdc at pin 4.
> >
> >Also, If I plug into the shape CV input I can hear (and see) the
> >same signal somewhat "shaped" That means everything is doing
what
> >I'd expect *except* the TL072 (which has been replaced twice now
> >from different stock) for the saw and square ouput. I've put the
> >600K/200K ohm resistors (600K in the feedback/200K to ground from
> >the input) on the saw stage for +-5 volt swing.
> >
> >Everything seems okay in the traces. What am I doing wrong? Is
the
> >47mfd cap to be removed? Has anyone else built a rev 3 pcb?
> >
> >Ken?
> >
> >Gee, don't tell my employer about this!
> >
> >Chub
> >
> >--- In cgs_synth@yahoogroups.com, "charlesosthelder"
> ><osthelder@n...> wrote:
> >> Now this is wrong. Tested the second VCO (had the correct
TL0__
> >> device in place!) and get the same result as the first. VCO
core
> >is
> >> fine - actually works very well! The sawtooth from the core
> >> completely goes away at the pin 1 of the TL072 for the saw
> >output.
> >> I checked for a simple short to ground, but no such luck. Cap
> >> polarity is correct and the TL072 has correct voltage at pins 4
> >and
> >> 8.
> >>
> >> Another oddity - the sub input and output work as expected.
But
> >if
> >> I plug my square wave audio into the square wave out jack,
which
> >is
> >> connected to the sub input when no plug is in the sub in,
> >frequency
> >> is halved!
> >>
> >> This is really odd. How can such a simple stage as the saw and
> >> square output amplifier be causing me so much grief? Has
anyone
> >> else built the rev .3 pcb? When I get a chance, I'm going to
> >follow
> >> the traces. In the meantime, I'm going to try to calm down.
> >>
> >> Any ideas?
> >>
> >> Chub
> >
> >
> >
> >
> >
> >See the following URLS for the CGS Modular Synth home page:
> >Main: http://www.cgs.synth.net/
> >Secondary: http://otherunicorn.0catch.com/synth/
> >Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
>
_____________________________________________________________________
__
> Ken Stone sasami@h... or sasami@c...
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<http://www.blaze.net.au/~sasami/synth/>
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