Cgs synth

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