I'm NO expert, but the first things I'd try is to be sure your power
wires are all good. Test the voltage somewhere on the PCB where you
know it should be getting +15 and -15. Then I'd replace the tl071.
On mine, I had a few bad solder lands on the PCB. I built a bunch of
CGS modules, and the filter was the only pcb w/ any problems, but it
had 3 bad lands on it. I found the one causing the problem by taking
a patch cable that was going into my VCA. I had the VCA turned up.
Then I put a signal into the LP, BP, HP, inputs (not all at the same
time) and took the cable going to the VCA and touched a bunch of
points on the PCB. I finally found one where I got no sound, where
there should have been sound. Traced it to the nearest component, and
bingo.. there was the bad connection. I didn't go touching random
spots w/ the cable.. but I followed the path that the audio takes.
You probably dont want to connect +15 to your VCA :)
I have no training in electronics, so this testing method may be a
really bad idea.. I dono. However, it worked for me.
wires are all good. Test the voltage somewhere on the PCB where you
know it should be getting +15 and -15. Then I'd replace the tl071.
On mine, I had a few bad solder lands on the PCB. I built a bunch of
CGS modules, and the filter was the only pcb w/ any problems, but it
had 3 bad lands on it. I found the one causing the problem by taking
a patch cable that was going into my VCA. I had the VCA turned up.
Then I put a signal into the LP, BP, HP, inputs (not all at the same
time) and took the cable going to the VCA and touched a bunch of
points on the PCB. I finally found one where I got no sound, where
there should have been sound. Traced it to the nearest component, and
bingo.. there was the bad connection. I didn't go touching random
spots w/ the cable.. but I followed the path that the audio takes.
You probably dont want to connect +15 to your VCA :)
I have no training in electronics, so this testing method may be a
really bad idea.. I dono. However, it worked for me.
--- In cgs_synth@yahoogroups.com, "janczmok" <jan@...> wrote:
>
> Hi all,
>
> i finally was able to finish the Synthacon VCF but it's not working
> as expected.
>
> CV input does not react at any input feed.
> Lowpass and Highpass are only passing 5% of the original value
> Bandpass seem to work correctly.
> The Resonance does not work at all, neither the frequency.
>
> Did somebody has a clue what could be wrong ? Soldering seems fine.
> I did use 2N2222 normal transistors.
>
> any help appreciated.
>
> --jan
>