Cgs synth

--- 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
>

> 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 :)

> a) I see the CV and FREQ IN at the "entry point" to the PCB, behind
> the 220K (nearby the CV input's) i just see _nothing_ at all, no wave
> or power behind
> the 220K ones. if i shorten the 220K it seems to "slightly" better
> working.
>
> Any more hints / ideas ?
>
> i'll replace the TL071 now..
>

> I was still able to see(hear) a very low signal after the input
> resistors. Then nothing after the one w/ the bad land.
>

> I was still able to see(hear) a very low signal after the input
> resistors. Then nothing after the one w/ the bad land.

>
>On 02.03.2006, at 03:25, c10h14no2i wrote:
>
>> I was still able to see(hear) a very low signal after the input
>> resistors. Then nothing after the one w/ the bad land.
>>
>
>Well. i changed the TL071CN - nothing changes.
>I resoldered everything. All values of the Resistors + Capacitors are
>o.k.
>no bad leads or anything other.
>
>I just don't see the 5V CV signal after the 220K... If i touch the
>1N2222 on the right end, i hear strong humming.
>
>If i don't see a signal on the other end: means short ? or anything
>else ?
>
>*sigh* seems i need to recheck EVERY thing again tomorrow ...
>
>--jan
>
>
>
>
>The CGS Modular Synth home page: http://www.cgs.synth.net/
>
>Yahoo! Groups Links
>
>
>
>
>
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>
>
>

--- In cgs_synth@yahoogroups.com, Jan-Ahrent Czmok <jan@...> wrote:
>
>
> On 02.03.2006, at 03:25, c10h14no2i wrote:
>
> > I was still able to see(hear) a very low signal after the input
> > resistors. Then nothing after the one w/ the bad land.
>
> addtion: i found one 10nF which should be 100nF and replaced and
> found one bad lead. But now it's completely silent :-(
>
> I'll get all parts again and resolder the whole PCB ...
>
> --jan
>

> Circuit may vary from current version, but this should help:
>
> http://www.cgs.synth.net/modules/pic/
> schem_cgs35_syntha_vcf_voltages.jpg
>
> There WILL NOT be 5 volts after that 220k because the transistors
> clamp it
> to 0V.
>
> Ken

> Circuit may vary from current version, but this should help:
>
> http://www.cgs.synth.net/modules/pic/
> schem_cgs35_syntha_vcf_voltages.jpg
>
> There WILL NOT be 5 volts after that 220k because the transistors
> clamp it
> to 0V.
>
> Ken
>