Cgs synth

I had no trouble with the VCO section, but I built it like my CGS VCO,
which uses a different selection of resistors in the control section.
My modification to the clock driver consists of replacing the 100n
capacitor on the output of the CA3140 with a link. I've added a comment
to my Bi-N-Tic page.

http://pugix.com/synth/cgs-bi-n-tic-filter/

Richard Brewster

djbrow54 wrote:

> My VCO didn't run correctly the first time either. With a scope I
> could see that the ramp output of the VCO (pin 6 of the CA3140) was
> very low amplitude. I replaced the MPF102 with a different FET and
> it worked fine. I have no idea why the original FET didn't work.
>
> The clock mod is for very low frequency response. The clock is
> capacitive coupled and there just isn't enough voltage swing to
> trigger the clock input of the 4024 at VERY low frequencies. I DC
> coupled mine so it wouldn't be an issue.
>
> Richard Brewster later posted something with the PCB trace not
> matching the schematic in this area. I don't know if he had an early
> PCB or what the issue was. Search for message 2164. This only
> affects the output of the 4024, not the VCO output.
>
> Check the VCO output on pin 6 of the CA3140. You can just connect
> this to an amplifier through a suitable capacitor to remove the DC
> bias. This needs to be working correctly before verifying the 4024.
> If it was like mine and only had 1V pk-pk - then the low frequency
> range is quite limited. It also could be an issue with the LM311
> voltage comparator.
>
> Dave
>
> --- In cgs_synth@yahoogroups.com, Tom Adam <tom.adam@...> wrote:
>
>> I'm about to build my bi-n-tic and I came across this link.
>> Check the clock driver mod. Is this what you're seeing?
>>
>> http://modularsynthesis.com/cgs/bi-n-tic/bi-n-tic.htm
>>
>> Cheers,
>> ToAd
>>
>>