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
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
>