On Mon, Jul 20, 2015 at 7:00 PM, Neil Baldwin neil.a.Baldwin@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:Thanks KenWith +/- 12V voltage to the CV voltage divider part I'm seeing about -0.6 to +0.6 V at the CV pin which is correct.However, with no input signal to Input, turning up the gain pot eventually results in horrendous feedback-type output.NeilOn 19 July 2015 at 11:34, Ken Stone otherunicorn@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:4.7 instead of 5 pf can be ignored. 100n instead of 220n will cut your bass response.It is ESSENTIAL that there be a pulldown resistor on the CV input e.g.: a 100k to 5k6 voltage divider is needed between your CV and the gain cells CV input.On Sun, Jul 19, 2015 at 8:16 PM, neil.a.Baldwin@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:http://www.cgs.synth.net/modules/cgs108_vca.html
I've built a couple of these to add CV amps to an existing project but am having trouble getting them to behave. Some things to note:
- they're running off 15V so I'm wondering if there are some resistor changes required?
- I had to substitue a couple of capacitors as I didn't have exactly the right values and they didn't appear to be that critical based on my loose understanding of this circuit: the 5pF on the board I changed for a 4.7pF and the 220n required on the input when wiring up I substituted with a 100n
With a 5V peak sine wave input I'm getting horrible distortion. My latest idea was to install a 50K trimmer instead of the 100K fixed resistor on the CV input wiring to see if I could dial in a resistance value that would work better but that's no been particularly successful.
Neil
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Re: Gain Cell
2015-07-20 by Ken Stone
You probably need more decoupling on the power pins to the cells. These cells have huge gain.