I tried substituting a 22K for the 100k going from pin 1 of the input summing TL072 to the base of the matched transistor pair (with 220 ohm resistor to ground). That did boost the gain into the ballpark, but had the negative effect of driving the match pair into non-linearity, distorting the signal.
Another option would be to increase the two 130K resistors on the output buffer. But I'm not sure what value to use to multiply the gain by 4 times. This buffer is doing a current-to-voltage conversion. I suppose if E IN = 1V and I want E OUT to be 1V, and now E OUT is 0.2V, since E = IR, all we need is a resistor 4 * 130K = 520. If I use a 560K, the gain would be 560/130, or 4.3. No 4.3 * 0.2 = 0.86, which is getting close. If I used 620K the result would be 0.95 gain.
What do you think? Should I swap the 130K resistors? I don't see any downside, except possibly increasing noise.
Thanks,
Richard Brewster
On 7/4/15 8:09 AM, Richard Brewster pugix@... [cgs_synth] wrote:
Then I will just have to find out and report back.
Thanks,
RIchard Brewster
On 7/3/15 11:27 PM, Ken Stone otherunicorn@... [cgs_synth] wrote:
I really don't know! I've never measured it. Nothing on it on Rene's site either.
On Sat, Jul 4, 2015 at 5:16 AM, Richard Brewster pugix@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:
Hello,
I'm building a pair of CGS64 VCAs and I need to know what the unity gain
CV level is, probably +5V, but I didn't see this in the docs. Reason to
ask is that I am using the optional initial gain pot, which is shown
hooking to a 100K resistor. If that pot goes zero to +15V, I probably
want a 270K or 300K there. The other CV input will be non-attenuated,
so I'm assuming that +5V to 100K will result in unity gain.
Ken?
Thanks,
Richard Brewster
http://pugix.com
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