Classic VCA troubleshooting

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ekoch
Learning to Wiggle
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Classic VCA troubleshooting

Post by ekoch » Tue Nov 29, 2016 9:13 am

I recently completed the Oakley 3u Classic VCA. I'm having an issue with the EXP cv. With the AC input pot turned all the way up, gain pot turned all the way down, I only get an audible signal from the VCA when EXP pot is at about 3 o'clock. This is versus the LIN pot where I get an audible signal almost immediately as I turn the pot clockwise. I've check the resistor values..nothing amiss there. I'm wondering if the issue is with the exponential converter at Q1 and Q3. Is there a significant difference between using BC560b and BC560c for Q1?

ekoch
Learning to Wiggle
Posts: 37
Joined: Fri Apr 29, 2016 10:20 am
Location: NYC

Post by ekoch » Tue Nov 29, 2016 9:14 am

Also I've adjusted the EXP trimpot all the way

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Synthbuilder
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Post by Synthbuilder » Tue Nov 29, 2016 9:51 am

I think your module may be working as intended. The EXP input appears to do very little until the input CV is quite large. Then it appears to rapidly increase right at the end. That's the nature of the exponential function.

If you turn up the gain on your monitoring system you should be able to hear the audio start to creep in as the EXP CV input is raised. It will be very very quiet at first, close the noise floor, but it should be there. If you are monitoring on a DAW you'll see your signal level meters start to register before you can probably hear it.

I find EXP CV inputs useful when controlling frequency modulation depths because you can control quite accurately at very low levels. I almost never use them for controlling audio at the end of the signal chain.

Tony

ekoch
Learning to Wiggle
Posts: 37
Joined: Fri Apr 29, 2016 10:20 am
Location: NYC

Post by ekoch » Tue Nov 29, 2016 10:07 am

That's really enlightening. Thanks so much, Tony. The VCA sounds beautiful!!

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