# Yet another painfully simple VCA? (But where to connect CV?)

**URL:** <https://lookmumnocomputer.discourse.group/t/yet-another-painfully-simple-vca-but-where-to-connect-cv/3100>\
**Category:** DIY STUFF\
**Created:** [March 6, 2021, 5:09pm UTC](https://lookmumnocomputer.discourse.group/t/yet-another-painfully-simple-vca-but-where-to-connect-cv/3100 "2021-03-06T17:09:13Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![tobias](https://avatars.discourse-cdn.com/v4/letter/t/c67d28/32.png) [@tobias](https://lookmumnocomputer.discourse.group/u/tobias)\
**Post date:** [March 6, 2021, 5:09pm UTC](https://lookmumnocomputer.discourse.group/t/yet-another-painfully-simple-vca-but-where-to-connect-cv/3100/1 "2021-03-06T17:09:13Z")

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Hello, I was looking for a very simple VCA solution and I found this:

> [@LPG/VCA circuit](https://lookmumnocomputer.discourse.group/t/lpg-vca-circuit/69/2):
>
> Hey! I’m guessing you mean this one?

But then I found also this one:  
 ![grafik](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/0/0303e75ef850cf81fb8575e564811762356ad82c.png)  
(on this website: [electro-music.com :: View topic - Single transistor VCA circuit](https://electro-music.com/forum/topic-33190-25.html))

Minus the coupling capacitors, both seem to follow the same one transistor plus diode approach. And the second has biasing for the base, which seems a good idea anyway?  
What puzzles me though: The first feeds CV to the base, the second to the collector.  
From the little I know about transistors, base current controls collector-emitter current so the first approach sounds reasonable since here CV controls the signal. In the other one, the signal controls CV? Is there a reason for doing this?

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**Author:** ![fredrik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/fredrik/32/682_2.png) [@fredrik](https://lookmumnocomputer.discourse.group/u/fredrik)\
**Post date:** [March 6, 2021, 5:57pm UTC](https://lookmumnocomputer.discourse.group/t/yet-another-painfully-simple-vca-but-where-to-connect-cv/3100/2 "2021-03-06T17:57:59Z")

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This is a “swing type VCA” that effectively modulates the envelope (when positive) by the signal. But it’s taken from the internals of a drum machine (808?), which is a controlled environment where the signal levels are well-known, so not sure how generally useful this approach is…

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**Author:** ![tobias](https://avatars.discourse-cdn.com/v4/letter/t/c67d28/32.png) [@tobias](https://lookmumnocomputer.discourse.group/u/tobias)\
**Post date:** [March 8, 2021, 1:00pm UTC](https://lookmumnocomputer.discourse.group/t/yet-another-painfully-simple-vca-but-where-to-connect-cv/3100/3 "2021-03-08T13:00:06Z")

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Well I breadboarded both solutions. In this case, e.g. in lack of a real voltage controlled _amplifier_ I actually liked the second one, i.e. the “swing type”, because using it I can use a high CV to actually make the output signal louder than the oscillator on the input. It’s a very hacky approach, though, but a good thing to keep in mind, I guess.