[sdiy] single transistor VCA (was OTA VCA)

Elain Klopke functionofform at gmail.com
Thu Mar 23 16:14:34 CET 2017


Ah, yes, it does appear to be backwards. That didn't help in my case,
sadly. Also, the one in the link you posted appears to be a PNP as opposed
to the NPN that I'm using. Does that make a difference?

As for the op amp buffer, I physically do not own any op amps at the moment.

On Thu, Mar 23, 2017 at 9:52 AM, Mattias Rickardsson <mr at analogue.org>
wrote:

> Hi,
>
> isn't the transistor placed in the wrong direction?
> http://electro-music.com/forum/phpbb-files/ms20vca_156_961.jpg
>
> And... what do you mean you went without the OP-amp buffer? :-)
>
> /mr
>
>
> On 23 March 2017 at 15:43, Elain Klopke <functionofform at gmail.com> wrote:
> > Hey all....
> >
> > So I breadboarded this up:
> > http://gaje.jp/blog/wp-content/uploads/2011/12/ms_type_vca.png
> >
> > I used a 2N3904 and didn't have an op amp buffer so went without it. the
> CV
> > input was provided by the two diode, two resistor and a cap AD generator.
> >
> > And no sound.
> >
> > Now with the labeling of 2.5V I'm guessing that the circuit is being run
> off
> > of a 0-5V power supply and the 2.5V is acting as a virtual ground. Since
> I
> > don't have the op amp in my circuit, I just went with connecting those
> 2.5V
> > bits to ground.
> >
> > I'm going to be putting together a bipolar power supply this weekend, so
> > I'll give it another go then.
> >
> > Also, my 2N3904 could be fried. The bag of them has taken a spill a
> couple
> > times and I've had to scoop them up by hand and put them back....
> >
> > Tips, tricks, and scathing criticisms welcome as always
> >
> > _______________________________________________
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> > Synth-diy at synth-diy.org
> > http://synth-diy.org/mailman/listinfo/synth-diy
> >
>
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