[sdiy] what opamp for "warmth"? (I know, I know...)

brianw brianw at audiobanshee.com
Fri Apr 7 04:20:39 CEST 2023


How would you use a single-transistor VCA in a circuit?

Would you need to AC-couple the input, bias with DC of about half the positive supply, feed through the transistor VCA, and then AC-couple to the rest of the circuit?

I'm assuming most of the analog signals will be bipolar, but some synths are all positive voltages so a 1TX VCA would fit nicely (like the TR-808).

Brian

On Apr 6, 2023, at 12:31 AM, Roman Sowa <modular at go2.pl> wrote:
> That's a single transistor VCA and indeed it sounds amazing, although a bit noisy as there is a lot of gain involved. I used it in my simple VCO and it makes fat sound out of otherwise boring clean oscillator.
> Here's a short video showing waveshapes on a scope. The input to VCA was variable trapezoid to add even more fattness:
> https://youtu.be/algsxOo6lns
> And when you add 2nd transistor in reverse, that VCA becomes clean as baby butt wipes
> 
> Roman
> 
> W dniu 2023-04-05 o 20:32, David G Dixon via Synth-diy pisze:
>> Whatever the VCA is in the Korg MS-20 really warms up the sound of that synthesizer.  You can find the schematic on the internet.  I have something redrawn by a fellow named Marjan Urekar that I looked at years ago.  It involves two transistors.  It is evidently also the VCA used in the Roland JX-3P.



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