[sdiy] Simple VCA?

[Aaron Lanterman]

On Apr 12, 2008, at 1:18 PM, Roy J. Tellason wrote:

> There's one circuit I ran across that I'm wondering about,  never  
> saw it
> actually used anywhere and I don't know how well this would work,   
> so I
> figured I'd toss it out for you guys to pick apart.
>
> It's a very simple circuit,  really.  An op amp inverting  
> amplifier,  one
> resistor going from the non-inverting input to ground,  one input  
> resistor,
> and one feedback resistor.  And,  a JFET connected between the two  
> input
> terminals with the gate lead labeled as being the gain input.


There's various variable gain amps with JFETs in the input circuitry  
of the Buchla timbre generators (see the Music Easel and 259  
schematics on Magnus's site). I never got around to fully figuring  
them out.

Also see http://users.ece.gatech.edu/~lanterma/sdiy/datasheets/transistors/AN-32.pdf

- Aaron