[sdiy] Simple VCA schematic, anyone?

[René Schmitz]

Hi Andre and all,

Andre Majorel wrote:
> Thanks. In the unlikely event someone wanted to build this as a
> stand-alone audio VCA, would this be the correct circuit ?
> 
>                _
>              +  | -
>        IN o----||----+--------       -----------o  OUT
>                _|    |        \     ^
>                      <         \   /
>              33 µ    > 330 R   =====   Any small
>                      <           |    signal NPN ?
>                      |           |
>                      = 470 p     |
>                      |           |
>    VC     o---^v^v---+-----------
>  (0~15 V)      1 M
> 
> Are the 470 pF cap and 330 ohm resistor part of the VCA ?
> 
> Would a BC550 do for the transistor ?
> 

You have to run the emitter into a virtual GND of an opamp, possibly via 
a DC blocking cap. Btw, this circuit has been used almost ubiquitously 
in the Rolands and Korgs analog Drummachines.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159