[sdiy] Simple VCA schematic, anyone?

[David Moylan]

If you're going into a virtual ground node can you parallel these for
simple VC mixing?

Dave

René Schmitz wrote:
> 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
>