[sdiy] PAIA 2720 VCA (was Circuit Boards / kits)

[Tom Wiltshire]

On 25 Sep 2008, at 14:44, Roy J. Tellason wrote:

> On Thursday 25 September 2008 08:33, harrybissell at wowway.com wrote:
>> On Wed, 24 Sep 2008 18:22:38 -0400, Roy J. Tellason wrote
>>
>>> So what do they use for a VCA?
>>
>> A differential pair, a transistor to sink current through the  
>> emitters,
>> and an opamp to revover the signal.  I added 1% resistors and it  
>> works
>> very well.  I think its a 741 (or 748)
>
> I have a vague recollection of seeing something of the sort  
> before.  I think I
> had a TI book that featured a circuit like that.  I haven't seen it  
> lately so
> I don't recall what particular amplifier it used or whether it used 1%
> resistors though.
>
>> schematics are online (somewhere)
>
> Hmm.

I think he means this:

http://www.synthdiy.com/files/2004/PAIA_2720-1_VCA.gif

T.