[sdiy] Simple VCA?

[ASSI]

On Samstag 03 Mai 2008, Roy J. Tellason wrote:
> This circuit,  assuming that the -IN/2 input was grounded,  would be
> pretty much the one I was referring to when I started this thread. 
> :-)

Sure, the ASCII art is even clobbered (w/ slight modifications) from 
Scott's post.  The analysis of how it should work is different.  My 
first idea about that was wrong, which I realized when I saw the 
circuit.

> Still looks pretty simple to me.  What "proper choice of op amp" do
> you refer to here?  What needs to be optimized for that choice?

Low input current, low input current drift and low input current offset.  
But I don't think that two resistors would kill anybody and they remove 
this particular concern.


Achim.
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