[sdiy] Interesting VCA circuit on MAT04 schematic

[Grant Richter]

Looks like a variation on the classic multiplier.

Compare LM1496

http://www.mit.edu/~6.301/LM1496.pdf

On Apr 25, 2006, at 2:22 AM, Aaron Lanterman wrote:

>
> http://users.ece.gatech.edu/~lanterma/sdiy/datasheets/transistors/ 
> mat04.pdf
>
> Check out Figure 9.
>
> The MAT04 is used sort of like... wait, this is weird. It looks  
> like the "lower half of an OTA," as in the VCAs on Rene's site -  
> but everything is switched around. The control is going in what I  
> usually think of as the audio input; and the audio input goes in  
> what I think of as the control input, but not before it goes  
> into... oh wait, are those OP-41 and 2N2222's facilitating  
> logarithmic conversion to cancel out the expo?
>
> And there's a copy of that structure. Interesting!
>
> Is this some kind of souped up Blackmer cell? The datasheet says  
> it's "widely used in professional audio circles."
>
> - Aaron
>
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