[sdiy] Interesting VCA circuit on MAT04 schematic

[HOSHUYAMA]

Hello Aaron and List,

That structure is used in M5241L and its brothers, which are
said to be comparable to dbx VCAs.

http://www.datasheet.org.uk/pdf/m5241l-datasheet/m5241l-datasheet.html
http://www.datasheet.org.uk/pdf/m5207l-datasheet/m5207l-datasheet.html

These datasheets include good explanation on the internal circuits.

Sam Hoshuyama
Saitama, Japan

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
> 
> ----------------------------------------------------------------------------- 
> 
> 
> Dr. Aaron Lanterman, Asst. Prof.
> and Demetrius T. Paris Junior Prof.    Voice:  404-385-2548
> School of Electrical and Comp. Eng.    Fax:    404-894-8363
> Georgia Institute of Technology        E-mail: lanterma at ece.gatech.edu
> Mail Code 0250                         Web:    
> users.ece.gatech.edu/~lanterma
> Atlanta, GA 30332                      Office: Centergy 5212
> 
> 
>