[sdiy] Interesting VCA circuit on MAT04 schematic

[Grant Richter]

Terry Michaels had a tri-sine converter using the LM1496 published in  
Electronotes.

He said it gave the best performance of circuits he tested.


On Apr 25, 2006, at 4:33 AM, jhaible at debitel.net wrote:

> No Blackmer derivate here.
>
> It's close to the MC1496 4-quadrant multiplier.
>
> The 1496 and similar structures have a linear input
> (the current sources ...), and a tanh input
> (the differential pairs). The MC1494 (and AFAIK,
> modern chips like the AD633, too), add linearising
> diodes to the nonlinear input. I think the wole thing
> is called Gilbert multiplier then.
>
> Now you can just leave the nonlinear input as it is,
> and take advantage of its nonlinearity.
> That's what the MAT-04 fig. 9 circuit does.
> Feed the signal into the linear input(s), and
> use the nonlinear input for expo gain control.
>
> Oh, and there's a difference to the 1496, too:
> The way the collectors of the "upper" transitors
> are connected, or not connected.
> Haven't analysed that part - may make the whole
> thing 2-quadrant.
>
> There have been VCA chips that use this principle:
> I remember some "3340" (*not* the CEM part; MC maybe.)
>
> BTW, I have used a 1496 in my first frequency shifter,
> also taking advantage of the nonlinear input.
> I feed the audio signal into the linear (lower)
> input, and the modulator into the nonlinear
> (upper) input. The latter makes a crude triangle
> to sine conversion, so I can use triangle waveforms
> for the modulator.
>
> JH.
>
>>
>> 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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>> and Demetrius T. Paris Junior Prof.    Voice:  404-385-2548
>> School of Electrical and Comp. Eng.    Fax:    404-894-8363
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>>
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