[sdiy] Interesting VCA circuit on MAT04 schematic

[JH.]

> Terry Michaels had a tri-sine converter using the LM1496 published in  
> Electronotes.
> 
> He said it gave the best performance of circuits he tested.


Yes, (without checking, just from memory) I think he used
the "linear" (lower) inputs, where you can optimise a single-stage
differential pair sine converter's performance by choosing the
right emitter degeneration resistor.

I think this EN article is exactly where I got my idea for the 
single chip modulator/sine shaper.

And I have to correct my last post:
Like Terry, I used the *lower* transistors for the modulator,
not the upper transistors.
http://www.oldcrows.net/%7Ejhaible/tonline_stuff/hjfs3_mo.gif
(Which, of course, means that it's not related to the MAT-04
circuit Aaron brought up. Sorry.)

JH.



> 
> 
> 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
> >>
> >> --------------------------------------------------------------------- 
> >> --------
> >>
> >> 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
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> >>
> >>
> >>
> >
> >
> >
> >
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>