home-made vca

[gstopp at fibermux.com]

     Okay this is good feedback from all you guys about VCAs...
     
     I *have* seen the data sheet circuits, usually in the 
     matched-transistor sections like the LM394. I have more reading to do 
     - this is the direction I want. However if I pick a design that uses 
     something like a MAT-02 or such, I might as well try an SSM VCA as 
     well. I'd really like to avoid using dedicated chips.
     
     I still have this desire to make something out of parts that you can 
     buy at the local electronics store. I haven't seen any Gilbert 
     mulitpliers, or else I would have tried that already - maybe I need to 
     look a little harder. I should probably get out my NTE cross-reference 
     and do some reading... if matched transistor pairs like the LM394 are 
     in the NTE catalog then that may be something to investigate.
     
     How about the VCA from the Electronotes Preferred Circuits Collection 
     that uses a 3046 transistor array plus a couple of op-amps? The 
     original Dave Rossum design uses 741's, but what if a TL072 is used 
     instead? Is the 3046 quiet enough, or matched well enough, or whatever 
     is needed spec-wise? I know that the same 100K/220 divider scheme is 
     used as in the 3080 designs, so noise may be an issue.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: home-made vca
Author:  Martin Czech <martin.czech at itt-sc.de> at ccrelayout
Date:    2/19/97 5:51 AM
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I would rather recommend the SSM2018T (ok it is not discrete)
or the SSM2118T. Very clean, noiseless, not expensive, low feedthrough, 
exceptional wide gain range,  very low dc offset,
and the "T" version comes already laser
trimmed, so one might get rid of those trim pots as well.
I use them in my vca circuit and will also use them in my biquad vcf.
     
I combined this with a home made log circuit, 
so I have both linear and exp control.
     
If I was able to get them from the shelf here in Germany, it should be no 
problem in the rest 
of the world.
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