AW: RE: PCB FOR MAT-0

[gstopp at fibermux.com]

     My suspicion about the waveform "folding" is that one of the NPN's is 
     saturating and the op-amps are fine... 
     
     The 3080 VCA I mentioned is from EN#63, an adaptation of a Walter Jung 
     design trick (the author of "The Op-Amp Cookbook"). Actually the 3080 
     has been around longer than the 13600/13700 and I'm embarrased to say 
     that I've never even tried the newer parts (for shame, I know). 3080's 
     are easy for me because I get tubes of samples :)
     
     Anyway this VCA is real easy - one dual op-amp, one 3080, 4 resistors, 
     2 diodes, in the minimum configuration.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: AW: RE: PCB FOR MAT-0
Author:  brad.sanders at circellar.com at ccrelayout
Date:    2/25/97 6:08 PM
     .
     .
     .
This sounds very much like a case of opamp nasties. With many opamps, if 
you exceed the common mode input voltage AND input current capabilities, 
you'll get this waveform "folding." Perhaps a better opamp? If you're 
using FET input opamps here, I'd be willing to bet that's the problem...
     .
     .
     .
Now, what's this about the electronotes gizmo? How would you rank the 
3080 based vca against more attainable devices, like the LM13700? 
I'm still just getting all this together, and I'd like to think I'm 
doing it right the first time... Of course, one usually never does - but 
I'd like to *think* so.