Electronotes Summary?

[gstopp at fibermux.com]

     Juergen,
     
     I've never had a problem with these VCA's, however I've never tried to 
     remove one supply voltage and leave the other attached, so I can't 
     tell you that it won't blow up...
     
     Also thanks for the reviews of the other modules. The ringing envelope 
     sounds like something I may want in the future.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: RE: Re[2]: Electronotes Summary?
Author:  Haible_Juergen#Tel2743 <HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de>
at ccrelayout
Date:    1/26/96 11:00 AM


Thanks for the list, especially the comments from Your 
experience with different circuits !
     
A few things for me to add and to ask:
     
>     VCA-3      3080-based linear         Really simple, works fine
     
In ENs, there is this strange control current circuit for 3080's almost 
everywhere. I see the advantages (vs. the usual opamp + pnp circuit):
(1) slightly cheaper, with stress on "slightly", and (2) it avoids the 1/hfe 
error of the pnp circuit.
But what about security? In the usual circuit I can easily add a 15k 
resistor
between the pnp and pin 5 of the 3080. In the EN's circuit, the OTA is 
directly in the feedback loop of the opamp; so if something goes wrong with 
the input voltage, the opamp might start limiting currents as late as at 
20mA. And how does the circuit behave when one of the supply
voltages breaks down, and the other one is still there?
These thoughts have kept me from using it, so far. Didn't You have any 
problems with that?
     
     
>     VCF-5      Variable-slope            Never tried
     
I've built a combination of Variable slope and switchable all pass / 
lowpass stages filter. The Variable Slope part by itself gives some 
interesting nuances, but it's not earth shaking different from other 
ota filters.
     
>     EG-6       Ringing ASR               Never tried
     
Just finished mine (slightly different design). Very nice!
     
JH.