home-made vca

[Tony Clark]

>    Some other problems I was having, I couldn't get the voltage control 
> to affect the gain of the circuit whatsoever!  The input signal would 
> greatly affect the output depending on signal strength and DC level.  
> According to the paper, it was designed for O-3V RMS signals, but I 
> couldn't put in levels that large without causing major clipping in the 
> output (but then my output gain was 5 times larger anyway).  Smaller 
> input signals tended to cause the output to distort and do all manners of 
> crazy things.

   Okay, I discovered what my main problem was, I forgot the input 
decoupling capacitor!  Doh!  Now it seems to work fine...sort of.
   Gain is about 1.5 now at max CV (which is roughly 1V).  Phase shift is 
pretty decent at 10kHz and above, but is pretty bad on the low end.  
Frequency response is horrible.
   Now a couple of interesting things, my circuit won't pass a square 
wave to save its life.  It works very well for sine and triangle waves 
(there's slight rounding on the peaks), but a square wave produces a 
great surfable curve on the output peaks.  No doubt I must still be 
missing something from the MAT-04 papers.
   Anyway, this is a very noise free circuit.  I'll work on the other 
problem and report when I have some better results.

   Tony

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I can't drive (my Moog) 55!
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Tony Clark -- clark at andrews.edu 
http://www.andrews.edu/~clark
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