tr606 Waterston BD pitch sweep

[WeAreAs1 at aol.com]

In a message dated 6/1/99 1:07:21 AM, you wrote:

<<Perhaps a vactrol (LED- light dependant resistor) would be the way to go.
Or 2 vactrols. Maybe with a voltage to current convertor before it if you
have room.>>

Somehow, I don't think a Vactrol would be fast enough for this application.  
Indeed, the main purpose for the Bass Drum pitch sweep is to more closely 
simulate the fast pitch envelope built into the TR-909 kick drum sound.  I 
don't think a Vactrol would respond fast enough to that kind of fast 
attack/quick decay envelope.

To impose the pitch sweep on the 909 kick drum, Roland used a transistor as a 
current-controlled resistor in the RC network, for what it's worth.  I don't 
remember if the 606 kick circuit is the same as the 909's, though.  I think 
the 606 was a simple resonant bandpass filter, if I recall correctly.  The 
909's was more complex, I think.   Still, probably worth looking at.

It sure would be great if there were Vactrols that had fast enough reponse 
for use in envelope circuits and for fast-attacking VCA's.  So much simpler 
to use than OTA's, and far fewer undesirable side-effects (distortion, noise, 
offsets).

Michael Bacich