[sdiy] Vactrol control ideas wanted

[René Schmitz]

Hi Harry,


> I'm planning a vactrol based phaser module (yeah, I know...
> how original :^)

In my tube based phaser I've used three expo convertors of the ARP-Style
(PNP/NPN). Its a six stage design, and this allows me to offset two of
the vactrols with respect to the third one. By that I get a "notch
spreading" control (one expo receives the Spread-CV directly, the other
inverted. I found this to be easier than to experiment with different
caps, and the big plus is you can change the character with a front
panel control. (I didn't bother to bring out a CV, but that would be
straight forward.)

> 2) Control the Vactrols by running them all in series, with one
> Photocell fed
> back into the control circuit.  This is an adaptation of the National
> Semiconductor
> "Analog Multiplier" found in AN-20.  However, this version will not have
> one LED
> illuminating multiple photocells.
> 
> pro: (subject to matching) the photocell resistance can be accurately
> specified
> con: its more complex

con: you also loose the dynamic property of the vactrol.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159