[sdiy] Vactrol control ideas wanted

[harrybissell]

Hiya all...

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

I have a couple of ideas for controling the Vactrols.. like to have
any feedback. Maybe you've been there, done that...

1)  Control all the Vactrols with a series current (possibly including
the
LEDs in an opamp feedback.

pro: its easy
con: it probably does not cause the interesting part of the sweep to
occur
over a wide range

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

Your thoughts ladies and gentlemen ???

H^) harry