[sdiy] Fairchild H11F1

[jhaible]

> This looks like a really neat device for phasors and VC envelope
generators,
> or anything where you want to piggy-back to an existing circuit to make it
> controllable. I have a cabinet-mounted programmable Minimoog that has
> Vac-Tecs soldered across the envelope pots and filter emphasis, and this
> looks like it would provide a great way to do the same thing.

I think it's just a FET with optical input instead of a gate electrode.
So the voltage range for linear, resistive operation ("VCR") is very small -
just as with any FET. You can operate it at higher voltages, but then it's
not
(approximately) a VC resistor anymore, it's (approximately) a VC current
source then. So in a VC ADSR it would turn the exponential slopes
into something more or less linear. Not much different from an ordinary
opto coupler with BJT I would presume.
Vactrols are very different - real resistors even for high voltages.

JH.