[sdiy] Vactrols == Optocouplers?

[Scott Gravenhorst]

And Vactrols also have a built in time delay.  Besides being more nonlinear
than a Vactrol, a phototransitor/LED optoisolator is much faster.  The
built in time delay is actually used as a feature in some devices that
employ Vactrols.  Note that the delay for attack and for delay is different.

Someone here has experimented with using an LDR with a combination of LED
and lightbulb to speed up a vactrol type device, though I don't know who it
is or what the results were.  Perhaps they'll see this and post.

I have played with optoisolators made with a FET and LED (H11F1).  These
devices are fast, but nonlinear.  The nonliearity can be reduced by
limiting the drain-source voltage to less than 100 millivolts which is a
problem in many circuits.  I still want to try to make a VCF with these.

"Colin f" <colin at colinfraser.com> wrote:
>> Oki, then optoisolator == vactrol?
>
>Nope. Vactrols have a light dependent resistor.
>Opto-isolators have a phototransistor.
>It's much easier to swap a fixed resistor for an LDR to make a circuit
>voltage controlled than it would be to adapt it to use the phototransistor
>in an opto-isolator. It would be easier to adapt the circuit to use an OTA
>configured as VCR if you cant find a vactrol.
>
>Cheers,
>Colin f
>
>
>
>
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