[sdiy] Vactrol tempco was: Vactrols subbed for dual-gang pot

[cheater cheater]

Dave,

> I'm pretty sure that the transfer (LED) or response (LDR) curves vary widely
> between different types/makes of LED *and* LDR making it hard to draw any
> general conclusions, so specific datasheets for the exact product(s) are
> needed I guess.....
> With the same LDRs mentioned in the original post, regular red LEDs
> performed the worst (in terms of response time and "off" resistance) with
> superbright white LEDs coming out best.
> Interestingly, different LEDs of the the same colour from different sources
> gave very widely varying results....
>
> All superbrights are not equal - my uncle ordered what were claimed to be
> superbright green 10mm LEDs from the net for a marine application,
> (navigation light)  but having seen them I then showed him a proper (small
> 3mm) one driven from only +5V, and the response was "get that f***ing thing
> out of my eye" !.... :-)
>
> Efficiency seems very varied, and I would bet the transfer curves vary
> tremendously between types.
>
> From what I've read/absorbed, the LED/LDR pair is not temperature stable -
> no problem in a noise maker, but may have some problems if tuning the cutoff
> FREQ of a filter to provide a specific frequency.
>

Hmm, good point. I wonder how you temp-compensate that :) could be an
interesting problem in creativity, imo. Definitely not your usual
worked-out-in-a-book example problem.

Cheers,
D.