LDR for Voodoo Vibe

[Gingertube]

Guys,
I have collected schematics, parts etc for doing a DIY Voodoo Vibe.
I was going to just buy a selection of LDRs and see which best suited but thought I'd ask first.
Anyone know the part number of what was actually used.

I'm looking at Silonex NSL-19M51 but data sheet doesn't give response time.
Alternate - I'm looking at Perkin Elmer VT900 Series VT93N2 which has rise time of 35 ms and fall time of 5 ms.

Thanks,
Ian

[soundguruman]

They all do basically the same thing, regardless of rise time. It's kind of silly to search all over for a certain brand and model of LDR.
Mesa has just put a bunch in parallel, to lower the ON resistance. Shows that it's not really a precision device, more primitive than precision.

[Steve Conner]

LDRs don't all do the same thing, as you'll see if you look at the Perkin-Elmer datasheets. They come in resistance ranges. I've seen ones used for controlling contrast in a high-end CRT monitor, that had a dark resistance of something like 1k, and an operating resistance of something like 10 or 50 ohms. You wouldn't get much love out of those in an audio circuit that was expecting a dark resistance of 5M.

[Mark Hammer]

If one was using an LDR for somethng like a gate, a compressor, or even an envelope-controlled filter, where was fundamental to how the thing might sound, then I'd say looking for "the right one" was appropriate. For phasers, it doesn't matter nearly so much. Even at their fastest sweep speeds, they are not particularly demanding. As well, phasers and vibes tend not to care very much about matching of LDRs. As long as the resistance is changing along with the LFO output, you're in good shape. I suppose the one place where you might run into problems would be with an LDR whose fall time to max resistance was excessively slow. But there you're looking for something with, say, a 300-500msec fall time, such that the LDR remains "stcuk" at low resistance when the speed starts to get above 3hz or so.