[sdiy] LDR decay time (was "2SA798 data")

harrybissell harrybissell at prodigy.net
Thu Apr 29 04:21:15 CEST 2004

Watch those data sheets....

the decay time is specified to some nominal resistance... usually 100K.
You will
probably find that gives a very OPTIMISTIC impression of the actual
time... which
is probably 5-10 times longer than that.

Don't use vactrols if you don't want / can't stand a slow decay time.
Or use them in
shunt mode where you turn them ON to attenuate.

Makes nice phasers, though. I suggest maybe a DIY-buy of these from
Clairex.  Who might
be interested ???  (min order is like $500 which would buy about 1,400
pieces - that is a little
out of my lifetime buy plans. I suppose I could try living longer :^)

H^) harry

mark verbos wrote:

> one of the models of theirs is very fast, but they also make slower
> ones. I think the fast silonex model (NSL-32SR3) is just as
> fast(1millisecond rise and 2.5 millisecond fall), but Hamamatsu
> conveniently leaves out specs on their "data sheet". The silonex ones
> are much easier to get, BTW.
> Mark
> Paul Higgins wrote:
>> Isn't there a Japanese brand of LDRs, Hamamatsu (sp?), that has a
>> faster response than most?  But I imagine the decay time is still
>> proportionally as long with respect to the attack time.  I remember
>> some people had mentioned the Japanese brand as being so fast that
>> they were more like VCAs when used in compressors, Mutron III
>> clones, etc., and not suitable when you want the "soft"
>> switching/turn-on characteristics of LDRs (e.g. the way that
>> Mesa/Boogie uses literally dozens of Vactrols in their amps--my Quad
>> Preamp has 32!).
>> -PRH
>> On Wednesday, April 28, 2004, at 05:55 AM, Harry Bissell Jr wrote:
>> > Arrgh you can say that again...
>> >
>> > in fact you could say that ALL photoconductive
>> > cells turn on faster than they turn off...
>> >
>> > (and in general, the higher the resistance range
>> > the longer the turn off time)
>> >
>> > This is due to the fact that you can bombard the
>> > cells with as many photons as you like (limited by
>> > vaporizing the cell :^) ... but you cannot remove
>> > any energy...
>> >
>> > unless you have a flashDARK...
>> >
>> > H^) harry
>> Paul Higgins
>> email: higg0008 at tc.umn.edu

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