How much voltage does it take to fry a vactrol?

[vin]

I've been trying to build a DOD440 then a McMeat with very little success. The DOD seems perfect- voltages all reading as they should, but the pedal does ...... wait for it...... NOTHING! 

So I bread boarded the circuit using an LED in place of the Vactrol diode section and it went up in smoke really quickly. I'm betting that even though my circuit might be correct - I may have, at some point, fried the brains out of my beloved VCL54/2 (and dammit I can't find my spare!!!!)

So does anyone know how easy it is to kill one of these things? They're really hard to get in Australia, and I think I just killed the last one in the southern hemisphere. Perhaps I best stick to less exotic circuitry until I'm a little more experienced.

[soulsonic]

The LED in the Vactrol will burn out just as easily as a regular LED if you give it too much voltage. If you the circuit on the breadboard burned-out an LED, then there's probably something wrong with the circuit you used and it killed the vactrol too. I'm not familiar with that circuit, so I can't help you other than to say that the vactrol is probably dead.

[vin]

R.I.P
yeah thanks.
Do you know how much is too much for an LED / Vactrol?

[soulsonic]

I can't say for sure because it depends on the specs of that individual one. The datasheet should have the voltage specification listed. Most LEDs want maybe 2v max.

[oskar]

Judging from the drawing from ggg
http://www.generalguitargadgets.com/pdf/ggg_ef440_sc.pdf
the maximum current over the LED would be somewhere around 3.5mA ( ~7V, 2k2 resistor ).
Well within all safetylimits. I think it should withstand at least 20mA continuous current!

[oskar]

might be correct - I may have, at some point, fried the brains out of my beloved VCL54/2 (and dammit I can't find my spare!!!!)

This one?
http://optoelectronics.perkinelmer.com/content/DataSheets/DTS_vtl5c42.pdf
It can take 40mA... quite alot! Anyway it needs a resistance to set the maximum current.
And here in Stockholm they don't grow on trees either...     

[R.G.]

Could you possibly have the LED in circuit backwards so the LED does not light ? Test the Vactrol itself with a 9V battery and a 4.7K resistor in series and swap the polarity both ways. Watch the resistance on the LDR side for a change from around 1M to much lower. If the LDR does not go low resistance one way or the other, it's dead all right. Repeat your tests to be sure before chucking it.

[Paul Perry (Frostwave)]

Don't throw it away even if it IS burnt out.
Because, with care, you can replace the diode.
No, I havn't done that myself - but I did get myself out of a hole by salvaging the LDR, which just happened to be EXACTLY what was needed for an optical wah I was fixing!

I would try just keep cutting off thin slices of the diode end, until the diode came out, the put a new diode in place & put it all back together with some kind of filler.

[vin]

Yeah I'll do a few tests on it then enter mad scientist mode.  I wanna know what makes em tick.

[Mark Hammer]

That circuit really ought to have a 1k8 fixed resistor in series with a 5k trimpot to replace R6 (2K2) so that one can successfully adjust the current drive to suit the light source being used.