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[Dylan]

So I've build a few vactrols, and everytime I do it, there's an audible click with every flash of the light. Can anyone tell me how to get rid of this click? Would put a resistor in series with the LDR help reduce that?

[Dylan]

Well I found something in my searches, and so no one posted anything I thought I might as well bump this thread to do so. This is for the initial "on" of a guitar pedal, but since my vactrol is just an LED going on and off I think it may just work. So check this out if you're having the same problemo as me:

http://www.muzique.com/lab/led.htm

[Circuitbenders]

nice one. 

I've just edited the thread title to include LED clicking.

[Gordonjcp]

The popping is caused by two things - there's a DC offset in the signal through the LDR side of your vactrol, and the edges of your light pulse are nice and square.

In the circuits linked in the previous reply, the resistor and capacitor act to give the LED a bit of an envelope, which should help.  Fiddling with the resistors and capacitor ought to give you something you can adjust to minimise the popping.  A better approach would be to try to eliminate the DC offset through your controlled circuit.

There *is* a reason why vactrols are seriously uncommon.