Vactrol question

[petemoore]

I started to getting all interestin in the DOD DNV Filter 440...but the vactrol thingy...what is that? HWere can I get one? Is there anything around here that might have one in it?
  It sounds like an attachment for my 'EUreka' vaccumm cleaner!!!

[Rodgre]

Have you tried Steve at Small Bear?

I'm not sure where my vactrol bin got filled up, but over the years, I've bought stuff from various mail order places, most recently, someone posted a link here about cheap ones...

Roger

[Mark Hammer]

"Vactrols" are a registered product name like "Coke" or "Kleenex" which tends to become used as a generic item name even though it strictly only refers to one brand.

Vactrols are a category of optoisolator, incorporating an LED and a photocell in a sealed unit so that no light lands on the photocell other than what the LED produces.  Other types of optoisolators have LEDs and assorted phototransistor arrangements.  You can stick the photocell-type vactrols wherever you would stick a variable resistor or a resistor you would like to noiselessly or automatically control.  

Vactrols come in a variety of flavours.  Most package a single LED and photocell (LDR), but some pack an LED and two photocells with a common contact (think of it like a center-tapped LDR) or an LED and two independent photocells.  Multi-LDR units always have LDRs vary resistance in the same direction.  While we're talking about resistance, not all vactrols have the same range of on (light) or off (dark) resistance values, and even when they do not all will get to those values at the same rate.  For audio purposes, it is often (though not always) preferable to have a fast attack and a slow decay time.  The slow decay helps to reduce audible ripple when the LED is being driven by a source that isn't all that well filtered.  This is not unlike the difference between a sluggish tachometer and one that showed you *exactly* how many revs you were doing RIGHT THIS SECOND.  The sluggishness increases its usability.

Type Vactrol and pdf into google and you are sure to get links connecting you with relevant material.

[toneless]

You can connect two LDR's(side by side).So you'll have three legs and then you'll have to try some different leds(colors).
I'm planing on doing this when i'll make the DOD440 but i don't know if it works...

Nick Prionas