homebrew vactrols

[Paul R. Higgins]

This probably goes to show how obsessive-compulsive I am (I'm assuming that I'm 
in pretty good company here on Synth-DIY), but I usually glue a green LED to an 
LDR using a high-tech catalyzed super glue.  The glue is made by a company 
called Satellite City, and is available at any good woodworking store, and also 
from Stuart-Macdonald Guitar Shop Supply.  I swab a little of the catalyst on 
the LDR, and apply a small drop of glue to the LED (flat ones work best).  Then 
you just slap 'em together, and the glue hardens in about one second.  Then, 
just wrap the LED/LDR in heatshrink, heat it (carefully) with a lighter or 
whatever, and plug any remaining openings with a little black silicone sealant. 
The Satellite City adhesive is really great because it is water clear when it 
hardens, unlike most super glue which turns white.

I've also seen some pretty inventive homebrew Vactrols made by putting the 
LED/LDRs in a 35mm film canister hot-glued to the PC board.  This is especially 
useful for the quad LDR used in the Univibe, etc.  Another less elegant approach
I've seen is just to glue the LED and LDR together, mount them horizontally on a
PC board, and goop a bunch of black silicone sealant over the whole thing.

Most of the LDRs that I buy seem to have a broad peak in the same range as that 
of green LEDs.  I can't remember the wavelength, though--540 nm?  Whatever it 
is, I looked it up in an old chemistry text of mine, and the closest thing was a
green LED.  

-PRH

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Paul Higgins
email: higg0008 at tc.umn.edu
University College, University of Minnesota
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