Homebrew Vactrols

[René Schmitz]

Hi all!

Thanks to all that responded!

I continued my experiments, and found that with the LDRs that I have
a red-orange high efficiency LED worked best. For a start I epoxy glued the
LDR 
on a 5mm LED and encapsuled the arrangement with heat shrinking tube. 
This keeps most of the stray light away. 

I measured the two units I made. I've driven the LEDs with the same
current, by connecting them in series. I only compared the resistances of
the two LDRs. 
(Couldn't get a reading on the current instrument, it was too dark! :) 
I found that they are not exactly related by a constant factor. At the high
end of 
the resistance, I had R1=1.7*R2 which turned into R1=1.2*R2 at the lower end.
I think I will have to make more of these arrangements to find a better
matched pair.

However, I think I should try a filter with these anyway. 
(I've never matched 3080s, too.)
I want to adjust the caps so that the RC constants are equal at the 
high-frequency end. Then as the cutoff goes down, Q will degrade. 
(Like with the highpass in the minimoog filter.) 
Or try it the other way arround, whatever sounds better.

Bye,
 René









transconductance | uzs159 at uni-bonn.de
isfutilepreparet | http://www.uni-bonn.de/~uzs159
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