[sdiy] Re: [sdiy] Volume control with LDR´s ?

Steve Ridley spr at spridley.freeserve.co.uk
Wed Feb 19 21:30:29 CET 2003

> As I recall, they had a fixed lamp and LDR, and the fader moved a smoked
> glass or shutter between the two gradually cutting off the light to the
> sensor.  No scratchy contacts to worry about.

Commonly used in organ and synth volume pedals too - Hammond,
Yamaha, Siel and many others..  

If you're interested in LED/LDR combinations (or Vactrols) as VCAs, 
Vactec have some excellent application notes on this sort of thing.  For
example, they use a dual vactrol (one LED and two matched LDRs) 
and use one LDR for audio control and the other to linearise the 
control.  I don't have the URL here at the moment, but seartch on 
Vactec and you should find it.

If you want some real fun with LEDs and LDRs, look up the 
Russian ANS synth - that should impress you.
> Ask Steve Ridley, I'm sure he's met similar beasties.

Hmmp!  How old do you think I am (-:    

Old enough to have worked on old valve/tube mixers with constant 
impedance stud faders when they were still regarded as just old.  
Sadly, the Radiophonic Workshop "Glowpot" mixing desk had gone
before I worked there.


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