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

[harrybissell]

The linearization scheme you're describing is in the National Semiconductor
Linear Apps databook (prlly online as well) as AN-20 "Analog Multiplier"

H^) harry

Steve Ridley wrote:

> > 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.
>
> Steve