Edson Brusque wrote:
>
> Hello Bob Blick,
>
> > If you get the data sheet for the National Semiconductor LM13600 there is
> > an application with a voltage controlled lowpass filter. It uses one half
> > of the chip, six resistors and one capacitor.
>
>     This chip is very interesting, althought National says it's obsolete.
> Can't find a substitute. :(


Hi, tone controls in audio equipment use a varable resistor
and fixed capacitor. There work pretty well as low pass
adjustable filters if the cap is to ground.

Someone here mentioned a bi-directional fet thingy that works
good as an adjustible resistor with audio, this would be ideal
and would give you voltage controlled low pass filter I think.
:o)
-Roman

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