[sdiy] Will LCD backlight PWM cause audio noise?

[Neil Johnson]

Richie Burnett wrote:
> Another trick which I have found highly effective is to feed your LED
> (or series/parallel LED backlight, load etc.) from the supply via a
> constant current source, then shunt the current via a transistor around
> the LED(s) when you want them to be off.

This is pretty standard in medium-to-high end mixing consoles.  Check 
the schematics for DDA, Soundcraft, Allen & Heath, etc, and you'll see a 
chain of LEDs with transistors or switches across them.  Especially, as 
you say, in the VU meters.

Neil
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