[LAU] Hum pickup in DI boxes

[Fons Adriaensen]

On Sun, Jun 13, 2021 at 06:00:59AM +0100, Bill Purvis wrote:

> I bought a Behringer ULTRA_DI DI20 active DI box and that seems to work well.
> Only thing is the Ground Lift switch seems the wrong way round to me. In the
> 'lift' position I get hum when feeding from the laptop with mains power, but
> in the ground position the hum disappears. No hum either way on battery
> power.

That's to be expected when you don't have transformer isolation. It also means
you've been lucky this time, things may not work out so well with another 
laptop or in other conditions (e.g. laptop on stage on a different mains
circuit and light dimmers all around).

Ciao,

-- 
FA