[LAU] Hum pickup in DI boxes

[Brandon Hale]

I'll definitely remember this, thank you Fons!

Brandon Hale

On 6/8/21 4:09 PM, Fons Adriaensen wrote:
> On Tue, Jun 08, 2021 at 03:54:31PM -0400, Brandon Hale wrote:
>
>>> Don't do this - ever. You could easily destroy your mic input(s) if the laptop
>>> power supply isn't as isolated as it should be (quite common), or the laptop's
>>> headphone output if there is phantom power on the mic input.
>> That was my bad in assuming he's not using the microphone inputs, but the
>> Behringer's aux inputs that have quarter inch jacks.
> Wouldn't make much difference. If the laptop is mains powered and happens
> not to be grounded you could easily have a hundred volts on the laptop's
> 'ground'. High impedance, almost 'static' and hence not lethal to humans,
> but more than enough to kill an audio input. Watched it happen more than
> once, the more spectacular case was when a certain university professor
> deciced to cut of the ground connection of his laptop's power supply in
> order to get rid of the hum. He didn't do that again.
>
> Anyway, without transformer isolation and separate grounds you will never
> get rid of the broadband interference generated by both the laptop itself
> and its switching power supply.
>