[LAU] Hum pickup in DI boxes

[Brandon Hale]

> 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.

Brandon Hale

On 6/8/21 3:39 PM, Fons Adriaensen wrote:
> On Tue, Jun 08, 2021 at 08:21:20AM -0400, Brandon Hale wrote:
>
>> Have you tried plugging in the laptop without the DI in between? I think
>> laptop outputs are balanced, low-impedance, so you shouldn't need the DI in
>> between. Even if this is not true, it's at least worth a shot.
> 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.
>
> Connecting laptops to a PA or recording system can be one of the most frustrating
> things you may come across as a sound engineer. In particular if the laptop's mains
> power supply is being used.
>
> You need a DI box designed for this task. Those made for guitar etc. usually
> won't do. Transformer isolation and a 'ground lift' switch are a must. This
> doesn't mean the DI-box has to be 'passive'. There are a few which have both
> transformer isolation AND phantom powered active amplification.
>
> The one I used when working at the  Casa della Musica in Parma was the Radial
> JPC <https://www.radialeng.com/product/jpc>. It worked perfectly, and I can
> really recommend it. Not the cheapest at around $200, but worth every penny.
>
> Ciao,
>