Quote Originally Posted by kkinnon View Post
Then how about powering all your recording gear, including the laptop, to the same power source. What you're trying to do here is avoid ground loops. It's not that hard.
No, not hard to put all the gear on the same socket strip but that only helps, does not fix the problem.

Reason being, every earth cable has an impedance, part resistive, part inductive. That impedance could easily add up to say 2 Ohms and if an earth current of 5mA was flowing that is 10mV of hum and possibly digital crap that the audio device is "sitting" on. 10mV is only 40dB or so below +4dBu so easily audible!

You could try bonding kit together with sturdy copper earth cables to lower the impedance but the best way is a quality transformer isolator.

Of course, the Old Studio Guys knew all this! That is why everything was balanced!