Heh. Seems I’m REALLY late to this party. But instead of opening another similar thread, maybe I write here.
I have a mini PC (Shuttle XH410G) and a Motu M4 USB audio interface. The computer has a laptop-style PSU, so as expected there’s enormous noise in the outputs when connected to a PA in a rehearsal room or on stage.
I managed to control this with an isolator box from Behringer (HD400 - https://www.behringer.com/product.html?modelCode=P0387) which is okay for the time being, maybe I will upgrade this to a higher quality transformer gadget.
What I noticed is that there seems to be some MIDI voodoo going on, probably because of the ground loop I eliminated with the HD400 at the output but not on the rest of my electrical system. Flickering MIDI activity notifiations in GP, some notes not played. I connect the midi controller keyboard to the Shuttle PC by USB cable.
Few days ago I rehearsed with my “small luggage” wchich consists of a late 2013 Retina MacBook pro - same interface, same controller keyboard. I had the same problem as with the Shuttle, MIDI haunting included. Sadly i did not check how it is with the PSU unplugged and running on battery. Will do that soon.
After some reading in the world wide web I now have the suspicion that the typical European “protective ground power plug” could be the problem. Disconnecting the ground wire is generally frowned upon (and pretty much a No-Go insurance-wise here in Austria), so I ordered a PSU for the Shuttle (19,5 V, 4,74 A, 90 W) that has the standard 2-prong plug like reading lamps and so on, you know what I mean.
Since this PSU will take about 2 weeks to arrive at my door step, I ask: Do you think this could be the solution?
There’s also USB isolators - but für USB 3 high speed interfaces something like that will set me back some 600, 700 Euros. Likewise a UPS - similar price if I calculate the worst case: 3 hours @ 90 Watts.