Topic: Ground Loops USB issues and cheap solution
I've got an ADI-2 DAC. I've really have a lot of USB stuff on my desk. Some USB 3 hard drives a 10 port USB 3 hub and a 10 port USB 2 hub connected to the USB 3 hub. Lot of gadgets I used to work includes some usb to serial 232 adapters. I also use a thunderbolt port with a display port adapter to drive an external display port monitor from DELL (exactly an old DELL 3011). I have also another external HDMI monitor.
All is driven by a DELL XPS 15 9560 using from the notebook one USB 3 port for the USB 3 hub, the thunderbolt port as described above and the hdmi port for the second monitor.
Well, when I connected the dac to the USB 3 HUB I suddenly notice some noise coming out from the speakers. My final is connected via the RCA outputs of the ADi 2- DAC. I've tried to switch the DAC connecting it either to the USB 2 HUB and directly to a free USb 3 port of my notebook. The noise still there. So i decided to pull out devices one by one leaving the DAC connected to the free USB 3 port on the notebook. After all comes the surprising thing that mutch of the noise is coming out from my DELL monitor connected trough the thunderbolt port (and the passive display port adapter). Just switching off the monitor for example is enough for much of the noise vanish. This was true even connecting the DAC to the USB 3 hub or the USB 2 hub. Anyway I further recognize some of the noise is also coming out from an USB 2 DVB-T adapter (expecially when the adapter is connected with the home service antenna) and some other from the USB hard drivers (expecially when they spin on from power saving).
I was reading all around trying to find a solution and I came up reading something about USB devices like this https://ifi-audio.com/products/idefender3-0/. Reading the specs of the devices says it will breaks USB ground loops simply disconnecting the +5V and GND out of out the USB. So as those devices still costs quite a lot and I was not sure if they really can solve all the issues. I read more on USB specification and I decided to work out a USB 2 cable on my own simply leaving the +Data and -Data connections alive (white and green) and cutting +5V and GND (red and black).
With not much surprise everything works like a charm and noise completely disappears even using a really cheaper USB 2 modified cable. I'0ve tried several USB port of my desk with all monitor hard disks and devices operating.
Don't know for sure if the above commercial USB ground loops devices will got the same result but I really guess so as they are not as cheap as an old USB 2 cable.
I also guess that creating ad-hoc usb cables with an external "super clean power supply" is also possible to completely isolate ground loops with some other USB powered type DAC.
Reading all around I found that those ground loops problems is very common. Not only, I've tried the DAC with another old PC and without any other special USB device connected I was able to hear some noises coming directly from the motherboard out of the speakers. In the case just disconnecting the USB from the DAC noise completely disappear.
In conclusion my question is: as ADI2-DAC / Pro (and maybe lot of some other DAC all around) is not USB powered, is there anything "terrific" connecting the DAC throught a cable without the GND and +5V rails coming out from the pc USB bus?
If there is, why the USB adapters above still claim to be safe just doing exactly the same thing?
If there isn't, why rme engineers still used to not isolate the USB port just throwing away the +5V and GND pins from the DAC USB port?
Best regards Massimo.