Topic: Ground Loops USB issues and cheap solution

Hi All,
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.

2

Re: Ground Loops USB issues and cheap solution

You not pass EMI tests anymore. It's not only about internal GND, but also shield. Commercial units therefore need to connect everything as suggested by the standard.

Connecting only the data lines has the potential to fry the USB chip port with unexpected static or spike electricity, either when switching units on/off or by disconnecting/connecting.

A proper solution is the Intona USB isolator:

https://pro.intona.eu/en/products/7054

As you spend so much time to research your ground loops you might have overlooked the most relevant one - between ADI and amplifier. If that amplifier can be run without ground all problems might be gone already.

Regards
Matthias Carstens
RME

3 (edited by massimo.mattia.info 2019-05-05 13:34:08)

Re: Ground Loops USB issues and cheap solution

Connecting only the data lines has the potential to fry the USB chip port with unexpected static or spike electricity, either when switching units on/off or by disconnecting/connecting.

So the ifi idefender3 is not safe?

As you spend so much time to research your ground loops you might have overlooked the most relevant one - between ADI and amplifier. If that amplifier can be run without ground all problems might be gone already.

Don't quite agree to run any amplifier without properly grounding it. Anyway this is especially true for a tube amp.

4

Re: Ground Loops USB issues and cheap solution

And I did not suggest that you remove ground when it is required. Especially with a tube amp. But that limits the possible solutions a bit. Did you ever check the ADI's phones output for noise? I expect it to be clean, with the basic problem being the grounded tube amp.

Regards
Matthias Carstens
RME

5 (edited by massimo.mattia.info 2019-05-05 15:31:05)

Re: Ground Loops USB issues and cheap solution

Thanks for your reply.

Yes head phones outputs still clear. I've tried with another amplifier, problem still there and not confined to the particular amplifier.  As I said simply switching off the DELL display port connected monitor (it's not necessary to pull off the thunderbolt/display port cable cable) by the apposite monitor button much of the audible noise disappears. Still have minor audible notebook CPU/GPU HDD noise coming out.

I've tried also to connect the dac, and amplifiers to different wall power socket with no success. Noise still there.

I've also investigated some other usb solutions. One cheaper solution over intona galvanic isolator (or ifi nano iGalvanic3), but expensive off the ifi idefender3, is this USB 3 optical cable reviewed here: http://archimago.blogspot.com/2015/05/m … tical.html

There are also other USB 3 optical solutions but the above is quite affordable since it is fully USB 2 (480mbits) compatible without any other support dongle. Some other solutions infact will require additional dongles for USB 2 compatibility connected at female end point.

Apparently this cable is still a hybrid solution. Not reallyt sure but the power rail is not cut along the entire cable length but seems still used only to power the female endpoint optical transceiver chip on the opposite side. That is enough for the reviewer to break his ground loop issues. More over that cable should have some how an "over current protection" built in (over USB 3/2 data rails on the female connector ???) as claimed in specifications sheet downloadable at the Corning home site.

But at this point my concerns is still there about the ifi idefender3 simple ground cutting the +5V and GND rail safeness (and obviously my home made usb cable solution!).ùBy the way the idefender 3 solution could be as cheaper as reliable. Having another 10meters cable upon the desk with the dac at only 0.5 meters by notebook still hurt my eyes as much as the noise is hurting my ears. But I still not want IFI to joke me and give them 60 euros to have the same result with an old inexpensive USB 2 modded cable by myself.

Re: Ground Loops USB issues and cheap solution

MC wrote:

Connecting only the data lines has the potential to fry the USB chip port with unexpected static or spike electricity, either when switching units on/off or by disconnecting/connecting.

A proper solution is the Intona USB isolator:

Any idea if the sBooster vBus2 would be "dangerous" in this way or not?

https://www.sbooster.com/sbooster-tweak … -isolator/

Re: Ground Loops USB issues and cheap solution

I could hear my CPU working on speakers, grounding was that bad. Even with RME unplugged from the power, some noise was leaking from PC. 
iFi iDefender 3 fixed that, speakers are now dead quiet when not playing anything. I almost returned RME (other DACs i had didn't have this problem!) smile

~~ sound sommelier ~~

Re: Ground Loops USB issues and cheap solution

hhrvoje wrote:

I could hear my CPU working on speakers, grounding was that bad. Even with RME unplugged from the power, some noise was leaking from PC. 
iFi iDefender 3 fixed that, speakers are now dead quiet when not playing anything. I almost returned RME (other DACs i had didn't have this problem!) smile

I had the same issue with my Multiface II and active monitor speakers, CPU noise on the speakers. Has kept me busy for years. With mic pre's, bass di's, effect pedals, there was so much going on groundwise I found it hard to troubleshoot. An Art Ground Isolator between the breakout box and the speakers solved it. It would be my first advice in cases like these (but the advice can be found somewhere on this forum, article by MC I believe...I got the info from here).

Re: Ground Loops USB issues and cheap solution

Had the same issue with my new ADI-2 DAC FS. Constant noise through the active monitor speakers, even worse when moving the mouse. So I went to eliminate influences one by one, until I found the actual culprit: a USB dock.

This is on a MBP which has 4 USB-C ports and no Ethernet port, so years ago I got a high-quality USB-C dock (from Lindy) to connect mouse/keyboard because at one point I had run out of USB ports.

To illustrate the connection setup:

MBP USB-C #1: Apple TB3 adapter -> Apple TB2 adapter -> Apple Ethernet dongle
MBP USB-C #2: Apple USB-A adapter -> RME ADI-2 DAC
MBP USB-C #3: DP dongle
MBP USB-C #4: Lindy USB-C dock -> USB-A -> Apple keyboard/mouse

So even though the ADI-2 was connected directly to its own, separate USB-C port, and the USB dock was connected to a different USB-C port on the other side of the MBP (which means it was connected to a different TB3 device internally), the USB dock was causing interference with the ADI-2 DAC.

Removing the USB dock made the whole setup dead silent.

Something to consider before buying expensive galvanic USB isolation.