• Registered: 2022-05-07
  • Posts: 15

Topic: Ground noise on phones 3/4

Hi,  this weekend I took my ADI-2 Pro with me to my parents (it's so compact and portable!) and they have pretty bad power, lots of humming from devices around the house.

I plugged my sensitive iems into the phones 3/4 port and was surprised to hear a quite loud low frequency hum when no music was playing. The hum disappeared if I touched the RME unit with my hands.

I understood that when connecting the Pro to a grounded amplifier with RCA cables while the pro itself has a two prong ungrounded PSU a loop may form that induces hum, but I expected the 3/4 headphone output to be immune to that.

As additional information: I was playing music from my phone connected through usb so that's also ground-free, and the Pro was powered by the 2-prong stock psu.

Anyone with ideas on why this may be happening?

2 Reply by KaiS (edited by KaiS 2024-05-21 20:35:34)

  • KaiS
  • DAW Mastermind
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  • From: Germany
  • Registered: 2020-02-05
  • Posts: 3,525

Re: Ground noise on phones 3/4

Due to ADI-2 Pro’s and DAC’s 2-prong only mains connector (no safety ground), the very small and non-dangerous mains leakage current builds up a mains 50 / 60 Hz voltage potential on the device and everything that is connected.

Your body is on ground potential (literally).
This voltage difference can move the IEM‘s driver diaphragm by electrostatic attraction - the sound that you hear.

Once you and ADI-2 are on the same electrical potential, either by touching ADI-2 or making an ADI-2 ground connection of any kind,  this hum disappears.

The later ADI-2/4 Pro SE has a new PSU with “soft ground”, that solves the problem while avoiding ground loops.
The PSU is available as spare, in case.

KaiS's Website

  • Registered: 2022-05-07
  • Posts: 15

Re: Ground noise on phones 3/4

Thanks for the explanation Kais! I mistakenly thought that the phones output would be immune to this leakage current. I have a Ferrum Hypsos laying around which is grounded so that should fix it too.

I was already typing up a reply on how the problem is not occuring right now at home but then I remembered I have it plugged into my laptop instead of my phone at the moment.

Indeed when I unplug the USB cable the hum is back so apparently grounding through the usb connection works fine too smile

4 Reply by KaiS (edited by KaiS 2024-05-22 10:56:48)

  • KaiS
  • DAW Mastermind
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  • From: Germany
  • Registered: 2020-02-05
  • Posts: 3,525

Re: Ground noise on phones 3/4

I’d like to make clear:

ADI-2 signal quality itself is completely immune against all types of ground related hum, be it ground loops or leakage current related ground potentials that can origin from various sources, e.g. computers through USB.

This means, the signal at all ADI-2‘s outputs stays 100% clean under all circumstances.


What ADI-2, like any other audio device, can‘t avoid:

Ground related issues that transit from the outside through ADI-2‘s case and therefore to it‘s audio ground (which, like always, have to be linked together) affecting stuff connected to it.

Most times nothing happens, but in certain configurations these stray signals become audible.


In your case, any simple 3-prong PSU would remove the mains potential.
Using the Ferrum Hypsos PSU, although overkill, will likely remedy, simply because of the 3-prong mains.

In other configurations (with power amps involved e.g.) just this 3rd prong can introduce a ground loop, so…!
ADI-2 offers balanced connectivity to fix ground loops, if the e.g. power amp offers balanced inputs too.


IMO the ADI-2/4 Pro SE’s PSU with “soft ground” is a good solution, as it eliminates leakage currents (even those introduced from other devices connected) without provoking ground loops.

KaiS's Website

  • Registered: 2022-05-07
  • Posts: 15

Re: Ground noise on phones 3/4

Thanks for the extra info!