[solved] High noise level at all times

Could we have some info on how you found out about the ground loop ? That could be super useful to other users in some circumstances.

Ideally it’d be great to have a “eliminate ground loops” wiki.


If the MOD Duo X sounds fine (no noise) when connected to headphones only (no output lines) or when it is the only device connected to a battery operated recorder , but is noisy when connected to other equipment, then I suppose that’s a hint that you have a ground loop.


@Azza wrote:

Could we have some info on how you found out about the ground loop ? That could be super useful to other users in some circumstances.

In my case I diagnosed a ground loop by putting a direct box (with the ground lift switch engaged) between my DuoX output and the input of my amplifier. After this change to the signal chain, the DuoX is super-quiet. For anyone with a direct box handy, this would be a test to try.


More thoughts: Using a direct box works great for breaking the ground loop, but isn’t so great if the downstream equipment requires a 1/4" input (for example, when going straight into a guitar amp, which is my use case). The problem is that most direct boxes have an XLR output, and getting back to a 1/4" instrument level signal is a hassle.

Inspired by @hgdaun I tried ordering an IEC Type II power supply, and this also results in very quiet operation. The power supply I’m using is a CUI SDI24-12-UD-P6 (Mouser P/N 490-SDI24-12-UD-P6). Using this power supply I can plug the DuoX directly into a guitar amp without noise problems. I don’t love the CUI power supply, though. The 12V wire seems pretty thin and vulnerable to damage. I did check its output on a scope before plugging it into the DuoX and the power seems pretty clean when it’s not driving a load.


One more follow-up for folks in the US & Canada. Another option that lets you continue to use the stock power supply with the Duo/DuoX is to use a device that breaks the ground loop at the plug. I tested with an Ebtech HumX (http://www.ebtechaudio.com/humxdes.html) between the stock power supply and the wall outlet, and this also resolved noise issues.


The headphone output on my ModDwarf that just arrived today is very noisy too. Using the power supply that came with it out of the box. It has the same noise regardless of whether I plug in any other connectors (other than power and headphones).

I also have had a similar but quieter noise on my ModDuo, though I am using a different power supply for that. Swapping the powersupplies results my ModDuo output become more noisy than it was before, and the ModDwarf being less noisy than it was before. But the ModDwarf is still much noisier with the good power supply than the ModDuo is with the bad power supply that came with the ModDwarf, so most of the problem seems to be with the internal circuitry of the ModDwarf. (note: I’m plugging both power supplies into the same wall outlet.) So in summary the noisiness from most noisy to least noisy is:

  1. ModDwarf with its original power supply
  2. ModDwarf with my own powersupply (from a labtop)
  3. ModDuo with the ModDwarf’s original power supply
  4. ModDuo with my own powersupply (from a labtop)

Now a trick as mentioned is to insert an audio ground noise loop isolator between the headphone output and your headphones…I happened to have one (I got mine for $6 from PJRC Store). That dramatically cuts down on noise coming into the headphones.

Though at least there is no noise on the actual balanced line outputs, when routed to another mixer or interface which accepts balanced line as input.

Anyway, as I guess I am a betatester for moddwarf, I’d recommend the devs take a look at this ground noise problem…and maybe consider including a headphone ground loop isolator when shipping.


Thanks again for sharing this and to share also the hack to solve it.
As I answered you in the other post, this is due to your Dwarf being a beta unit. Please report it on the beta tester forum thread (I know that you were not there before…no worries :slight_smile: ). This way it will be taken in consideration so it can be fixed for the normal production series of Dwarfs

ok. I’ve posted in the beta channel: https://forum.moddevices.com/t/headphone-output-noisy-without-audio-ground-noise-loop-isolator/5429

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Perfect :slight_smile: Thank you

In my setup I was able to fix this issue by using a power supply without ground. Tried my 12V from a Blofeld synth first, but 0.5A leaves the MDX in a rather confused state. Changed it for one of those PSU’s with selectable output and max 1.5A, and the noise is gone.


I have just tried my MOD DUO X through my new Spark 40 practice amp and the Ground hum is off the scale, tried all my leads and only used TRS, plugged into the same power outlet as the amp so that they share a common ground but still very loud high pitched noise even when all jacks are unplugged.
Just ordered a new 12v screened power supply, should arrive tomorrow so I will test it out and post my findings.

Welcome to the community, @Sorkycat.

I am not an expert in the topic of ground loops and would need more reading to make any assertions here. For the most part, using a non-grounded power source and or lifting the ground in all but one of the audio sources is a valid approach, as long as at least until one of them is still connected to the ground. So, using power sources without the 3rd prong can be of help. Or else, employing an audio transformer will help isolate one side of the audio chain from the other. Some companies also produce hum filters, so that you don’t have to fiddle around with power cables. (Germany’s Lehle builds excellent ones).

HOWEVER: for the performing musicians out there, one has to be careful and make sure there is at least one path to the ground. It used to be common practice to just saw off the 3rd (most times central) connector and not have to deal with hum noise, but that carries a potential life threat. I myself already got a light shock when I touched the microphone with my lips years ago. It’s better to play with an annoying hum behind you than lift ground altogether. Ground loops are very common in some venues that were not exactly projected for music (bars, restaurants, etc.) and even our own homes. Keith Relf of Yardbird’s fame died in his own basement after touching the strings of his guitar. Argentina’s Augustin Briolini also died when he touched his microphone. More recently, Grimes collapsed in Ireland after receiving a shock.

If you will be performing with your MOD, specially with stringed instruments, make sure there is an effective ground connection from your amp and/or microphone before lifting the ground of either. I used to carry a tester with me (~ 10-15 USD) and test the socket where my amp was to be plugged. Inversions of ground and neutral or live and neutral are not that uncommon.

Let’s all make good music and be safe. :smile:


Thanks for your info on this age old subject, I am only a home user and have read about removing the ground from effected instruments so it’s good to know that it works, I will wait to see if my new power supply sorts this out, it only cost £10 or about $13 but it’s great to have a community like this to offer advice and suggestions :+1::+1::+1:

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Just a little update, I decided to remove the the ground on the Mod Duo X power supply and tested it again and the hum has completely disappeared :+1: its now like a totally different unit and sounds crisp and clear and like the machine I wanted from the start, I’m now blown away because if I’m honest I was a little disappointed with the sound until this workaround fixed it.


How do you “remove the ground” on a DC power supply? like … how can it still move current without a negative lead?

The DC comes out of the transformer, I cut the moulded plug off the power lead and fitted my own plug but did not connect the Green and Yellow (ground) to the third pin (UK) plug type
This removed the ground and removed all the hum and interference

Just to reiterate what QuestionMarc wrote:

Electricity is not to be trifled with.

I’m a qualified Electrician, the output side that goes into the Mod Duo x is only 12v dc, the incoming ac is separated by the transformer coils, at worst under fault conditions you would damage your unit, I’m a home user and all my sockets are protected by RCD’s

It works for me and I’m not telling anybody else to follow my path, the power supply that comes with the unit has problems with ground loops and this has certainly fixed my issue


Also, my amp is fully grounded so the TRS jacks ground my Mod but instead of having 2 routes to ground it all goes through the amp

It’s a persistent problem with the Mod duo x unfortunately. The newer versions of the OS made a big positive difference so upgrading should be step 1. For me balanced cables on the output helped a lot too. But I still get noise issues when the MOD duo x is part of a large-ish setup. With some workarounds it’s sort-of under control but this is definitely the Achilles heel of this otherwise awesome piece of gear.