RME ADI 2 DAC FS (ground?) hum- any ideas?

[Jimbob54]

So- I made the mistake of spring cleaning and re-organising my AV rack yesterday. Today whilst using the RME with some sensitive IEMs I had a noticeable (assume 60hz or thereabouts) hum. So I started doing some testing. Observations:

1. Touching the join between the device and the IEM jack stops the hum
2. Hum present regardless of source selected (USB or Toslink)
3. Hum present with nothing other than IEM connected to RME
4. Hum present when RME in standby
5. Hum present if I move the RME to a new room, on its own into a power socket away from anything else.
6. Touching any of the empty metal sockets to the rear stops the hum.
7. Physically lifting the RME stops the hum.

So its a ground loop right? But why now, why with nothing else connected? Have I damaged something during the spring clean? Power supply issue?

I have deployed a temp fix- connected the unused coax jack to another (unused) device thats grounded- as long as I keep the other device plugged in on standby- no hum.

But something aint right, surely?

Any suggestions? Am I missing something basic but fundamental? Little bit concerned if I wanted to relocate the RME to a new location without the ability to connect to something grounded (eg my home office/ dining table) I will be hummed at.

Any help appreciated. @MC_RME ?

 

[MC_RME]

The leakage current of the ADI's external power supply runs to ground, whereever it finds one. With nothing connected you (your body) is the ground. The phones are in the way and therefore emit audible hum. Touching the chassis short-circuits the path of the leakage current, so it won't flow over the headphones anymore. Solution is the same as always: either connect a grounded device to the ADI, or directly connect it to ground.

Because of cases like yours we changed the power supplies to grounded ones. But as we have a lot of stock currently only the 2/4 Pro comes with it. And even that one will fail in case your power outlets don't have PE/ground (like many in Japan, Thailand...).

The last resort (if someone is unwilling or unable to connect it to a solid ground) is the use of a linear power supply. Their leakage current is basically free of harmonics and therefore typically inaudible.

 

[Music1969]

The last resort (if someone is unwilling or unable to connect it to a solid ground) is the use of a linear power supply. Their leakage current is basically free of harmonics and therefore typically inaudible.

Cheaper is simply buy an iFi Groundhog

It has an RCA connector that you can connect to ADI-2 RCA or digi coax

Use normal power cable for your country

 

[Blumlein 88]

Did you try flipping polarity of the PS lead, looks from pictures like it goes either way? Obviously don't know as much as MC_RME, but sometimes one direction is better than another for hum.

 

[MC_RME]

Even cheaper is AliExpress:

https://www.aliexpress.com/item/1005003998301320.html?gatewayAdapt=4itemAdapt

@Blumlein 88 : polarity doesn't matter for this case. Leakage voltage will be half the power voltage (55 V or 110 V), no matter how you plug it in.

 

[Music1969]

Even cheaper is AliExpress:

https://www.aliexpress.com/item/1005003998301320.html?gatewayAdapt=4itemAdapt

But where do you attach that to ADI-2? You need an RCA adaptor ?

Groundhog comes with RCA attachment , ready to go.

 

[Jimbob54]

The leakage current of the ADI's external power supply runs to ground, whereever it finds one. With nothing connected you (your body) is the ground. The phones are in the way and therefore emit audible hum. Touching the chassis short-circuits the path of the leakage current, so it won't flow over the hedaphones anymore. Solution is the same as always: either connect a grounded device to the ADI, or directly connect it to ground.

Because of cases like yours we changed the power supplies to grounded ones. But as we have a lot of stock currently only the 2/4 Pro comes with it. And even that one will fail in case your power outlets don't have PE/ground (like many in Japan, Thailand...).

The last resort (if someone is unwilling or unable to connect it to a solid ground) is the use of a linear power supply. Their leakage current is basically free of harmonics and therefore typically inaudible.

Thanks. Im in the UK (sorry, should have said in OP) so maybe one of the new PS might be a solution but from the sound of it, unless I want to move the unit to somewhere where I cant ground it, the best solution is what I have already done, connect to a grounded device. I can confirm even with sensitive IEM I cant detect the hum with the unit connected to the grounded device.

My main concern was that I might have damaged the PS (or unit itself ) during my move around but it sounds like things are operating as expected (and the unit works which is always a good sign).

Thinking about it, I suspect I originally had the unit connected to a grounded device so never got the hum for a couple of years. I stripped back my set up meaning the RME was only connected to a Toslink source and 2 ungrounded headphone amps so I think mystery solved!

Regards

Jim

 

[raindance]

So what you had was not a ground loop, it was the lack of a ground for the filtering to filter to. Relatively uncommon these days and much easier to solve than a ground loop.

 

[Jimbob54]

So what you had was not a ground loop, it was the lack of a ground for the filtering to filter to. Relatively uncommon these days and much easier to solve than a ground loop.

So, given how I had wired it up (only toslink in, headphone /IEM out) would one always run into this issue then? (I imsgine the same would apply if all I connected was a phone etc via USB?). If so, it hinders the device useability a little?

 

[raindance]

So, given how I had wired it up (only toslink in, headphone /IEM out) would one always run into this issue then? (I imsgine the same would apply if all I connected was a phone etc via USB?). If so, it hinders the device useability a little?

Perhaps in this particular revision of the unit. I don't see any reason you can't add a ground in this situation though.

 

[Jimbob54]

Perhaps in this particular revision of the unit. I don't see any reason you can't add a ground in this situation though.

On my AV rack with plenty of empty plug sockets (so I could use a grounding plug) and already grounded equipment to hook to, its not an issue and that is exactly what I did. If plug sockets are scarce and there is no grounded equipment near to connect to (think a kitchen table as a desk with only 2 or 3 sockets , one of which is for laptop) then it might be a nag.

Anyway- current hum issue solved.

 

[MC_RME]

So, given how I had wired it up (only toslink in, headphone /IEM out) would one always run into this issue then?

No. It depends of how good you (!) work as ground path. Put on rubber shoes, stand on a chair etc. and there is still leakage current produced by the SMPS, but it can't flow over the headphones and your body anymore - no hum. Also the make of headphone (its ability to let the current run to your ears) is a factor. So no, not anyone would notice this effect.

@Music1969: I may be optimistic to expect people in 2023 to have minimal skills of cutting off a connector and connecting a pure wire to whatever point on a chassis, or even solder on an RCA... If not the expensive solution is always there to be ordered. The AliExpress solution at least starts with an isolated AC plug - I would not dare to recommend making such a cable completely DIY...everything with mains calls for trouble...

 

[Music1969]

@Music1969: I may be optimistic to expect people in 2023 to have minimal skills of cutting off a connector and connecting a pure wire to whatever point on a chassis, or even solder on an RCA... If not the expensive solution is always there to be ordered. The AliExpress solution at least starts with an isolated AC plug - I would not dare to recommend making such a cable completely DIY...everything with mains calls for trouble...

Yes the solution I proposed was for someone not interested in any DIY at all.

For DIY there's lots of options.

 

[Jimbob54]

I may be optimistic to expect people in 2023 to have minimal skills of cutting off a connector and connecting a pure wire to whatever point on a chassis, or even solder on an RCA

In my case your optimism is misplaced ;-)