2020 Mac Mini (Intel) - Ground Loop Troubleshooting

[SkiTahoe]

First time posting in this forum and new to the audiophile community.  I did do a quick search within the forum, but If there is a thread that already discusses this, feel free to point me in that direction.   

 

I'm using a 2020 Mac Mini as my Roon Core (TIDAL/QNAP NAS) and sole music source.  My components are as follows:

 

2020 Mac Mini Intel i7 -- two prong plug

Samsung 55" TV as my Display to the Mac Mini via HDMI -- two prong plug

Mytek Brooklyn Dac+ (AQ Coffee USB Cable) with Sbooster BOTW P&P ECO MKII Power Supply -- three prong plug

Naim Nait XS 3 Integrated (AQ Mackenzie RCA Interconnects) -- three prong plug

Monitor Audio Gold 100 (AQ Rocket 33 Speaker Cables)

 

There's a hum coming from the speakers that increases as I turn up the volume on the Naim.  All components are plugged in to a medium quality Isotek power strip.  If I unplug the USB running from my Mac, the hum stops.  Same if I unplug the RCAs running from my DAC to the Naim.  So I figure there is a ground loop related to the Mac or an issue with power coming from the USB port.  The shop I purchased my equipment from is basically telling me that this is a common problem and the main issue with using a computer as my audio source.  I'd rather not get a dedicated streamer or music server if at all possible as I enjoy the convenience a computer offers.  

 

I've run through many of the first suggestion type solutions without any luck:

 

- Plugging everything into the same outlet

- reversing the mac mini plug 

- AQ Jitterbug

- Ifi idefender+ 

 

Now, I'm starting to move up the cost chain when it comes to solutions, but I wanted to see if anyone in this forum has had success resolving this type of issue without any major investment.  Any help would be greatly appreciated.  

 

[The Computer Audiophile]

I would start as simple as possible, then add components back into the system to find if a specific component is the cause. 
 

For example, only connect your amp and speakers. Is there a hum? Then move down the line. 
 

I did this once years ago and found the hum was related to my house ground wire. 

[The Computer Audiophile]

Oops. Just re-read your post. Forget my first suggestion. 

[mevdinc]

The first possibility that comes to mind is that HDMI connection between your Macmini to TV.
Especially if you have RCA connections you will definitely experience ground looping problem.

 

I did experience this myself with my active speakers. Even though my DAC and actives were connected using XLR cables I still experienced grounding problems because my DAC was also connected to my cinema processor with RCA.
So, when I removed the RCA interconnects between the DAC and the processor the humming would disappear.

After a lot of experimenting and searching the net for possible solution, I ended up buying a couple HDMI cables with sheath current filter. This greatly reduced the humming, cannot remember if it completely eradicated the problem or reduced it to the acceptable level, as I am using a different setup now and don't have any problems.

Since removing RCA and USB connections solve your problem then it sounds like you are experiencing very similar to I what did. So, I would also suggest trying removing your HDMI cable to see if the problem goes away.
Good luck. It's such an annoying problem and very difficult to get rid off.

 

[SkiTahoe]

Appreciate the replies.  When I remove the HDMI cable from my Mac, the humming reduces slightly (or at least changes), but doesn't go a way completely.  Would any basic HDMI cable with that feature suffice?  

 

I've been researching some other options but I don't know if I'm misunderstanding the purpose of these products:

 

Jensen Iso-Max CI-2RR RCA Stereo Line Input Isolator Hum Eliminator -- Place in between my DAC and Amp?

Ifi Nano IGalvanic 3.0 -- Break the ground/power through the USB cable?

D/D converters (M2Tech, Denafrips, Matrix) -- Run AES/EBU or Digital Coaxial?

USB Regenerator (Intona, Uptone, SOtM) -- Clean up the USB signal?

 

It sounds like plenty of people use a Mac Mini as a source.  What's different or missing from my setup that might be causing the hum?  Thanks again.  

[The Computer Audiophile]

9 minutes ago, SkiTahoe said:

Appreciate the replies.  When I remove the HDMI cable from my Mac, the humming reduces slightly (or at least changes), but doesn't go a way completely.  Would any basic HDMI cable with that feature suffice?  

 

I've been researching some other options but I don't know if I'm misunderstanding the purpose of these products:

 

Jensen Iso-Max CI-2RR RCA Stereo Line Input Isolator Hum Eliminator -- Place in between my DAC and Amp?

Ifi Nano IGalvanic 3.0 -- Break the ground/power through the USB cable?

D/D converters (M2Tech, Denafrips, Matrix) -- Run AES/EBU or Digital Coaxial?

USB Regenerator (Intona, Uptone, SOtM) -- Clean up the USB signal?

 

It sounds like plenty of people use a Mac Mini as a source.  What's different or missing from my setup that might be causing the hum?  Thanks again.  

 

 

Yes, many people use Mac Minis and other computers without issues. 

 

You could try the very cheap and possibly temporary solution of putting tape over the power pin of the USB cable. This will isolate the power, but will only work if your DAC doesn't require power over this USB cable. 

 

Here's how to do it. 

 

[AudioDoctor]

I have a 2011 Mac mini here in the house that still gets used as a source and weirdly I found that when I had it connected via USB to a DAC, and a 3.5mm to RCA cable also plugged into it, and the same component as the DAC, it hummed like crazy. Disconnecting the 3.5mm to RCA cable stopped it immediately. The fix, for me, was to buy another Raspberry Pi4 and connect the DAC to it instead of the mini directly.

[sandyk]

10 hours ago, The Computer Audiophile said:

 

 

Yes, many people use Mac Minis and other computers without issues. 

 

You could try the very cheap and possibly temporary solution of putting tape over the power pin of the USB cable. This will isolate the power, but will only work if your DAC doesn't require power over this USB cable. 

 

Here's how to do it. 

 

Further to what Chris has suggested.

 If you find this helps, check out https://uptoneaudio.com/products/uspcb-a-b-adapter

[SkiTahoe]

Using both an older 2013 Macbook Pro and a 2020 Macbook Pro, I was able to do a couple more tests using the grounded extension cord shown below.  With the 3 prong plug, the humming stops.  This includes connecting the TV via HDMI as a display.  Switch to the 2 prong plug and the hum returns, albeit at different levels, with each Macbook.

Is there a way to ground the Mac Mini?

 

I will also try placing tape over the power pin, but maybe I just use the older Macbook as my source.      

 

IMG_7147.HEIC

[The Computer Audiophile]

I can’t believe I haven’t run into this yet. 
 

Looks like @barrows has grounded his Mac Mini. 
 

 

 

 

[One and a half]

This situation is very typical and the drama is caused by too many SMPS and not enough grounding.

 

The MacMini like the Apple laptops with the separate power block float their DC output without referencing to ground (PE). This can create 50% mains voltage on the DC power jack to the Mac Mini, thoroughly not right.

 

Since the TV uses the same system and more SMPS in that device, the problem is made worse. Differing voltages on the Mac mini, TV appear at the USB connector of the Mytek and the drama continues.

 

By replacing the MacMini AC cable with a 3 core cable, the cable provides some RF attenuation, but conducted noise will still be present, so that changed the pitch of the noise. I hope all components are wired to the same power strip?

 

To isolate the problem, fire up everything and disconnect the USB cable to the Mytek. If there is noise, unplug the TV. If still noise, unplug the MacMini. By now, there should be no hum with Naim at full volume.

The Mytek is probalby grounding the whole system, not the greatest. Please report back on the findings. What signal lead into TV, Cable?

 

[barrows]

I grounded my Mac Mini (I have since moved on from it) by making a simple grounding cable which plugs into one of the unused USB jacks.  The cable just has a single 18 AWG wire, terminated to the USB "A" plug ground connection on one end, and a three pin AC cable on the other end with the wire terminated to the ground pin.  I was making a number of wiring changes at the time, so I cannot say whether this resulted in sound quality improvement, but from a technical perspective it  stops "high impedance" leakage currents from the internal SMPS from escaping. 

[The Computer Audiophile]

48 minutes ago, barrows said:

I grounded my Mac Mini (I have since moved on from it) by making a simple grounding cable which plugs into one of the unused USB jacks.  The cable just has a single 18 AWG wire, terminated to the USB "A" plug ground connection on one end, and a three pin AC cable on the other end with the wire terminated to the ground pin.  I was making a number of wiring changes at the time, so I cannot say whether this resulted in sound quality improvement, but from a technical perspective it  stops "high impedance" leakage currents from the internal SMPS from escaping. 

 

Similar to this, without the passthrough?

 

https://www.electrahealth.com/Premium-USB-Grounding-Adapter-for-Laptops-and-Other-Devices_p_159.html

 

 

[The Computer Audiophile]

or this

 

https://www.filteremf.com/buy/usb-ground-cord/

 

[w1000i]

Just ground the mini PC. use any cable and let it touch any port.

[AudioDoctor]

Neat...

[SkiTahoe]

15 hours ago, One and a half said:

This situation is very typical and the drama is caused by too many SMPS and not enough grounding.

 

The MacMini like the Apple laptops with the separate power block float their DC output without referencing to ground (PE). This can create 50% mains voltage on the DC power jack to the Mac Mini, thoroughly not right.

 

Since the TV uses the same system and more SMPS in that device, the problem is made worse. Differing voltages on the Mac mini, TV appear at the USB connector of the Mytek and the drama continues.

 

By replacing the MacMini AC cable with a 3 core cable, the cable provides some RF attenuation, but conducted noise will still be present, so that changed the pitch of the noise. I hope all components are wired to the same power strip?

 

To isolate the problem, fire up everything and disconnect the USB cable to the Mytek. If there is noise, unplug the TV. If still noise, unplug the MacMini. By now, there should be no hum with Naim at full volume.

The Mytek is probalby grounding the whole system, not the greatest. Please report back on the findings. What signal lead into TV, Cable?

 

 

If I disconnect the USB cable from the Mytek, the hum stops.  The TV is fed by HDMI from both my Mac Mini and an Apple TV, no cable.  All components are plugged into the same Isotek power strip.

 

Some other questions:

 

Would a Toslink cable 3.5mm to full be a good option rather than USB?

What about USB to a D/D converter like the Denafrips Hermes or M2Tech Hiface Evo, then AES/EBU or Toslink to the Mytek?

 

It's weird that I don't have this issue with both laptops, just the Mac Mini.  I'll see if I can find a USB grounding cable like mentioned above as I don't feel confident fabricating my own.  

[March Audio]

Hi

 

I talked about ground loops here:

As people have already pointed out grounding the Mac may help by reducing the noise currents flowing in the audio interconnect shields.  If it doesn't you can try a galvanic isolator.  Hopefully the cheap solution will work first.

 

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

 

Edit:

I just looked at your interconnects and became a little suspicious about their construction.

 

Our Triple-Balanced Geometry uses a separate ground-reference conductor, so the cable's shield is never used as an inferior conductor.

 

This implies an increased resistance for the low signal conductor as its not using the shield which is the last thing you want if you have ground loop issues.  I suspect the shield is only connected at one end.

 

Try swapping these cables out for one of normal construction, with a thick low resistance shield.

 

[One and a half]

53 minutes ago, SkiTahoe said:

 

If I disconnect the USB cable from the Mytek, the hum stops.  The TV is fed by HDMI from both my Mac Mini and an Apple TV, no cable.  All components are plugged into the same Isotek power strip.

Oh, the noise is coming from the mini. Also 10/10 for plugging all into the same power strip.

53 minutes ago, SkiTahoe said:

 

Some other questions:

 

Would a Toslink cable 3.5mm to full be a good option rather than USB?

What about USB to a D/D converter like the Denafrips Hermes or M2Tech Hiface Evo, then AES/EBU or Toslink to the Mytek?

This a minefield of a question and there are numerous threads devoted to that topic.  It depends....

a) your player software

b) cabling

c) best noise reduction for the system

d) format of the hires files you have or plan to

 

For now, let's get the hum under control, because that will wreck everything else, foundation must be sound 😀

 

As @March Audio explained, the USB cable may only be shielded at one end. Rob the printer cable and try that instead., needs to have USB2.0 printed on it somewhere though. Try for hum with the printer cable. Hopefully it would have gone down. By all means find that cable with the 120V connector and the USB ground, the mini usually has 4 ports, anyone will do. That will bring the hum closer to zero. 

 

On a personal note only, offer this advice. For over 3-5 years I played around with USB transmission fixes till I was blue in the face. The lot was scuttled by replacing with a network streamer, still sounds great two years on. If you're thinking of hardware, then have a look there. The Denafrips gear is good stuff, but USB has this limitation of transmitting higher freq noise from the computer to the DAC which is difficult to control let alone remove. 

 

53 minutes ago, SkiTahoe said:

 

It's weird that I don't have this issue with both laptops, just the Mac Mini.  I'll see if I can find a USB grounding cable like mentioned above as I don't feel confident fabricating my own.  

 

[March Audio]

Hi 

 

Actually I was referring to the audio interconnects not the usb 😀

 

At the end of the day this is a fundamental flaw of single ended RCA systems where the low signal wire is also used to connect component grounds together.

[AudioDoctor]

Beyond my, and others, suggestion of a transmitting the audio over the network rather than a USB cable plugged directly into the mini, make sure you have a good quality power strip. Preferably not the cheap throwaway from Target, or worse.

 

I use these:  https://zerosurge-com.3dcartstores.com/8R15W-I_p_17.html

[March Audio]

Ethernet is indeed a potential solution as it is galvanically isolated.  It achieves the same as the Intona USB isolator I mentioned above. 

 

Just be aware that mains filtering in itself wont solve this issue.  In fact it can make it worse.  Typical Mains RF filters have Y capacitors which connect line to ground. This can end up feeding mains currents into the low signal (shield).  Its the same reason why the SMPS for the Mac is introducing these noise currents and creating an audible hum.

[SkiTahoe]

Thought I would post a quick update.  I've pretty much given up trying to remove the ground loop with the setup as is, and I may end up just using the Macbook Pro, but trying to troubleshoot the Mac Mini hum has been interesting and definitely a learning experience.  I ended up ordering one of these:

https://www.jensen-transformers.com/product/ci-2rr/

Funny thing is that it helps significantly.  If I go full volume on the integrated, there is still a hum, but way better than it was before.  Does anyone have feedback on if/how much these affect sound quality?  

 

Beyond this, I'm going to try a D/D converter just for fun and to play with different inputs to my DAC.  

[Josh Mound]

I have the same Mac as you, but whenever I’ve run into this issue, it’s been the DAC that I’ve needed to move to break the loop. Does a “cheater” plug on the DAC’s cord end the loop? If so, an Ebtech Hum-X should safely solve the problem in place of the cheater. 
 

Also, moving one or both of the components to a pure sine wave UPS might solve the issue. 

[One and a half]

12 hours ago, SkiTahoe said:

Thought I would post a quick update.  I've pretty much given up trying to remove the ground loop with the setup as is, and I may end up just using the Macbook Pro, but trying to troubleshoot the Mac Mini hum has been interesting and definitely a learning experience.  I ended up ordering one of these:

https://www.jensen-transformers.com/product/ci-2rr/

Funny thing is that it helps significantly.  If I go full volume on the integrated, there is still a hum, but way better than it was before.  Does anyone have feedback on if/how much these affect sound quality?  

 

Beyond this, I'm going to try a D/D converter just for fun and to play with different inputs to my DAC.  

The RF versions of the ISOMAX are awesome, for the likes of Cable TV/FM systems. For audio.  There's only one shop, at Lundahl transformers. Functionally, they do the same job as the ISOMAX, but, the price can be eye watering versus the quality, Some Lundahl transformers are thousands, choices.