Ground Loop Problem -- Mac mini with Chord Qutest

[Habacomike]

My system has developed an increasingly frequent and now constant hum that makes playback untenable.  I've come to believe that the issue is a ground loop problem by two of the components:  the Mac mini server and the Chord Qutest DAC.  If I subtract the DAC, there is still a hum, but it is much less evident than with both components.  If I unplug the Mac mini, the DAC still contributes a big hum.  So, any ideas on how to fix it?  There's this thread (below) that seems to suggest a Jensen transformer, but would I need just one or two?  Or is there something else that I should try first?

 

[bogi]

10 hours ago, Habacomike said:

If I subtract the DAC, there is still a hum, but it is much less evident than with both components.  If I unplug the Mac mini, the DAC still contributes a big hum.

Any change, like a new device plugged into a mains socket near your audio chain?

 

Could you try Qutest analog output with some other (pre)amplifier or headphone amplifier, if that hum is present without your usual amplifier? Could you try to power your amplifier from some other mains socket?

Did you try some other +5V supply for Qutest?

 

Could you feed your Qutest with other digital audio source, like notebook or phone?

 

If that hum was not present previously then some of your components, maybe a power supply, could cause it. Jensen transformer is designed to fix outcome of ground loop but if you didn't experience that hum before, IMO more effective and better for your audio components and resulting sound would be to find the hum source. I suggest to follow Chris's advice from the first answer of the thread you linked.

 

[avta]

If you have not already done this try plugging all your devices into the same power strip or extension.

[Habacomike]

5 hours ago, bogi said:

Any change, like a new device plugged into a mains socket near your audio chain?

 

Could you try Qutest analog output with some other (pre)amplifier or headphone amplifier, if that hum is present without your usual amplifier? Could you try to power your amplifier from some other mains socket?

Did you try some other +5V supply for Qutest?

 

Could you feed your Qutest with other digital audio source, like notebook or phone?

 

If that hum was not present previously then some of your components, maybe a power supply, could cause it. Jensen transformer is designed to fix outcome of ground loop but if you didn't experience that hum before, IMO more effective and better for your audio components and resulting sound would be to find the hum source. I suggest to follow Chris's advice from the first answer of the thread you linked.

 

No recent additions to the system.  Both the Mac mini and the Chord Qutest DAC have ground loops and are each sources of the hum.  In fact, I can feel a current when I touch either component and it is powered.

 

So, the question is will the Jensen transformer solve the issue?  And do I only need one (between the DAC and the pre amp) or two (also between the Mac mini and the DAC)?

[Habacomike]

1 hour ago, avta said:

If you have not already done this try plugging all your devices into the same power strip or extension.

They are all powered by the same power strip.

 

[Racerxnet]

If you can feel current you have other problems to solve. Test the curcuit that the strip is plugged into. Curcuit Testing devices are cheap. Start there. 

[Habacomike]

Thanks but I don’t see how that helps:  I know there is a ground loop, neither the Mac mini or the Chord Qutest are grounded, and the feeling of current touching either confirms it. So what’s to be gained by measuring it?  Can anyone answer whether a Jensen transformer will fix the problem and if so do I need one or two?

[avta]

I can’t imagine a situation where you can “ feel “ the “ current “ that wouldn’t be dangerous with household current. I suggest you disconnect your system from power and consult an electrician. 

[bobfa]

If touching the boxes, you get a shock.  It is NOT the devices.  You have a grounding or neutral problem.  Start with a tester like the one below at the wall socket.  I would not use the system until you know.  this can be VERY DANGEROUS.

 

IF you do not understand this get an electrician

 

 

One thing that can happen with USA two-phase systems is the neutral can get pulled off of the ground with changing loads in the house.  (and bad wiring)

 

 

https://www.amazon.com/Amprobe-ST-101B-Socket-Tester/dp/B008E07IEO?keywords=AC+grounding+tester&qid=1687033192&s=lamps-light&sr=1-32

 

 

[Habacomike]

Yeah, tested the wiring the wiring is fine.  I found that the power line for the DAC was close to the RCA interconnect from the Mac mini to the DAC and was evidently causing EMI.  The mini still has it's slight (3 volt) leakage to the case which is evidently quite common in Apple products.

 

Thanks.

 

 

[astrallite]

Even if every device is fully grounded, the issue could still be caused by something else like an ungrounded cable line, or even noise caused by dimmers. If it's something electrical with your house and the electricians can't figure it out, the only way around it is to break the loop by eliminating all analog connections, which means using fiber optic connections whenever possible, whether that's for video or audio.

[Habacomike]

Thanks.  Moving the power cable has solved the problem for now.