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Ground-loop issue with MacBook Pro 2019

Postby dDog45 » Wed Apr 07, 2021 12:04 pm

Hi, I have just recently bought myself a MacBook Pro 2019 as my new music production computer and have run into a ground-loop issue that I cannot seem to solve.

I've read through many of the existing forums covering this topic but none of the solutions are working for me. For reference, I'm in the UK where houses are typically grounded.

I've tried a different interfaces (focusrite and audient), different speaker cables, different instrument cables, different USB cables, removing the ground from my speaker cable, unplugging the Mac, moving the set-up throughout the house.. but none of these seem to make any difference.

I can record line sources with no issue (keyboard and drum machine), and when I'm just monitoring there isn't an issue, but as soon as I plug a guitar in there is a really bad loop that goes away when i touch any part of the system (Mac, guitar, interface, speakers, cables, etc.). Also this definitely isn't an issue with the instrument or interface as they both worked fine on my old computer (Windows desktop)

I'm using Genelec monitors which are also constructed from aluminium, which I think provides another opportunity for a grounding issue?.. again though, this wasn't an issue on my old computer.

Does anyone have any suggestions? I'd greatly appreciate any help anyone can offer me.

Thanks in advance!
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Re: Ground-loop issue with MacBook Pro 2019

Postby blinddrew » Wed Apr 07, 2021 12:25 pm

A full list of exactly what's plugged in when you're experiencing the issue would be good.
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Re: Ground-loop issue with MacBook Pro 2019

Postby dDog45 » Wed Apr 07, 2021 12:42 pm

Hi thanks for your reply.

This is the equipment list when the issue occurs:

Guitar <TS cable> Audient interface (9V power supply) <USB-C> MacBook (96W Power supply USB-C) <USB-C)> Audient interface <TRS to XLR cable> Genelec 8010's
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Re: Ground-loop issue with MacBook Pro 2019

Postby Sam Spoons » Wed Apr 07, 2021 1:13 pm

The fact that touching the metal part of the instrument makes it go away suggests a lack of earth. That is supported by the problem not changing when you unplug the computer but it not being there with your old desktop.

Your desktop will have had a solid connection through to the mains earth, the MBP does not (my 2020 MBP measures ~1k between the earth pin on the plug to the USB C connector or the chassis). If nothing else is providing a good earth in the system that may be the problem. Easy to test, just use the tips of the jacks on a guitar lead to connect the chassis of an active speaker or interface to a known earth (the screws on a mains socket maybe*) and see if it goes away.

edit:- Pretty sure that will be right, the Genlecs have no mains earth, the 9V wall wart supplying the Audient interface probably doesn't and the MBP definitely doesn't.

* If you mains sockets are in plastic plasterboard boxes this won't work and you'll need to find a different earthing point.
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Re: Ground-loop issue with MacBook Pro 2019

Postby Hugh Robjohns » Wed Apr 07, 2021 1:34 pm

This doesn't sound like a ground loop to me. It's more likely to be the reverse -- an absence of a decent ground -- which is allowing the guitar to serve as an aerial and pick up whatever electromagnetic interference is floating in the local environment.
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Re: Ground-loop issue with MacBook Pro 2019

Postby dDog45 » Wed Apr 07, 2021 1:53 pm

Hugh Robjohns wrote:This doesn't sound like a ground loop to me. It's more likely to be the reverse -- an absence of a decent ground

Thanks so much for this information! Does this mean that when I don't have a guitar plugged in, even though there is still no earth, there is also nothing to pick up the interference?


Sam Spoons wrote:Easy to test, just use the tips of the jacks on a guitar lead to connect the chassis of an active speaker or interface to a known earth (the screws on a mains socket maybe*) and see if it goes away.

edit:- Pretty sure that will be right, the Genlecs have no mains earth, the 9V wall wart supplying the Audient interface probably doesn't and the MBP definitely doesn't.

* If you mains sockets are in plastic plasterboard boxes this won't work and you'll need to find a different earthing point.

Thank you too! Unfortunately it is plastic plasterboard boxesI have so this mean you think this test wouldn't work?

Is there any solution to this issue then? I've heard that the MBP extension leads do have a ground in them - so would purchasing one possible provide a ground for the entire system?

Thanks again
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Re: Ground-loop issue with MacBook Pro 2019

Postby Wonks » Wed Apr 07, 2021 2:04 pm

What guitar is it? Single coils or humbuckers? If single coils, maybe it's just background noise being picked up by the single coils.

The fact that the buzz goes away when you touch the strings would normally indicate to me that there is a ground in the system and that your body is then grounded and stops acting like an aerial for noise. Maybe your MBP power supply is putting out RF noise that your old desktop didn't.

However it's possible that the lack of a system ground is a problem (though this often shows up to some extent or other in general operation). One cheap and easy way to add a signal ground (not a safety ground) is something like this:

https://www.thomann.de/gb/harley_benton_groundbox.htm

Which simply adds a ground connection to your guitar cable shield. You'd probably need to fit a UK mains plug to it if you were in the UK, but you could easily make your own if you are into DIY electronics. This is only for use in an all double-insulated system where there is no signal ground reference connection, and must not be used to replace a missing safety ground in a non-double insulated system.

Or you can make up a grounding cable with one end connected to ground in a power plug (but you must 100% know what the ground connection is in the plug, don't ever guess!) and the other end with a crocodile clip on the end that you can connect to say the shell of an XLR connector plugged into your interface.

You can always quickly test this grounding out with some bare-ended wire wrapped around some grounded metalwork and some metal part of a plug on your interface before moving to a more permanent solution.
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Re: Ground-loop issue with MacBook Pro 2019

Postby Sam Spoons » Wed Apr 07, 2021 2:13 pm

dDog45 wrote:
Sam Spoons wrote:Easy to test, just use the tips of the jacks on a guitar lead to connect the chassis of an active speaker or interface to a known earth (the screws on a mains socket maybe*) and see if it goes away.

edit:- Pretty sure that will be right, the Genlecs have no mains earth, the 9V wall wart supplying the Audient interface probably doesn't and the MBP definitely doesn't.

* If you mains sockets are in plastic plasterboard boxes this won't work and you'll need to find a different earthing point.

Thank you too! Unfortunately it is plastic plasterboard boxesI have so this mean you think this test wouldn't work?

Is there any solution to this issue then? I've heard that the MBP extension leads do have a ground in them - so would purchasing one possible provide a ground for the entire system?

Thanks again

Anything that has a good earth will work for the test, even the chassis of you desktop computer but I'm confident that is the problem, having tested my 2020 MBP and found it has around 1k ohm between the chassis and the earth pin on the PSU plug.

An alternative to the Thomann 'GroundBox' would be one of these https://www.groundology.co.uk/earthing/earth-connection-plug-uk thiugh you'll have to make a suitasble termination at the equipment end (connect the wire to the sleve on a TS jack plug and stick it in a spare socket on the interface maybe).
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Re: Ground-loop issue with MacBook Pro 2019

Postby dDog45 » Wed Apr 07, 2021 2:32 pm

Sam Spoons wrote:An alternative to the Thomann 'GroundBox' would be one of these https://www.groundology.co.uk/earthing/earth-connection-plug-uk thiugh you'll have to make a suitasble termination at the equipment end (connect the wire to the sleve on a TS jack plug and stick it in a spare socket on the interface maybe).

Will this product not do the same as the extensions lead I mentioned? https://www.apple.com/uk/shop/product/M ... sion-cable

Surely this would ground the MBP?




Wonks wrote:What guitar is it? Single coils or humbuckers? If single coils, maybe it's just background noise being picked up by the single coils.

The fact that the buzz goes away when you touch the strings would normally indicate to me that there is a ground in the system and that your body is then grounded and stops acting like an aerial for noise. Maybe your MBP power supply is putting out RF noise that your old desktop didn't.

However it's possible that the lack of a system ground is a problem (though this often shows up to some extent or other in general operation). One cheap and easy way to add a signal ground (not a safety ground) is something like this:

Hi, thanks for your suggestions

It's a P90 guitar with dual on/off toggles - so can be used as single-coil or a humbucker

The noise goes away when I touch any element of the system - even down to the tuning heads or the stands for the speakers.

Also, im not very sure of the difference between a safety and signal ground.. Could you possibly expand on this?

Thanks!
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Re: Ground-loop issue with MacBook Pro 2019

Postby Sam Spoons » Wed Apr 07, 2021 2:59 pm

dDog45 wrote:
Sam Spoons wrote:An alternative to the Thomann 'GroundBox' would be one of these https://www.groundology.co.uk/earthing/earth-connection-plug-uk thiugh you'll have to make a suitasble termination at the equipment end (connect the wire to the sleve on a TS jack plug and stick it in a spare socket on the interface maybe).

Will this product not do the same as the extensions lead I mentioned? https://www.apple.com/uk/shop/product/M ... sion-cable

Surely this would ground the MBP?

No, I have on from my old MBP on the new MBP's PSU but the earth connection is not continuous at low resistance between the plug and the computer.

edit:- I've just checked and the 1k ohm resistance in the earth path is within the PSU itself.
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Re: Ground-loop issue with MacBook Pro 2019

Postby dDog45 » Wed Apr 07, 2021 3:22 pm

Sam Spoons wrote:edit:- I've just checked and the 1k ohm resistance in the earth path is within the PSU itself.

When you say PSU are you referring to the 96W Plug or the internals of the computer?

Also, that product you mentioned before.. I will also have at least one jack socket available on the interface but I'm not very confident I entirely understand what you mean in your explanation of connecting it as such? Do you mean that product just gives out a ground and you feed that ground to the interface through a TS cable?
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Re: Ground-loop issue with MacBook Pro 2019

Postby dDog45 » Wed Apr 07, 2021 3:26 pm

Also, just to reiterate.. I only have this issue when a guitar is plugged in. I'm still not sure why this is the case
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Re: Ground-loop issue with MacBook Pro 2019

Postby James Perrett » Wed Apr 07, 2021 4:06 pm

Your guitar is acting like an aerial and, with no ground, any screening in the guitar or cable is less effective than it could be.
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Re: Ground-loop issue with MacBook Pro 2019

Postby dDog45 » Wed Apr 07, 2021 4:30 pm

James Perrett wrote:Your guitar is acting like an aerial and, with no ground, any screening in the guitar or cable is less effective than it could be.

So would the device mentioned above (Thomann Groundbox) be the best solution then? as it adds a ground to the guitar signal.

Thanks for your reply!
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Re: Ground-loop issue with MacBook Pro 2019

Postby James Perrett » Wed Apr 07, 2021 4:52 pm

dDog45 wrote:So would the device mentioned above (Thomann Groundbox) be the best solution then? as it adds a ground to the guitar signal.

It should work provided they can supply a suitable UK mains plug.
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