Ground loop problem?

[HobGoblyn]

Hi all, please bear with me while I try and explain my problem.

Due to medical problems, I currently need to be able to use my music software while sitting in my armchair, hence need a computer and speakers on an over the chair/bed  type table on wheels , and I have a 37 note midi controller keyboard that comfortably sits across my armchair.

I have a MacBook Pro M1 with powered Presonus  Eris 3.5 monitors attached.

I’ve only had the Mac for two weeks, initially I had a mains powered soundbar plugged into it, and when  using this, I didn’t notice the problem,  unfortunately it sounded awful hence returned it  and got the Presonus Eris 3.5’s instead.

The left  Presonus Eris speaker has all the controls/inputs/power socket on it, (right  speaker simply has speaker cable socket on it with the speaker cable coming from the left speaker).  It’s powered by one of those  figure 8 plugs (C7) which can plug in either way round and  obviously doesn’t use the earth pin in my UK plug or wall socket.



First, the problem. 

Initially, I had a stereo 3.5mm  jack to  twin RCA,  with the 3.5mm jack plugged into the MacBooks headphone port and the two RCA’s plugged into the speakers RCA ports.

The MacBook wasn’t connected to the mains (MagSafe cable from mains charger not connected to MacBook)

When using my MacBook Pro, after about 5 odd minutes,  when I move my hand along the laptop case (when typing/using trackpad), I can feel a tingle where my hand touches it.  If I hold my hand  completely still on the case, I can’t feel anything , but as soon as I move it, tingling is there.

Very hard to explain the sensation, almost kind of feels like some weird haptic feedback and sort of feels like there’s a slight resistance between the case and my moving hand.  The slower I move my hand the greater the sensation.

If I remove my hand completely, sometimes the sensation is still there when I put it back, other times it’s fine for a few mins before the problem returns.

The second I unplug  the mains plug for my new Eris 3.5 speakers, the problem goes away.   When I plug it back in, it’s fine at first, then it comes back.

I’ve got my wife to unplug and re plug in the Eris mains cable so I could see/feel with 100% certainty that unplugging them stopped the sensation immediately.




What  I’ve tried.

1:   Tried a stereo 3.5mm to 3.5mm cable from MacBook headphone port to the Aux in on my Eris speakers.


2:  I purchased a “Presonus Audiobox Go” audio interface. 

The  Audiobox is connected to the speakers by two balanced 6.35mm TRS  cables

This came with a "USB C"  to “USB  A” connector to connect to the laptop,  but as my MacBook  only has USB C/ thunderbolt sockets, I tried with a spare USB C to USB C.


3: Audiobox still connected to the speakers by two balanced  6.35mm TRS cables

Used the USB C to USB A cable that came with the Audiobox, the USB C plugging into the Audiobox,  the USB A plugging into Anker USB hub, the hub plugging  into my  MacBook


With any of the above (tried in all MacBook ports) the problem is still there.

Before buying the Audiobox, I tried different wall sockets and a different fig 8 (c7) mains cable.  Most tests were done without the MacBook being attached to the mains but I did a few with it charging, nothing made a difference.


So currently the speakers are connected to my Audiobox by balanced cables, the Audiobox is connected to my Anker USB hub by USB C to USB A   and My Anker USB hub is connected to one of the MacBooks USB C/Thunderbolt ports. The problems just as bad as as my original try and still, the second my speakers are unplugged, the problems gone.

Any suggestions please

Thanks

Links below to speakers etc



Eris 3.5 Speakers
https://www.amazon.co.uk/PreSonus-Eris-3-5-Gen-Studio-Quality/dp/B0CC36XVLM/ref=asc_df_B0CC36XVLM/?


Audiobox Go Audio interface
https://www.amazon.co.uk/PreSonus-AudioBox-GO-production-Instruments/dp/B09N557CYK?


Anker Hub
https://www.amazon.co.uk/Anker-Upgraded-Delivery-Pixelbook-A83460A2-Gray/dp/B07ZVKTP53/ref=asc_df_B07ZVKTP53/?

[tooki]

The tingle is from the interference suppression capacitors on an ungrounded switching power supply, a question that has come up many, many times here on the forums. It means your housing is floating at 1/2 mains voltage, but at an absolutely minuscule current, which is why this is not only allowed by code, but required, in order to meet EMI standards. This is normal and expected from a properly filtered supply. The fix is to actually have a ground, e.g. by tying the speakers’ case to ground (if it’s metal), or using your MacBook with the grounded mains cord (not the snap-on plug) on its power supply.

[themadhippy]

passive DI box on the audio lines should clean things up

[tooki]

passive DI box on the audio lines should clean things up

This isn’t a ground loop problem, nor an impedance mismatch. So how exactly do you think the DI box would solve this? (Bear in mind that I already gave the solution above.)

[themadhippy]

it will break the physical connection between 2 items that when joined together are causing the tingle,which id guess is going from the speakers ground to the metal work of the un plugged mac.Being the speakers are using a 2 pole mains connector id bet its double insulated ,and adding an earth is a no no ,at least in the uk's  electrical rules

[Someone]

adding an earth is a no no ,at least in the uk's electrical rules

Citation required...

Adding a functional connection back to earth is perfectly safe and compatible with electrical compliance worldwide. Otherwise you'd be prohibited from connecting devices together (since once of them could have a functional earthing connection). This is all explicitly allowed (61010 3.2.2 for example) and not some sideways interpretation.

[Ian.M]

Its a bit old, but this summarises Apple's f***ed up grounding nicely:
https://apple.stackexchange.com/questions/17575/how-to-properly-ground-a-macbook-pro

Although it fits, a 'figure-8' mains lead is unsuitable for an Apple PSU with a stud, as it does not provide a ground so wont ground the leakage current.   You need a lead that properly grounds the stud, which will then ground the leakage current from both the Apple PSU and the speakers (via their audio signal cable shields).

Apple duckbill mains extension cables for their PSUs, with three pin mains plugs *USUALLY* properly ground the stud.  All the direct to wall socket adaptors, including the UK one do *NOT*, in spite of its metal ground pin on the BS1363 plug side.

You need to confirm there is continuity from the PSU ground stud to the USB C plug shell, (just in case Apple have managed to   f**k that up on new models!) then order a Apple Power Adapter Extension Cable (UK) from a supplier with a liberal enough returns policy that you can send it back if there's no ground contact in the slot the ground stud goes in.  The first thing you should do, before you even uncoil the lead is check continuity from the ground pin to the slot.

If both the PSU and its mains lead have ground continuity, your mains leakage current shock/'tickle' will just go away.   N.B.  if you connect more audio devices and any of them have a grounded PSU you may get a ground loop.  If you get any hum as a result, first makes sure that the Apple PSU extension lead and the grounded audio device are plugged into the same extension lead or double wall socket, with their mains power leads right next to each other, and if that doesn't cure it you may have to resort to reverting to the Apple UK duckbill to wall socket adapter  to remove one of the grounds to break the ground loop, and let the whole setup get its ground through the audio device.   Don't hot-plug a grounded audio device if the Apple PSU is not grounded!

[themadhippy]

after a kip another  solution past  between the eyes,one   ive use sevral times over the years when dealing with leaky guitar amps and singist getting a tingle from the mic,as  your using a balanced line cut the the earth on the SIGNAL line.

[themadhippy]

This is all explicitly allowed (61010 3.2.2 for example) and not some sideways interpretation.

For the designer/manufacturer,not by some random bod in the street.

[Shock]

"When using my MacBook Pro, after 5 minutes I can feel a tingle where my hand touches it."
 
Use wireless speakers and grounded/earthed power adapters is the easiest way. If still an issue get the power adapters replaced under warranty then get a p.a.t. or electrician in to test your devices or wiring.

If the midi keyboard or controller is connected to your laptop don't rule that out as a source of the issue either.

[Nominal Animal]

FWIW, this is why I like class II isolated MOPP-rated (medical) AC-DC supplies: no tingles.

Class I AC-DC supplies have a class Y capacitor between the DC side and the AC for keeping EMI down; class II do not.

Per IEC60601-1, MOPP rated supply can leak at most 50µA from the DC side, 100µA in single failure condition, which should not only be safe, but also below the sense threshold (to 50/60Hz 120V/240V AC mains supply).

I do also use digital isolators much more often in my own projects than others do, but it is at least as much about helping protect against my own blunders than anything else.  We don't have polarized sockets here, and if a computer and a peripheral are powered from different sockets (different mains circuits), they may have different phases, which leads to ground currents between class I supplies.  It also means that if connecting via USB serial to a separately-powered SBC or router, an isolator on the serial RX and TX lines will not only stop ground loops from happening and voltage (ground potential) differences from breaking anything, but also will nicely act as a voltage level translator.

For analog audio, I'd use a transformer-based passive galvanic isolator, i.e. unbalanced-to-balanced audio transformer or "DI box" with "earth lift" (as themadhippy suggested).  Eris 3.5 input impedance is 10kΩ, and frequency response 80Hz to 20kHz.  As a dirt poor hobbyist, my choice would be a pair of Triad Magnetics' TY-250P from Mouser.  The three-pin 3.5mm TRS audio connector would have Tip (Left) connected to pin 4 on one, and Ring (Right) to pin 4 on the other, and Sleeve (0V) to pin 2 of both.  Both would have pins 6 and 7 linked, and the balanced output at pins 5 and 8 connected to 1/4" TRS connectors tips and rings, respectively.  Sleeve would be unconnected, or both connected to the metal enclosure containing the transformers.  Each TY-250P has -0.1dB to +0.6dB response from 80 Hz to 20 kHz at 10kΩ input impedance, which isn't "studio quality", but not too bad either.  With either cables or female connectors, and using silicone to keep the transformers in place, it should all fit in e.g. Eddystone/Hammond 27969PSLA cast aluminium box.

So how exactly do you think the DI box would solve this?

A pair with "earth lift" will break the ground connection between the speakers and the Mac.  The audio signals pass through the symmetric transformers, typically 600Ω:600Ω.  The Eris 3.5 has two balanced inputs as 1/4" TRS connectors (sleeve is for ground/shield), so it will act as an unbalanced-to-balanced transformer also.

Since there is no leakage current path to ground from the active speakers' ground to Mac chassis to human to physical ground, there would be no tingle either.

The cables would be a bit funky: 3.5mm TRS in, sleeve/0V/GND connected to two transformers input only.  Output is a pair of 1/4" TRS, with their sleeves possibly connected to the transformer enclosure (for shielding), but then that enclosure could give you the same tingle.  I'm not sure such cables exist off-the-shelf.

[HobGoblyn]

Thanks everyone.

While electronics is one of my two hobbies, even after your much appreciated explanations, I would be lying if I said I fully understand exactly what’s going on.

On a separate note, my bedside lamp is one of those all metal ones that you touch anywhere to turn on and off. It also has a usb socket.

Normally it turns on and off at the slightest touch but if I plug my iPad into it to charge, sometimes I have to touch the lamp  3 or 4 times before it works, and thinking about it, when the iPads charging, I also get the same (but a bit stronger) tingling if I rub my fingers over it.

I don’t want to use wireless speakers due to latency, I’ve tried Bluetooth ones and the latency was unbearable.

The speaker cases aren’t metal (although I could try running an earth from one of the unused sockets on the back)

The iPad charger is their 140w one.

There sadly doesn’t appear to be any continuity from the psu ground stud to the usb-c.  As Ian.M says, Apple do an extension cable that also connects to the ground stud and doing a lot of research today, a fair few people have said it solves their problem, but no continuity from mine so not worth buying.

I did try running a cable from the wall sockets earth, and  I touched it against the MacBooks metal case when the tingling was present.  I thought this would have helped but it made the tingling much worse, hence me not fully understanding what’s going on.


The midi keyboard will be connected to the Mac via the same Anker usb hub,  haven’t got that far yet.

I’ll double check the continuity tomorrow on the off chance I was doing something stupid

Note: This is a 2nd hand MacBook hence changing the power adapter under warranty isn’t going to happen

[wraper]

The tingle is from the interference suppression capacitors on an ungrounded switching power supply, a question that has come up many, many times here on the forums. It means your housing is floating at 1/2 mains voltage, but at an absolutely minuscule current, which is why this is not only allowed by code, but required, in order to meet EMI standards. This is normal and expected from a properly filtered supply. The fix is to actually have a ground, e.g. by tying the speakers’ case to ground (if it’s metal), or using your MacBook with the grounded mains cord (not the snap-on plug) on its power supply.

Well it's not really required, as you could use a shield between transformer windings and do other stuff. However it's the easiest and cheapest thing to do.

[Someone]

This is all explicitly allowed (61010 3.2.2 for example) and not some sideways interpretation.

For the designer/manufacturer,not by some random bod in the street.

No, as I said in the full quote.

adding an earth is a no no ,at least in the uk's electrical rules

Citation required...

Adding a functional connection back to earth is perfectly safe and compatible with electrical compliance worldwide. Otherwise you'd be prohibited from connecting devices together (since once of them could have a functional earthing connection). This is all explicitly allowed (61010 3.2.2 for example) and not some sideways interpretation.

Adding a technical earth can be as simple as a plug with the earth wire coming out the back of it. Which is a perfectly legal "appliance" and readily available. Nothing against the electrical rules there. Or going further to your new position, very few jurisdictions restrict the owners of equipment from modifying it.

So the challenge remains. What regulation/law/legislation is in the way? You say it exists but cannot point to it. I say it does not exist, I don't have to (and cannot) present a complete lack of that law.

[Whales]

While electronics is one of my two hobbies, even after your much appreciated explanations, I would be lying if I said I fully understand exactly what’s going on.

The power bricks you are using (to charge your macbook and to power your other equipment) input dangerous mains electricity and output safe, isolated low-voltage electricity.  They are "safety devices" that are designed to almost guarantee that you cannot be electrocuted by anything plugged into the low voltage side, like a laptop, or even if you put the output lead into your mouth like a small kid might.

The problem is that these power supplies are hyper-optimised for their goals of safety, radio compliance and low-cost.  What if they gave you the sensation of being gently electrocuted, but don't actually electrocute you?  That's perfectly fine!  That doesn't break any of their goals.  And if it makes them cheaper and emit less radio interference then that's even better.

Seriously.  That's the reason.  That's the thinking behind it.

I'd prefer to also give you some more technical detail on what's going on.  Have a look at this circuit diagram of a power supply similar to what you might find in your laptop charger:


(stolen from https://www.electrothinks.com/2021/02/12V-2a-switch-mode-power-supply-with-lp2704a.html )

On the bottom-left you can see the dangerous 240V mains coming in.  On the right you can see the safe, isolated 12V coming out.  I've highlighted the dangerous and safe halves of this circuit.  Touch anything on the red side and you may get electrocuted, touch anything on the blue side and you'll be fine.

There are three key components that bridge the dangerous and safe sides.  From top to bottom: a capacitor (C6), a transformer (T1) and an optocoupler (U1).

The transformer does a really good job at isolating the dangerous side from the safe side.  It doesn't let electricity through directly, it smuggles the electricity through a magnetic field to get it from one side to another, and in a very controlled manner.

The optocoupler similarly does a really good job at isolating the dangerous side from the safe side.  It doesn't let electricity through directly, it smuggles the electricity by converting some to light and using something similar to a solar panel on the other side to detect it.

The capacitor... it doesn't do so well.  It straight up lets electricity from the dangerous side go to the safe side.  It doesn't smuggle.  It doesn't even launder.  The only saving grace is that it only allows a little bit across. 

That's your tingle. 

The evil class Y capacitor leaks a tiny bit of dangerous mains across to the safe side, into your laptop and then into you when you touch its case.  It's enough to feel but not enough to harm you.   (Technically it could harm you if you attach it to subdermal metal probes in your body, especially if they're close to your heart or in your brain.  Please don't do that.)

The evil class Y capacitor reduces the (unwanted) radio emissions of the power supply without needing to kill anybody, so the designers consider it a win.

You can exorcise the evil in one of two ways:

(1) Remove the capacitor, or
(2) Attach the output GND to mains ground.

Removing the cap is difficult because the power supply is in a welded or glued plastic shell.  You probably don't want to muck with dangerous power supplies if you don't have much experience.  Not to mention that operating a source of radio interference in a hospital is ethically questionable.

Attaching the output GND to mains ground is a much easier solution.  The key to understanding this is to imagine yourself as being at mains ground (close enough) and the two wires coming out of the power supply being at these voltages when compared to you:

   +12V:   12VDC + 90VAC of mains tingle from the Y class capacitor
     GND:   0VDC + 90VAC of mains tingle  from the Y class capacitor

If you attach the power supply output GND to mains ground then you will suppress the tingle voltage:

   +12V:   12VDC + 1VAC of mains tingle from the Y class capacitor
     GND:   0VDC  + 1VAC of mains tingle from the Y class capacitor

You can achieve this in many ways, including:

* Attaching a USB cable between your macbook and something with mains ground (the USB shield will connect the earths)
* Using a power supply with a three-prong plug (has mains ground) instead of a two-prong plug (ungrounded)

Does that make sense?  The technical section might have gone a bit off the rails, please feel free to ask questions.

[themadhippy]

So the challenge remains. What regulation/law/legislation is in the way? You say it exists but cannot point to

5.8.1 - Class  II equipment

Class  II  equipment has reinforced or double insulation. As well as the basic insulation for live parts, there is a second layer of insulation, either to prevent contact with exposed conductive parts or to make sure that there can never be any contact between such parts and live parts. The outer case of the equipment need not be made of insulating material; if protected by double insulation, a metal case will not present any danger. It must never be connected with earth, so connecting leads are two-core, having no protective conductor. The symbol for a double-insulated appliance is shown in {Fig 5.20}.

EN-60335 section 27 "Provision for earthing"

"Class 0 appliances, class II appliances and class III appliances shall have no provision for protective earthing. Class II and class III may incorporate earth for functional purposes"

Adding a technical earth can be as simple as a plug with the earth wire coming out the back of it.

Adding a functional earth is a bit more than just chucking an earth in,can you guarantee  exposed conductive parts parts wont became live in the event of a fault?

Nothing against the electrical rules there. Or going further to your new position, very few jurisdictions restrict the owners of equipment from modifying it

until someone is seriously injured or killed  thanks to your modification.

[Someone]

So the challenge remains. What regulation/law/legislation is in the way? You say it exists but cannot point to

5.8.1 - Class  II equipment

Class  II  equipment has reinforced or double insulation. As well as the basic insulation for live parts, there is a second layer of insulation, either to prevent contact with exposed conductive parts or to make sure that there can never be any contact between such parts and live parts. The outer case of the equipment need not be made of insulating material; if protected by double insulation, a metal case will not present any danger. It must never be connected with earth, so connecting leads are two-core, having no protective conductor. The symbol for a double-insulated appliance is shown in {Fig 5.20}.

EN-60335 section 27 "Provision for earthing"

"Class 0 appliances, class II appliances and class III appliances shall have no provision for protective earthing. Class II and class III may incorporate earth for functional purposes"

Adding a technical earth can be as simple as a plug with the earth wire coming out the back of it.

Adding a functional earth is a bit more than just chucking an earth in,can you guarantee  exposed conductive parts parts wont became live in the event of a fault?

Nothing against the electrical rules there. Or going further to your new position, very few jurisdictions restrict the owners of equipment from modifying it

until someone is seriously injured or killed  thanks to your modification.

Bolded the bits where you are conflating things and arriving at your incorrect claim that users cannot connect a ground.

Did you know there are class I and class II products and the only difference between them is the inlet/cord ? It is true a class II appliance cannot have a protective ground path, but that does not mean it is illegal or against the rules to add one, because then it becomes a class I appliance and that rule no longer applies. Cheap and easy to go in that direction, I'm unaware of any class II construction that would fail class I after bonding a protective earth. This is aside from adding a functional or technical or earth which that quote backs up as a-ok and not prohibited as you first claimed.

And again, you've chopped the quote to make it seem like I'm the one leaving things out:

adding an earth is a no no ,at least in the uk's electrical rules

Citation required...

Adding a functional connection back to earth is perfectly safe and compatible with electrical compliance worldwide. Otherwise you'd be prohibited from connecting devices together (since once of them could have a functional earthing connection). This is all explicitly allowed (61010 3.2.2 for example) and not some sideways interpretation.

Adding a technical earth can be as simple as a plug with the earth wire coming out the back of it. Which is a perfectly legal "appliance" and readily available. Nothing against the electrical rules there. Or going further to your new position, very few jurisdictions restrict the owners of equipment from modifying it.

So we're left with it being absolutely ok from the quote you are trying to use to support your (shown to be false) claim. Neither is that a clause prohibiting a class II appliance having a function earth, or a clause prohibiting the public from modifying their equipment.

Adding a functional earth is a bit more than just chucking an earth in, can you guarantee  exposed conductive parts parts wont became live in the event of a fault?

We already have that guarantee from the existing design. Adding a functional or technical earth is not changing any of that. It's what happens when you otherwise interconnect that equipment with a path back to ground through the audio cables.

[themadhippy]

but that does not mean it is illegal or against the rules to add one, because then it becomes a class I appliance and that rule no longer applies.

And who certifys  the device now fully complies? are you confident your certification will stand up in court? In this case the speaker  manufacture has decided  for proper functioning of the  equipment no connection to earth is required.

It's what happens when you otherwise interconnect that equipment with a path back to ground through the audio cables.

so were does the microphone thats fed into the speaker complete its path to ground?Or the double insulated (as most are) playback device?

[Someone]

but that does not mean it is illegal or against the rules to add one, because then it becomes a class I appliance and that rule no longer applies.

And who certifys  the device now fully complies? are you confident your certification will stand up in court? In this case the speaker  manufacture has decided  for proper functioning of the  equipment no connection to earth is required.

Where is the requirement for a certification? People can generally do what they like with their own equipment. Note that no earth required does not imply no earth allowed.

It's what happens when you otherwise interconnect that equipment with a path back to ground through the audio cables.

so were does the microphone thats fed into the speaker complete its path to ground?Or the double insulated (as most are) playback device?

They don't have too, but they may.

You said they may not, which is incorrect.

It is clear you don't know what you're talking about but are intent on arguing away. How is this helping the OP?

OP was uncomfortable with the tingle from leakage (which we assume is within safe limits, and can be checked), adding a technical earth will solve that without impacting safety or compliance. Perfectly legal and safe.

[Someone]

I did try running a cable from the wall sockets earth, and  I touched it against the MacBooks metal case when the tingling was present.  I thought this would have helped but it made the tingling much worse, hence me not fully understanding what’s going on.

The cases of those computers (as with many others) is anodized and non-conductive on the surface. A drain for the leakage needs to be electrically bonded to the system, such as a USB shell or the shields of the audio connectors. Easier would be to buy a power adaptor that already has the bonding built in. But that can/will cause ground loops as soon as you introduce another protectively earthed devices into the system.

[tooki]

So how exactly do you think the DI box would solve this?

A pair with "earth lift" will break the ground connection between the speakers and the Mac.  The audio signals pass through the symmetric transformers, typically 600Ω:600Ω.  The Eris 3.5 has two balanced inputs as 1/4" TRS connectors (sleeve is for ground/shield), so it will act as an unbalanced-to-balanced transformer also.

Since there is no leakage current path to ground from the active speakers' ground to Mac chassis to human to physical ground, there would be no tingle either.

The cables would be a bit funky: 3.5mm TRS in, sleeve/0V/GND connected to two transformers input only.  Output is a pair of 1/4" TRS, with their sleeves possibly connected to the transformer enclosure (for shielding), but then that enclosure could give you the same tingle.  I'm not sure such cables exist off-the-shelf.

The tingle is from the interference suppression capacitors on an ungrounded switching power supply, a question that has come up many, many times here on the forums. It means your housing is floating at 1/2 mains voltage, but at an absolutely minuscule current, which is why this is not only allowed by code, but required, in order to meet EMI standards. This is normal and expected from a properly filtered supply. The fix is to actually have a ground, e.g. by tying the speakers’ case to ground (if it’s metal), or using your MacBook with the grounded mains cord (not the snap-on plug) on its power supply.

Well it's not really required, as you could use a shield between transformer windings and do other stuff. However it's the easiest and cheapest thing to do.

Thank you both for the clarification, much appreciated.

[tooki]

Its a bit old, but this summarises Apple's f***ed up grounding nicely:
https://apple.stackexchange.com/questions/17575/how-to-properly-ground-a-macbook-pro

Although it fits, a 'figure-8' mains lead is unsuitable for an Apple PSU with a stud, as it does not provide a ground so wont ground the leakage current.   You need a lead that properly grounds the stud, which will then ground the leakage current from both the Apple PSU and the speakers (via their audio signal cable shields).

But this is the same as with any device powered by an ungrounded PSU.

And in this instance, the MacBook wasn’t even plugged in, it was running off battery. It’s the leakage from the speaker PSU that OP was feeling.

[Shock]

Might want to check if your power adapter was part of a recall if you have an old one.

[themadhippy]

Where is the requirement for a certification? People can generally do what they like with their own equipment. Note that no earth required does not imply no earth allowed.

Yes you can,but the minute something goes wrong your on the hook

They don't have too, but they may.

You said they may not, which is incorrect.

?? what i said i was "adding an earth is a no no ,at least in the uk's electrical rules"

It is clear you don't know what you're talking about

your right i didn't spent a large part of the past 30+ years working in the events industry dealing with temporary electrical infrastructure . What i do know is  a  functional or technical earth is not just the shield on an audio cable. to quote the uk wiring regs definition

Functional earth is the earthing of a point or points in a system or an installation or in equipment for purposes other than safety, such as for proper functioning of electrical equipment .The connection of any functional earthing should be made to the installations Main Earth Terminal and be clearly labelled as to its purpose.

so your put a wire into plug most certainly isnt compliant,even if you used a pink cable.

[HobGoblyn]

While electronics is one of my two hobbies, even after your much appreciated explanations, I would be lying if I said I fully understand exactly what’s going on.

The power bricks you are using (to charge your macbook and to power your other equipment) input dangerous mains electricity and output safe, isolated low-voltage electricity.  They are "safety devices" that are designed to almost guarantee that you cannot be electrocuted by anything plugged into the low voltage side, like a laptop, or even if you put the output lead into your mouth like a small kid might.

snip...........

Wow, many thanks, that's a very clear explanation, Had to respond rather than just hit the thanks button.

Have learnt something new today

Again many thanks