I can hear my PC think through my speakers

[AnalogSteph]

I think it's actually within (former?) the IEEE regulations common to the UK and EU that ground is sometimes connected/tied to the NEUTRAL phase of domestic mains.

Sometimes? That's standard around here - a TN-C-S system (should also be called PME in the UK and MGN in NA).

There used to be installations which would have PE branching off the neutral at each outlet as only 2-wire wiring was in the walls, but I don't think that has been a thing since, like, the early 60s? My old room 20 years ago was like that, house from the 1950s. Makes any ground loops that much worse since PE potential can vary a fair bit between outlets.

 

[audio_tony]

I think you misinterpret the meaning of 'ground'. I don't mean the EARTH. I'm refereing to the source or sink of electrons, IE the common ground. If you get a continuity tester/DMM then you'll quite possibly find there's continuity across the negative/black to the case, and sometimes to the neutral cable. I think it's actually within (former?) the IEEE regulations common to the UK and EU that ground is sometimes connected/tied to the NEUTRAL phase of domestic mains.

Most UK homes use the TN-C-S earthing system, which connects mains earth to neutral at the mains inlet board.

I found this to be the issue with a Dell laptop to my hifi some years back. Right back to the official laptop PSU, NEUTRAL mains converted to DC, sharing the negative-DC to the ground/cabinet of the hifi. Reasonably new Sony amplifier, and also a 70's JVC receiver. All double-insulated. I had ground-rail noise coming from the laptop which I had connected thru a USB soundcard, then via 3.5mm to RCA to the amplifier. All galvanically connected.

On all the Dell laptop power supplies I've ever measured, the DC poles are floating with respect to mains.
However in some models there is often a small value (1nF or so from memory) capacitor which bridges from the mains side to the DC side.
This is usually responsible for feeling a light tingle if you touch one pole of the DC connector and mains ground.

I've just checked my Dell PSU (it has a 3 prong inlet) and the outer pole of the DC connector is actually connected to mains ground.

My HP laptop on the other hand, has a 2 pin inlet, and that does float above mains ground, resulting in a tingle when touching the DC barrel connector (this often depends which way around the figure of 8 connector is plugged in).

I have to admit to some confusion regarding your statement:

Right back to the official laptop PSU, NEUTRAL mains converted to DC, sharing the negative-DC to the ground/cabinet of the hifi.

I seem to recall that in the distant past some Dell laptop PSUs had a 2 prong inlet, which floated above mains ground (and there was usually some potential between the DC connector and mains ground, as I mentioned above.

EDIT: @AnalogSteph has just posted clarification on the TN-C-S earthing.

 

[antcollinet]

Most UK homes use the TN-C-S earthing system, which connects mains earth to neutral at the mains inlet board.

But there should never be a connection nutral to ground after this point. Apart from anything else, it would most likely trigger the distribution board ELCB.

 

[audio_tony]

But there should never be a connection nutral to ground after this point.

Yes I know that. I don't think I suggested any such thing in my post?

 

[antcollinet]

Yes I know that. I don't think I suggested any such thing in my post?

No you didn't. Posts further up were (I think) suggesting that it was happening.

 

[yewneek]

Most UK homes use the TN-C-S earthing system, which connects mains earth to neutral at the mains inlet board.



On all the Dell laptop power supplies I've ever measured, the DC poles are floating with respect to mains.
However in some models there is often a small value (1nF or so from memory) capacitor which bridges from the mains side to the DC side.
This is usually responsible for feeling a light tingle if you touch one pole of the DC connector and mains ground.

I've just checked my Dell PSU (it has a 3 prong inlet) and the outer pole of the DC connector is actually connected to mains ground.

My HP laptop on the other hand, has a 2 pin inlet, and that does float above mains ground, resulting in a tingle when touching the DC barrel connector (this often depends which way around the figure of 8 connector is plugged in).

I have to admit to some confusion regarding your statement:


I seem to recall that in the distant past some Dell laptop PSUs had a 2 prong inlet, which floated above mains ground (and there was usually some potential between the DC connector and mains ground, as I mentioned above.

EDIT: @AnalogSteph has just posted clarification on the TN-C-S earthing.

I've just checked my Dell PSU (it has a 3 prong inlet) and the outer pole of the DC connector is actually connected to mains ground.

Once you have that mains ground/Earth rail bonded to the DC ground that's where the USB digital birdies come flying in. It's the galvanic connection and it's simply there, unavoidable.

With my current set-up I elected to go for a discrete USB audio interface that has balanced outputs, the Focusrite Scarlett Solo gen.3. I learned the hard way that separating the audio from the outputs with balanced conections is pretty much the only way to go. Or you can do it with optical decoupling, or an isolation transformer.

 

[antcollinet]

I've just checked my Dell PSU (it has a 3 prong inlet) and the outer pole of the DC connector is actually connected to mains ground.

Once you have that mains ground/Earth rail bonded to the DC ground that's where the USB digital birdies come flying in. It's the galvanic connection and it's simply there, unavoidable.

With my current set-up I elected to go for a discrete USB audio interface that has balanced outputs, the Focusrite Scarlett Solo gen.3. I learned the hard way that separating the audio from the outputs with balanced conections is pretty much the only way to go. Or you can do it with optical decoupling, or an isolation transformer.

That is fairly normal for class 1 equipment. The whole chassis (if metal) should be connected to mains ground. That is what the mains ground is for.

 

[audio_tony]

No you didn't. Posts further up were (I think) suggesting that it was happening.

Are you referring to my reference, re: a small value capacitor from mains to DC ground?

This is what I'm referring to to and is very common in many switch mode PSUs. Although isolated by one diode drop, there is still sufficient voltage there to give a nice tickle when contact is made between 0V and mains ground.

 

[phofman]

IIUC that Y cap is necessary for the class II switched-mode PSUs to pass the EMI tests, to prevent the secondary outputs from radiating the switched-mode frequency like an antenna against ground. https://www.eevblog.com/forum/begin...pacitor-between-primary-and-secondary-ground/

 

[antcollinet]

Are you referring to my reference, re: a small value capacitor from mains to DC ground?

This is what I'm referring to to and is very common in many switch mode PSUs. Although isolated by one diode drop, there is still sufficient voltage there to give a nice tickle when contact is made between 0V and mains ground.

View attachment 398827

I wasn't referring to any of your posts.

 

[audio_tony]

I wasn't referring to any of your posts.

I'm sure you can see my confusion! My apologies for being a bit thick lol.

 

[antcollinet]

I'm sure you can see my confusion! My apologies for being a bit thick lol.

View attachment 398856

Quite possible I was not being clear. Posts further up (by someone else)