Help finding ground loop

[mylittlehouse]

Hello all
I need a little help if anyone can advise.
I moved into a new house and my active speakers are buzzing with a low ground loop hum
The house is 1970’s and has a dual rCD protection.
No supplier earth so its using an earth rod.
I have tested live and neutral volts, volts between earth and live and drop is no more than 1 volt difference.
It’s driving me mad.
If i take my system to another house it doesn’t buzz only in this s house, the system has speakers all connected to a preamp, all devices are two core only there is no earth on anything.
When a speaker which is made from aluminium on a metal wall mount its worse. When I take it off its less but changes which speaker is buzzing.
The speakers are all connected with a 8 pin cable that carry’s sound and trigger and every cable as a ground built in.

Does anyone have any thoughts how to identify if a specific appliance is causing this or if its the circuit itself. The speakers are connected with the TV and built in pre amp to one socket and rear speakers are on another socket.
I have tested every socket with a socket tester and there is no open connections and voltage is the same across all of them.
I know it could be that there are two sources of ground that can cause the loop but i cannot work out where it is if its that.
There appears to be one earth from the dust board to a terminal block which goes to the earth rod, the earth rod is connected to the main metal water pipe from rod to pipe, the boiler has a earth cable to the incoming connection and all rad feed and return, hot and cold have earth connected between them

Any thoughts? I am at a loss what to test to get rid of this annoying buzz that must be on the neautral unless its coming via the sky cable that is connected to the TV or the mains.

I have an electrician coming on Wednesday to change a single socket to a double and add another double on the other side of the master bedroom and they will check the earth but wonder if I am missing something.
Cheers
Sean

 

[Harry Bloomfield]

Ground loops are where items are connected to two earths of slightly different potential - hence you get some 50Hz current flowing along the ground via it's interconnections and screening. Even plugging two interconnected items in via two different sockets can cause this. Sometimes it can help to cut the screen braiding between units.

 

[mylittlehouse]

Is there a way to test this using a multimeter please?
My speakers are wall mounted and are mainly made of metal but only live is neutral from the mains.
Is there a way to test it to be sure as removing the grounding cable might work but I would have to kill two very expensive cables or maybe put rubber washers between speakers and the wall and use plastic screws maybe.

 

[mylittlehouse]

I have two rings one for kitchen and one for rest of the house, both parts of the system are on the same ring, but I cannot see if they are connected to another earth let’s say

 

[Harry Bloomfield]

Is there a way to test this using a multimeter please?
My speakers are wall mounted and are mainly made of metal but only live is neutral from the mains.
Is there a way to test it to be sure as removing the grounding cable might work but I would have to kill two very expensive cables or maybe put rubber washers between speakers and the wall and use plastic screws maybe.

Maybe this will help you understand the problem better...

https://www.thebroadcastbridge.com/content/entry/11485/getting-rid-of-audio-ground-loops

 

[SUNRAY]

If i take my system to another house it doesn’t buzz only in this s house, the system has speakers all connected to a preamp, all devices are two core only there is no earth on anything.

This isn't a real earth loop if as you say there are no earth wires. Do not disconnect any interconnects.

What happens if the units are stood on a wooden table or similar?

 

[bernardgreen]

Are any of the units supplied with mains via a 2 pin plug, ( only Live and Neutral and no mains Earth. )

The internal "ground" ( 0 V of signals ) of these units will be floating at an AC voltage somewhere between Neutral and Live ( typically at about 120 V AC ) When this floating internal ground is connected via a signal lead to another internal "ground" that is Earthed via the mains plug then a current will flow along that connection. This will introduce mains hum in the signal lead.

 

[AdrianUK]

This is your friend here ......

At least in terms of being able to electrically 'separate' the parts in order to work out what is happening.

 

[mylittlehouse]

Are any of the units supplied with mains via a 2 pin plug, ( only Live and Neutral and no mains Earth. )

The internal "ground" ( 0 V of signals ) of these units will be floating at an AC voltage somewhere between Neutral and Live ( typically at about 120 V AC ) When this floating internal ground is connected via a signal lead to another internal "ground" that is Earthed via the mains plug then a current will flow along that connection. This will introduce mains hum in the signal lead.

Hello there
Sorry been fault finding.

My system is Bang and Olufsen, the TV has a 2 pin plug (live and neutral) there are seven active speakers all with a 2 pin plug.
the system has no earth connection the mains.
All speakers are aluminum body

All speakers are connected to the TV via a screened powerlink cable (8 pin din) that carriers a switch wire, low voltage left and right, common ground and a screened ground on the outer RJ45
So if I understand you correctly the system is not grounded via its power source but could we an issue with one of my cables as the system is only grounded to itself unless one of the walls touching the aluminum is providing a ground.

This weekend I plan to cable test every interconnected cable for a circuit and also check if there is any cross talk across cable pins.

driving me nuts

 

[SUNRAY]

What happens if the units are stood on a wooden table or similar?