Earth loop hum

[robbieg]

Hi,

Running VoIP from my laptop with the power supply connected to the mains introduces a 50Hz earth loop hum into the headset that is really annoying for the other party. Unplugging the laptop from the mains and running on batteries fixes this problem - but the batteries run down! Also, muting the microphone also fixes the problem for the other party - but they can't hear me speak.

Can anyone suggest a possible solution. I understand about removing the earth wire from the plug but the power supply is already connected via a 2-wire Euro cable and the 3pin plug in the wall has a plastic earth pin.

Thanks in advance.
Robbieg

[gs]

Does this happen just at home or on more than one site?

Sounds like a faulty connection inside the laptop, removing the earth may fix it, and could be tested quickly to see if it does stop it from happening. However remember if you plug in anything else that requires earth... it wont be there.

[robbieg]

Thanks. But the power to the laptop is already by just 2 wires. There is no earth!

It actually happens on two laptops (different makes) so I am guessing it is premises based rather than machine based. I'm not sure if it happens in another location.

We have two offices that have an electricity switchbox in each, but one office feeds off the other office switch box. They each have their own earths. The broadband is distributed to the second office via mains (i.e. Powerline).

The problem happens in both offices and is fixed in both locations by unplugging the laptops from the mains.

I was thinking that the hum might be due to the Powerline networking but I still can't get my head round the fact that the hum goes if I pull the mains plug out.

[gs]

This will seem quite hard to believe, but I discovered a similar issue in my new house, if using a power supply over 500w in my PC I was getting a light crackling noise, I suspected an earth continuity problem.

So I removed my Fuse Box and replaced with a Wylex COnsumer Unit, also replaced my tails for the electrics and all cabling to my power sockets.

Same issue.

Got a mate out who is an electrician, seems that the cables from the mains into my house are old and a bit dodgy... shouldnt cause an issue, but the power company wont replace them.

Currently checking out a few different ways to trya nd resolve this. Going to try a 'Monster Surge Protector' first then try a non-switching UPS that runs off the battery all the time... lets see what happens.

[robbieg]

Thanks.

I'd be intersted to hear more about the surge protector.

Thanks for getting back.

[gs]

I know 'normal' surge protectors dont make any difference, have tried 3, each around the £10 mark. All they will protect from is a surge from a firdge or your heating system or such like, nothing major.

The 'Monster' surge protector and others like it are designed to filter out EMI so you get a crystal clear picture on your HDTV... they are supposed to get rid of static on the screen for electricity that is slightly off voltage/frequency so in theory shoudl stop my issue. Got a mate that has one I can test to see if it works, if it does its a £50~60 investment.

If it dont work... then Im getting a UPS that doesn't switch, most cheap UPS run off of the mains, but when a spike/brownout is detected they switch over to battery backup in under 0.05 of a second (usually). Not what I need to try and stop this EMI issue... so I might have to spend over £100 to get one that runs off the battery 24x7, and the mains power simply charges the battery all the time.

Hopefully I will know which works by next week sometime... Ill try and rememeber to post back 😛