Subwoofer Hun (ground loop?)

TheCyclingProgrammer

Not sure if this is the best forum for it but anyway...for a while I’ve had a problem with an audible hum from my subwoofer in a 5.1 home cinema setup. It’s connected to a Denon AV receiver on the other side of the room by a cable that runs under the floor.

I’ve tried all sorts of things to eliminate it, disconnecting things from the receiver to see if it got rid of it but nothing worked.

Then, based on a tip, I read about how grounding the amp to the subwoofer can potentially fix it. The subwoofer is connected to the household ring main earth but the amp is not as it is double insulated and doesn’t have an earth wire. I used some flex I had lying around to create a fly lead which I connected to an amp chassis screw and when I touched the other end one of the the plug socket screws, the hum disappeared.

Can somebody explain to me why this gets rid of the hum and if there’s any reason not to just leave the fly lead connected between the outlet screw and the chassis and leaving it earthed? Is this safe?

kwikbreaks

There's a whole article on the subject on Wikipedia - https://en.wikipedia.org/wiki/Ground_loop_(electricity)

In essence there must be a small current running in your signal lead grounds because the chassis of the amp is being grounded by them. Running your own piece of wire to ground the amp chassis to the same mains earth has stopped that.

I'd leave the grounding wire in place if it gets rid of the hum.

Jon_01

This must be the German version then?

John_Gray

An alternative meaning is a (usually female) term of endearment: "honey", more usually abbreviated as "hon" but pronounced "hun".
As in "You OK, hon?"

Even more alternatively, it might be a typo, as kwikbreaks has cleverly spotted!

TheCyclingProgrammer

Well yes, obviously it was meant to say "hum". That's what happens when you post late (it may have been autocorrect).

kwikbreaks - thanks, I vaguely understand the concept of a ground loop although I believed a ground loop was caused when two pieces of connected equipment had more than one path to earth, hence the loop. I couldn't quite figure out where the loop was in the prior arrangement - obviously the amp and sub are connected by a shielded cable, the sub is connected to the ring main earth, the amp is not, so I couldn't quite get my head around how the chassis to ring main earth was breaking the loop.

Like you say, if it fixes it then I may as well leave it, I was wondering if there was any safety reason not to that I was missing. The circuit is RCD protected and so a live earth fault situation would trip?