Ground Loop Hum

[Cyndale]

Hi,

I hope somebody can help me out here.

I have two valve power amplifiers and a valve preamplifier and I had ground loop problems, after checking the web, it was suggested to disconnect the earth connection from the preamplifier or one of the power amps to break the ground loop. I tried this and wallah it worked and it has been like this for years.

Just recently I came across an article about ground loop hum and it made me a bit nervous. It suggested under no circumstances should one disconnect the earth from any of the plugs and gave all the reasons why, which seemed common sense to me.

If I plug in one amplifier and turn it on, there is no hum, if I insert either the preamp or the other power amp without turning them on the hum comes back. I've tried doing the same with the other amp and the same thing happens. I have disconnected loudspeaker/interconnect cables and reversed them the other way round but to no avail.

Anybody got any ideas of how to get rid of the ground loop hum?

[Rocker]

Question: are the two amplifiers and the pre-amp all plugged into the same socket or extension block. If not, this ought to be your first test so plug everything into the one extension block.

[Cyndale]

Yes they are plugged into the same mains block. As i said if i have one power amp plugged in and on, as soon as i plug in the preamp or the other power amp a hum arrives.

[nige2000]

try connecting a wire to the cases of the amplifiers together, it will provide shortest earth/gnd path
worth a shot

[randytsuch]

Tubes need high voltages, so yeah, you need the ground connections for safety.

Good luck

[Cyndale]

I tried connecting an earth cable from one amp to the other, no joy! Made sure I was getting metal and not paintwork.

I have read so much over the last couple of days on the web and most of the stuff is telling you about what causes a ground loop but very little on remedies. I have tried another mains block, same result.

The hum/buzz is just there when I turn on the amps but doesn't increase in loudness when I turn up the volume.

[Diapason]

Now you don't want to listen to me cos I haven't a clue, but isn't there a school of thought that as long as a ground is connected *somewhere* in the system you're safe enough to lift ground on a couple of components? So you might be ok as you were?

[Fran]

Can you try moving your cables (interconnects) around a bit and see if the intensity of hum changes? Also try disconnecting the components one by one in your system to see if one is contributing hum? I've seen SPDIF connections doing this for example.

[ho66es]

hate chasing hum :( possible an rca shield is connected to earth on both units involved allowing them to form the dreaded loop? have a look inside, may be as simple as removing a connection? weirdly I had to add one to fix a hum lol

[Cyndale]

Now you don't want to listen to me cos I haven't a clue, but isn't there a school of thought that as long as a ground is connected *somewhere* in the system you're safe enough to lift ground on a couple of components? So you might be ok as you were?

I hear you, I was doing as you said, one of the earth wires disconnected for years, no hum.

But just recently I read that it is dangerous and will show up as such if something goes wrong with the equipment - like a serious electric shock.

Strange, that there is no hum when one amp is plugged in and turned on, plug in the turntable, no problem, plug in subwoofer, no problem, plug in preamp or other amp - HUM!

If I turn up the volume - hum doesn't increase.