[Tom M]

My amp produces a ground loop hum when pluged into centain outlets in the house. In most rooms the amp will hum on 2 out of every 3 outlets. I tested this using a heavy duty extension cord and plugging the amp into each outlet in all the rooms the extension cord would reach. If is matters, the extension cord I used for this test was the three ponged kind you would use for power tools. Am I fine or do I have a serious wiring problem in this house. Because, only one outlet in each room doesn't cause the amp to hum. Could this be a bad amp design?

 

[lini]

Tom M: That's difficult to say - it depends on what else was connected to the amp and the different outlets et cetera.

Greetings from Munich!

Manfred / lini

 

[BDA_ABAT]

Most likely an issue of some of your house power outlets not being grounded. If you hear a hum when plugged into your AC AND that hum disappears when you add a cheater plug (you know, the kind of grey plug that accepts three prong plugs on one side, but have only two prongs coming out the other side), that's a ground loop.

If you take off the cheater plug, then plug the amp into a different wall outlet and don't hear the hum, most likely means that your amp is not grounded because the wall outlet is not grounded.

Good luck!

Bruce

 

[JunktionFET]

Oddly enough, I have experienced such hum in every house I've lived in.

Though I doubt it would meet UL approval, Nelson Pass's DIY designs use a bridge rectifier between the AC ground and the chassis, so that the ground is isolated until there is enough potential across the diodes for them to switch on. Seems like an elegant solution.

 

[Tom M]

Quote:

Originally posted by BDA_ABAT Most likely an issue of some of your house power outlets not being grounded. If you hear a hum when plugged into your AC AND that hum disappears when you add a cheater plug (you know, the kind of grey plug that accepts three prong plugs on one side, but have only two prongs coming out the other side), that's a ground loop. If you take off the cheater plug, then plug the amp into a different wall outlet and don't hear the hum, most likely means that your amp is not grounded because the wall outlet is not grounded. Good luck! Bruce

When using a cheater plug or the ground lift switch on the back of the amp, the hum disapears. Both my preamp and my tuner have a three prong plug but only the amp,which also has a three prong plug, hums.