Transformer hum-DC off-set killer

Posted by: leslie on 24 April 2002

Someone on the Audioasylum site suggested that wiring a 25amp bridge rectifier into either the live or the negative feeds to the transformer could reduce the hum. The rectifier was wired into the line using the + and -ve terminals and the ac connections were not used. He called it a DC off-set killer. Has anyone tried it? What is the theory behind the idea? When I tried it with an old Snaps the fuse blew and although I am not an electrical engineer I cant work out why putting it in the line should draw additional current? Help please.

Posted on: 24 April 2002 by Manu

That's completly crazy.
If you are right about the connexion, only the + or - part of the sinewave enter the transformer. The output voltage will be lower, and distorted. And it doesn't kill dc offset, it creates a mean voltage. It cannot exist a DC offset on mains line, as it comes from a transformer.

Don't try it.

Emmanuel

Posted on: 24 April 2002 by Lo Fi Si

I'm not sure it's the same thing, but bridges can be used as earth loop breakers.
Check this out. I think it explains how and why the idea works.
http://sound.westhost.com/earthing.htm

Simon

Posted on: 25 April 2002 by jpk73

Sometimes a transformer hums when the mains contain DC which usually is blended by devices like a hair drier. It's possible to remove this DC, but don't ask me how. I guess it should be done by the manufacturer...

- Jun