AC Hum from Stereo Speakers

[Voyager407]

I am presently traveling in a 2000 Land Yacht 390 XL. The speaker system has a push-button that powers a three-position switch: Stereo, Video, and Off. The speaker system and the radio itself are 12v DC and operate fine when we are dry camping. However, when we are connected to AC power, there is usually an awful AC hum when we are listening to the radio and have the speakers set to Stereo. (You can't hear the radio if you switch the external speakers off.) Sometimes the hum is so loud that you can't enjoy the music at all! Most of the time, if we switch the radio off, the speakers STILL emit this awful hum!

I know this sounds like a ground loop problem, but why is there no hum when we watch and listen to the TV (broadcast, cable, or DVD) through the same speakers set to Video?

I would appreciate any advice you might have.

[HowieE]

My first guess would be ac coupling directly into the radio antenna from the convertor. Try disconnecting the convertor while the radio is on and the hum is there. If the hum goes away trace the antenna wire and see if it comes close to the convertor.

[wlj1943]

Defective diode in the OEM Magnetek converter converter can cause this.