Audio Systems: Speaker hum, bose speakers, 12v power supply

Question
QUESTION:  I have a Bose system which I use as a tuner. The bose goes to a Carver amp which power my outdoor speakers. Ive narrowed the speaker hum, which is present even when the bose tuner is powered off, too the 12v power supply on the bose. Unplug the adapter (12v) hum is gone. Now what?

ANSWER: It sounds like a 12v DC supply in which case you are developing a ground loop from your main power to the Carver amp. There are several fixes. The cheapest one is to buy ground lift power connectors and attach them to the AC power plugs of the Bose speakers and/or the Carver amp. The other involves cutting the shielded audio cable on the input cable to the Bose speakers. You can also purchase audio transformer isolators that can be used at the input of the Bose speaker. Lastly the cleanest of all is to use cat5 baluns on either side and run a piece of cat5 cable from the Carver to the Bose. Usually one of the above will solve your problem. The baluns being the most involved but producing the best results.

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QUESTION: I forgot to mention that none of the equipment has grounded plugs, so I guess it would not be a ground loop? Also you said the cat5 balums from the carver amp to the Bose tuner or speakers?

Answer
Grounding is not necessarily done thru three wires. Most electricians cut corners and ground to one of the two conductors. Those adapters are non polarized which means that they can be reversed in the socket.

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