Originally Posted By: jazzmammal
...No noise until I plug in an audio cable into either the audio input or output on the back of the SC. The instant the cable makes connection I get the noise...


Classic AC Ground Loop symptom, stop focusing on the USB and correct it at the analog inputs and outputs, which are the circuits actually being affected, regardless of where the multiple AC ground occurs. Audio Isolation Transformers inserted there should stop the problem cold and safely.

Power Conditioner is not likely to help here.

If you are in the US, try connecting the AC of the unit via a three-prong to two-prong AC adaptor, UL listed. That will break the multiple path to AC ground and thus usually clears up the problem. Other countries this may not be legal to do. That means you would have to find and purchase Line Level Audio Isolation Transformers for the analog inputs and outputs.


--Mac

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