With today's laptops, experience has shown this problem is in all probability caused by the AC Ground Loop when the earphone jack is used as Line Output (or even if the laptop has a dedicated Line Output).

To achieve product safety standards and appease outfits like UL, CSA, etc. the laptop manufacturers carry the third prong AC ground from the power supply right through to the chassis common of the laptop.

*The way to prove that it is indeed the AC Ground Loop causing the hum is simple enough with a Laptop: Temporarily UNplug the AC from the socket while the system is up and running and humming, let the laptop run from its internal battery.

If the hum and noise disappears when doing the above, you need the Ground Loop Isolator in between your audio output and the input to amplifier.



--Mac

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