Home subwoofer amp hum?

[rmitch47]

Hello all and I like the forum, thank you! Anyway I have a 400 watt home powered sub and lately I have been getting a hum, it increases when gain is increased! Weird thing is, it has the same hum even when it isnt connected to my receiver. I already tried changing the 3 prong plug to 2 prong plug thinking it was ground hum, but it wasnt that. Im thinking its a cap letting ac through, I was wondering what ppl thought. Again thank you, rmitch47

 

[audioguru]

Maybe its input cable has a broken or missing shield.
Maybe a filter capacitor in its power supply has failed.

 

[crutschow]

If the hum is there with no audio input cable connected, then I suspect a power supply filter or decoupling capacitor has failed.