60 Hz Hum from Powered Sub

Have not read all responses. So at the risk of repeating, the most common cause for a subwoofer hum is cheap cable or a cheap cable that eventually went bad. Poor shielding is the most common exact culprit on a cheap cable. Power cord is also a possible culprit. Solid copper 75 ohm Quad Shield RG6 terminated with a RCA plug is an inexpensive alternative to all the other types of subwoofer cables that are offered, sold or recommended as being the best. None of those offerings will be quad shielded. The solid copper coax RG6 cables are easily found and are probably the least expensive of all the options.   

nob and tube

Knob and tube. Cost me a fortune to replace after some flood damage.

OK. So I was wrong about one thing. The permanently attached power cable is a 2-prong, polarized version, where you can't invert it in the wall socket. So there was no way to use a cheater plug to get out of this. 

@jea48: It is definitely the middle YouTube video hum. Great videos, BTW.

This is a pretty old unit. $400 gets me a basic 12" Emotiva sub that will run rings around it. I may open it up and take a look at the caps. If it looks like there's something obviously amiss, maybe I'll try to do a repair. It's not worth paying someone to work on it given what it is...

I really appreciate all of the advice!

Hey,

If you get the hum with NO audio connections and just plugged in you need to have it serviced. It’s probably a power cap that’s going. Get them all replaced before it blows.  If you can afford it and they are available, get higher temp caps than you originally had.  They'll have a much longer lifespan.

Best,

E

If you're going to open it, be careful to discharge all large electrolytic capacitors through a resistor. These caps can store some high and potentially lethal voltages for a long time. All plate amps I've worked on use 105C capacitors.