60 Hz Hum from Powered Sub

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.

I assume the DC power supply uses full wave rectification.

: a rectifier that converts alternating current into continuous current and that utilizes both halves of each cycle of the alternating current.

120 ripples per second.
I would think if it is a bad electrolytic cap in the DC power supply the hum buzz would sound like this:

120Hz Hum
https://www.youtube.com/watch?v=pC4Uzt0qm2E

or this,

Like a 120Hz buzz
https://www.youtube.com/watch?v=pf-vULfjYK8

If you added a new electrical device, it could be anything from a cooktop to a heater. This device could be causing a DC on mains issue which causes  the transformer to buzz. So you need to isolate the noise. If the driver is making the noise, it is most likely a ground issue somewhere, aging components or aging sub cable with deteriorating connector. If the transformer is buzzing, it is most likely the DC on mains issue. Emotiva makes a specialty filter that works if that is the issue. If the sub is old, its not worth fixing unless it has a special connection for some reason.