60 Hz Hum from Powered Sub

spacecadet65   said:

08-30-2021 9:13am

The hum is present whether there is an audio source connected or not.

Funny, I was using my sub's Line Input/LFE connection via RCA cable from my loop out right/left connections on my power amplifier and all was well.

Now using the high level speaker input connection with the amps plug adaptor off my speaker terminals and I get the 60Hz hum.

Need to mess around with it more, but why would the power amp to the LFE be fine, but not the high level speaker terminals (producing hum)?

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!