60 Hz Hum from Powered Sub

Hi All-=

I have an older (late 90's?) Tannoy PS110 powered subwoofer. It has a 3-prong (grounded) permanently connected power cable. Over the last month it has developed a 60 Hz hum. I've plugged it in different locations in the house to rule out ground loop. The hum is present whether there is an audio source connected or not. Is it time to just move on or is this something worth repairing? Could this be something simple, and if so, how can I diagnose it? Any suggestions are appreciated!


Thanks cleeds I got a phone call from a city official I been waiting on.. I got excited, only took a month for the call back. :-)

Excuse me, I meant to say sub panel, and must be bonded at the main.

At the a sub a jumper can be between the TWO. It will work but I separate and have found it to be a source of noise in my house wiring.

I check ground and commons for amperage to ground. It always amazes me what I find there and the difference between the TWO.

A 220/240 sub panel, with a blower motor using L1 and L2 and in the same sub panel, stereo receptacle (s) being uses on one or the other hot rails. That is a no no in my system for noise..

My house is quiet and I have a  mix of nob and tube on the old AND Romex on all the new construction.  SOOW 4/3/g feed both shops, and 12/2/g for all shops, basement, kitchen and attic outlets..

The house is 14/2/g and nob and tube.

Bottom line OP shared grounds can make noise..:-)
@ spacecadet65,

Which sound best describes the hum you hear from the sub?  

60Hz hum  

60Hz buzz  

120Hz hum  

Did you try a 3 wire to 2 wire cheater plug yet?  
Make sure you insulate the ground tab on the cheater so it does not contact the 6/32 trim screw that holds on the outlet cover plate. The 6/32 screw is grounded.
Almost all subs have a "plate amp" with a switching power supply and are very prone to this type of problem. Check with Tannoy and see if they have an exchange program where they send you a rebuilt plate amp, which you can change out yourself. If not, some repair shops will work on the removed plate amp, saving a lot of shipping cost. Also if you remove it, sometimes it is easy to spot a split cap.
Are you using the low or high level inputs to the sub? If you're using the low, it's probably a bad cap in the subwoofer. You might just try the high level inputs if you have them. I know that cured the hum in my older Sunfire sub years ago. I replaced all big electrolytic caps and it still hummed, no matter what I did. This just might work? It would be a temporary cure until you either upgrade to a newer and better sub, or decide to send it in for repair. Good luck.
Power your sub from the mains plug which is also connected to your other devices. Basically, all the earth potentials of all the devices must be on the exact same potential. If there is even a few millivolts difference, you will get the dreaded hum. Every device must be on a STAR connection, meaning plug everything into the SAME mains outlet with the shortest possible power cables.