Subwoofer mains hum


Standard Member

This is more a Hi-Fi question than AV, but hopefully you'll forgive me and someone can help.

I have recently purchased a Wharfedale SW-150 subwoofer which is being driven by my old Technics SU-A700 MK3 stereo amp. Very happy with it.

However I am getting a pronounced and clearly noticeable mains hum when the Technics amp is powered off.
  • The subwoofer is connected from my amplifier “B” speaker output to the speaker level input connections on the subwoofer. I use 2.5sq mm pure copper speaker cables and banana plugs. Both left and right channels are connected.
    I do not have sub out on my amp.
  • The hum stops immediately when the amplifier is powered up, even if no source is playing. I guess the amp is grounding the negative cables but only when switched on.
  • The hum still occurs if I remove the speaker cables completely from the back of the amplifier.
  • The hum stops if I remove the speaker cables from the back of the subwoofer.

  • This is clearly an induced current in the connecting wires which, being speaker cables, are unshielded - and then gets amplified by the subwoofer. I have tried moving them away from any mains cables and using a different (UK) mains socket for mains power but it persists.

I am considering getting some shielded speaker cables with a shield wrap that could be earthed to ground, in the hope that this might eliminate or reduce the induced current in the conductors. eg

Does anyone have any experience of this approach, and it it likely to work ? Anyone got a better idea ?

The long term solution is to save up for a new amp with sub out, but that isn't on the cards for a while.

Need help.



Active Member
I had the same problem with a rel sub and changed the socket it plugged into and no more hum. I tried moving cables and better sub cable and couldn`t get rid of it until i tried another plug socket and to my supprise no more hum.

fatboy frank

Distinguished Member
Last edited:


Novice Member
Hi marvin. I have this sub sw150, and i also have the 'hum'. I attribute it to the sub power cable. Or the socket on the sub it plugs into. To eliminate the annoying hum, you have to physically grab the cable and push or pull it, up down or left or right. Once the hum stops you must find a way of lodging it in place. With a rock or something to keep the cable in its new position. And yes, i do mean physically tug at the power cable.

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