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SOLVED - Sub hum, lots of tests 99% sure it's the amp?


Active Member
My sub has been humming for a while and these are the results of my tests:

  1. Disconnect phono cable = no hum
  2. New sub cable = hum
  3. Plug sub into same 4 gang as the amp = hum
  4. Different sub = hum
  5. Unplug all speakers = hum
  6. Unplug HDMI but not speakers from the sub = no hum
  7. Add HDMI one at a time (Chromecast, PS3, Sky) hum increases gradually!
So, I reckon something is up with the amp (Onkyo TX-NR609). Even if you don't fully plug in the HDMI from a switched-off component and just touch the case the sub hum increases. Unfortunately I don't have a spare receiver to test with.

Anything else I can test or is it definitely the amp - and can I fix it?

Many thanks.


Active Member
Oh and the sub still hums even if the amp isn't plugged in. Grounding problem in the amp?
I can take the whole setup into work and try there to see if it's a problem with my electrics. Just trying to narrow it down!


Active Member
After a couple of weeks of headscratching and trying more cable / plug combinations and adding a filter nothing was doing the trick. I knew it was a grounding problem and it was only when I actually tried setting up the whole thing in a separate room that I noticed the obvious problem - them receive isn't grounded at all. The thing has a plastic earth pin so no wonder there was a problem with ground loop hum. My TV, PS4 and Chromecast don't have earth connections either, only the sub.

So, a bit of rewiring and the problem is 'solved' by lifting the ground on the sub. Far from ideal but what other solution is there - manually ground every other piece of electrical equipment plugged into the amp?


Well-known Member
Thanks for your feedback on this issue - I have epic hum that comes and goes on my system, it's damn annoying... lol

It gets much worse when you switch the oven on - what's that all about?! :laugh:

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