Mains interference on monobloc

Hi all
just purchased a minty Musical/F M-A50 monobloc to beef up the H/T setup (for centre channel) only to find that it is really sensitive to mains (or poss EM, etc) noise. If I plug in the DVD player (or the freeview box) or if I switch on the TV at the main switch the M/Fidelity generates a nasty hum that is not volume dependent. Any ideas on how to cure this without costing an arm and a leg or reducing the sound quality (too much)?
BTW I've tried using different sockets (one in another room!!), a Belkin suppressed/protected extension lead and moving the amp away from the TV - still only works fine without the other appliances energised..........

 

Do you have all these appliances plugged in to your Hi-Fi?

If so, it sounds like a ground loop. Try plugging the monoblock in with only the centre pin of the RCA plugs. you can normally manage this if you almost pull the plug out, but not quite. See if it stops the hum.

 

Let me know when you find the solution ....I've a liitle of the same but the hum is very low level so not totally intrusive.

 

Thanks guys, thinking about "ground loop", which is a good place to start with google if you have a similar problem. Difficulty is that the hum is there with or without the input connected to another appliance. It must be coming from the mains supply and the normal method to remove this is from the signal path using an isolating transformer, such as illustrated in this good article (sold in car audio supply stores):
http://www.users.bigpond.com/bcolliso/earth-loop.htm
Wonder whether anyone has got decent results with a supply conditioner, such as the one from Maplin
http://www.maplin.co.uk/Module.aspx?ModuleNo=46830&criteria=conditioner&doy=22m3
or a Russ Andrews unit (such as the silencer)??
I'll report back if I get anywhere.
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If you get hum from the amp when it is not connected to any device, only the mains then it may not be a ground loop.

Have you tried playing with the path of the wires (so they always cross at right-angles etc..) and tried moving the amp about to see if you can find the source of noise?

Otherwise.. it does just sound sensitive to mains.

Do you have a dimmer light?

 

heard about dimmers and I do have one, will check type as that is important AFIK. regarding the supply I have plugged it in well away from the TV etc and it seems to pick up the TV interference - wondering if there is some earth problem that involves the aerial earth interacting with the ring main earth via the TV, cables to/from TV (ie at the DVD or Freeview box) - got me old man coming over tonight and he is an engineer with lots of TV, radio, hifi, fixed wiring experience - wish me luck. Worried that MFidelity stuff is very mains sensitive - can anyone confirm this? or offer a solution please?? grovel grovel
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DO you have cable TV, or an aerial amplifier? There can be a problem with an earth loop via the TV signal coax sheilding, and since the DVD/Freeview and TV are usually connected together, would behave just as described.

The cure in this case would be a 'braid breaker' on the incoming 'aerial' connection.

 

The dimmer will only make a noise if it is on or partly on. If you get the problem while it is completely off then it ain’t that.

 

Check that the interconnect cable on the A50 is the right way round. May sound daft but some cables only connect the shield at one end which should usually be connected at the source end.

 

mmm....maybe....I'll upgrade it to my only uni-directional interconnect and see, thnx
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I suffered from a humming noise on my monoblock set up a few years back and my problem was solved by tightening the electricity cables in the 13 amp socket feeding my system.
It can be quite surprising the way electric cables work loose.

 

Mine seems connected to a dab ...when connected to the pre with ic's or digi coax....if I use the optical there's not a hum. So for the time thats the way things will be connected.