HI-FI

> Room restrictions mean that I can only use small front loudspeakers
> (KEF Cresta, bookshelf sized). This, in turn, implies a need for a
> subwoofer. I bought a KEF PSW 1000 with the Crestas, since that seemed
> to give a decent sonic match.
>
> A little while ago, I was forced to dismantle my entire system
> (because a new TV aerial system was being installed in the block of
> flats where I live, and the workmen needed access to the corner of the
> room behind it). Ever since I reassembled it, Ive found that I had a
> mains hum audible through the speakers. Its mildly irritating in the
> main speakers, but utterly unbearable if the subwoofer is turned on.
> Ive been managing without the subwoofer.
>
> Yesterday, I (at last) found the time to try to trace and rectify the
> source of the annoying noise. It seems to be the subwoofer itself. The
> hum disappears if I either unplug its signal cable from the amplifier
> or unplug the subwoofer from the mains. Moving the subwoofer doesnt
> help, so the issue doesnt seem to be its proximity to other equipment
> etc.
>
> As things stand, then, I have a system which really needs a subwoofer,
> but no usable subwoofer.
>
> So...
>
> Anyone got any bright ideas as to why a subwoofer should be causing a
> mains hum in the rest of the audio system, and how it might easily be
> cured? I dont really want to spend out on a new subwoofer if I can
> avoid it. And if I do, I dont know what to get. A KEF PSW 1000.2, I
> suppose, unless I splash out on an entire new set of speakers...
>
> Peter.

> Anyone got any bright ideas as to why a subwoofer should be causing a
> mains hum in the rest of the audio system, and how it might easily be
> cured? I dont really want to spend out on a new subwoofer if I can
> avoid it. And if I do, I dont know what to get. A KEF PSW 1000.2, I
> suppose, unless I splash out on an entire new set of speakers...

>A couple of things to try.

>Firstly, try and route the mains cable away from thre signal cables.

> I
>use ferrite chokes on all of my mains leads as an extra precaution where
>signal and mains leads need to be close.

>Secondly, its possible that the shielding in your signal cable got
>damaged during the dismantling process. Can you try a different cable to
>see if that helps?

>Finally, some sort of mains conditioner might help. I get a lot of hum
>from the sub. on my Kef 100 system. Adding an Isotek filter cut down the
>noise quite significantly.

>Its possible that installation of the aerial system has caused a loss
>of earth somewhere - that could cause such a problem. Can you check the
>aerial guys work?

> Its possible and well known for kit to fail after a
>move - its happened to me in the past. However, given that the sub. is
>a solid lump my money is on something external, like the TV aerial work.
>As a last thought: does the sub. hum if you connect to the mains
>somewhere else in the house? If not, then you have a local issue somewhere.

>Good luck.

>Assuming it doesnt hum on its own, Id say you have a screen off
>somewhere. Hum tends to be caused by no ground connection - or too many.
>;-)

> >Assuming it doesnt hum on its own, Id say you have a screen off
> >somewhere. Hum tends to be caused by no ground connection - or too many.
> >;-)

> Uh... This is the land of the moulded plug. I tend to assume that KEF
> and Denon (amp manufacturer) know what earthing their products
> require. Im reluctant to go hacking plugs off and, in any case, am no
> electrician: I wouldnt know what to do after.

> Whilst your analysis of the problem may well be valid, Ive no idea
> what to do about it... except to buy a new sub...

> Yesterday, I (at last) found the time to try to trace and rectify the
> source of the annoying noise. It seems to be the subwoofer itself. The
> hum disappears if I either unplug its signal cable from the amplifier
> or unplug the subwoofer from the mains. Moving the subwoofer doesnt
> help, so the issue doesnt seem to be its proximity to other equipment
> etc.

> Does your subwoofer power cable have a 3 prong power plug? The problem
> is the noise in your electrical system transferring to the sub via the
> earth point of the power plug. Just replace it with a power cable with
> a 2 prong power plug, removing the earth point in this way will remove
> the noise from transferring to the sub. Your sub is well shielded so
> the earth plug is not required, I run my sub with a 2 prong plug.