New cable = 'hum' on subwoofer...Why?

vansboy

Hi All!

B&Q in Luton clearing out loads cables/connections, so bought a 3m Masterplug phono-phno extension, to replace the standard one supplied with the Philips home cinema system we have. I'd already upgraded the other speaker cables.

It sent a really loud buzz to the sub, so phoned the really helpful people on Masterplugs freefone helpline & they said it wasnt compatible.

So took it back & got refund & swaped it for a 1m cable from their Performance Series. They couldn't say if this was suitable or not, on the fone, though!

Result now is a posher cable, without the loud buzz, but there is a noticable 'hum' instead!! It's not apparent with the standard cable, though!

Is this doing any good/bad to the system or sub, or should I revert to the thin original wire (it really is thin) that Philips provided?

Thanks in advance!

VB

fwor

It may be that you've inadvertently created an "earth loop". Is it possible to tell whether the cable screen is connected to the plug at both ends on the old cable? Some cables are only connected at one end.

You can ~sometimes~ test and temporarily eliminate an earth loop by turning off all of the kit and easing out the phono plug(s) at one end so that only the central pin is connected - this only works on plugs with long central pins, though.

And no, the hum should not do speakers or amps any harm as long as it's not tooo (i.e. unbearably) loud!

spud17

A buzz would seem to indicate a poor connection, possibly inside plug.
On the other hand a (50hz) hum is an earth loop.
Does the new lead follow the same route as the original, if not, does it pass close to e.g. amplifier or something else with a transformer?
Refit the original lead to eliminate something else being disturbed whilst removing/reconnecting.