This is called a ground loop. It's caused by
audio equipment being at different ground
potentials. The potentials will balance
themselves out by sending a current over any
available connection. In this case, it's over the
analog interconnect cables to your powered
speakers. It's grounding itself through your
powered speaker amplifier.
Since the Squeezebox has a "floating ground" (note
the power supply has only two pins and does not
use the 3rd grounding pin) I don't know what to
tell you regarding its cause or possible
solutions. Usually the solution is to provide a
better path for the equipment to ground itself.
This involves making sure the units are plugged
into the same outlet and ensuring the outlet
ground is OK by using a circuit tester. As a last
resort, you can connect the two components' cases
together using speaker wire.
None of this won't do much in your case since the
Squeezebox has a floating ground, so I'll leave
that one to the more experienced.
However there's something you can do to minimize
this. The hum is coming from your computer
speaker amplifier. So if you turn it up it will
get worse. The idea is then to have as large a
gain on the Squeezebox as possible and as little
gain on the computer speaker amplifier as
possible. So set the SB's volume to maximum and
turn down the computer speakers' volume to suit.
This won't eliminate the problem, but it will
minimize it.
I'm at a loss as to where the ground loop would be
coming from. Since the SB has a floating ground,
it cannot "generate" its own ground loop, it
merely "passes it along" and acts like a link in a
chain. Is there anything else connected to the
computer speakers? Is the SB wired? If it is,
it's the Ethernet cable that's not grounded
properly. Try disconnecting the cable. The hum
should disappear immediately...along with the
music, unfortunately!
max.spicer wrote:
> Whilst I wait for my T-Amp to arrive, I've got my
SB3 plugged into some
> Labtek computer speakers. The speakers themselves
don't actually sound
> too bad, but they have a fairly loud hum when the
SB3 is plugged in.
> When powered on, but with nothing plugged into them,
they are fine.
> The moment I plug in the SB3, they start to hum.
However, if I touch
> the exposed metal parts of the rca connectors, the
hum goes away. I'm
> not suggesting that this is the fault of the SB3,
but is there anything
> that people can suggest to sort this out (short of
standing touching the
> connectors all the time!)? My limited electrical
knowledge tells me
> that I have mains hum and that there is a grounding
issue.
>
> One thing of note, is that I'm fairly sure the
speakers didn't hum when
> plugged into the SoundBlaster Live in my computer.
>
> Thanks,
>
> Max
>
>
--
___________________________________
Mark Lanctot, [EMAIL PROTECTED]
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