In article ,
david wrote:
Obviously, the soundcard is not receiving the "balanced" signal for
which it is designed, but I cannot imagine how to generate a
"balanced" input to it.

Balanced lines usually involve XLRs - you mention RCA and phono, but these
are the same thing?

And the manual does indicate that it should
work with an unbalanced signal of the kind that I am supplying to it.

With a balanced system, you normally strap the 'cold' wire to ground for
unbalanced connection.

When connected in this way, there is a near-constant hum in my system,
at a level high enough to be distinctly irritating. When the
soundcard
outputs are connected to the amp, the hum can be heard through my
loudspeakers, whether or not the computer is turned on, or even
connected to the mains power supply. The computer is normally
connected to the same power supply as the amplifier, and so they
should
be grounded at the same level. However, unplugging the computer (so
that of course it is no longer grounded) seems to make no difference
to
the hum.

If it's humming with no earth to the computer, it suggests that there's no
ground connection between it and your amp.

--
*Puritanism: The haunting fear that someone, somewhere may be happy.

Dave Plowman London SW
To e-mail, change noise into sound.