In article , david
wrote:
Could anyone please offer me some constructive suggestions:

Almost a year ago, I bought an Echo Mia soundcard and installed it in my
computer. Up to now I have not got it to work properly, suggesting that
my set-up is incorrect.

My set-up: the soundcard is installed within a new-ish Dell Dimension
PC. It is connected to my stereo via two pairs of mono leads, each
manufactured with an RCA jack on one end and a phono jack on the other.
These are plugged into a (high quality) DIN-phono adapter, since my
amplifier has five-pin DIN inputs and outputs. The amp operates at DIN
level (a lower signal level than the line level used by modern
equipment) and is a Sugdens A48 made in 1976. The soundcard is
connected to the amplifier via the Tape input/output.

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

I am not yet certain that we have clearly understood the nature of the
problem you have. Hence I'm not yet sure that the response others have
given are optimised.

Afraid I don't know the sound card you are using as I don't use IBM
machines much. I assume that you are using the four coaxial leads to
connect to the tape in/out pins of the DIN socket on the Sugden.

What are the details of the 'balanced' connections on the sound card? In
particular, what are the outers (shields or braids) of the coax cables
connected to at the soundcard end of the link?

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.

Similarly, whenever the amplifier is connected to the soundcard's
inputs the signal that it receives includes a constant hum, so that any
recordings I make with it from my sound system are marred by the hum
that is recorded along with the music.

Please let me know if you have any suggestions for reducing or
eliminating the hum.

It may be as someone has suggested that you need an isolation transformer.
Although I am not yet sure of this. There may be a simpler solution.

Can you confirm that the Sugden *is* signal grounded? i.e. that the outers
of its cables are connected through to the earth pin on the Sugden's mains
plug? What I am not sure of as yet is the reason why you still hear hum
when the computer is off and disconnected from the mains. This cannot be a
loop via the earth, so sounds like lack of shielding (electrostatic) or the
signal wires acting like a magnetic loop.

Slainte,

Jim

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