On Sun, 1 Sep 2002 22:52:13 -0400, "Matt M" wrote:

>I need to get audio from a desktop computer to a small receiver in an edit
>suite. I am using 2 - 20' male to female mini plug extensions from the
>computer then a mini-plug to RCA splitter to the receiver (all new cables).
>Now the problem: I get a hum when I hook it all up, but the hum goes away
>when I eliminate one of the 20' extensions. Now the confusing thing is that
>I can interchange the extensions and it works (which I assume means that all
>the cables work) but when I hook the two extensions together the hum
>returns. There doesn't seem to be anything along the path of the cables
>that would interfere, and I tried switching out the right and left
>connections just in case something got crossed over in the cables but
>nothing helps. And unfortunately I need the distance.

If you have another ground return between the computer and
receiver, changing the cable length (and ground resistance)
may make the hum worse, as may having simply insufficient
shielding in the extension cables... BTW, the cable
capacitance in long runs (especially with these skinny
cables) is also likely to roll off the HF content in the
signal. I would place the receiver closer, and use long
runs of speaker cable (also a problem, but less of one ;-),
or make really good, low-capacitance cables yourself...
Having seen the problems in audio gear, it still amazes
me that computers, with all their connecting wires, suffer
few ground loop problems...