[D]

On Oct 18, 3:59 am, Laurence Payne NOSPAMlpayne1ATdsl.pipex.com
wrote:
On Wed, 17 Oct 2007 13:15:59 -0700, "Richard Crowley"

wrote:
"D" wrote ...
The hum is from speakers, not from the case. Yes, either of the
headsets work OK on another computer.

Then it is possible that the sound card has a problem.
Since the sound card feeds power into the microphone in
the handset, the filter capacitor on the microphone power
may have a problem that is letting 50Hz hum get injected
into whatever microphone is connected. You would not
hear this unless a microphone was connected. Since the
headsets work OK on another computer, that casts the
suspicion back on the sound card.

Perhaps the sound card just has the problem that it's a Soundblaster
Live! and you're using the mic input. A SB's Line in/out is
acceptable quality but the mic input is a joke.
Thanks Richard Crowley and Laurence Payne for your explanations!
A Sony ECM-T6 microphone and another desk-top microphone don't hum! A
new Koss sb/45 headset and Philips SBC HM300 headset hum from their
microphones.
How to make Koss sb/45 headset microphone work?
Best regards,
Dima