Could be that the mic power gets shorted out.? You could try a big electrolytic cap instead, shorting the hum to ground but not the DC.
Thanks -- recommended spec for the cap? I took a 16V 47?F, tied the negative lead to the shield and when I touch the positive lead to the plug ring wire the mic goes totally dead, as before.
(Or is that cap too big so it's still effectively shorting out?)
Or just connect the mic to both inputs.
@Gerwin:
I have tried to get rid of this hum many times, both with ultrasonic mic or normal audio. It is the raspberry Pi and the cheap sound card that will make it impossible. There are two solutions.
Thank you -- I have done this before with a Pi and was moderately successful when I covered the audio interface in grounded foil, and surrounded the mic itself with grounded foil (not the front of the mic of course)... that had almost no hum (and I wasn't even using shielded cable for the mic-interface connection -- long story). I also note that when I plug my twin PiP mic into this interface (tip and ring wired to different capsules, shared ground) there is no hum at all (though the overall quality is poor).
-c
