solving hum problem using external mic with camcorder

[David94114]

Hi -

I hope I am posting in the right forum, & if not, apologies...

I am trying to use an external electret condenser mic with my Sony camcorder's external mic-in connector which has "plug in power".

It works great if I am running on batteries; but generates bad 60Hz hum if running on AC power. The microphone itself has no AC connection, so there is no possibility of the typical ground loop problem.

I do notice that the hum varies quite a bit depending on how I actually hold the camcorder; for example touching the metal plate that holds the tripod screw often makes the hum go away, if the mic is clipped to my own body, but not if the mic is across the room. I have heard that sony uses "floating ground" in its camcorders; perhaps this is what makes it so sensitive?

I tried two different mics - on a capsule only, running on the camcorder's plug in power. THe other is an AudioTechnica At-35s, which is battery powered, and which supposedly is designed for camcorders. Both mics work fine on battery but both hum when using the camera on AC power. So I doubt it is the mic that is the problem.

Any suggestions as to how to get rid of this hum? I have considered but not yet tried the following:
1.) cut into the power supply cord and add some more filtration?
2.) add blocking cap to the connection between camera and mic?
3.) ground the shielded cable that connects to the mic to the tripod socket instead of just the sleeve of the connector?

I am eager to try some things but don't want to take a risk of damaging the camcorder. Any suggestions would be appreciated.

Thanks in advance.
- David