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Posted by David on 03/27/07 06:02
Thanks, Richard and EHSTC -
Let me share with you the results of my experimentation and further
research.
1.) Per Richard's suggestion, I tried a resistor in series with the
ground connection. Specifically, I got a three wire plug, and wired
up only the ground pin, through the resistor, and then clamped the
wire from the resistor to the base of the camcorder at the tripod
socket. Starting high and working downward, I first attempted this
with a 100K ohm resistor and that somewhat decreased the hum but
didn't get rid of it. Then I tried a 1K ohm resistor and that
silenced the hum. So clearly the current involved is quite low. I
couldn't hear the difference between having the 1K resistor and no
resistor at all.
2.) I then thought about ground loops. The Sony camcorder has a two
wire plug on the brick, not a three wire, and I read on a web site
somewhere that the Sony uses a "floating ground" - which I think means
that the camera chassis is not connected to the signal ground of its
electronics. Since the only thing I have connected to it is a
battery powered external mic there is no possibility of a ground loop
here. Similarly, the only other piece of gear that I use with it
that does plug in, a Behringer mixer, also uses a two wire AC cord to
a "brick" so presumably it has a floating ground as well.
Rich, I will experiment with routing the wires in different
positions. I did notice that the hum varied with the orientation of
the camcorder, but didn't nail it down the way you did.
In any case, it is hum-free for now when grounded, whether battery
powered or AC powered, so I am a happy guy. Thanks for the help.
- David
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