buzzing sound on video camera

[canada]

We're shooting some video using a Cannon GL1, and the audio is recorded on the camera using two Sure wireless headset mics and two AKG condenser mics (not wireless) all the mics are running through a Behringer mixer, and the main XLR L and R outputs of the mixer are fed into a Beachtek DXA-4P box, which is plugged into the camera's Mic input.

We're getting a buzzing sound, like an electrical buzz, when we watch/listen to the recordings on the MiniDV tape from the camera.

Here's what I've tried already without success:
-I unplugged the A/V cable from the camera and that seemed to fix the problem for a few hours. Then the buzzing started up again the same as before.
- I made sure there were no power cables running along audio/video cables
-I tried another camera (we have two GL1's)
-I tried two different mixers, including a crest X-eight
-I tried turning off the mixer completely. we still could hear the buzzing through the headphones in the camera
- I eliminated the Beachtek box and ran a mini cable from an aux out of the mixer directly into the camera's mic input

none of the above fixed the problem. what else can I do?

[kbob]

It could be as simple as you're overloading the mic input. I don't remember offhand whether the gl has a line level input or not. If it does, then try that-you might need to adjust your menu settings for that to work correctly.

If not, then try turning the output levels way way down

[canada]

Thanks Kbob. I turned the mains way down on the mixer and turned up the mic chanel instead, and that helped alot.

Then a thought occured to me... this is an electrical buzz right? it's a typical film set with lots of high powerd lights... with dimmers. duh! why didn't I clue in? as a test, I plugged in one of our big spotlights with a dimmer into the same wall outlet as the camera and bingo! there's the buzz again. I turned off the light and it was so quiet that I could hear myself breathing through the mic.

Some times us sound guys have to think like an electrician (which I am not) I think I have the problem solved, but then again, that's what I thought yesterday and then the problem came back, so I'm still open to suggestestions/thoughts.

[kbob]

if you don't have noise the way you adjusted it prior to the discovery, I'd leave it that way-if you're actually plugged into a mic input, that is. Worth breaking out the manual.

[sien]

Sounds like a ground loop between your mixer and your camera.
You seem to have tried turning off your mixer and still hear the buzz
through your headphones.
I would go direct from the wireless into your beachtek unit and see if
that stops the buzz.

Or you could try to insert something like the
RDL AV-HK1X “HUM KILLER” Audio Isolation Module
http://www.rdlnet.com/product.php?page=244

http://www.milestek.com/SHOP/PRODUCT.ASP?ID=90%2010208
AUDIO XLR ISOLATION TRANSFORMER