in-line add-on mic buzzes

[vince-cctv 0]

I recently bought an 8-camera + DVR kit called the Poseidon-85 made by NightOwl. The camera are 1/4 CMOS color, with IR night mode. No audio.

 

 

There were cameras with mics built in, but the price jump up too much. Instead I found some really cheap in-line powered mics on ebay made for cctv setups. The mic has a "splitter" for the power jack to get power from the existing power cable for the camera. I supplied my own 50 foot RCA audio cable to run alongside the factory camera cable. Sounds like a good plan right? Cheaper than buying a camera with audio built in?

 

Yes, but....

 

When the camera and the mic are on, there is a very loud buzzing being picked up by the mic. So much that it muffles speech in the recorded zone. If I unplug the camera's power that is right next to the mic, sharing the same power cable, the buzz stops and the mic records beautifully. Connecting other cameras to the DVR does not introduce buzz to the DVR, only when connecting the powered mic and a camera on the same power cable.

 

Both mic and cam run on 12VDC.

 

A fix might be to just get another separate power cable for the mic. BUT, I already have the cameras setup and wires run, (and buried!)... if I could conquer the buzz the cables could remain as they are.

 

Sorry for the long explanation, but I'd rather over-explain my setup than not explain enough and get no progress on the topic.

 

I'm quite comfortable with a soldering iron and semiconductors, so I'm wondering if there's a way to isolate the buzz somehow with a capacitor or 1:1 transformer.... but this is where I'm stuck. Anyone have input about this?

 

I checked the grounding for the camera and the mic, and even tried running the mic audio without ground. Stumped.

[ljarrald 0]

sounds like the DC adaptor is cheap and doesn't regulate the power...

try putting a voltage regulator on the output of it.

[vince-cctv 0]

Not a bad idea! I have some and will try this over the weekend and report back.