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Posted by Stuart on 08/28/07 05:51
"Rick Merrill" <rick0.merrill@NOSPAM.gmail.com> wrote in message
news:RomdnfGIW6lvck_bnZ2dnUVZ_uygnZ2d@comcast.com...
>I am feeding from a audio board/console only designed for a *line* output
>not a mic output.
>
> The video camera is only designed for an external *mic* input with AGC on
> (and does not have a line input nor AGC off).
>
> The wire from the audio board to the camera external audio input is
> about 24 feet long and is unshielded.
>
> We experience noise on the camera that 'breaths'.
>
> What approach would you suggest?
Re-stating your dilemma - you have an audio console with line level out and
a camera that only has mic level in? That's a horrible mismatch in level
(volts) and impedance and a recipe for severe distortion and noise - there
are a number of solutions...
You need to reduce the output level down to near mic level with a simple
pad such as the one shown here
http://www.tkk.fi/Misc/Electronics/circuits/line_to_mic.html this involves
the use of 2 x 20 cent resistors in a basic set up. The attenuator will stop
the AGC from pumping or 'breathing'. If you can disable it all the better.
The cable should be shielded and although the console is probably unbalanced
(you could check the specs) the shield should only be connected at the
console end. If the console has a balanced output, then this will reduce the
possibility of external noise pickup in the cable.
If you want to get more opinions and solutions just Google "Line level
signal to microphone input adapter" There are DI boxes that the recording
industry and musicians use - some are just nice looking and expensive black
boxes with 2 or maybe 3 resistors inside, others are powered with a small
amount of gain.
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