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Posted by Stuart on 08/28/07 06:07
"Stuart" <stuart@whodunnit8.com> wrote in message
news:CJOAi.26936$4A1.12917@news-server.bigpond.net.au...
>
> "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.
A better illustration and photograph
http://staff.ace.ac.nz/centres/technology/BruceWeb/Projectrp/kploaded.htm
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