Level matching is more imp

#203710
AvatarIan
Participant

Level matching is more important than impeadance matching providing the source impeadance islower than theload impeadance. (It used to be important when transformers were used in the outputs and inputs of audio equipment, which is rare there days.)
What that means is that if you plug into the external speaker (or line) output of a radio, or tape or digital player, computer device etc the output impeadance of that device will usually be low, 150 Ohms or less. The level out depending upon the volume setting on the device will be between -10 and +20dBM. If you plug that into the mic input of your camera (the input impeadance of your camera is 3k Ohms) the impeadance matching will be OK. What will be a problem is the level difference as your camera is expecting about -40 to-50dBM maximum input level and you will overload the input of the camera which will make the sound pretty distorted. The impeadance match will be fime but you will have about 40 ot 50dB too much level.

In theory you could turn the volume of the source device down low and all would be OK but the signal to noise ratio would be bad and if you managed to get the level OK there would most likely be a lot of hissand noise in the background of yourvideo.

It is easy to build an attenuating lead with a simple L attenuator in line. (Two if it is stereo)If you are handy with a soldering iron a series 10k resistor in the centre conductor with a 47 Ohm accross the centre conductor to the shield (at the camera end), per channel,will do the trick. You will be able to get an electronics tech to make one or your local electronics store may have one in stock. Please remember the attenuator will be directional.T attenuator(s) can be bi directional but require a few more components and become a bit more load impeadance sensitive.

Cheers Ian

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