An audio amplifier is an electronic amplifier designed to amplify the audio signals of low power from a capture device (microphone, musical instrument) or storage (tape, CD, etc.). in order to feed a enceinte.Un preamplifier acts as a first amplifier stage located closer to the signal source. In accordance with the theorem Friis, it is he who is the guarantor of a good signal to noise ratio at the output of the system as it is to succeed in extracting a very small electrical signal. The oscillators are found in all applications so it is desired to electrically measure a physical signal downstream of a transducer of some sort.

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