| 摘要 |
PURPOSE: An audio amplifier is provided to minimize white noises and prevent degradation of sound by varying an amplification ratio corresponding to an input signal. CONSTITUTION: An A/D converter(30) converts an analog input signal into a digital signal. A ROM(50) stores the first and second amplification ratios for controlling gains of a pre-amplifier(20) and a main amplifier(10). A controller(40) reads the first and second amplification ratios from a digital signal from the A/D converter to outputs the first and second gain control signals corresponding to the amplification ratios. The pre-amplifier amplifies an analog input signal into the first amplification ratio in response to the first gain control signal. The main amplifier amplifies an output signal of the pre-amplifier into the second amplification ratio in response to the second gain control signal. A speaker(11) converts an output signal of the main amplifier into an audio signal.
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