| 摘要 |
PROBLEM TO BE SOLVED: To eliminate noise generated from a speaker when the power is supplied or when the power is switched off without needing a mute circuit composed of a switch, and to adjust volume outputted from the speaker without using a volume. SOLUTION: The number of transistor pairs to be operated is changed by a control circuit. For instance, a mute operation is performed by bringing all transistor pairs in an initially operating mode to the stop mode in turn to reduce the number of transistor pairs in the operating mode and finally stopping the operations of all the transistor pairs. Volume outputted from the speaker is also adjusted to an optional level by operating the number of transistor pairs, which corresponds to the sound level instruction of a user inputted to the control circuit.
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