| 摘要 |
PROBLEM TO BE SOLVED: To attain a maximum volume automatically depending on the impedance of a speaker by operating the input impedance of the speaker and switching the tap of a power supply transformer supplying power to an amplifying circuit based on the operation results. SOLUTION: The audio amplifying circuit comprises an amplifier 3 for feeding an input audio signal to a speaker while amplifying, a power supply circuit 8 supplying power to the amplifier 3 through a transformer 10 having a plurality of taps, a current detecting circuit 6 detecting an output current from the power supply circuit 8, and a control circuit 7 for operating the input impedance of the speaker based on the level of the input audio signal and the output current detected by the current detecting circuit and switching the tap of the transformer based on the operation results wherein the maximum output is prevented from lowering through switching of the tap at the time of using a low impedance speaker. |
