| 摘要 |
<p>An audio amplifiencircuit comprising: a voltage-gain amplifier 16 and a current-gain amplifier 17 in series thereafter between an input node 11 and an output node 12; power supply lines 18 for supplying power to the audio amplifier circuit; an outer negative feedback loop 20 around the current-gain amplifier 17 and the voltage-gain amplifier 16; an inner negative feedback loop 20 around the voltage-gain amplifier 23; a first switch 27 for selectively connecting the power supply lines 18 to the current-gain amplifier 17; a second switch 28 for selectively switching the inner negative feedback loop 23 or the outer feedback loop 20 to the voltage-gain amplifier 16; and a control circuit 36, 37 arranged to control the switch during power supply switching. On supply of power: the power supply lines 18 are disconnected from the current-gain amplifier 17; the inner feedback loop 23 is switched to the voltage-gain amplifier 16 and subsequently, after a delay sufficient to allow the output of the voltage-gain amplifier 16 to stabilise, the power supply lines 18 are connected to the current-gain amplifier 17; and the inner feedback loop 23 is switched to the voltage-gain amplifier 16. When power is removed, the inner feedback loop 23 is switched to the voltage-gain amplifier 16 and subsequently the power supply lines 18 are disconnected from the current-gain amplifier 17. The audio amplifier circuit further comprises a charging path 25 including resistance means 26 for charging the output node 12 of the audio amplifier circuit to its quiescent level through the resistance means 26; and a fourth switch means 30 for selectively opening or closing the charging path 25. When power is supplied the fourth switch means 30 is closed and subsequently, after a delay sufficient to allow the output node 12 of the audio amplifier circuit to be charged to the quiescent voltage, opening the fourth switch means 30.
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