| 摘要 |
PURPOSE:To reduce the noises produced when a power supply is switched on and off by detecting the variation of the power supply voltage in ON and OFF states of the power supply respectively and then applying the muting to an audio signal. CONSTITUTION:When an amplifier is kept on, a power supply switch 2 is set at the side B. Thus a relay 15 is turned on together with connection of a contact E-C. A transistor TR21 is actuated later than the relay 15 owing to the presence of a delay circuit consisting of a resistance 17 and a capacitor 19. When the TR21 is turned on, the base biases of muting TR6 and 7 are lost. Thus a muting state is released to prevent that the noises given to audio signals iN8 and 9 are mixed into speakers 11 and 12 when the amplifier is turned on. When the amplifier is turned off, the switch 2 is also turned off by a circuit consisting of resistances 23 and 24 and a capacitor 20. Thus the relay 15 is turned off after a TR22 is turned on.
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