| 摘要 |
PURPOSE:To erase noise caused at power-off by providing a detection circuit and a control circuit minimizing the amplifier gain of an audio output circuit across a resistor of a power line limiting the output level of the audio output amplifier. CONSTITUTION:When a power switch 8 is turned off, the output voltage of a power supply circuit 22 starts decreasing, the tuner is untuned, noise is caused and it is sent to a video/audio detection circuit 21 and an audio output DC control circuit 4. On the other hand, a voltage Vb at a terminal of the audio output limit resistor 5 has a large load such as the video/audio detection circuit 21 and the audio output DC control circuit 4. The voltage Va is a voltage stored in an audio output ripple rejecting capacitor 7, and the discharge load consists of an audio output amplifier 6 and an audio output limit resistor 5 and is comparatively small. Then the voltage Va becomes larger than the voltage Vb st the power-off, a potential difference detection TR 23 is turned on, an audio erasure pulse is obtained at its collector and sent to an inverter 13, resulting in being fed to the circuit 4. The gain of the preamplifier is minimized so as to allow no noise to be fed to the audio output amplifier 6.
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