| 摘要 |
The level of a playback signal is detected by an AGC detector circuit and a current relating to the detected playback signal is supplied to a switching circuit. Furthermore, a constant current generated at a constant-current generator circuit is also supplied to the switching circuit. In accordance with the detection result of a no-signal detector circuit, the switching circuit outputs a constant signal when there is no signal and a current for the playback signal level when there is a signal. A current-voltage converter circuit converts the current from the switching circuit into a control voltage, which is supplied to the AGC amplifier as a gain control signal. As a result, the control voltage in the AGC amplifier can be set to a constant for when there is no signal so that the gain setting can be improved.
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