| 摘要 |
PURPOSE:To reduce popping noise at the time of the audio elimination of an audio amplifier with a squelch function and to reduce popping noise widely in other muting operation by controlling a collector side and thus preventing the collector voltage from rising. CONSTITUTION:A signal 'B' has a level 'H' only during the watching of a priority CH and a level 'L' for other channels, and is inputted from a control terminal B. Semiconductors Q2 and Q3 are turned on with the signal 'B' at the time of the priority CH, the collector voltages of the Q2 and Q3 falls, and a transistor (TR) Q1 turns off correspondingly to mute an audio output. At this time, the voltage at a collector terminal (a) is V1 (I.R) and suppressed between the collector operating voltage V/2 of the TR Q1 and 0V. The voltage of a peak pulse during repetition accompanying dual watching drops to V/2 and variation width is also suppressed narrowly to V/2-V1, thereby reducing popping noise.
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