| 摘要 |
PURPOSE: A monitor listening-in apparatus of the exchange is provided to improve the sensitivity of a monitor listening-in speech sound and to eliminate noises in monitor listening-in. CONSTITUTION: A monitor listening-in apparatus consists of an excessive voltage prevention part(30), a speech monitor listening-in part(32) and an amplification part(36). The excessive voltage prevention part(30) comprises two diodes(D1,D2) which limit a voltage between a tip and a ring to a specific value. The speech monitor listening-in part(32) comprises four resistors and an inverse amplifier(34) which amplifies a monitor listening-in speech sound inputted from a tip terminal and ring terminal inversely. The amplification part(36) comprises three resistors and a non-inverse amplifier(38) which amplifies the output of the speech monitor listening-in part provided through a resistor(32).
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