| 摘要 |
PURPOSE:To prevent the reduction in speaker sound volume of a speaker slave equipment due to a wire resistance between a master equipment and the slave speaker by providing a constant current amplifier driving the slave speaker equipment and an operational amplifier applying arithmetic processing to a voltage generated in a calling line and a constant current amplifier extracting a reception signal on the master equipment. CONSTITUTION:A transmission signal inputted from a transmitter of the master equipment 1 is subjected to power amplification by a constant current amplifier 23 and sent to a calling line by a constant current. Thus, a voltage in response to the impedance of the calling line 3 and the speaker 21 in the case of viewing from an output terminal of a constant current amplifier 13 and a transmission signal is outputted at the output terminal. That is, even if the impedance of the calling line 3 is increased, since the output voltage of the constant current amplifier 13 is increased to compensate said increase, the current flowing to the speaker 21 is unchanged and the speaker 21 is driven by a constant power. Thus, the sound volume of the speaker is not effected by a wire resistance and the wiring for a long range is attained.
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