| 摘要 |
PURPOSE:To cope with the fluctuation, etc. in an input level to a telephone device which is caused by the state of connection of a trunk line while the trunk line receives a loudspeaking speech, by providing an AGC circuit to a telephone amplifier, and absorbing the fluctuation in the level to be fed without providing any amplifier at the side of a sound source. CONSTITUTION:An AGC circuit is provided to an amplifier 14 of each of telephones 3-a-3-k which receive the signal of input level e1 from a signal source. Then the level e3 to be supplied to an amplifying stage is set at a certain value which does not depend on the level e1. These telephones 3-a-3-k containing amplifiers 14 are connected in parallel to a channel 8 and a signal transmission line 9 which are connected to a main device 1. Thus a key telephone system is formed. Thus the sound information is applied to the amplifier 14 under the control of switches 28-30 connected to sound circuits 25-27 of the device 1 and then delivered to a speaker 54. In this case, the fluctuation of the input level to the amplifier 14 which is caused by the control state of switches 28-30 is absorbed by the AGC circuit. Thus a certain level is always secured for the sound output given through the speaker 54. |
