| 摘要 |
PURPOSE:To prevent an uncomfortable impulsive tone from a speaker by not only cutting off a DC voltage to an amplifying circuit by a switching transistor TR but also muting the amplifying circuit by a muting TR when a dial signal is transmitted. CONSTITUTION:When dial buttons of a dial pulse generating circuit 13 are depressed for the purpose of transmitting the dial pulse signal, a muting signal is generated from the circuit 13, and a switching TR 23 is turned off to cut off the supply of the DC voltage to an amplifying circuit 22. Simultaneously, a muting TR 25 is turned on to mute the circuit 22. Therefore, the impulsive tone is not generated from a speaker 7 even if the DC voltage to the circuit 22 is changed quickly. When the transmission of the dial signal to the other party is terminated, a terminal MT goes to the high level again, and the signal applied to the TR 23 through an inverter 24 goes to the low level, and therefore, the TR 23 is turned on again to apply the DC voltage to the circuit 22, and the TR 25 is turned off.
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