| 摘要 |
PURPOSE:To control the acoustic pressure below a fixed level even when a trouble occurs in a sound outputting device which impresses an acoustic signal upon telephone lines, by amplifying the acoustic signal of a sound converting circuit to a saturated level and by removing the out-band wave with a filter. CONSTITUTION:A frequency signal (v1) corresponding to a push button signal is outputted from a sound converting circuit 1 and impressed upon the base of a transistor Tr1 through a condenser C1 of an amplifier circuit. The acoustic signal (v1) is amplified to a saturated level by the transistor Tr1 and impressed upon another transistor Tr2 as a signal (v4) after the signal (v1) is supplied to a filter circuit compound of condensers C2 and C3 and resistances R6 and R7 as a signal (v3) and the out-band wave is removed, and then impressed upon a speaker from the emitter output of the transistor Tr2. When the condenser C1 is not well opened, the base electric potential of the transistor Tr1 becomes a normal level and no sound output is issued from the speaker. Moreover, even when the short of the condenser C1 is inferior and condensers C2 and C3 are inferior, sound outputs higher than a specified level are not generated. |
