| 摘要 |
PURPOSE:To automatically control the signal level to be fed to a speaker to a proper level and to block an input to a speaker when a trouble takes place. CONSTITUTION:The output of the output amplifier of a transmitter 11 is subjected to level adjustment by the sound pressure adjusting variable resistor 19 of a sound pressure controller 12 to control the sound pressure of a speaker 21 within a preset level. When the output level of the amplifier 11 is raised when a trouble such as deterioration in parts takes place, the level is detected as at 13 and is compared with a reference level Vs so that the output polarity of the comparator is inverted to render transistor 17 conductive by means of output adjusting resistors 15 and 16. Then, a relay 18 is operated to block the output to a speaker 21 by means of a relay contact 20, thus controlling the sound pressure. |
