| 摘要 |
The speech signals generated by a microphone (11) are fed to the input of a pre-amplifier (12), which has a control input (8). The amplification factor of the pre-amplifier can be changed by feeding a control direct current to the control input. The amplified speech signals reach a power amplifier (14) via a volume controller (13). An earphone (15) is connected to the output of the power amplifier. The output signal of the amplifier is also fed to a threshold stage (19), which generates a pulse signal when the said output signal reaches or exceeds a threshold value. The pulse signal is fed to a switch stage (20), which discharges an integrator (18) which is connected to the control input (8) of the pre-amplifier (12), for as long as the control signal is present. The amplification factor of the pre-amplifier (12) is thus reduced, for as long as the output voltage of the power amplifier (14) exceeds the threshold voltage. After the control signal disappears, the voltage of the integrator (18) rises considerably more slowly than it previously sank. Correspondingly, the amplification factor slowly increases, until a pulse signal appears again. In this way, an effective limitation of the sound level is achieved, but the non-linear distortion factor is kept extremely low, even if the limitation is high. <IMAGE>
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