PURPOSE: To expand remarkably the range of a reproducing frequency toward a low frequency without decreasing the dynamic range of a power amplifier by changing automatically a low frequency boosting amount by a low frequency input signal level.
CONSTITUTION: An output signal I of an LPF15 is full-wave-rectified by a rectifier circuit 17 and enters an integration circuit 19. A DC output of the integration circuit 19 is level-shifted toward a negative voltage and the characteristic is as shown in a straight line 22 of Fig. (b). The output characteristic of an inverting circuit 20 becomes as shown in a straight line 22' of Fig. (b) by inputting an output of the integration circuit 19 to the inverting circuit 20. Then in order to limit the maximum boosting amount, a limiter circuit 18 is provided to an output side of the inverting circuit 20 and a control voltage Vk shown in a polygonal line 22" of Fig. (b) is obtained. In the control voltage Vk obtained when the level of the input signal component of a low frequency region reaches a power amplifier saturation level 11 to a voltage required to turn off a VCA 16, no saturation in the low frequency signal component is caused in the power amplifier 4 while having a margin to the dynamic range.
MORI TOORU
AWANAKA YASUAKI
| JPS56172072U | 1981-12-18 |