| 摘要 |
PURPOSE:To perform excellent level weighting operation up to fine sound volume by setting boost characteristics of a low frequency range to a practical value through a filter circuit which uses an amplifier with gain ''3'' for an input signal, and varying the amount of attenuation in an intermediate frequency range by more than a specific value. CONSTITUTION:An input signal terminal 10 is connected to the output terminal an operational amplifier 13 through resistances 11 and 12 in sequence, whose connection point is connected to the uninverted input terminal of the amplifier 13 through a capacitor 14 and this univerted input terminal is grounded through the parallel connection circuit of a resistance 15 and a capacitor 16. The inverted input terminal of the amplifier 13 is grounded through a resistance 17, and connected to the output terminal of the amplifier 13 through a resistance 18. The amplifier 13 and resistances 17 and 18 constitute the amplifier 19 with gain ''3'', and the output of the filter circuit 20 is fetched from the output terminal of the amplifier 13. A variable resistor 22 is connected between the terminal 10 and output terminal of the circuit 20, and an output signal is fetched from the sliding terminal of the resistor 22. Thus, excellent level weighting operation up to fine sound volume is performed. |
