as seen in fig4 the unit 106 includes a pair of operational amplifiers 107 and 108 the operational amplifier 107 includes an inverting input at pin 2 a non inverting input at pin 3 and an output at pin 1 the operational amplifier 108 includes an inverting input at pin 6 a non inverting input at pin 5 and an output at pin 7 positive dc power is applied to pin 8 and negative dc power is applied to pin 4 turning back to fig3 a and 3b and particularly to fig3 a a resistor 109 is connected from the input 102 to the non inverting input 5 of the operational amplifier 108 and a resistor 111 is connected from the input 102 to the inverting input pin 6 of the operational amplifier 108 a capacitor 112 is connected from the input pin 5 to ground the output pin 7 of the operational amplifier 108 is connected to the non inverting input pin 3 of the operational amplifier 107 a resistor 113 is connected between the inverting and non inverting input pins 2 and 3 respectively of the operational amplifier 107 while a capacitor 114 and a resistor 116 are connected from the input pins 2 and 3 respectively to ground a resistor 117 is connected between the inverting input pin 6 of the operational amplifier 108 and the non inverting input 3 of the operational amplifier 107 a positive dc voltage is applied to the pin 8 and the pin 4 is connected to the ground the gain of the operational amplifier unit.