5.2 The Amplifier-Filter-Unit of the Seismograph

The amplifier-filter-unit of the seismograph is simply constructed from few component parts. The voltage supply for the Ic's can be bought as a kit for self-assembly at an electronic shop. - The amplification-factor k_v is adjusted by the ratio (R₂ + R₃) / R₂ , the cutoff frequency f_cutoff of the low-pass filter is determined by
1 / [2π · (R4 · C3 · R5 · C4)0,5]
The rest can be taken from the following circuit diagram.

Fig. 45: Circuit-diagram of the Amplifier-filter-unit of the seismograph