The circuit shown in the figure has a more efficient action, with an attenuation of 12 dB per octave from the cutoff frequency, calculated by the formula next to the diagram. Note that C3 must maintain the ratio of half the value of C1 and C2. The operational amplifier used is of the type with field effect transistor at the input such as those of the TLC series or the CA3140. The power supply must be symmetrical, and the input impedance is very high.
