Operational amplifiers with field effect transistors at the input are ideal for applications where the signal sources are of high impedance, as in the case of piezoelectric transducers. The circuit shown in the figure has these characteristics, making it possible to use very high polarization resistors. The network formed by R1 and C1 determines the lower cut of the frequency range. The power supply used must be symmetrical and operational amplifiers of the same characteristics can be used.
