We found this amplifier with high input impedance and low capacitance, using FET, in a documentation from the 70's. The FET can be the BF245 and the PNP transistor the BC558. The supply can be done with voltages from 5 to 12 V. The gain is given by the relationship between R3 and R5. Consumption is very low, making it possible to use a battery for power.
