FET Buffered Analog Voltmeter

This is a voltmeter circuit that use FET as the buffer to improve the input impedance. This circuit uses A2N3819 FET which provides a solid-state VOM. Beside that, a cathode follower in a VOM of this circuit is The 2N3819. The calibration of this circuit is done by adjusting R12 (scale/sensitivity) and R14 (zero offset).  Since FET has very high input impedance, we can choose R2 through R9  to give total resistance about 10 MΩ. High impedance (1M) resistor R10 is used to protect this circuit. Capacitor C2 is used to filter the noise and RF pickup by providing AC bypassing. Here is the schematic diagram of the  circuit: