Fig. 8

Electromagnetic shielding metallic box. Apart from the preamplifier stage, the amplification and filtering stages (second to sixth) are all arranged inside a metallic box for electromagnetic shielding purposes. The total PCB circuits are mechanically adapted at the inner side of the box top. That arrangement allows us to adjust the total voltage gain through applying torque to the potentiometer screw at the variable gain amplifier. A connector at the outer side of the metallic box provides power supply at the amplification and filtering stages through an outer switch