PURPOSE: To facilitate the design for the print panel by building the offset control resistor into the operational amplifier in order to take no consideration of the offset control circuit for the conducting pattern design of the print panel.

CONSTITUTION: The terminal of offset control resistor VR is connected to the offset control resistance terminal on the base of the operational amplifier. Then the container cap containing an opening drilled at the center is covered so that the adjustor such as screw head A of resistor VR may be exposed outside. Otherwise the offset control resistor is put onto the container of the operational amplifier, and the offset control resistance terminal of the operational amplifier is connected to the terminal of the offset control resistor via the insulator lead wire. Thus the offset control resistor to be installed separately can be omitted, facilitating the design for the print panel.