An amplifier system can include a feedback amplifier circuit having an amplifier, a feedback capacitor connected between an input terminal and an output terminal of the amplifier by at least one first switch, and a reset capacitor connected across the feedback capacitor by at least one second switch and between a pair of reference voltages by at least one third switch. A slidable member is provided between a guide receiver portion of a pickup and the guide portion. The platen also has first ribs, second ribs and third ribs, respectively supportable of front and rear end portions of the sheet, formed in the marginless recording region, and spaced at suitable intervals perpendicular to the conveying direction. A pawl is connected to the trigger and operationally engages the gear member to increment the gear member once per trigger pull. The filler material is replaced by an air core under the differential signal traces. The stirring member is rotated around an axis of the shaft in a specified rotational direction to stir the developer, the specified rotational direction proceeding from the lowest part of the container body to the developer discharge port.