A disk drive is disclosed comprising a head actuated over a disk including a plurality of tracks defined by servo sectors, wherein each track comprises a plurality of data sectors. The disk drive further comprises a preamp circuit operable to amplify a read signal emanating from the head to generate a pre-amplified read signal. A first gain setting of the preamp circuit is calibrated in response to a plurality of the servo sectors, and the first gain setting is adjusted in response to a plurality of the data sectors.