A disk drive preamplifier (preamp) includes a write driver that has two pairs of programmable bypass current sources not connected to the write current source to compensate for the inherent magnetic asymmetry of the write head. One pair of the programmable bypass current sources provides a fixed bypass current in one direction. The other pair provides a fixed bypass current in the opposite direction. Prior to writing, only one of the pairs of bypass current sources is selected and programmed with the correct value of bypass current. When the write driver generates the positive and negative write current pulses during writing the selected bypass current sources provide a fixed offset to the amplitude of the write current pulses.