Circuits, systems, and methods for generating and calibrating bias for a magneto-resistive (MR) sensor. The circuit relates to a preamplifier circuit in a magnetic storage system, including an amplifier having an input coupled to a first MR sensor node, a first feedback path comprising a feedback resistor, the path configured to receive an amplifier output from the amplifier and to provide a feedback output to the first MR sensor node, a charging circuit configured to generate a current, apply the current to the first MR sensor node, and sample a voltage between the first MR sensor node and a second MR sensor node to produce a sampled voltage, the charging circuit operating when the feedback path is activated, and a bias circuit configured to apply a bias voltage across the first and second MR sensor nodes and to adjust the bias voltage to match the sampled voltage, the bias circuit operating when the feedback path is deactivated. The present invention advantageously provides for fast and accurate calibration of bias across an MR sensor that compensates for bias error introduced by the feedback path.