Abstract: A circuit for measuring signal output of a transducer includes an amplifier having a differential input and a single ended output referenced to a fixed potential. One transducer terminal is coupled through a source follower to an input terminal of the differential input and the other transducer terminal is coupled through a source follower and a resistive element to the other input terminal of the differential input whereby the transducer terminals are isolated from the fixed potential. A voltage to current converter converts the voltage at the single ended output to an output current that is applied to an input branch of a current mirror. A first output branch of the current mirror supplies a current equal to the converter output current to one terminal of the differential input. A second output branch of the current mirror supplies a current equal to the converter output current to the other terminal of the differential input.

Abstract: A multi-stage amplifier having a plurality of switch mechanisms, one for each stage, that are individually controllable to vary the gain of the amplifier without compromising bandwidth. The amplifier may be embodied in a magnetic storage medium magnetic storage medium that includes a preamplifier in which the multi-stage amplifier is embodied.