A process and a small, sensitive, low noise, high gain, power amplifier used in the process, for exploiting the anisotropic magnetoresistance effect in a ferromagnetic thin-film. The magnetization of the thin-film is biased to lie along the hard axis. The amplifier is configured so that a sensing current in the thin-film flows at an angle of forty-five degrees to the nominal direction of magnetization, and the current to be amplified produces a magnetic field parallel to the easy axis of the thin-film.