The AM 502 is a DC-coupled differential amplifier with excellent common-mode rejection capabilities and high gain for low-voltage measurements. The DC OFFSET capability permits nulling up to one volt DC, so that low level, low frequency signals impressed on a DC level can be amplified without the degradation often introduced by AC input coupling. High and low frequency —3 dB points can be selected at the front panel to suit the application. Signal inputs and outputs are available at the rear connector as well as at the front panel. A front-panel lamp indicates most over-range conditions of excessive input signal (either differential or common mode), excessive gain, or excessive offset.