A preamplifier for a laser rangefinder receiver having two signal level modes comprises, in accordance with this invention, a light detector having a first load resistor, and a buffer having an input connected across the load resistor and an output to the receiver. A first diode is placed in series with a second diode, with the second diode being connected in parallel with a second load resistor. A positive feedback path is provided from the output to the junction of the first and second diodes, wherein the first and second diodes are nonconductive during a low signal level mode, and conductive during a high signal level mode.