The paper describes a fast spectroscopy amplifier designed for application in conjunction with a natural diamond detector (NDD)-based spectrometer of neutrons, high-energy atoms and charged particles in thermonuclear fusion plasma experiments. The amplifier has the following distinctive features: a non-conventional shaper of spectrometric pulses; a precision "digital" base-line stabilizer; an effective built-in pile-up rejecter operating in a broad band of amplitudes. The amplifier is designed for applications at count rates up to 106 Hz with the time-to-peak for shaped pulses Tpeak≧220 ns, base-level pulse width t w≧560 ns, and the resolving time of the pile-up inspector T res≧45 ns.