The paper presents a shaping amplifier developed to boost the count rate of a soft X-ray spectrometer AMPTEK based on a fast silicon drift detector (SDD). The amplifier differentiates step-like signals from the charge sensitive  preamplifier of the SDD and gains the output signals for digitizing. The rise time of the output signals is reduced in regards with that of the AMPTEK shaping amplifier whereas the noise of these amplifiers is kept at the same level.  The shorter rise time allows better resolution of closely overlapped output pulses and reduces the pile-up effects at high input count rates. The design of the amplifier is presented in the paper as well as its tests for noise, linearity and resolution of close overlapped pulses.