We present a spectroscopic system constituted by a Silicon Drift Detector (SDD) coupled to a CMOS charge sensitive preamplifier, named SIRIO, specifically designed to reach ultimate low noise levels. The SDD, with an active area of 13 mm 2 , has been manufactured by optimizing the production processes in order to reduce the anode current, successfully reaching current densities between 17 pA/cm 2 and 25 pA/cm 2 at + 20 ° C for drift fields ranging from 100 V/cm to 500 V/cm. The preamplifier shows minimum intrinsic noise levels of 1.27 and 1.0 electrons r.m.s. at +20 ° C and -30 ° C, respectively. At room temperature (+ 20 ° C) the 55 Fe 5.9 keV and the pulser lines have 136 eV and 64 eV FWHM, respectively, corresponding to an equivalent noise charge of 7.4 electrons r.m.s.; the noise threshold is at 165 eV. The energy resolution, as measured on the pulser line, ranges from 82 eV FWHM (9.4 electrons r.m.s.) at + 30 ° C down to 29 eV FWHM (3.3 electrons r.m.s.) at - 30 ° C.