Pre/Power Amplifiers

This second-gen Progression 'Stereo' shows worthwhile gains in performance, in all key areas, over the 'mk1' [HFN Apr '18]. The latter was rated at 3x300W/2x600W into 8/4ohm and achieved 2x325W and 2x575W with peaks of 365W, 690W, 1.33kW and 2.29kW into 8, 4, 2 and 1ohm loads under dynamic conditions at <1% THD. The latest S350 version is rated at 2x350W/2x700W into 8/4ohm and achieves 2x390W and 2x650W, respectively, with a boost to 395W, 760W, 1.44kW and 2.53kW into 8, 4, 2 and 1ohm loads under dynamic conditions [see Graph 1, below]. That's an increase of ~2.5A in maximum current, nudging the S350 over the 50A margin. Idle draw is higher too, from 113W to 137W here, suggesting a slightly richer bias, and while the overall gain is unchanged at +24dB, the S350 enjoys both lower noise and a wider 82.8dB A-wtd S/N ratio (re. 0dBW). The original Progression Stereo offered a lower 79.6dB but, as a rule, none of D'Agostino's power amps are designed with very low noise in mind (~85dB re. 0dBW is a target figure for today's amplifiers).

Nevertheless, the S350's refinement is further reflected in its lower distortion – again, not super-low by some standards but still low enough at 0.018-0.046% (20Hz-20kHz/10W) and impressively consistent with frequency at all power levels [see Graph 2, below]. Also very consistent with frequency, rather than especially low, is the S350's output impedance at ~0.17ohm (20Hz-20kHz) while the frequency response shows some slight 'sweetening' with a gentle drop to –0.65dB/20kHz out to –2.3dB/100kHz. The S350's subsonic bass is flat down to ~1Hz so you might care to engage the subsonic/warp filter on your phono stage if you are running a vinyl front-end! PM