Integrated Amplifiers

A key feature of all Class D amps, particularly those running from switchmode PSUs, is very high efficiency (~85% here) and cool running from, typically, a very slim chassis. So the Stellar Strata is more powerful than it looks, matching its 150W/4ohm rating at 110W/8ohm and 175W/4ohm, the Class D architecture yielding little or no difference under dynamic conditions at 100W, 180W and 235W into 8, 4 and 2ohm, falling to 135W/1ohm as a result of its 11.6A current limit [see Graph 1, below]. The trend of gently rising distortion of 0.003%/1W to 0.0085%/10W and 0.035%/100W is slightly lower under continuous conditions but the steep increase in THD vs. frequency from 0.0075%/1kHz to 0.055%/10kHz and 0.12%/20kHz (all 10W/8ohm) is a function of the amp's output filter. The latter also influences frequency response and sensitivity to speaker loading [see boxout, p55] but the 81dB A-wtd S/N ratio (re. 0dBW), while lower than 'average', is still a few dB ahead of other, similar, Class D amplifiers.

The performance of the ESS 9016K2M-based DAC stage and 'Gain Cell' preamp is indirectly influenced by the ICEpower amp because various functions are powered directly from the latter's switchmode supply. Tested at the '77' volume position (2.1V output re. 0dBFs), the A-wtd S/N is a generous 105dB but jitter is very high indeed via all inputs at 6500psec and 3100psec (48kHz and 96kHz/24-bit, respectively). THD falls to a minimum of ~0.004% over the top 40dB of its dynamic range through mid and high frequencies [Graph 2, below] but increases to ~0.1% at low bass frequencies. Response depends on choice of filter (fast/slow linear phase and minimum phase) at –0.3dB/20kHz, –3.3dB/20kHz and –0.4dB/20kHz, respectively. PM