Integrated Amplifiers

Although the Stellar Strata MK2 still employs the same ICEpower 200AS2 Class D module as the MK1, here it achieves far closer to the 215W/4ohm output spec’d in the 200AS2’s datasheet. PS Audio has not changed its specification, but the MK1’s 110W/8ohm and 175W/4ohm output is increased to 2x117W and 2x206W in this MK2, respectively. Again, headroom is limited, so output under dynamic conditions is fixed at 120W, 233W and 268W into 8, 4 and 2ohm, falling to 162W/1ohm with its 12.7A current limit [see Graph 1]. Distortion increases with level from 0.006% to 0.04% from 1-100W/8ohm, and with frequency from 0.013-0.3% (20Hz-20kHz/10W/8ohm). The A-wtd S/N is improved by 2dB to 83dB in the MK2 over the MK1 even though the amplifier’s gain is unchanged at +36.8dB.

The ICEpower 200AS2 module’s inductive output filter causes a rise in impedance at ultrasonic frequencies that impacts both distortion and response with changes in loudspeaker load. Unloaded, the Strata MK2 has a huge resonance/response peak of +27dB/48kHz, flattening out into 8ohm loads to the tune of +1.6dB/20kHz (peaking at +4dB/43kHz) and ‘flatter’ still into 4ohm at +0.25dB/20kHz before drooping to –2.2dB/20kHz into 2ohm and –5.5dB/20kHz into 1ohm.

The DAC has been upgraded to the ES9018K2M (from the ES9016) here but the 105dB A-wtd S/N is unchanged and jitter remains very high at 7000psec. THD falls to a minimum of ~0.0045% over the top 40dB of its dynamic range through mid and high frequencies [Graph 2] and response depends on choice of filter (fast/slow linear phase and min phase) at –0.1dB/20kHz, –3.1dB/20kHz and –0.2dB/20kHz, respectively. PM