Integrated Amplifiers

There's no shortage information on PS Audio's website about the proprietary building blocks employed in the Stellar Strata – its 'Gain Cell' op-amp receiving comprehensive discussion – but 'ICEpower', once a B&O technology, and 'Class D' are nowhere to be found. Which is a pity because, evidently, PS Audio has selected these OEM modules for use as the beating heart of its amplifiers for reasons of performance. So why not celebrate the fact?

In practice, PS Audio's choice of ICEpower's '200W/4ohm' 200AS2 stereo Class D amplifier for the Strata brings with it far greater parallel with the Stellar M700 [HFN Apr '20] than the M1200 monoblock [HFN Jan '21] which features ICEpower's latest 'Edge' version of its technology. So it's the M700 and Strata that retain the familiar foibles of 'traditional' Class D amplifiers. Here the module's inductive output filter [the two coils, lower right of inside shot, p54] causes a rise in output impedance at ultrasonic frequencies [up to 21ohm/48kHz, red trace, inset Graph] that impacts on both distortion and response with changes in loudspeaker load. Unloaded, the Strata (ie the 200AS2) has a phenomenal resonance/response peak of +29dB/49kHz [grey trace, inset Graph]. Into 8ohm [black trace] it rises to +1.8dB/20kHz before peaking at +4.2dB/46kHz, but is 'flatter' into 4ohm at +0.3dB/20kHz [orange] before drooping to –2.2dB/20kHz into 2ohm [blue] and –5.7dB/20kHz into 1ohm [green]. So the treble response of the Strata may depend very heavily on your choice of partnering loudspeaker. PM