Pre/Power Amplifiers

In our review of PS Audio's Stellar M700 monoblocks [HFN Apr '20] I showed how its choice of ICEpower (now autonomous from its B&O parent) module brings with it some familiar foibles of 'traditional' Class D amplifiers. Specifically, the module's inductive output filter – an inescapable reality of Class D operation – causes a rise in output impedance at ultrasonic frequencies that impacts on both distortion and response that varies with loudspeaker load.

These are issues long-since dealt with by the competing Hypex UcD, Ncore and Eigentakt Class D modules developed over many years by designer Bruno Putzeys [see HFN Jun '17, Jan '19 and Aug '20, respectively, for examples]. Key to the Hypex modules' insensitivity to speaker load impedance is their 'wrapping' of this self same filter network within the amplifier's feedback loop.

However, tucked away under the long list of innovations claimed for ICEpower's latest 'Edge' version of its technology [stereo card pictured above, and now scalable over an impressive 50W to 7kW range] is the following revelation: 'all important feedback nodes in the audio path are routed to external pins of the controller creating a flexible and future-proof design... enabling our partners to implement their own proprietary modulator and feedback loops using ICEedge'. This is exactly what PS Audio engineer Darren Myers has achieved, ensuring the M1200 is not only more powerful than the M700 but also significantly more consistent and predictable in its performance with different partnering loudspeakers. PM