NAD Masters Series M22 power amplifier
The Masters Series M22 is based on a version of Hypex Electronics' model NC400 NCore amplifier module that has been customized for NAD. Fundamentally, the M22 is a pulse-width-modulating (PWM) amplifier that's DC-coupled from end to end, lacking even an output-blocking relay. (The M22 uses much faster electronic protection instead.) DC protection also includes a useful 12dB/octave high-pass characteristic at 2Hz, not by means of a traditional DC servo but via a feed-forward design that derives a low-passed signal from the input and subtracts it from the main signal at a later stage. The NCore design makes use of negative feedback, and uses a modulator that was linearized using a mathematical analysis of oscillator behavior. The distortion and output impedance remain low throughout the audioband.
The M22's specifications are impressive, particularly in terms of continuous power output and distortion250W into 8 ohms, both channels driven, and <0.003%, respectivelyeven without reference to the amplifier's weight of only 19.6 lbs. But that's not uncommon these days. What struck me is that, aside from the power-output specs, which are correlated with Ohm's law, none of the specs are differentiated by load impedance, which counters standard practice. Given that speaker loads are complex, consisting of resistive and reactive elements, load-invariant amps are likely to suit a wider range of speakers, and perform better across the audioband with each of them. And as I expected, the M22 performed well with my two sets of quite different speakers. But I'm getting ahead of myself . . .
The M22s arrived in NAD's standard packaging for its Masters Series models: outer and inner cardboard boxes and, inside the inner box, upper and lower blocks of some soft-covered material, formed to fit the M22's contours. This unknown material is much more dense and reassuring than any comparable packing substance I've seen. (Note that the M22's shipping weight is more than half again that of the amp itself.) Cutouts in the forms accommodate boxes for the M22's accessories: a power cord, a leather-cased USB drive filled with documentation, and four magnetic footers. The amp itself, as it emerged from its velour bag, felt more like a solid block of sculpted metal than an electronic device. I put the M22 in place, slipped the footers under its generously sized pointy feet, and appreciated that the latters' magnetism kept them in place even when I moved the amp around.
Setup and Operation
Connections were made with AudioQuest Earth XLR interconnects, AudioQuest Oak speaker cables, and a Kubala-Sosna Emotion AC cord. I flipped the rear power switch on, and the NAD logo on the M22's front panel glowed amber to indicate that the amp was now in standby mode. To turn the M22 on and play music required that I gentlybut not too gentlystroke the soft-touch standby switch that's recessed on the amp's top front edge. (I'd had difficulty getting the same switch on the M27 to work consistently well, and now took greater care.) My first touch was evidently too light, so I repeated it; the M22 remained off. More trials taught me that a light touch was fine, and that the M22 took a few seconds to respond: Pressing the switch again too soon only kept it in standby. (Without tactile feedback from the switch, and with a delayed response from the amp, why would users not hit it again? And why use such a nonstandard, no-feedback switch in place of something simpler?)
That's not my only gripe about the M22's switching. Apparently catering to EU demands, the M22 arrives configured to switch itself into standby after about 30 minutes without an audio signal. That's an effective way to conserve energy, but, unlike many US amps, the M22 can't then detect the reappearance of a signal and switch itself out of standbyyou have to switch it back on again manually. Unless you're a real power miser, I recommend following the simple steps outlined in the manual to deactivate this function.
Okay. Start again. I flipped the rear power switch on. The NAD logo glowed amber to indicate standby mode. A gentle stroke of the standby switch andafter a short wait the music came alive.
Bowers & Wilkins' 800 Diamond speakers (unofficially, the D2 versions) and I have cohabited in my Manhattan listening room for some years now; I know them well enough that even small changes in my system's sound are easily perceivedsometimes vividly so. Compared to my experience with the other three amps I had on hand (details to follow), the M22 immediately conjured a big, wide soundstage populated with colorful instruments and voices. Individual sounds were natural and balanced, and not conflated with the surrounding ambience. Images, too, were stable. Moreover, I found it more than a bit uncanny to open my eyes and see that only this one little box was powering two quite large speakers and filling my room with the San Francisco Symphony and Chorus (led by Michael Tilson Thomas), soprano Isabel Bayrakdarian and mezzo Lorraine Hunt Lieberson, and the pipe organ of Davies Hall, in Mahler's Symphony 2, Resurrection (2 SACD/CDs, SFSO Media 821936-0006-2), all at full cry: >100dB spl! Obviously, the M22's compactness need not earn it any special treatment in evaluations of its sound.