I cued up three unison vocals on Eda Karaytug's Gönülden. Now the same Nordic signature meant that the two male singers on either side of Eda's sinuous reach an octave higher separated out better into distinct personalities. The attendant audiophile term was 'more air'. It registers as a sense of added space around individual performers. The fatter Pass harmonics injected extra connective tissue. Wherein lies the classic conundrum whenever one plays with 2nd-order harmonics. On structurally simple material, they enhance and enrich the proceedings. On more complex stuff, they congeal a bit. What one prefers depends on personal priorities – the Pass for more saturated tone, the Nords for higher perceived resolution. In a subtle way, this also affects our subjective perception of speed on rhythmically more convoluted fare. The Pass will seem subtly slower or more settled, the Nords more propulsive.

That things wouldn't be that straightforward was demonstrated by George Duke's Dukey Treats which I have as a pre-master right off the recording engineer's final mix, hence with dynamics uncut before the mastering studio dumbed them down for mass consumption. The famed ultra-low output impedance of the Ncore monos had the funky bass and brassy syncopations of "Everyday Hero" act like synthetic drum machines. They read them maximally dry and rigidly damped but simultaneously fell short in wallop, slam and juice. Here the Pass sailed into a glorious sun set with a surprisingly fat lead. It transformed the rollicking tune with decisively more grunt, growl, swagger and slam. By contrast and on this type of fare, the Nords behaved desiccated. They acted as unwelcome control freaks. On certain loudspeakers, such absolute domination is boss. I'm thinking of the Mark & Daniel Maximus 2 monitor which first had me want to own my own set of drive-anything class D. On our Audio Physic, that control was simply overdone to overshadow all other virtues.

The upshot? Despite class D enjoying a reputation for superior bass—hence its near automatic employ in active subwoofers—our beefy class A amp showed it to be unrealistically damped in the upper bass. This flatly undermined the true 'power' of that region and rendered things too dry and rigid. It felt as though all the chill dudes in George's band suddenly wore starched white shirts buttoned up to the top. No bopping Adam's apples. By the same math, lovers of hard-edged electronica could flock north. It's a matter of perspective. What behaves as a minor liability on some music can turn into a real asset on other types.

Running through the same tracks again but now versus the 1MHz DC-coupled fully balanced LinnenberG Liszt monos—200 watts like the Nord but class A/B and significantly costlier—turned tables. The Germans had far better treble elucidation than either our class A or D alternates. That made for the highest subjective resolution, the most complete ambient recovery, the sharpest focus. On the textural wet/dry axis, they pitched themselves between Pass and Nord. On bass weight, they proved closer to the Ncore. On related bass textures, they were the most elastic and buoyant. Where the XA-30.8 had the most shove and mass, Ncore the ultimate if pinched control, Ivo Linnenberg's circuit was the most adroit.

To wrap up, Rev D had undoubtedly elevated my earlier assessment of Colin North's Ncore 500 interpretation. My personal issue was owning alternatives which remained superior regardless. That put me outside their circle of trust and ideal target audience. Just so, I did have one application where they were ideal: those groundbreaking Raal Requisite SR1a ribbon ear speakers. Their interface box disables all unwelcome effects of excessive damping factor on the character of textures and music's motion through time. Textbook 'perfection' of extreme damping from massive negative feedback was the very thing my ears actually wanted defeated or annulled. With the SR1a, I had a most effective exorcist. With Nord's new-found tonal weight and higher density from a retooled input buffer, still zero noise, cool operation, compact form factor and high cost/power ratio, our refreshed class D monos had morphed into delightful SR1a managers.

As it turned out, preceding the Nord with our Nagra Classic Preamp clearly passed on subtle Swiss tube textures. That was a neat and unexpected trick which made for terrific results. Tubes + class D? Quite. In fact, one can press even farther out into that dark alley and upgrade Nagra's small-signal triodes with proper Japan-issue Takatsuki 300B. I'd done just that during the all-too-short stay of Vinnie Rossi's superlative direct-heated L2 line stage.

Direct-coupling such filamentary power triodes to class D without output transformers or coupling capacitors made for stunning results. There are off-beat paths then for even 'advanced' practitioners of the hifi arts whereby to harness the strengths of class D whilst overcoming its remaining weaknesses (if one owns classic class A or A/B gain circuits and speakers which reveal them as such). For me those were unexpected but welcome lessons from my Easter 2019 reunion with class D!