Expanding the Class D Conversation: How Would You Characterize Their Differences?

RECAP POST: This has been such a great --but long thread – that I decided to just add a summary of the main comparison. No need to comment if you have been following along. This is for people coming late, and for the final thought added below about Class A/B – raising the question as to whether a really good Class A/B might do what I want and that the Class D direction is, perhaps, misplaced.

LISTENING REPORT: Over multiple evenings, I ran a structured listening comparison of Class D amplifiers in my home system: a Holo Audio Spring DAC feeding a Burson-based preamp into custom speakers (15" JBL woofers, Beyma AMT tweeters) in a treated room. The contenders were the NAD M23 (running Purifi’s Eigentakt v1 module), the AGD Audion Mk. III monoblocks (GaN-based Class D), and my reference Pass XA-25. Volume was carefully calibrated at the listening position across a varied playlist — Ives, Gould’s Goldbergs, Steely Dan, Eno, Armstrong/Fitzgerald — drawn from Qobuz streaming and local hi-res files.

The AGD bested the NAD M23 v.1 in most meaningful categories. Imaging was more definite, macrodynamics faster and more dramatic, and instrument separation in dense orchestral passages (Ives, Ravel) noticeably cleaner. The biggest differentiator, though, was tonality at high SPL: the NAD could turn metallic and "shouty" on transients — a snare hit on Steely Dan, synthesizer swells on Eno, soprano peaks on Mozart — in a way the AGD simply never did. Bass was excellent on both. The NAD remained competitive on simpler material and quieter passages, but it hits a real-world ceiling where brightness and fatigue set in.

Against the Pass XA-25, the AGD’s strengths became liabilities in some respects. Where the AGD’s retrieval of detail could occasionally feel scattered — foregrounding background instruments at the expense of orchestral hierarchy — the Pass delivered everything with an effortless coherence and naturalness. Saxophone and vocals on the Pass were simply more human and sultry. The AGD was never quite strident, but on passages where it edged in that direction, the Pass wasn’t close. Both produced excellent soundstages and handled piano admirably.

So the search continues. And I’m opening it up to Class A/B. What I’m after in a Class D amplifier is what the best Class A designs do almost automatically: presence, organic tonality, and a coherent musical picture that doesn’t fray under pressure. The AGD is genuinely impressive and clearly a step forward from the NAD, but the Pass XA-25 still demonstrates what I’m reaching for. I’m increasingly uncertain whether Class D, at any price point I’m willing to consider, can fully close that gap — or whether Class A/B might still give me that combination in the qualities that matter most to me. 

And, yes, I realize this may be about the "right amplifier" and not the "right topology." That said, there has been something really nice – dynamics, snap, transients, etc. – in "Class D" as a group. So I’m not quite willing to abandon that label as a convenience.

P.S.Why else could I want what Class D offers that the Pass does not? The key point is that this would be an *additional* amplifier, not a replacement. The Pass isn’t going anywhere. But there’s something the better Class D amps do — a boldness, a speed, a dramatic snap to dynamic events — that the Pass, for all its magnificence, doesn’t quite deliver. The Pass puts music in the room with you, naturally and effortlessly; the best Class D amps launch that music at you. That combination of organic naturalness on one hand and kinetic, high-contrast excitement on the other is what I’m chasing. Whether any Class D can provide the former without sacrificing it to the latter remains, for now, an open question.

@hilde45 , ​Reading your final comments, some questions have occurred to me. You basically refer now to PASS XA-25 and did not mention SIT 3, do you  consider that XA-25 totally dominates SIT 3? From what I read, XA-25 gives a bit plane soundstage compared to F7 and SIT amps, but you may of course have other experience. I did not completely grasp the "grip" in class D and "presence" in class A. To me, the "presence" implies a feeling that the musicians are right there in your room. This yields all the naturally perceivable acoustic characteristics, don't you agree? 

By the way, ​earlier in this thread I complained about the mids and highs of my ​Chinese Pass F7 clone​. It is ​now  opening up (still with quite a few run hours). It may be the best amp I ha​ve ever had in my second system.  The mids and highs became quite nice. I think now that F​7 is a seriously good amplifier, which changed my ​earlier attitude towards Pass gear. ​My previous experience ​with main line Pass gear was that they produce an artificially coloured sound reproduction (I  don't drink Koka-kola,  I prefer plain water or tea without sugar: to me, tea loses its flavor if sugared). But F7 plays quite soft and natural, deep base, clean mids and highs. So I got now also interested in XA-25 and SIT amps (I wonder how they compare to F7). ​

@niodari 

I’ve only experienced the PASS XA-25 and the SIT 3. The Pass has, overall in my system, a punchier feel to notes and percussion, firmer tonality – richer, deeper broader hue, clearer articulation and more 3D dynamics, a bit wider soundstage – overall, just more present and real.

That said, the SIT-3 has many of these qualities in superior ways to other amplifiers – plus, a supremely delicate and natural presence. Grip is articulation + dynamics + speed -- taut bass, effortless in fast transitions. Yes, presence is the feeling that the musicians are in the room but it’s also a certain tonality. Not edged with clarity – as every class D amp I've heard either does or nearly does – but more like present from the middle outwards. A warmish hue.

Good to hear about your ​Chinese Pass F7 clone​. I don’t find my Pass – which is really unique in the Pass line (read about it) does not have an artificially coloured sound. I have heard good things about the F7. You describe it like I would describe my Pass.

All of these amps are present and tonally gentle, rich, and real in ways the AGD, NAD, Hypex I have tried are not. Without tonality and presence, they are not nearly in the same league, in my opinion – with my speakers, in room, for my tastes, of course.

I hold out hope that Atmasphere may be the amplifier that reaches into the category of sound that I’m interested in. My hope is that his decades of experience as a tube amp designer gives him the experience and ear for that, at least.

I'm late to this very good discussion. At this year's Axpona madhouse the only thing that made me rethink redoing my just finished system was the Devialet class A/D equipment. Even in those poor (acoustic wise) rooms they were the standout. Lordy!  

They are not cheap but given their integrated chops they have considerable value. They can also be used as mono AMPs yielding 600 Watts per side if 300W per side isn't enough. The remote volume controll just plain sexy. 

Oh là là. Its sont fantastiques. J'adore ça, Daddyoh!

Here is my two cents: I have not experienced listening to many Class D amps, but I have not yet heard one that would sway me into buying it over a comparably priced A/AB amp. That said, there are advantages in weight and size of most Class Ds. But they seem to lack the weight of the bass and they sound rolled off in the highs to me. In all fairness it could have been the amps I have heard (none above the$6K price point). But I am still not convinced.

And as a side note, I have a close friend that has an incredible system with Sound Lab A1 speakers with a home-made tube pre-amp and Jeff Rowland amps & DAC. He has personally known Mr. Rowland since at least the 1980s when Jeff was just doing electronic repairs and started developing his own amplifiers and formed Rowland Research. I remember my friend telling me about the excitement Rowland had about the "new" ICE module that was the beginning of the Class D era. That was over twenty years ago. After trying to make the Class D amps, Rowland eventually gave up and abandoned the technology as he could never get fully satisfied with the end result; he could not get the sound to be up to his high standards. Today, if you look at the brands offering Class D, it seems to be many of the mass marketing manufacturers, because they can be made affordably. Now of course there may be exceptions to that, with some specialized boutique firms still trying to make it work. I think that speaks for itself: the sound of Class D is still evolving, but when a well respected high end amplifier engineer leaves it aside, I will too.