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

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

I'm currently trialing the NAD M23 (1st gen. Eigentakt-based), and I find it intriguing enough to want to understand it better — which means understanding the broader sonic landscape of class D. So I'm crowd-sourcing.

In a recent exchange, the estimable Ralph Karsten (Atma-Sphere Music Systems) made two comments that stopped me cold. For those who missed it, here's what he said:

"IME, class D amps vary in sound more than tube amps, which is to say, quite a lot."

"IMO there is a bigger difference between various class D amps than you hear between various tube amps. IOW just because you heard one class D amp says nothing about how the next one might sound."

Link: https://forum.audiogon.com/posts/2885828

As I think through this more carefully, these are genuinely important claims. My own experience with tube amps confirms that they produce audibly distinct characters across topologies and designs. If Ralph is right and class D exceeds that range, then generalizing from one class D experience to another is even more hazardous than I assumed.

One specific question for Audiogon members:

If you have a Class D amp or have compared class D amplifiers, how would you describe their character(s)?

Here are some criteria I use:

  1. Frequency balance — Is the tonal response even across bass, mids, and treble, or does it favor certain regions?
  2. High-frequency texture — Are the highs extended and smooth, or edgy, grainy, and fatiguing?
  3. Bass definition — Is the low end tight and articulate, or loose and bloated?
  4. Midrange character — Does the midrange feel present and natural, or recessed and thin?
  5. Transient speed — Does the amp respond quickly to dynamic attacks, or does it sound sluggish and rounded?
  6. Dynamic range — Does it scale convincingly from quiet passages to loud ones, or compress the difference?
  7. Soundstage width and depth — Does it create a convincing three-dimensional image, or sound flat and narrow?
  8. Image specificity — Are instruments and voices placed precisely, or do they blur and wander?
  9. Background noise floor — Is the silence between notes actually silent, or is there grain, haze, or hash?
  10. Long-term listenability — After an extended session, do you want to keep listening, or has something been quietly fatiguing you?

If you can include relevant system context — room, speakers, preamp — please do. Those variables will help me interpret what the amp itself is contributing.

I'm less interested in rankings than in understanding what Ralph mentioned, namely the [vast] range of sonic signatures class D is capable of. Eigentakt, Hypex, Pascal, Purifi, GaN-based, etc. — all fair game.

Price is no constraint here — I'm interested in the full range of what's out there.

hilde45
niodari's avatar
niodari
380 posts
 
@hilde45 , I just put my current perceptions, observations and suggestions, without firm conclusions.

Besides the First Watt F7 clone, ​ about two months ago I got an NHB 108 DartZeel Chinese clone, which I have now in my main system. Just plugging in, I was pleasantly surprised by the deep soundstage for an SS amp, perhaps, not worse than that of my EL 34 SET amp. I left it in my main system to break it in, it should have now close to 300 hours. It got much better after about 250 hours of working time. I will return the SET to my main system to carry out more careful composition.  It is clear that the clone has a very nice soundstage. In the rest, I am not that sure. I think now that it still  lacks mid and high frequencies compared to the SET, the bass can also be that "soft". I will try to post about my findings.  I wonder if this $400 clone sounds worse than $7.5K AGDs - ​I would like to ​have AGD monoblocks​ in my system for some time​.​ 

Besides the two Chinese clones that I recently purchased (they are so cheap that there is nothing to lose) and the SET​, I have a few other class A, AB (tube and solid state) and class  D amps. Each of them is good in some things and not that good in some other things. ​ As mentioned, I consider the bass ​and low mid frequencies of F7 ​clone almost outstanding, not precisely colored, but rather beautiful.​ But​, its  hi-midrange and highs, are ​not that good, there is an obvious lack in them. ​T​hough, since my favorite instrument is ​(acoustic) base, I still enjoy the amp.​ It is possible that original F7s have no above defect, but it is a bit surprising what happens with the mid-rage when low​s are that good​ (I suggest that the original F7s are still less colored than main line PASS amps, but cannot be sure since I did not audition an original F7 amp)​.​ LSA GaN Voyager has much better mids and highs, but low and low​-mid frequencies ​are insufficient​ and, not much but a bit dry. ​Again, since Chinese clones are so cheap (except the shipping from China), there is not much to lose. 

hilde45's avatar
hilde45 OP
6,022 posts
 

@niodari Thanks!

atmasphere's avatar
atmasphere
12,418 posts
 

As to the sound reproduction, I think, so far, Class D does not outperform class A/B and class A. 

@niodari I've not found that the case at all. Class D has proved itself able to keep up with or surpass the best of class A or AB. Its all in implementation. 

This is not to say class D is 'better'. It is to say its 'able'. IOW, someone can make a class A amp that might sound better, but to do so they would have to get a lot of things right. I'm not seeing that product in the market right now. But I'm sure its possible. Same for class AB. 

Bottom line: if the designer knows what they are doing and if the design is properly implemented then the class of operation isn't important. The result is, OTOH, paramount. 

 

hilde45's avatar
hilde45 OP
6,022 posts
 

As to the sound reproduction, I think, so far, Class D does not outperform class A/B and class A. 

@niodari I've not found that the case at all. Class D has proved itself able to keep up with or surpass the best of class A or AB. Its all in implementation. 

Over the past few years I've worked through a fairly wide range of amplifiers — Atoll, Akitika, Van Alstine, Sun Valley, and several others — each with genuine strengths and each ultimately pointing me toward a clearer sense of what I actually value in reproduced sound. When I landed on the AGD Audion monoblocks, something clicked that hadn't quite clicked before. 

What the AGD does particularly well is resolve the leading edges of transients without hardening them, maintain tonal density in the midrange, and deliver bass that is both tight and texturally informative rather than merely present. Imaging is precise without feeling artificially etched, and the overall presentation has a coherence — a sense that the music is arriving as a unified event rather than as layered components — that I found absent or only partially realized in earlier amplifiers. I have a strong sense that the amps by @atmasphere  would also fit this description, but I still need to try them.

But I think the more honest and useful observation is this: these comparisons only mean something once you've identified what you're actually listening *for*. Dynamics, precision, tonal color, soundstage depth and width, micro-detail retrieval, low-frequency control — these are separable dimensions, and different amplifier topologies genuinely do different things better. A well-implemented tube amplifier may do things with harmonic texture that solid-state doesn't. A high-bias Class A design may have a particular ease at low listening levels. The sweeping judgments — "Class D sounds sterile," "tubes are always warmer," "solid-state is always more accurate" — collapse distinctions that matter.

What I found is that once I was clear about looking for a certain (and different) cluster of priorities, the AGD wasn't merely competitive with amplifiers costing considerably more. In the areas I weight most heavily, it was superior. Other Class D amps I tried were not. What results is the *lack* of an overall verdict on Class D as a category. Instead, what I got is what atmasphere points out -- that one arrives ats a verdict on *some particular* implementation, evaluated against *my* preferences, in *my* system. Which is, I'd argue, the only verdict that actually means anything.

bartsw's avatar
bartsw
244 posts
 

@atmasphere 

Class D has proved itself able to keep up with or surpass the best of class A or AB.

Agree. I think that discussion was over years ago. I'd even say at least a decade ago and 'reproduction' doesn't get more accurate than class D. I use Hypex,ICE, Purifi as reference for comparisons, but it does not mean I like reference. It's all subjective preferences now.

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