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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
koestner
740 posts
 

@hilde45

This should be printed out and nailed to the front door of your nearest Hi-fi store.

I am very much anticipating your comparisons of the NAD M23 vs. the Pass XA25

Thanks.

hilde45's avatar
hilde45 OP
6,020 posts
 

@koestner Here is a summary of the trials for NAD M23 vs. Pass XA-25.

I’m moving on to AGD vs. M23, starting today.

System & Room Conditions
Listening room treated with diffusion panels, absorbers, and bass traps. Signal chain: Intel NUC streamer (Roon) → Holo Audio Spring DAC → solid state preamp → amplifier. Power conditioning via Audience Adept Response aR2p High Resolution Power Conditioner. Speakers: sealed, large format with JBL 15-inch drivers and Beyma AMT tweeters, mounted on Townshend platforms.

NAD M23 vs. Pass XA-25

Session 1 — February 18, 2026
Conditions: Solid state preamp set to achieve 81.7 dB, C-weighting.
Overall verdict: Slight edge to the Pass.
•    M23 demonstrated superior clarity and microdetail retrieval — in complex passages, background elements were more distinctly resoluble
•    Pass offered better tonality and timbre, with rounded leading edges on higher notes that nonetheless remained truthful and musically involving
•    Soundstage marginally wider on the M23; the Pass was entirely adequate spatially
•    Both handled instrument and voice articulation well
•    Pushing the Pass to approximately 51 on the preamp revealed no harshness — the sound remained magnetic and engaging at elevated volume

Session 2 — February 19, 2026
Conditions: Preamp set to create louder session +4 dB increase from Session 1; 85.5 dB C-weighting.
Overall verdict: Edge to the Pass — less on its own merits than on tonal failings of the M23 at higher volume.
•    M23 clarity remained highly engaging — more hidden notes and rhythmic details surfaced
•    Bass was taut, detailed, and full (string bass especially)
•    Female vocals repeatedly approached a cringe threshold — a hardness or forwardness that prompted a "turn it down" response
•    M23 was rhythmically fun with a wide soundstage
•    M23 was favored early in the session; the cumulative effect of the edge-of-cringe moments shifted the verdict by the end

Session 3 — February 20, 2026
Conditions: Mid-day listening with new program material; volume dialed back to 82.3 dB C-weighting. Solid state preamp at 40 (NAD), 43 (Pass).
Overall verdict: Slight edge to the M23.
•    Stjepan Hauser with the London Symphony Orchestra performing the Nocturne in C-Sharp Minor was markedly more engaging through the M23 — more dramatic orchestral presence, deeper bass weight, and a resonant, detailed cello sound (the body of the instrument was audible)
•    Wide soundstage consistent across multiple tracks
•    Percussion accurately placed and natural
•    M23 surfaced details that the Pass tended to smear or obscure
•    Pass excelled in its characteristic areas: vocals intimate, organic, and fully human-sounding; piano natural, percussive, and accurate
•    None of the harshness or cringe moments from Session 2 appeared — possibly attributable to the lower listening level

Emerging Pattern, NAD M23 vs. Pass XA-25:
Across three sessions a reasonably consistent picture is forming:
•    M23 leads on: resolution, dynamic articulation, bass definition, and soundstage width
•    Pass leads on: tonal naturalness, timbral roundness, and organic vocal and piano reproduction
•    The M23’s central liability appears to be a volume-dependent edge — a tendency toward hardness or brightness at higher levels that the Pass does not share
•    The Session 3 result (slight M23 edge at lower volume, no harshness) suggests the M23’s tonal character may be level-sensitive, which would be a meaningful variable to isolate in future sessions

 

decooney
2,565 posts
 

@hilde45  M23’s tonal character may be level-sensitive, which would be a meaningful variable to isolate in future sessions

A really good point to note. Each of us may prefer to listen at different volume levels. Some amps sound better than others at LOW volume levels, and at the same time, the same amp can also sound fatiguing at LOUDer volume levels.  

hilde45's avatar
hilde45 OP
6,020 posts
 

To anyone following: I now have the AGD Audion Mk. III in the house. It is being compared with the NAD M23 and the Pass XA-25. The Hypex which was part of this comparison is out of the loop. (Eliminated!)

Reflections coming.

@decooney 

I've done a few tests where everything was played louder and softer. Great point.

bluethinker's avatar
bluethinker
324 posts
 

@hilde45 - I’m looking forward to your observations on the AGD Audion MKiii and the other amps. I have heard great things about that Pass amp… I’d love to hear it at some point. 

For whatever it’s worth, I did feel they took a few days to settle in my system. I asked ChatGPT if there would be a legitimate reason a class d amp would need time to adjust to my system and it did provide a legit (at least it felt so to this non engineer) explanation. Of course it also reminded me that my perception of the sound was changing over time, which I heartily agree with.

It was really after a week where I felt comfortable comparing the Audions (paired with the spectacular LTA premap) to my Luxman class a solid state and CJ and Qualiton tube amps. 

 

 

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