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

@earthbound 

So what would Class AB be classified as OP?

If we follow the point I’m trying to make – i.e. that within an engineering design type the sound can vary – then "Class AB" might not fall into a single classification. 

Rather than talk about Class AB as *one* kind of sonic cluster, I looked around for various descriptions of some Class AB amps and then sorted them into two.

Class AB Amps:

Seamless: Organic, Warm, Enveloping, Layered, Intimate Midrange, Blooming Bass

• McIntosh MC452 / MC462 / MC601 
• Parasound Halo JC-1 / JC-1+
• Jeff Rowland Model 6 / Model 10
• Luxman M-900u
• Quad 303 (reissue)
• Classé CA-2300

Articulate — Clean, Detailed, Punchy, Precise, Controlled, Dynamic, Forward Midrange, Taut Bass

• Bryston 4B³ / 7B³ / 14B³
• Benchmark AHB2
• Parasound Halo A 21+
• Krell KAV-2250
• Hegel H590

Again, if Ralph is right – that there is no one "sound" for Class D amps – then we are best off not calling it "the Class D sound" and, as above, assigning different tonal categories to different class D amps.

@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.

@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

@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.  

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.