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

Having had class a, ab and set, someone mentioned the switching rate of the ab and its affect on clarity. I will assume this isn’t always the case but may help explain what I feel is missing with my current sound. The 300b set has super clarity and was dead silent, 2 qualities that I’d like to have more than I have now. But, to me it lacked power and oomph. So I went back to ab which just sounds good with every genre of music and has more power. Just much more satisfying to me across the board. I’m hoping class d will have attributes of both. Fingers crossed. I keep discovering “new” sound. I guess I don’t have expectations of what my perfect sound is so I’m going to keep trying different pieces of gear and topologies to hopefully get to where I want to be. 

@decooney It’s interesting that you say,

"There may in fact be those who will continue to like Class A/AB solid state, others for all tubes, some for hybrids, and some pure Class-D, just like different types of food."

I started this thread with a quote from @atmasphere, who said,

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

If Ralph is right, then maybe we’re not helping ourselves get clearer about preferences by talking about "class A" etc.

Yes, we need linguistic shorthand to convey clusters of sonic characteristics we prefer, but if amps vary a lot within each "class" then aren’t we just confusing ourselves at exactly the point we’re trying to get clear?

Maybe instead of "Class A" preferences are described with a label like, "Seamless" meaning: organic, warm, enveloping, analog-like, layered, intimate midrange, blooming bass.

Instead of "Class D" preferences are described with a lable like, "Articulate", meaning: clean, detailed, punchy, precise, controlled, dynamic, focused soundstage, forward midrange, taut bass.

Finally, I would mention Westminster.  WestminsterLab is Class A because its output devices conduct continuously through the full waveform (no crossover switching like AB or D), but it achieves efficiency by using a highly regulated, tightly controlled power supply and optimized bias that minimizes wasted current outside the linear operating window. In other words, the signal path remains pure Class A, while the power architecture is engineered to reduce heat and excess dissipation without altering the conduction behavior of the output stage.  Basically a Class A amp that behaves a lot like a Class D.  These things are awesome and I had a pair in for a few months and have heard them on some incredible systems.  

I asked someone associated with Westminster if their design was similar to the KRELL DUO XD lineup of Class A amps and I was told that it was. There is a thread on WBF forum on Westminster where this was answered.

I returned the Meitner MA3i DAC to my friend today and needed a DAC for the office, so I dusted off the RME DAC I had lying around and paired it with the Class D GanFet 6.5 amp to drive the Magnepan Mini. I got this DAC for $500 used.

In comparison to the imersiv D-1 + CODA #16 amp with the Mini or the Meitner MA3i + CODA #16 with the Mini, the $1500 worth of Class D and RME does not embarrass. This in comparison to close to $30k of the best DAC and Class A amp tech around compared to this 5lb Class D GanFet amp. I am really impressed with this amp.

I am going to give the imersiv D-1 DAC + Class D GanFet one more round together but this time I am going to try some of the 2nd Order Harmonic Distortion settings on the imersiv D-1. I have 50 settings that I could apply with this DAC to juice it up.

 

Disclaimer attempt: Please don’t rake me over the coals too much for trying this, LOL  It was an experiment. 

The results are puzzling if any of it is close to being remotely true.  I queried an AI engine, asking what the real sonic differences a human might hear when comparing a high quality Class AB solid state amplifier design to a high quality Class-D amplifier design running Purifi modules. The last bullet is odd.  Being a midrange focused listener myself, it would be fun to hear from others who might have differing feedback and opinions. I’ve read a lot about Class-D Midrange, in the top shelf amps, hmmm. 

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The biggest audible differences tend to be:

🔹 Midrange texture vs neutrality

Class AB may feel slightly richer.
Purifi will feel more exact.

🔹 Bass character

Class AB: weighty, rounder
Purifi: tight, ultra-controlled

🔹 Emotional perception

Some listeners interpret small harmonic differences as “engagement.”
Purifi aims to remove that entirely.