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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
decooney
2,565 posts
 

"@bartsw - @hilde45 passive switchers don’t add noise. Sometimes I truly think two amps sound different but they are not."

Old tip - avoid low quality switcher boxes. When helping friends shopping audio chain stores for amps and speakers, the first thing we’d do is listen, and then ask to remove all of the amp and speaker switcher boxes. Then direct connect all of it.  Immediately hearing differences, in some cases quite notable.

ime, results can vary, and notably so when mediocre quality switch boxes are used for amps or speakers. Having used both, and more so with mid-grade available parts, I’ve found both types to be impactful to the sound in several unexpected ways. 

A passive switcher adds extra wiring, extra switch contacts, longer signal path, and comes down to impedance, contact quality, layout and parts quality used.

Can add micro-resistance, contacts can oxidize over time, and smear low-level detail. Can cause slight loss of transparency, softened transients, and many times hearing reduced air in the sound overall. 

Check this more  - If an active preamp used has higher output impedance and two amps have lower input impedance, then adding a passive box can possibly alter frequency response slightly, dull highs, reduce dynamics, mess with imaging too.

In my prior tests with both type switch boxes, determined a mediocre switcher box will blur differences, especially things like midrange texture, harmonic density, and decay.  Low quality and poorly built switchers can also introduce grounding issues.

Ive found a direct cable swap, the most accurate, and while painful to do, but can be more definitive. I would rarely do it for comparisons if the switch boxes were designed and built with extremely high quality parts, and still then - probably not. 

 

hilde45's avatar
hilde45 OP
6,031 posts
 

@swaudiofan 

As I collated all the collected information in my head, I came to the conclusion there was/is something audibly different about these two classes of amplifiers. 

This is a great observation. I, myself, would feel hindered by changing rooms, changing components, level-matching, and other factors which would problematize the comparison. If you were able to hear differences and you think you could factor out all those changing variables, then you have come away with some genuine insight!

swaudiofan
48 posts
 

@hilde45  

The changing o the rooms was not really a factor as regardless of the volume being played, room acoustics, etc. there was just something (still unnamed) that was similar with all the Class A/B amps that I did not sense with the Class D's.  And I own a real good Class D.  Will definitely be looking into this more as when I left Chicago, I wondered if I am to consider making a change from D to A/B.

atmasphere's avatar
atmasphere
12,421 posts
 

The changing o the rooms was not really a factor as regardless of the volume being played, room acoustics, etc.

@swaudiofan The sound at shows is notoriously fickle and often poor. When you hear something that sounds good it is often the exception rather than the rule. The rooms vary in size slightly from one to another so they are not a common denominator; different speakers act differently in the same room as well. In some rooms there will be side wall reflections that cause harshness and in others where directivity is more controlled the room might sound smoother, just on account of those side wall reflections alone. 

If the volume is too high, most any room at a show can be easily overpowered. That's never a good thing. 

Not all class D amps sound alike. They vary quite widely in sound; some being far more musical than others.

So a show is not a good place to draw any conclusions!!

hilde45's avatar
hilde45 OP
6,031 posts
 

@atmasphere 

Steve Guttenberg agrees with you. He said he can't make a very good judgment either. In his Best of Axpona video, he says this:

"I just want to say this right up front that for describing sound quality, well, I can't I can't do that because show conditions are less than ideal. Let's just say that. But I do get enough do get enough to know that I want to move forward with doing a review. That's the best I can offer."

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