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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
hilde45's avatar
hilde45 OP
5,993 posts
 

@kirkwallace Thank you!

@tonnesen 

Thank you for this — really appreciate the care and detail you brought to your impressions. We have quite a bit in common: I've heard all those amps as well, and I've also visited the YG showroom, so your reference points resonate with me.

I think you've actually put your finger on exactly why it's so difficult to draw firm conclusions from comparisons like ours: room acoustics, amp-speaker synergy, and perhaps most importantly, what specific sonic characteristics produce an emotional response in a given listener — all of these vary enormously. Your Songer S1x pairing is quite different from my system, and what makes the AGD "click" emotionally in your room with your speakers may involve entirely different mechanisms than what I'm hearing in mine. Two listeners could hear the same two amps in different systems and come away with opposite rank-orderings, and neither would be wrong.

So rather than seeing our impressions as contradictory, I'd treat them as independently confirming that these are both serious contenders worth attention — and that the AGD in particular seems to hold up across a surprisingly wide range of contexts. The YG visit is a good example of that. Thanks again for sharing this so thoughtfully.

atmasphere's avatar
atmasphere
12,402 posts
 

Rowland eventually gave up and abandoned the technology as he could never get fully satisfied with the end result; he could not get the sound to be up to his high standards. Today, if you look at the brands offering Class D, it seems to be many of the mass marketing manufacturers, because they can be made affordably. Now of course there may be exceptions to that, with some specialized boutique firms still trying to make it work. I think that speaks for itself: the sound of Class D is still evolving, but when a well respected high end amplifier engineer leaves it aside, I will too.

@cooperdude6 Its easier to control variables when you design and build the class D module in house, rather than buying one off-the-shelf. Its also very easy to screw up the performance of a good module if there are problems with the input buffer or the power supply. Finally, switching noise is a big deal; it can mess with other parts of your system. IMO/IME, GaNFETs allow the designer to really keep the noise floor down because they have no leads like MOSFETs do. So you can control stray parasitic inductances in a way that is very difficult with the older MOSFETs. 

I really don't think the sound of class D is even a thing. Some class D amps are very good and others are junk. That is why there are such big differences between the 'sound' you get out of them. 

mike_in_nc
1,250 posts
 

@atmasphere --

Ralph, I'm wondering: Do you have any inclination to develop a higher-powered version of your Class D amps?

atmasphere's avatar
atmasphere
12,402 posts
 

@mike_in_nc Yes, some. 

As I keep pointing out to people though, if you can't make the speaker fly with 125 Watts (or 250) you'll need an amp that makes 1200 Watts (or 2500) because that's 10dB higher, which to your ears sounds twice as loud.

What that means is the speaker you have might be too inefficient to be practical. Inefficient speakers have three other problems:

1) speaker cables are far more critical!

2) the amplifier driving a hard to drive speaker will make more distortion; i.e. will not be sounding its best

3) the speaker itself will have a phenomena known as 'thermal compression' which will limit dynamic impact. 

There is no way to get around these problems other than using a speaker that is easier to drive and more efficient. There's no reason at all why anyone should have less resolution on that account; quite often easily driven speakers have more resolution rather than less. This is unsurprising as its easier for the amp to move the speaker cone to do its job. 

Ultimately (at least in my case) the goal is to get the best sound possible. That is done with an easier to drive speaker. I've not found an exception to this in 50 years but you never know...

bartsw's avatar
bartsw
226 posts
 

@atmasphere I would have thought you need power for full-range applications such as home theater, although this is a 2 channel discussion. That's one reason that draws me to class D.

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