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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
5,997 posts
 

General update: I'm getting my hands on an AGD to try against the NAD M23. I will report. That will mean I've had three types of amps to try out in a short time – Hypex-based, Purifi-Eigentakt-based, GaNfet-based. I'm pleased about this.

I tried the NAD M23 with my 6SN7 tube amp last night. Zero fatigue. Other good Class D attributes were there.

@sdl4  Thanks. I'm not sure how critical the LPS is; I've heard there are now very good switching power supplies. I bet it has more to do with Ralph's ears and brain – to put it simply. I have a dealer near me (about an hour away) and if I can, I'll try his amps. 

I've also heard on a video that AGD's ganfets are from a supply that are specially audio-apt. Not sure what the others' are, but in all cases the engineer has to adapt his/her materials to the application. 

@verdantaudio 
Thanks for your long and descriptive post. Appreciate you relating your extensive experience.
I didn't find that a tube in front of a very well implemented Hypex/NCore took the edge off.

I'm curious about the Pascal modules, and obviously about AGD. The NAD M23 sounds pretty good but I appreciate your comment about the C298. That is sounding like a real bargain, especially used. Wonder if it could be modded/upgraded somehow to take it to the next level. I know a tech...

Sunfire story is super interesting! Really have not read much about Linn. You have me curious. Thanks for that!

The Merrill and Wesminster anecdotes are also very helpful. 

@ashoka  Your statement "class D was preferred because of Efficiency and cost." If that was all there was to it, you're right – there would not be a debate. But there is a debate, so...

@parkergetdean 
Super helpful to know about the SMSL PA200s. Jay Iyagi praised the heck out of them on a recent YouTube but then...

@greenngoldcheesehead 
It's good to keep in mind how good some of the class A/B amps are at doing what people laud about Class D. There's this notion that "Class D" are the future and then I think, "Wait – aren't there really good Class A/B amps out there? Yes, there are." But maybe they can't quite do what people like with Class D? Not sure, really.

@yyzsantabarbara 

Thanks for the GREAT description. Fascinating how a DAC can really impact even the strong sound character of the amp that follows, even creating, with the Class D 6.5 amp "a juicy Class A like sound." Of course, some people are not looking for a Class D amp with a Class A sound. They want something good but different than Class A. 

Good to know the 6.5 does not have glare; interesting that it was "lifeless" in the wrong combination. In other ways, it seems to really shine; makes me wonder about some of the SMSL amps. They sound like budget-helpful options, possibly. (Not necessarily for you, just generally.)

verdantaudio's avatar
verdantaudio
1,563 posts
 

@hilde45 I will say the limit to my tube/hypex experience is Rogue and AVM 5.2.  Those I think are good.  Primare has no tube and I don’t fine them edgy at all. 

NAD is an amazing value.  I think you will struggle to beat it at those price points. 

AGD sounds a bit more liquid than NAD.  NAD sounds like a good bipolar to me while AGD sounds more like a MOSFET or maybe a MOSFET/bipolar hybrid.  They are awesome.  

Regarding Linn, the older Chakra amps at the Klimax level are really, really good in the sub $20K price tier.  I have never heard their Akurate level amps which are not crazy expensive.  I should probably borrow one for demo. 

The new amps using the new PSU tech are not for the faint of heart in terms of price.  The 800s are a hair over $100K/ pair and the 500s are in the $65K range.  That said, they legit go toe-to-toe with NAGRA, Burmester, D’ag, etc... and hold their own.  

hilde45's avatar
hilde45 OP
5,997 posts
 

@verdantaudio Thanks for the continued, helpful description. The audio community is really fortunate to have you as a dealer and willing to participate in conversations. 

I decided to do a little research on Linn, and came across this really interesting review in Stereophile. The discussion here about linear vs. switching power supplies really helps bust myths/opinions about switching power supplies if they are done right. Linn is quite a company, it seems, and offers an interesting forward path.

foggyus91's avatar
foggyus91
612 posts
 

@parkergetdean you should really try a quality class D. Oh and run them in. 

Also curious as the the components that comprised the system used to audition. 

I had two SMSL PA200s in dual mono mode a month ago. They were very harsh,  with limited sound-stage, I returned them.

foggyus91's avatar
foggyus91
612 posts
 

@verdantaudio You make no mention of the Canor AI 2.10 that you are the US importer?

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