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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
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audioguy85's avatar
audioguy85
2,049 posts
 

@decooney you are welcome! Yes, there is some pretty good lower cost stuff, hidden gems to be found. I think the NAD c268 is one of them. I think the trick is you pair 2 of the c268’s with a good tubed/hybrid preamp such as Rogues RP-1. You get a power house class D mono block set up, driven my the 3D holographic tubes to make some magic. 

NAD c268 $1299/Rogue RP-1 $1695 (v-1 version)

Use some speakers that lean a bit to the warm side. This is what I did, impressed. 

I sort of came up with the idea of this pairing by taking a cue from Rogue’s Mark O’brien and his design of the Sphinx integrated amp. The difference is i trippled the  power of that amp.

hilde45's avatar
hilde45 OP
5,994 posts
 

I think the trick is you pair 2 of the c268’s with a good tubed/hybrid preamp such as Rogues RP-1. You get a power house class D mono block set up, driven my the 3D holographic tubes to make some magic. 

@audioguy85 This makes a lot of sense to me. When I listened (details are throughout this thread) to the NAD M23 ($5k) and the AGD Audion monoblocks ($8k or so) with a solid state amp, my reaction was, "No way this is worth the money, compared to my Pass and Quicksilver tube amps." However, when I paired them with my 6SN7 tubed preamp, they both sounded really, really good. My first reaction, was, "I wonder if an even lower priced NAD plus a tube preamp might just give me all I want?" For example, the C268 is out there, now, used, for $750. That's a tiny fraction of the cost of some other options. Would it be as good as the others? Probably not. Would it come pretty close? That's a really good question that I'm still curious about. Now, I do like to listen sometimes with a solid state preamp, too, and I'm pretty sure the c268 would not cut it. But with a tubed preamp... Hmmm.

 

audioguy85's avatar
audioguy85
2,049 posts
 

@hilde45 yes, I am glad you are catching onto what i explained, as far as my setup. I would agree, a solid state pre may not cut the mustard with the c268...may be too clinical, analytical, maybe  even cold sounding. Although, some reviews have described the c268 as leaning to the warmer side, which is against the norm for most class D. By using the tubed pre, I think you are ensuring a warmer sound signature. Plus you will get that magic of the 3D holographic sound tubes are known for. I highly recommend to use 2 of the c268’s to get that power, as mentioned 300 watts. However, the one draw back with these amps bridged is that you gotta have 8 ohm speakers. My tannoy eatons are 8 ohm nominal impedance. 

One more thing...I also use my Music hall A3 Analog phono preamp with Alps blue velvet volume control connected directly to the RCA inputs on the NAD C268's. A more direct path to that tubey sound. 

decooney
2,564 posts
 

re: NAD 268 in bridged mode. Well, looks like i’m out with 4ohm speakers.  Good to know. Thanks for sharing that @audioguy85 

Manual: NAD 268 Op Manual - English

"In BRIDGED MODE (switch at ON (MONO) setting), the C 268 will produce approximately 300W into an 8 ohm loudspeaker. In this mode, the amplifier sections will react as though the speaker impedance has been halved. Low impedance speakers (under 8 ohms) are not recommended when using Bridge Mode as these may cause the amplifier’s thermal cut-out to operate if played at high levels."

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