Comments please on: NAD M23 vs c298 vs. other newer Class D

We get it that you are an engineer. Here is the curve ball question about the "sound". When you compare your own Atma-Sphere TUBE amplifiers to your new Class-D mono amplifiers, what can you share about the sound - What is similar and what is different about the sound stage, depth, placement of the singers voice (more forward or back), and what about channel separation and instrument separation. 

@decooney On the systems I play a lot (home and at the shop) our OTLs and our class D amps sound very similar. There are two main differences. The first is that the class D amps are slightly more focused, so its easier to tell what's going on in the rear of the sound stage, there's slightly more detail. 

The other difference is how bass is played. On the shop speakers I don't notice this as much as at home. My home speakers are 16 Ohms and 98dB and use horns. They are designed to work with amps with a high output impedance. The class D amps have a very low output impedance and so don't make as much energy in the bass regions of the speaker where there are impedance peaks. To sort that out I had to change the settings for the midrange and tweeter, which are controls on the back of the speaker. Most speakers don't have these controls because they are intended for amps with a low output impedance. 

Once I got that right I didn't miss the tube amps at all. 

So in a nutshell they sound very similar as they share the same smooth character in the mids and highs. 

"@atmasphere ...they share the same smooth character in the mids and highs."

Thanks for the reply Ralph. The last comment about mids and highs, we see a lot about the better Class D amps having these characteristics of "smooth", or for many of them. Now how much of that comes as a tradeoff losing something else, I guess I’ll just have to try a few different Class-D amps down the road on my own system and speakers and room to figure out if I’m a future candidate buyer or not.

In the solid state and tube amp world, we can find amps that are smooth up top/mids, and also bring sparkle at the same time, and that can be tricky too, except with tube amps, its trying different input/output tubes to get there, as we all well know. Now leaving my tube amps on a lot, that’s another discussion, constraint.

I’m following @hilde45 ’s NAD M23 test and the whole Purify vs. Hypex testing sessions going on. Also, realizing that all Class-D amps are definitely not the same, and looking closely how some can still use transformers, and mosfets, and various things in the circuit and platform design closer back to my own SS amp roots.  I also noticed the M23 has a version-2, and what causes such changes, hmmm. 

I look for your amps in the show videos too, and hopefully we’ll see even more of yours paired up with some of the larger sized speakers we all know and enjoy.  Thanks again Ralph for sharing your thoughts, and accomplishments here on Agon.

Also, realizing that all Class-D amps are definitely not the same

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

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

There is so much variation in how an amp interacts with a speaker, and so much variation in speakers and their behavior – it would seem that the combination with the variety of tube amps out there would make the number of combinations staggering. 

If I understand it, most class D amps shouldn't interact very much given their low output impedance.

I guess, Ralph, the question becomes where does the variability you cite for Class D come from – to the point that they are *more* variable than tube amps?

For those following along:

2/17/26 Listening report, NAD M23 (Eigentakt 1) vs Hypex NCore DIY amp:

Observations: NAD winning still

• NAD still smoother; never cringey
• More timbrel presence in NAD
• Bass more accurate and full in NAD
• Sound stage more compressed in Hypex

Wife  listened to both:

• Hypex was: “one dimensional,” “muddy/congested”, “more confined in the center (sound stage)” “felt like it had less power”
• NAD was: “like movies, Dolby; really big filling the space”