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

I've owned a NAD M23 for 2 years. I've previously owned many solid state A/B amplifiers, my favorite being a Parasound HCA-1200 (circa 1990). My M23 is running with a NAD M66 and Focal Sopra No. 2 speakers. Plus a bunch of other stuff you can see in my profile. I was running the M23 with KEF R7 Meta speakers initially and it was HIGHLY revealing and detailed. Not to the point of fatigue but, about 0.5% short of that. I will add that I'd never heard a combination of pre-amp/amp (M23/M66) that resolved details so clearly in my 40 years of HiFi. It was quite remarkable. 

I noticed after a couple hundred hours, the pre-amp/amplifier really came into their own, developing a natural and pleasing sound, without harshness. Initially, it sounded a bit thin to me on the bottom end but that isn't the case any more. 

I have my system in the living room of my home. The room is about 450 square feet and has been treated with some acoustic tiles, large rugs and canvas art. I am also running DIRAC Live room compensation for both the main speakers and DIRAC Bass Control for 2 KEF KC-92 subwoofers which makes a HUGE difference in sound. 

As many have pointed out here, room acoustics and dynamics are a significant influence on the sound of any system and should be the first consideration before investing in expensive equipment. Case in point... I once purchased a pair of Definitive Technology tower speakers that each had a 12", powered, side firing subwoofer in them. I had never anticipated the experience with a new set of speakers as much as I did those. I'd previously owned Infinity Kappa 8 towers which were magnificent. At the time (early 2000's) I had no concept of the importance of the room on the overall listening experience. Despite moving those monster speakers about 100 times, and twirling every dial on the rear, they were the worst sounding speakers I'd ever heard. That's what poor placement and corner loading 12" subs will get you. 

As for the M23, I absolutely love the sound of the amp and its ability to drive nearly any speaker. I know that NAD makes their own Class D modules, to their specifications, under license from Purifi/Eigentakt. That may make a difference in terms of overcoming some traditional criticisms of Class D. The M23 measurements are quite remarkable and the power output and current are conservatively rated. Having said that, I've never owned a Class D, audiophile grade, primary amplifier. My past experience with Class D was with powered subwoofers and car audio gear. So, I have no basis for comparison other than Class A/B.

In short I'd say the M23 delivers industry leading measurements and performance for a very good price. I paid, $3,800 USD for mine. Now, it's $5,000 with the tariff increases but, you can find them pre-owned for much less. You'd be hard pressed to find a better amplifier (quality, appearance, performance) for the money than a pre-owned M23 in my opinion. It is the finest amplifier I've ever owned, and I've owned a lot of them. 

Hope that helps!

@connollymj  Thank you SO much for your detailed and really well written reply. It affirms why I want to try this amp. I have a completely dialed in room, now, after recognizing how critical both treatments and measuring-listening are to achieving a balance. This is a dedicated, DIY room, with DSP for sub control, and I can add absorbers or other treatments if needed. So, I’m ready to hear the level of detail and bass control you are describing – especially if the other aspects (magical midrange, layered soundstage) remain part of the mix.

I have two different custom preamps to try with it. I’m hoping there is synergy with both of them. Here are some technical descriptions (in case anyone is curious) from the designer: 

PREAMPS:

SS: The SS preamp uses Burson Buffer modules  (all discrete components) fitted with Black Gate capacitors and wired with solid silver. The input and volume control uses a relay based stepped attenuator fitted with very low noise Vishay resistors. Its power supply board is also an older Burson module. It has about 4dB of gain. 

6SN7: The other preamp is also custom, and  uses a 6SN7 tube for gain and has a combination anode resistor and current source on the plate. That is direct coupled to a pair of 6AH4 triodes acting as cathode followers.  A 5Y3 is used for rectification with all film capacitors in the B+ supply. The B+ uses a CLCRCRCRC filter network and is then regulated. Heaters are run on DC. Its input selector is a Grayhill switch and attenuation is via a Goldpoint stepped attenuator. 

In your setups, I can see why you were almost at "too detailed," so the fact that it stopped shy of that for you gives me a lot of hope.

Your comment about it changing after a couple hundred hours was also interesting. If I buy the M23 used, hopefully those changes will already be present.

I’ve only ever tried a Class D custom amp built around a Hypex module. I’ve never owned any others. 

I’m seeing used M23 around $2500 to $2800; a big break in price compared to new, but if I don’t like it, that’s a huge chunk of cash to have sitting on a shelf. That’s why having time to evaluate is so critical.

Thanks again for your really interesting and useful comments.

To @hilde45 its going to be interesting if you proceed with a NAD M23 Class-D amp and compare to other Class A and AB SS and tube amps in your well treated room.  

While I’ve not heard one on my system, I do notice if I turn up my full home theater system and watch those higher definition videos with good microphones where they flip back-and-forth between the M23 and Pass Labs amps we both know well, the midrange body and weight of the M23 in the midrange is more bold and forward. No way to trust this, but I have heard this multiple times comparing other amps on these limited video recordings. Not a trustworth test, but it is A vs. B fwiw.

I wonder if that noticeable weight of the midrange and slightly rounded off top end of the M23 is apparent in several real-life listening sessions when paired with your SS and Tube preamps in your treated room. Will be interesting if you try this.   

Update: I got the NAD M23 to try out. Hesitant to say too much because I don’t want to prejudice myself, but so far it is more dynamic and detailed, including in the bass, than my other amps (Pass XA25 and Quicksilver Mono 60’s with KT77 tubes). I’m driving 97db speakers (15" driver plus AMT tweeter) and currently using the solid state preamp.

Sounds: 

Midrange sounds really nice. Not thin or analytical but definitely less warm and rounded. But much better than the Hypex I had in here.

Great energy with dynamics and transients -- easy to get the toes tapping.  Hearing some new notes (maybe even instruments) and richer textures in tracks I know really well.

A couple tracks pushed me back in my seat with some brightness -- but I’m pretty sure it was the volume setting and/or the track itself. (In other words, it would happen on other amps, too.)

Sound stage is really good so far -- perhaps less depth than the tubes, but I imagine that’s to be expected.  Need to listen more.

The big test will be to see if, over time, it gets fatiguing and if there is ultimately something that seems not very interesting about it. Performance wise, everything is going well, but it needs to be listened to for a lot longer, and it needs to be compared with the other amps, and it needs to be tried on the other speakers. If I’m going to spend $3000 on this thing, it has to pass a lot of tests. The most important test is that it has to be interesting and bring something new to the table. Otherwise, I’ll just wind up looking at it on a shelf, thinking about the hassle of selling it used. 

hilde45 - Nice initial feedback. What pre-amp and sources are you running? If ever an amplifier demonstrated ruler flat frequency response and nearly perfect measurements don't exactly produce beautiful results, the M23 would be the poster child for that category.

For me, I'm constantly seeking perfection in playback so I can tweak the other variables in my listening environment as needed if the I know the source is true. I find the M23 to nearly flawless on the measurments front, but understand that isn't necessarily the sound everyone wants.

Despite many seeking perfect measurments, I believe most are actually seeking listening bliss. Those are very different objectives in my opinion. Nonetheless, I am very happy with my M23 and am considering buying a second (pre-owned, version V1)  and running them as mono block amplifiers. 

It would be hard to find an amplifier that measures better than an M23. However, that clinical grade amplification leaves much to be desired for many audiophiles. A bit like a professional marathon athlete vs. Sydney Sweeny. One is the epitome of efficiency and performance. The other...

Which is the end game partner? The perfect athlete or the stunning head turner? Absolute performance vs. hedonistic pleasure? Do both exist in a single product? If so, please point me in that direction!