Could Class D really be that good?

Yes, the amount of distortion and its spectrum has some correlation to sound. However, it is not the major or only thing that makes and amp SOUND the way it does. You can give me 3 pairs of Atmasphere amps and I will change some of the parts in one to really bad sounding parts.....leave one of them stock and in the 3rd one I will change a bunch of parts and execution that I know will make the sound better. They will still all measure the same. Ralph or anyone would be able to pick them apart..........even on a double blind test.

All Hypex amps sound different from each orther. All Purifi amps sound different from each other. Please read the review on 10 Audio on the NAD Purifi based amp and then the review he did a little later on my modified VTV Purifi amp......way different and better sound. All parts and execution change the sound. I mod all these amps so I know that they all sound good stock.....but way, way better with mods. Yes, some do not believe it....they only believe in measurements. My mods do not change measurements.....they change the way an amp sounds.

I have been modding and manufacturing gear since the 1970s.....Everyone likes what I do......everyone (I mean, those that listen). If you change the coupling cap in a tubed piece of gear.....or brand of tube....or brand of resistor.....you change the sound.....but you do not change how it measures (obviously, the tubes must have the same gain). All op amps have a sound. Many amps out there right now (all the Fosi and Ayima amps,etc.) with sockets in them so you can "opamp roll". All the various op amps measure such low distortion that they do not change the measurement of the amp......but everyone can hear the difference in sound between the different op amps. This is why the best versions of Purifi and Hypex use discrete op amps and super low noise regulators (because they sound better). All the discrete opamps have a sound, as well. VTV sells various op amps for those that like different flavors of sound. I modify the Sparko labs Pro opamps to give better sound (one of my favorites, so far, along with the LKS discrete op amps). Warren at VTV sells various amps and he slightly prefers the Purifi (and especially the high powered Purifi) modules to the Nilai and NCX500 that he sells. He is a tube guy so he really likes the tube buffer in front of the Purifi module. Listening to a very modded VTV Purifi amp as I type.....Wow, what a great sound.

I am probably going to have a tour with a stereo dual mono high powered modded VTV Purifi amp soon. This way, this less than $3K (delivered including mods) amp can be compared to Atmasphere, Orchard, Hypex, Nilai and others. This dual mono stereo amp will do 222 watts into 8 ohms, 436 watts into 4 ohms and 750 watts into 2 ohms. I will warrantee the modded amp for 2 years. Fun stuff. Low distortion class D modules with serious tweaks equals serious goosebump factor.

@ricevs

Thank you for the write up / advices. I pretty much agree with what you said there regarding the sound signature heavily depending on how the modules are implemented. The reason I put so much effort there investigaing measurements is because there are still significant variations in the performance specification among the diy or commercialized products based on the same Hypex / Purifi modules. A few notes / questions here if you don’t mind:

- I am interested in VTV Purifi with tube buffer as well but I still want to see the detailed measurements there like ASR; I won’t bet / invest 2-3 grands just for experimentation. Hopefully ASR could have a chance to evaluate the product.

- Discrete op-amp like Sparko S3602 is certainly top notch but, according to FFT freq. spectrum analysis, the TI LM4562 is no slouch either and only costs 1/6. I know you might throw in the similar comment like they will sound differently even measurement is alike BUT I wish to hear your opinion in case if you had some experience with it.

@lanx0003 I have not listened to the Apollon but I had given it some research. Just on looks & the couple extra features & upgrades I would have preferred that model. But I really didn't need a new amp..was just curious about the newer Nilai tech & power supply. The Stereo DIY was the cheapest I could find & I figured worst case scenario (no difference from Ncore) I could resell it with minor loss. Basically I wanted a taste of the newer tech at cheapest price. Personally I like the look of the Apollon. 

Now that I know firsthand about the Nilai I at least wish I would have gone for the mono blocks. Although I certainly don't "need" them for extra power.

Definitely there are ways to change the sound of these amps with whatever op amp or buffer. There are quite a few selections to choose from depending on the company. Problem is..which one or ones sound best? Is there a popular opinion on which one is subjectively "best"?

Going back to the Elac class D amp I mentioned the input stage made all the difference. I had heard the basic Ucd modules ​but Elac did a Jfet or Class A input driver that took that mediocre module to a new level imo. 

I while back when I was looking at different amps I liked the idea of the VTV tube buffer but it seemed a little pricey & I don't recall seeing any specs for it. My opinion was I'd be better off going with a tube preamp then an add on tube buffer. Which I'm a big fan of pairing Tube pre's with Class D...or really any amp lol. I've experimented with a few different pairings. Tube pre with low power supply noise & a smidge low harmonic distortion sounds good to my ears. I just started & almost finished with a new preamp build to pair with the Nilai. Minimal circuit design & the designer provides specs. Small parts list so upgrading to V-caps, mundorfs, AMRG carbon films & such wasn't too bad. 

All op amps have an intrinsic sound.....and how you know this is to listen. There is no monolythic integrated circuit IC (that I know of) that sounds as good as a really great discrete circuit. This is from testing (and designing and making my own) op amps for 25 years. If you have an integrated circuit op amp......you need to upgrade it. So, which discrete op amp sounds the best?......I personally like the LKS and the modified Sparko Labs 2590 the best. When I was modding Oppo 205s I changed the stock 4562 to Sparko 3601 but then went to the LKS (I had modded the LKS DAC so I knew those op amps were probably really great). When I saw them for sale on line I emailed LKS and they sold some of them directly to me. They were much better than the 3601s....Of course, I removed the connectors on the opamps and soldered my own 6n copper leads to the op amp.

I find the Weiss very detailed but lacking depth and musicality. The Sonic Imagrery, and New Class D too transistory sounding. I have not listened to the latest Burson or the Staccato, and I am sure there are others that might be better.

Adding a tube buffer will ADD tube sound. That is what it is for. It will not measure as good, as no tube has the low noise of a great op amp. The tube buffer in the VTV has an op amp after the tube.....so it really is just adding tube sound. Warren at VTV loves how it sounds. It is his reference. He uses the stock 2950 as the op amp on that board. Warren has never heard any of my mods (to the op amp or to his amps). If you are buying the tube buffer it is because you want tube sound....not for its measurements. Tubes add liquidity, space and palpability.....they make for a more "musical" sound. I personally think that if you want a tube in your system.....that it be only one. Too much tube sound makes it slow. This is why people like a tube preamp with class D...or other solid state ammps. A nice combo. I tweak my whole system enough that even without a tube I get very musical and revealing sound. Most people do not know how to tweak that well so a tube piece of gear is a nice way to get to heaven.

The Nilai amps have built in buffers and regulators....so the only tweaks you can do is to mod the output filter caps and change all the wiring and jacks and damp the chassis (yes, it is a worthwhile improvement).

Yes, the amount of distortion and its spectrum has some correlation to sound. However, it is not the major or only thing that makes and amp SOUND the way it does. You can give me 3 pairs of Atmasphere amps and I will change some of the parts in one to really bad sounding parts.....leave one of them stock and in the 3rd one I will change a bunch of parts and execution that I know will make the sound better. They will still all measure the same. Ralph or anyone would be able to pick them apart..........even on a double blind test.

When you change parts, you change the distortion so the sound changes. This is easily measured and correlated to what we hear. So they would not measure the same. Distortion is literally the sonic signature of any amplifier.