Could Class D really be that good?

I have also made known on this forum in another thread about a Import Chinese Origin, Four Box Modular Class D Power Amp compared to a £50K Soulution Power Amp on a £200K system, or £150 400 system with the Import Amp.

@pindac ,

What is the name of the amp you're referring to?

@lanx0003 I am not sure if it will be detrimental to performance, and I imagine a lot of factors come into play (efficiency/sensitivity of your speakers, listening volume level, driving impedance/load of the speakers, etc.). I didn’t see any results from anywhere testing the V3 Mono specifically with a 5A power supply versus a 10A, making it even more difficult to say.

-Ed

@thecarpathian To acquire an answer to this inquiry, will take a little time as I am out of touch with the person who presented the Power Amp.

Plan B, I have trawled the mails of the Amp owner on their preferred forum, I am 99% sure the Link in the follow up post is the Amp I was able to be demo’d. ( I'll Post Link separately incase this post gets dumped if the link is refused). 

What I do know is the Amp’s were a Punt Purchase by an individual who is a adept EE and has a lot of DIY Builds under their belt. Also the Amp was purchased to be part of OB Speaker DSP Amp assembly.

The Amp was in the owners view so impressive for the outlay, the owner wanted it to be experienced as a Monoblock for the entirety of the Frequency Range.

I also know the Amp’s in question had a couple of changes to the original schematic/topology, as a few components were swapped for parts the Amp’s owner had in their spare parts collection. I recollect talk of a change in the Power Supply Module. I also know through the discussion had, that the changes were not expensive or complex and thought of as quite simplistic.

Whilst Trawling the Amp Owners mails, I have learned the Owner is now a vociferous advocate of the Neurochrome 686 Power Amp’s, I my self can not disagree, I have very positive indelible memories from all experiences had, where these Amp designs are used.

The Amp Owner makes the statement ’World Class for Extremely Sensible Monies’. To make such a statement is of interest, as one very good friend of this person, is the owner of LDA who does make World Class Amplification.

@pindac ,

That's terrific!

Thank you for taking the time to search this up.

The first time I read the asr Link is today in the last few minutes, I am glad my description of listening to this Amp design, supplied Signal from a Vinyl Source and Soulution Pre Amp', seemingly suggests the measured performance is able to produce sound that is quite attractive to some individuals preferences for a produced sound.

Some of the Neurochrome owners I know, and have been instrumental in their becoming users of Neurochrome designs are now, seriously investigating (actually building) up to date designs from Purifi, which is the evolved design from Bruno Putzey. 

I had a Krell FPB 200:amp, with a Pass Labs Aleph P preamp driving a pair of Martin Logan ReQuest speakers, and a dealer talked me into trying a Peachtree Nova 220:se to replace my Krell am and Pass preamp. I was totally amazed at the sound quality and performance of the Peachtree integrated amp, which was a class d amp. I let my ears make the decision……I sold the Krell amp, and Pass Aleph P preamp and used the Peachtree from then on out. The Krell and Pass systems were both Stereophile grade A systems.

Class D got better.

My nearfield desktop audio system is very crowded and had no space for an A/B or A amp of any kind when I switched to passive monitors ~6 years ago. Thus I was pushed into the alien (to me) world of class D amps. I did a ton of research, looking in particular for any class D amps described even occasionally as "musical" and pleasing to the ear. All that research led me to a gently used ICEPower design, the Wyred 4 Sound ST-500, which I sited standing on one side on my desk (w/the mfr’s OK). That cool running amp immediately worked well for me. It sounded great, had none of the obnoxious brightness and thin harmonics some ascribe to class Ds. Until a month ago I wasn’t tempted to change.

I never really stopped following class D, and had become curious about NCore modules used by various amp makers. The one other (to me, somewhat affordable) class D brand I read positive things about is Bel Canto. I looked for their stereo NCore amp, but instead found a cherry pair of 600M monos. After installing them  IMS, I can verify that they, too, sound quite musical. They have somewhat more resolution and better soundstaging than the ST-500, which is nice to have.

I got pushed into class D by space considerations but must say I’m quite impressed with the sound of the 3 examples I’ve used in my system. I've had 4 pairs of studio monitors here with these amps (ATCs, KEFs, Aerial Acoustics, Harbeths) and all worked extremely well with these amps.

@eddnog  I got in and pledged for two Monos with two 48v/5a PSUs. I felt fortunate making the last-minute decision and went with two independent PSUs because later today I saw this https://www.youtube.com/watch?v=wjWVSFCR5MI where the host experienced noise/interference issues using one block.

Do you not know that within each class of amplification there are good and not so good designs. This also holds true in Class D amps.

@phd believe it or not, there are people out there who simply write off Class D and some even Class AB right off the bat without so much as a blink.

-Ed

Interesting thread as I too need to replace a now dead integrated in my office system that took up too much space.  Right now I am using a backup ATI 1502 amp with a passive pre (also too big) driving Spendor S3/5s. I've been looking at Class AB options with smaller footprints. I have only heard one D amp, a Rogue Sphinx v1 5-6 years ago. I was not taken but it seems that so many manufacturers have gone to D amps that I have been "reading up". I am not incline to play with the small 3255 amps but sounds like enough folks have been sold on the other versions of D tech that it could be time. I cant hear any of them where I live so that is the rub but a good return policy does reduce the risk. I will keep reading this and other threads on this. Maybe old (preset bias) dogs can learn new tricks...

I for many years have been very very socially active in relation to my interest in audio. My times as a exhibitor to the general public/ audio enthusiasts has created an experience where my exhibiting space has been endlessly full for the duration of the event.   

With this today as being one fundamental attached to my Hobby, I end up travelling a lot with equipment.

Certain equipment especially the Valve Based design are very fragile, or in the case of the owned Power Amp's (Stupidly Heavy), for managing at my age and being with arthritic ailments.

In the past five years, I have been slowly learning about audio equipment, that is extremely impressive to my preferences, non-Valve and much lighter in weight.

In any of the Amp's I have referred to in this Thread, I have found all that I require, when I retire the Valve Amp's.

Additionally my research has also assisted with my discovery of a system, except speakers that can be transported in a Wheeled Suitcase. This is quite something for somebody who really does like to go all in with their support offered for arranged social events in relation to Audio and Audio Enthusiasts.

I have no doubts if I were to change direction and utilise alternate Power Amplification, my exhibiting a system publicly, will still create as much interest as has the other times experienced.

Note: There are routes into exceptional quality Power Amp's capable to stand toe to toe with respected Brands. The cost associated with getting to this place is not too much.

If a Manufacturer of a Amp, had the BOM of the Amp's being referred to, there is no real way of knowing the final costing to be the RRP.  Certain Brands with a larger profile in the market, are possibly gong to add 10 - 20 x in uplift costing,  as a reasonable conjecture. 

I have it on good authority the Company in the Link to follow, offer a very high quality Class D Power Amp at reasonable monies. This is an Amp' I have recently been demo's for quite a few hours as a debut listen.

....I want to know what's Next after Class D....and from what edge of tech will it rise from....

D has already made substantial 'waves' (lo-rent pun) and has evolved rather quickly.....

Anyone have a warmed-up crystal ball handy? 

45 lb. > 45 oz. > ? 

45 grams?   No more heavy amps...... ;)

Eddnog, that pretty much leaves Class A amps. Not many "Dyed In The Wool" audiophile is going to get rid of their expensive, heavy, Class A monoblocks and replace them with them light-weight, cheaper Class D amps even if they sound better!   Or will they?

@pindac Truly amazing stuff that Audiophonics has accomplished. Built on Purifi/Hypex modules/ps, the HPA S400-ET has been highly praised by ASR based on its excellent measurements. The compact size version, LPA S400-ET, has almost identical specs and performance in a half-size chassis. Similar to the Fosi Mono, the S400-ET offers multiple gain settings, dual replaceable op-amps, XLR inputs, and quality parts inside. The upgraded binding posts in the back are attractive. The sound quality is also highly regarded, surpassing class A/B or even class A based on the limited reviews I could find. I really don’t need to repeat all the positive reviews, but without exception, let me include its performance curve in the chart for the last time before wrapping up. It is almost neck-and-neck there with the Benchmark. The Fosi Mono starts losing its pace at higher loads, but that’s understandable given its price disparity.

You know what? This beast only weighs 12 lbs, so I could easily carry it back on the next trip to France. I guess that is one of the advantages of class D.

There actually was an extensive discussion on Audiogon a year ago.

https://forum.audiogon.com/discussions/new-class-d-amplifiers/post?postid=2543479

@lanx0003 In the not too distant, I will put up a link to a Build of the latest Purifi design I have linked previously within this thread.

There are already some build tweaks already known for this design and these are being incorporated into the build I am following.

When all is in use, I will ad the link to the build thread.

This as a design will be cheaper than the Audiophonics Option and be a few steps forward in the design choices. It may even be cheaper as a commission build, if the DIY idea is not appealing.

Further miniaturization of everything everywhere is inevitable.

@pindac Please forward the link once you have it. I also dived into the DIY project based on Purifi 1ET400A and Hypex NC400. I am particularly interested in the hybrid one with tube buffer made by VTV. Although its price tag is relatively pricier, marrying a tube buffer might be a rather good idea. The idea is not new and, the more I think about it, the more I feel it is doable. We could biamp a tube amp (or low-wattage class A) and these powerful class D modules, where the tube amp/class A is used for the tweeter/midrange and the class D is used for the bass driver.  What do you think?

Has anyone heard the Aavik I180 or 280 Class D integrated amplifier?  I hear it is magnificent.  A true Class A/B killer.  Thoughts? 

@pennfootball71 Have you heard any of the Aavik amplifiers?  Word on the street is they are true A/B killers.  Aavik is one of the brands within Denmark Audio Group, Borressen Speakers and Ansuz cables being the other two.  

I have heard Active Driven OB's with a configuration for Amplification with similarities to the method suggested by yourself.

The OB's although with 4 Drivers and a Amp for each Driver with Class D for the Lower Frequencies, has been the best Speaker Array heard in a unusual venue.

I would strongly suspect if heard in the home set up, they may be the best Speakers experienced over multiple years.

I made it known recently, that very recently, a friend who is a EE, has bought into a DHT Pre Amp Design, and in using this with a Neurochrome Amp, it has blown them away with what is on offer. I am yet to receive an Demo', but some of the Local HiFi Group have, and they are thoroughly impressed with the experience had.

I myself am still remaining thoroughly impressed with the Pass Korg B1 design for a DHT Pre Amp, especially after it has a few well known circuit mod's added.   

I could not agree more, @pindac. Such a ’bybrid’ amplification could be even better on a active crossover system. A good (mini)DSP could easily lead us there, which will be more convenient than the passive crossover system. A lot of class A / tube amp or these class D module amp do not even have ’pre-out’ or ’line-out’ any more for bi-amping.

@audiophil88 I have heard the Aavik D it is good on Borreson but if you look on the Aavik website their flagship amps are pure class A. Why do you think that is?

I added a THD (%) scale, which corresponds to the dB scale, into the graph for comparing more affordable NAD C268 ($1k) and the Bel Canto S300iu ($2.5k) with the Fosi V3. As shown, the NAD C268 is comparable to the Fosi V3, but the Bel Canto is far inferior. Again, measurements do not mean everything, but the THD measure does give an indication of the sound clarity. I just provided you with the data in one place for your convenience, and it is your discretion how you interpret the data.

@lanx0003 The THD really doesn't tell you how musical an amp might be. A better indication is distortion vs frequency. If it rises at too low a frequency, higher ordered harmonics might be unmasked and so contribute to brightness and harshness. Ideally (and a number of class D amps can do this) distortion vs frequency should be a ruler flat line across the audio band.

Zero feedback tube amps (like most SETs) have always been able to do this. But a good class D can do it better, with lower distortion (which obscures detail).

Once DvsF is sorted, the next hurdle is the actual distortion spectra. Ideally a 2nd harmonic should be the most powerful, followed by the 3rd with succeeding harmonics quite low in comparison. In this way the lower orders can mask the presence of the higher orders, allowing the amp to be as smooth as possible. Again, some class D circuits are very good at this, challenging SETs and other tube amps on their own turf.

@atmasphere Thank you for the very helpful information. I recalled someone asking / commenting about the musicality and I have examined all the ASR measurements but could not find one appropriate to be an indicator.  After a brief search I was only able to identify two gears (see below) that ASR give the THD vs frequency chart. I am not sure what the thought process was behind making this chart obsolete.

The THD vs frequency chart was soon replaced by the following load-dependent THD charts by frequencies.  As you may know, the load-dependent THD is usually tested using 1kHz tone in the industry but was later criticized because it ignores the adverse effect of higher frequencies over 1kHz on the overall THD measure.  So, including Erin, the reviewers start tests using multi-tones.  As shown in the following chart, the 15kHz frequency has big jumps in THD levels, while the better class D module like Purifi demonstrates a much more controlled increase in THD at these high audible frequencies.   

The phenomenon of even-order harmonic distortion (HD) contributing to a "pleasant" or "musical" sound in tube amps, while odd-order HD in transistor designs may sound "edgier," is a well-known concept among audiophiles. However, the idea that modern class D modules can also produce a "sweetened" or "musical" sound despite lowering total harmonic distortion (THD) might seem contradictory.  Can you provide some actual test done for those class D circuits demonstrating how they accomplish what you have described in the last paragraph?

@lanx0003 Sure! Just look at the harmonic spectra of the Purifi module. You'll see a dominant second.

Keep in mind that in a class D amp, the things that cause traditional solid state amps to sound harsh and bright might not exist. For example, in our class D the primary non-linearity is caused by the deadtime used in the output section (something that all class D amps have). In our circuit this results in lower ordered harmonics.

When feedback is applied to most tube and solid state A or AB designs, it is traditionally applied to a non-linear input to the amp (the cathode of an input tube or base/gate of a differential pair at the input of a solid state amp). The feedback signal is thus distorted and so does not do its job properly. This causes higher ordered harmonics and IMD. This has been documented by both Norman Crowhurst (technical writer for Sams publications) and 20 years later by Peter Baxandall.

In most self-oscillating class D amps this technique is not used. So they often lack the higher ordered harmonic generation common to 99% of traditional solid state designs.

Since the ear uses harmonics to tell the difference between sounds, you can see that class D amps are capable of very different distortion as opposed to traditional solid state. So I don't see it as counter-intuitive that a class D amp can have a lot more in common with the sound of a tube amp than regular solid state amps. 

Of course, class D designs vary a lot in their sound so YMMV. IME they can vary more than the sound of tube amps, which can very quite a lot! The point here is don't write off class D because you may have heard one that sucked. As with class A or AB, the sound quality is a function of design and execution rather than the class of operation. 

@atmasphere Just look at the harmonic spectra of the Purifi module. You’ll see a dominant second.

These are freq. spretrum FFT plots for THD and IMD from the published Purifi 1ET400A data sheet. For IMD, all spikes are beyond the audible freq. range so not a concern there. But, in the THD plot, where is the ’dominant’ 2nd HD? All odd- and even- order HD are almost inaudible.

@lanx0003 

I was looking at a different article. In this one we see a dominant 3rd (my memory playing up; I still seem to recall seeing a dominant 2nd) which is treated by the ear in much the same way as the second and is the only odd ordered harmonic for which this is so.

A dominant 3rd suggests cubic non-linearity; if so the circuit is inherently lower distortion than when a 2nd is dominant (which suggests a quadratic non-linearity). Our OTLs, being fully differential and balanced, have a dominant 3rd.

@atmasphere  I was there initially but just like asr said "... The third harmonic hovers around -130 dB which again, is almost at the limit of what we can measure..."   It is inaudible either at that noise floor.

I am sure that, with such a low noise floor the Purifi / Hypex class D modules provides, the sound from it is transparent bar none.  I also concur with you that the resultant sound traits hinges on how the modules is implemented.  But I don't think the sound will be sweetened approaching to tube amp unless specifically with a filter or other component.  Maybe that is why VTV adds the input tube buffer.  Just my two cents.

@lanx0003 The differences you hear in the sound of amps, if FR isn't an issue (which most of the time it isn't) is the difference in distortion of whatever amps are being compared.

There are three things that define those differences. What frequency, if any, that distortion rises (IMO/IME this aspect of amplifier distortion is the most important), the distortion spectra and finally how much distortion. There's no filter that would make a solid state amp sound like tubes; just the distortion signature. So if a class D has the same distortion signature as a good tube amp, it will sound like a  good tube amp simply on that account. 

This is because our ears use harmonics to identify any sound. So you can see that if an amp is to sound musical, its distortion signature must be as innocuous as possible. To that end, the 2nd or 3rd must be significantly higher amplitude than succeeding orders, so as to mask them. That is literally what has kept tubes in business these last 60 years.

I agree that class D is well past the point of being "mature", by at least a few generations at this point. Class D amps can be amazing, or sometimes mediocre, just like tube designs or class A etc.

Nice to see quality become available at such a low price like this amp. I'll be looking into it for a small bedroom system.

@tubeguy80 DIY Audio Forum, will offer up extended info from builders on these Amp Designs, Bruno Putzey is  a point of reference.

I’ve really grown to like class d, and I’ve certainly noticed how different modules bring a differing palate of sound to your speakers. They can be neutral as heck, or, like the older ICEpower modules, have tons of slam. Having said that, has anyone tried to contact Red Dragon audio? I’ve sent the guy several emails, and no response. Are they going out of business? I was interested in one of their amps, because based on the reviews I’ve read, they seem to have the sound signature that I like from class d. 
Any info would be appreciated.

Let's get real. While the Fosi stuff is good, especially for the money, amps such as Technics SU-G700M2 at 10x the cost are 2-3x better.

I can't speak on the newer chip amps but I purchased a Hypex Nilai recently. To me it is a step above the Ucd & Ncore's I tried briefly in the past. I purchased the DIY model and feel it is a great amp for the money. Subjectively speaking of the class D modules i had tried in the past I found them to be a hair dry..touch analytical & 2 dimensional at times. For the low noise, transparency, power & size I still think the Ncore is a good amp.. especially when you consider the price. If I was still into Surround/Multi speaker movie systems I would be all about Hypex/Purifi modules. 

I tried an Elac Alchemy amplifier built around the older Ucd modules and felt that Class D amp was good for the money. Definitely better than just the basic older Ucd module but I still felt the top end wasn't as good as say a good class AB. Still a solid amp for the money in my opinion, I used a pair of them for almost a year. 

Anyway, the Nilai is definitely an improvement in my opinion. It's hard to describe an amplifier but I just find it smoother & groovier than D's I've tried in the past. I've only used it for a few weeks now but I can't find any faults in it. If Class D is able to improve upon this and keep it at these low costs I think that is a win for a lot of audiophiles. I definitely welcome more builders designing amplifiers around these new modules.. especially this Nilai.  

@atmasphere So if a class D has the same distortion signature as a good tube amp, it will sound like a good tube amp simply on that account.

Agreed. But I want to emphasize, with the low 2nd HD found in these Purifi / Hypex class D, you won’t be able to have distortion signature comparable to a tube amp and possibly produce the tube-like smooth sound. Let me give you an example of sound color signatures built in the Smsl Su-8. The 2nd, 3rd and other higher order spikes in the standard setting (upper left) are insignificant (-120dB, similar to Purifi / Hypex. Users could elect the "Tube 1-3" sound signatures to experience the emulated tube sound, where you could find the 2nd-order HD boosted to -90dB in Tube 1 (light) setting and -70dB in Tube 3 (strong) setting. That tells me the 2nd order HD needs to have high enough ’dominant’ spike (relative to 3rd & higher-order) to exhibit the tube-like smooth sound.

Here is the FFT plot for a real good tube amp, McIntosh 40, which confirms with the above. But, interestingly, Mc40 actually has slightly higher non-dominant 3rd hd.

Most agree that the 2nd harmonic is innocuous to the human ear; the real issue here is are the 2nd and 3rd able to mask higher ordered harmonics. I've heard the argument before that if they are 90dB down you aren't going to here them, which I think is false due to the fact that the ear uses higher ordered harmonics to sense sound pressure and it has over a 120dB range.

But if the 2nd or 3rd is masking them, then you have a 'tube amp' signature. The lower the distortion overall though, the more transparent the amp becomes.

@mattw73

I’m impressed with both the Nilai Mono and Apollon St in terms of their specifications. However, I lean slightly towards the Apollon for a couple of reasons: (1) it offers 25% more reserved maximum power in both 4 and 8 ohms (despite a slight sacrifice in dB noise in 4 ohms), and (2) it has the lowest measured power on/off noise, which is inaudible. Additionally, while the Nilai Mono has the advantage of being a stable 2-ohm load amplifier, the Apollon Stereo is half the cost of a pair of Nilai Monos. If you or anyone else has experience with these two amplifiers especially how they sound, I would greatly appreciate any advice or insights you could offer. Thank you!

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.

Did you not read what I said?  I said the amps will all measure the same.....this is absolutely true.  While it is true that when changing parts the distortion changes....because all noise and veils are distortion.  However, you CANNOT measure a change in measured distortion when changing passive parts.  I can hear the difference in 2 inches of wire.....try measuring that!  We have been down this road many times.  You are one of the few people on the planet who BELIEVE what you just said.  Again, you cannot measure the difference in distortion by changing passive parts, damping, fuses, cables, etc.....no way Jose!  Lift your cables off the floor.....you get lower distortion....try measuring that!  Try removing the steel plate and bolt off your toroidal transformer and raise it off the chassis with a one inch piece of wood and be amazed at the sonic difference....try measuring that.  Please, come over to the "dark side".....it is way more fun than re-stating the same BS.  You will learn a lot and your products will get even better and you will make more money.  A win for everyone.  But many will take their "opinion" to the grave.....It is called being "dead right".  I am wrong many times.....I change my mind....it is fun....it is an ever changing game....infinite and full of surprises.....I learn new sonic things most every week.

I definitely have no experience with op amps but believe in their ability to change a piece of equipments performance. After building the Nilai the first things that come to mind are wanting to upgrade the jacks along with internal dampening. The caps could be a major hassle due to space..the wiring not so much.

As much as I love the beautiful inaccuracies or pleasant mild distortions/coloring of tubes I do appreciate low noise linear solid state gear as well. I pulled a tube pre off the Nilai yesterday and enjoying now straight from dac. With certain music I prefer the visual perceptions I can get from tubes and a clean power amp. Kinda funny how I strive to find & appreciate an amp like the Nilai due to its engineering and impressive specs & then look for different ways to add changes to its sound. Not with just passive parts. 

Whilst Discussing OP Amps, the OPA 1656 is one known to be selected for use in place of other OP Amp's.