Atma-Sphere Class D… Amazing

@klh007, As you posted above, @ddafoe's System details says he owns the Meitner MA3 DAC.

@ddafoe Is your DAC a Meitner? If not will you reveal it?

I had a photo of the inside of the amp that is the subject of this thread and commented that the parts could not justify the price. 

@fsonicsmith, how many other audiophile products (that many folks purchase and enjoy their sound) would this statement be true for?  Plus, how do you factor in the cost of custom designed and manufactured circuits/technology?   Do you know how much Atmasphere (or other manufacturers with custom tech) spend to develop such tech?  Unless you have listened to the amp in question and compared it to many other similarly priced products, your statement seems off-target from my perspective.

Here is a photo of the inside of my DAC, which after owning various models from SimAudio, Berkeley, Bricasti, RME, and Mojo Audio is my favorite so far, it also costs way more than I ever thought I would spend on a digital front end and it has next to nothing under its cover.   Does its lack of parts justify its MSRP? 

So far I find the Atmasphere Monos to be in line performance wise with my slightly more expensive Pass XA30.8; I have not popped the cover off my Pass to compare them as in the end it doesn't really matter to me since I'm using my ears to decide which amp I prefer.

@rajugsw 

Nice pic of your Class D amp. I noticed that you're using a toroid instead of the Hypex power supply you used in your earlier version of the amp. The Atma-Sphere Class D amp uses a toroid as well. What difference in sound do you notice when comparing the toroid to the Hypex?

I have been a member here for ten years and I have just had my first post ever removed by the mods.

I had a short quote from a S'Phile interview with Charles Hansen which I duly attributed by author and source so that could not be the reason. 

I had a photo of the inside of the amp that is the subject of this thread and commented that the parts could not justify the price. That could not be the reason. Oh, yes, I think it was. 

I was never remotely involved in the ugliness of a certain poster. I bring that up only because of this- Tinear123 has a very nice system and I would be most interested to hear his long term assessment of this amp. He says he won't be posting because of the aforementioned ugliness. That's a shame. I hope you, Tinear123, should you see this, will reconsider. 

aavik makes wonderful class d amps and integrated, highly recommended 

Agree to an extent still love that tube sound. 

@mglik you maybe very shocked…. If you get a chance roll a set of these in your system. 
 

@bluorion I am running a Atma-Sphere MP-3 with Vcaps, Caddocks, and dampening. Running a Aqua LaScala DAC, Innous phoenix Reclocker as we speak with Roon. Much of what I listen to to Hi Rez…. It’s pretty damn good…  compared to the other Class D amps which I’ve had in my system. These are definitely the best. And probably in the center of the price points of the others. They in my opinion are better than the Class A SS I’ve also had in my system. I’ve listed all the amps I’ve had in the system earlier on in this post. 

@mglik ,

I, too, own Atma gear (MP-1, MA-1-stock).

We both know Ralph is a consummate stereo equipment designer.

So, for me, I have put my deposit on his new Class D amps.

The big question, as a Vandersteen owner, is the fact that it uses Feedback. Ask any Vandy diehard, and you'll know that amps with Zero Feedback work best for these speakers.

So, am going to give these a try, and also try to get my dealer to set up a demo comparing them to  his Zero Feedbackamps, if possible.

Bob

I have been anxiously awaiting Ralph’s Class D.

Am a big A-S fan and joyfully use his MP-1 preamp.

Since “going home” to Quad ESL 57s, I have cycled through several amps to find the best match for the Quads.

I have the chance to put money down to get on the waiting list (6-8 weeks) for the A-S Class D. May still do that, but have bought an ARC Ref 80S.

I was floored by the sound of the ARC Ref 160S at a friend’s. The best system I have heard. Was so engaging that I couldn’t not listen.

So far, I have decided that the ARC Ref sound may have attractive “tube qualities” that Ralph’s do not. That is, a level of organic/real. 
And even though price does not represent quality, the $16K Ref 80S should be in a different league from the $5400 A-S. 
This is only a guess. Not yet hearing the A-S amps. But still thinking that those tube qualities are yet to be captured by a SS amp. 
As a previous die hard SET guy, that sound is called sweet. To non tube guys, it is called colored.

I agree with @grannyring . Class D GaN FET (Orchard Audio Ultra) is the future and all Tube, Class A, Class A/B Amplifiers are antiquated Dinosaurs ! But a high quality DAC (PS Audio DirectStream Sr.) and a highly resolving Tube Preamp )BAT VK-50SE fresh form the Factory with new Mundorf Paper in OIl Capacitors - I couldn’t afford the Transformer upgrade) ARE A MUST !!

​​​​​​

I suppose it’s still possible to have an opinion without some folks getting angry? Ralph, myself, and all Agoners have thoughts and opinions. No reason to make fun of or attack these opinions. This forum is simply a place to share them.

I will add to my opinion here. Class D integrated amps with tube preamp sections will also grow in popularity. Tube preamps will continue to sell well in the future.

Amplifier performance is also held back by the amplifier itself completely independent of the speakers. We are not producing flawless and perfect amplifiers. Yes, how amplifiers interact with imperfect speakers also plays a critical role sonically. No doubt.

@fsonicsmith, no need to stop posting on this thread, but it would be helpful and kind if you worked on your demeanor and respected opinions that differ from yours.

What preamps work well with these class D amps?

I agree with Ralph regarding future sales of tube amps. Sure, some will always want to own one, but sales will erode dramatically over the next 10 years. Seems like a rather reasonable statement. Innovation in Class D amplification will continue and magnificent sounding options will be introduced at ever increasing speed delivering sonic improvements many felt impossible just a year or two ago. 

I said I was done but this is such nonsense. Amplifier design and amplifier performance has been dictated by the limitations of loudspeakers. There is no perfect amplifier because there is no perfect loudspeaker.  "Magnificent sounding options" and "Sonic improvements many felt impossible just a year or two ago". What flowery and prosaic language! That's a good one. The euphonic nature of tubes happens to suit the limitations of many loudspeakers in a manner that solid state often fails. Charles Hansen wrote about this towards the end of his life. https://www.youtube.com/watch?v=9L0k3-cporQ&t=5s  Think of an amp as a complimentary solution to a problem elsewhere in the chain, not the source of the problem and impediment to sonic bliss.

 @atmasphere backs up his words with his actions.   That makes for a strong case.   We will see. 
 

About 12 years back I was on the brink of going with tube amps to get the sound I wanted but decided to look forward and try the newer evolving technology (class d amps) rather than backwards.  I have great faith that advancements in technology move things forward.  Been a Class D amp fan ever since.  Still have a tube preamp sitting idle currently but never took the tube amp plunge.   class D did  the job better for me.  No looking back now at this point.   Kudos to Ralph for being forward thinking and having always had a great appreciation for good things past. 
 

I agree with Ralph regarding future sales of tube amps. Sure, some will always want to own one, but sales will erode dramatically over the next 10 years. Seems like a rather reasonable statement. Innovation in Class D amplification will continue and magnificent sounding options will be introduced at ever increasing speed delivering sonic improvements many felt impossible just a year or two ago. 

You have side-stepped your bold declaration that tube amps, the entire category bar none, are on their way out.

@fsonicsmith That was not my intent. To my understanding I've not side-stepped this issue at all:

IMO power tubes are on life support- even in the guitar industry class D has been making significant inroads in the last couple of years. Its clear that any manufacturer of amplifiers now has to contend with class D technology in a way that they did not a decade ago; in particular manufacturers of tube amplifiers will find their market shrinking dramatically over the next ten years. The reasons for owning tube amps (the 'sound') is being heavily eroded by advances in class D technology; any manufacturer that ignores this does so at their own peril.

Would you please expound upon your statement: "keeping distortion vs frequency linear across the audio band"? I am afraid I don't quite follow.

@atulmajithia In order for an amplifier to exhibit the same smooth character as the music itself, in order to not sound bright, distortion must not rise with frequency. This is one of several characteristics needed to allow the amp to be musical and not bright. If a tube amplifier is zero feedback and has sufficient bandwidth (not including the output transformer if one is present) then this really isn't a problem. Of course the designer needs to pay attention to other issues but distortion vs frequency is pretty important.

The ear is very sensitive to higher ordered harmonics since it uses them to sense sound pressure. It also assigns a tonality to all forms of distortion and higher ordered harmonics get the value of 'harsh and bright'. In addition distortion products occurring in the Fletcher Munson region (3-7KHz) causes distortion in that range to be more easily heard.

TIM is a product of an amplifier having high feedback but also has part of the amplifier outside of the feedback circuit so unable to compensate for certain types of distortion. An example might be the base of a transistor in a differential pair, wherein the input signal is applied to that transistor while the feedback is applied to the base of the transistor's mate. This is a common circuit in many solid state amps over the years. Class D amps  of the self-oscillating variety (like ours) don't have that kind of input circuit and so avoid this problem.

@atmasphere

Thank you for your patience and great explanations. With regard to the high-lighted statement below:

That is why we never ran feedback with our OTLs, since keeping distortion vs frequency linear across the audio band is pretty important if you want the amp to not sound harsh. That’s easy in a tube amp if you don’t run feedback! Our OTLs have as few frequency poles as you can get in a tube amp and even with them we ran into issues with their phase margin. IOW, very difficult to prevent oscillation even with a carefully designed feedback loop if running large amounts of feedback. Conventional amounts were no problem but had all the downsides that have given feedback a bad rap in high end audio.

Would you please expound upon your statement: "keeping distortion vs frequency linear across the audio band"? I am afraid I don't quite follow.

Also, since you mentioned that your Class-D amp uses a fairly large amount of loop feed-back, which helps keep THD down, would you please inform what your amp produces by way of Transient Intermodulation Distortion (TIM)? In that light, since there are many different methods of measuring TIM, and also since it's very difficult to measure, would you please inform which method(s) were used?

@atmasphere  Thanks for the helpful comments in response to my questions about  the choices of switching frequency and power supply for your Class D amps.

 

 

How much hubris can a man possibly have to make such a pronouncement! This man has solved the problems leading to 20 years of "terrible missteps" of all that came before him?

People have been jumping all over @kuribo, which as @noske described earlier in a puerile fashion, with Troll and Fan Boi descriptions. But this seems like more like what they are describing.

When someone has 40 year in the industry, and brought balanced XRL to home audio, it is different than PS Audio YouTube videos.
 

One can only be so humble and demur, and honesty is not exactly overdoing it in a self promotion way.

I am not sure how Ralph can respond and communicate any better than he has? He certainly does much better than I can do in the sense, but I am also not an expert in the field.

. Who is Ralph to declare that his subjective opinion of the sound of his own product is absolute? Ralph will no doubt diplomatically respond that he is not just referencing his own Class D amp. If so, than tell us Ralph which other Class D amps are you declaring to be subjectively better than the best tube amps other than your own?

He also said that if people like the absolute best numbers and even lower distortion, that Bruno has those in the Purifi Class-D that they sell.

Perhaps you could be so kind as to look me up three, five, or ten years down the road and tell me when my ARC Ref 150SE and ARC Ref 80 power amps have been rendered value-less. on the market so I can inquire of my accountant if I can declare a depreciation deduction.

We can also roll in ARC with Purifi and Atmasphere, but that does not change the fact that they are running a business and have decided that a move to Class-D is a direction that they want to be poised for.

if one asks hard questions, or makes statements that are not appreciated they are referred to as Trolls and Fan Bois, and if they respond civilly then they are referred to as an ambassador.

But that is fine. I will not say another word in this thread and I truly wish you the best.

^great^

@fsonicsmith - I guess time will tell if Ralph's assessment pans out, but I'm essentially with you none of my tube amps are going anywhere unless I purchase some other tube amp, or the powers to be come breaking down the door to mandating its cart-off.

Ralph, I think you missed your calling. You should have been the US Ambassador to North Korea, China, or Iran. You have side-stepped your bold declaration that tube amps, the entire category bar none, are on their way out. But that is fine. I will not say another word in this thread and I truly wish you the best. I am confident enough in my high-end audio world to not let a different opinion-even yours-bother me any more than it has (which was relatively minor). Perhaps you could be so kind as to look me up three, five, or ten years down the road and tell me when my ARC Ref 150SE and ARC Ref 80 power amps have been rendered value-less. on the market so I can inquire of my accountant if I can declare a depreciation deduction.

You may have already covered these issues earlier in this thread, but could you please explain a little more about the following two issues with regard to your Class D amps?

1. I noticed that the switching frequency for your amp is 500 kHz while several other GaNFET amps use a higher switching frequency. Did you decide that 500 kHz represented a "sweet spot" for switching frequency in your design? Does the choice of higher rates have unwanted side effects that can adversely affect sound quality?

2. What factors entered into your choice of a toroidal power supply rather than a SMPS? What number and size of capacitors did you use in the power supply and how did you decide on the amount of storage needed?

The allure of a higher switching speed is increased loop gain which allows for more feedback. The downside is that you need to have deadtime and that value is a constant that does not change with switching frequency. Distortion thus increases with the switching frequency, so I guess in a way there is a sweet spot. The other issue is the faster you switch, the crazier the stray inductances become which can result in parasitics at some pretty high frequencies!

We used a toroid simply because a SMPS really should be custom-built for its application. There are a good number of advantages to SMPSs such as voltage regulation and oddly, lower noise (wasn’t the case 30 years ago!). But you have to be careful about current limiting issues which can really be a thing if the amp is subjected to lower impedance loudspeakers and in particular ones with crazy phase angles. So its easier to simply use a toroid.

And Ralph, you have responded to virtually everyone else’s questions and statements including those of the bizarre troll, and yet you won’t respond to mine asking-earnestly- whether your class D amp has true balanced topology and if not, the sonic compromises if any?

Sorry- that was an oversight on my part. If you don’t know, we’ve been pushing balanced operation longer than anyone else in high end audio; our MP-1 was/is the first balanced line preamp ever made for home use. Its not something we backed away from in the class D!

Who is Ralph to declare that his subjective opinion of the sound of his own product is absolute? Ralph will no doubt diplomatically respond that he is not just referencing his own Class D amp. If so, than tell us Ralph which other Class D amps are you declaring to be subjectively better than the best tube amps other than your own?

:) as Capitan Kirk once said ’Who do I have to be?’

Seriously though we think our class D sounds better than our tube amps although we’ve not done serious comparison with our bigger tube amps. We think our tube amps sound better than most other tube amps so its a simple logic statement at that point. But I really wasn’t commenting on our amp in particular; I was commenting on the fact that class D offers a technique (rather than specific amps, although there are class D amps out there that get very nice comments such as the AGD and Orchard) wherein this is possible, since it is very easy to develop the Gain Bandwidth Product that will allow the designer to support an enormous amount of feedback at all audio frequencies. Prior to the recent evolution of class D this really was extremely difficult until the mid 1990s with solid state and impossible with tubes.

That is why we never ran feedback with our OTLs, since keeping distortion vs frequency linear across the audio band is pretty important if you want the amp to not sound harsh. That’s easy in a tube amp if you don’t run feedback! Our OTLs have as few frequency poles as you can get in a tube amp and even with them we ran into issues with their phase margin. IOW, very difficult to prevent oscillation even with a carefully designed feedback loop if running large amounts of feedback. Conventional amounts were no problem but had all the downsides that have given feedback a bad rap in high end audio.

Class D offers a way around that problem. We started with zero feedback prototypes but found out quickly that a zero feedback class D amp has to have a very stable oscillator for the triangle wave, else you get a high noise floor as the oscillator drifts in frequency. With self-oscillating designs this source of noise is eliminated.

How can you then, in good conscience, even offer your tube amps for sale?

Funny thing about that, people still want them and don’t always believe things that I say, as we’ve seen on this thread. You get used to that over time :) But I can see a day when our tube amps become custom order only or gone altogether.

This man has solved the problems leading to 20 years of "terrible missteps" of all that came before him?

No. Class D has been an evolving tech for quite some time. Clearly others have gone before us and it is they that solved the lion’s share of difficulties, Bruno Putzeys in particular. In a way I think we were lucky in that in our design it worked out that the primary distortion sources tended to produce lower ordered harmonics, so although the overall distortion is much lower, the actual distortion signature otherwise would make you think you’re looking at a tube amp.

how can you possibly tell the thousands of us with tube amps and preamps that if we only gave your Class D amp a good audition we would come to the realization that your Class D amp is subjectively superior?

If you look back you’ll see that I answered that question several times on this thread for kuribo. He seemed unable to accept the answer, as best I can make out because he thinks the autonomic senses and taste are the same thing.

One thing that is a bit of a hurdle, now that you bring it up, is the higher output impedance of zero feedback tube amps in particular. This causes some ’warmth’ the class D won’t have because the tube amp will likely have a slight FR error in the bass associated with the impedance rise with most speakers have in this region. The ear interprets that extra bass energy as a bit of warmth and it causes the perception to tilt slightly away from the highs.

Once you compensate for that (on my speakers I used pink noise to set them up with each amp comparison since the driver levels are independently adjustable), then you see what is really afoot.

I have always expressed my appreciation for Ralph's contributions on this Board. Don't believe me? Look at my previous posting history and you will see for yourself. But up until now I never saw such promotion-as here-of his own product. 

In time, the tube amps will be gone. Not because of a lack of tubes but because they've been eclipsed and people will wonder why they go through the hassle when subjectively better sound is available at less cost. That hasn't happened yet simply because class D has taken some terrible missteps in the last 20 years.

How much hubris can a man possibly have to make such a pronouncement! This man has solved the problems leading to 20 years of "terrible missteps" of all that came before him? 

How is this pronouncement any different than those of the dumb prognosticators who declared vinyl dead once Philips-Sony came out with CD players in 1982 or so? Vinyl is far more of a "hassle" than tubes. 

Who is Ralph to declare that his subjective opinion of the sound of his own product is absolute? Ralph will no doubt diplomatically respond that he is not just referencing his own Class D amp. If so, than tell us Ralph which other Class D amps are you declaring to be subjectively better than the best tube amps other than your own? 

Ralph, how can you possibly tell the thousands of us with tube amps and preamps that if we only gave your Class D amp a good audition we would come to the realization that your Class D amp is subjectively superior? How can you then, in good conscience, even offer your tube amps for sale? 

As I type this I am wearing a mechanical watch, a Carl Bucherer Scubatec that costs the same as Ralph's amp, needs an expensive cleaning and lube every six to eight years, does not have the accuracy of a five dollar cheap digital watch, and has to kept on a watch winder or re-set once the mainspring's power reserve runs out. By analogy this would be the same as someone like Ralph stating that I should or will eventually realize that my preference for mechanical watches is folly. 

And Ralph, you have responded to virtually everyone else's questions and statements including those of the bizarre troll, and yet you won't respond to mine asking-earnestly- whether your class D amp has true balanced topology and if not, the sonic compromises if any? 

@j-wall - This is going to be a bit of a round-about answer:

I've been a SET fanatic for several years, primarily 45 and 46 SETs.  I just love the presense and intimacy that those SETs provide with my 98dB + speakers. 

I have been on the lookout for a Class D alternative that could provide or at least approach that SET sound that I have fallen in love with.  After watching a video (don't recall which) where Ralph was describing his Class D monoblocks and based on his outstanding reputation, I ordered a pair.  This was a leap of faith for me as it was the most that I had paid for any piece of audio gear except for speakers.

I've had them in place now for a little over a month and will say that I'm not dissappointed.  They are certainly the closest to the SET sound that I have heard from a solid state amp.  They are not quite up to the SET sound that I was looking for, but they come very close.

No question, Class D has come a long way and that will likely continue to improve.

Coincidently, while waiting for the Atma-Sphere  amps to arrive - a friend recommended that I try another Class D stereo amplifier which is Paschal based.  I won't mention the name here (since this is a thread on Atma-Sphere Class D). 

Is it as good as the Atma-Sphere, probably not, but it is very very good and I plan to do an A/B test with them in the near future.

Neither of these amps will replace my 45/46 SET amps, but they are outstanding alternatives.  I'm sure there are many other excellent Class D amps out there, but I have not had the opportunity to hear them

@drhamp what are your thoughts on them? Have you been a class d user before? I'm very interested. 

I ordered the monoblocks on May 27 and received them on Aug 16, so a bit under 3 months for me. Definitely worth the wait.  I was quoted a 3 month wait and it came in just under that.

Talk about audio (however defined) on this esteemed forum. There are many issues to explore and many wonderful contributions. Address the many questions raised.

What is with this with character assassination? That is what inexperienced and puerile teenage girls do at school when they have a crush on some boy.  

Great question, I do not think many dealers are keeping much stock anymore. The last few years it seems that you had to wait for an appliance to come in from the distributor. Even pre pandemic I can remember having to wait a week or two. 

Has supply started to catch up with demand? What is the normal wait time for these amps? Are Atma-Sphere dealers likely to have them in stock? 

Thanks,

aldnorab 

I find it interesting that Ralph is predicting the eventual demise of tubed power amps. Aside from the supply chain issues and embargos with Russia I think they will be around for quite some time. Now I do like some of the newer class D amps including Ralphs. I think that the goal has been to get as close to the sound of a tubed amplifier with more efficiency and reduced cost. I recall reading an interview of that Bruno P fella and he said as much. 

Wish there were more GaN integrated though. Trying to cut back on boxes. 

Ralph has a winner as do Orchard and AGD. 

Guess we need to stop feeding the 👹

Sad that most of you realize this so late when I said that few pages ago.

Remember, a troll will first bring YOU ALL to his level and then beat you through his experience of trolling.

Folks need to refrain from responding to trolls, however tempting it might be. Check his history on this site. Join date, responses to topics, etc. He had an agenda and you all fell for that. Hopefully some lessons learned.

I’d suggest not questioning or addressing kurobo on this thread… let’s keep on track for/about Ralph’s amp. 
 

Reading through the various opinions on these amps, some prefer the Weiss opamp, some the Burson, others Neurochrome, and others have said that the stock Purifi buffer is their choice. Some describe one op amp one way, another describes the same op amp another. Measurements show no differences which can be considered to be audible. They may all be "hearing" the same way, but their brains clearly do not seem to be interpreting the input in the same way. We see this same thing with cables and all the wacky tweak products- none of them can be shown in most cases (poorly designed cables, for example, would be an exception) to do much of anything, yet some people swear they turned their system up to an 11, others say they hear nothing. Previous experiences, mood, biases, go a long way to explain this perception paradox, This is why I find no real value in subjective comments regarding equipment on forums such as this.

@kuribo if the nueroshrome, purifi (etc.) opamps all measure the same, then what do you attribute people listening preference to? Or is it a psychological preference/bias?

I respect Ralph for so many things and count his incredible patience with kuribo here among them. But in my heart of hearts I wish he’d spend the time developing an even more affordable stereo version of these monos (hint hint) rather than using that otherwise valuable time trying to reason with a troll who can obviously never be reasoned with. Better to realize that 98% of the people here greatly respect you and your work while kuribo gets 2% on both counts so why waste your time? Again, why would a guy who puts no faith or credence in anyone’s subjective opinion (save his own) even be here where everyone looks for, values, and shares subjective opinions?  I suggest again that we just let kuribo keep typing away in his mother’s guest room or basement that he probably shares with her sewing machine and creepy dresses and ignore the useless drivel that’ll only become more useless, ridiculous, and annoying.  Easier said than done, but I think if we put our heads together we can do it.  Let’s Go!!!

Forget him , can the thread  get back on point.

Worse, is he is using an Audioholics  video with that nasty Gene. 

3 of a perfect pair. 

He's running it with an iron hoof fist.

the unsavory character seems to have started another thread on a nad unit using.............. wait for it.............. purifi modules!!!

ho’s a ho, born to ho, just gotta ho...

Hopefully, this thread can get back on track with Atmasphere class d owners sharing their experience with the amp. 

@ghasley +1003… besides thread hijacking…. People should be respectful of others threads.  And not Hijack them…. Such BS..

@ghasley +1001

@ghasley + 1000

@ricevs Yes, Ralph is correct and the others are wrong. Ralph solved the unsolvable with his original OTL design. He worked on his design for years until he solved the technical challenges. Who are you to question his credibility? Who are you to post a meaningless piece of excrement $300 dac as your proof of concept that op amps must be rolled? And to do it in a thread that the OP created to discuss  Atmasphere class d?

You know, there was a time not long ago when people like you and the other obnoxious poster would just go elsewhere rather than to purposefully disreepect someone like Ralph. He has been here since the beginning of Audiogon, answering questions, never hawking his own gear, just providing honest and forthright answers to those trying to understand something. And then an amateur tweaker like you comes along and disparages Ralph? The other guy too? You are both pimping your own agendas but why did you pick this thread and Ralph?

You two should be ashamend of yourselves…you have no credibility and just because you’ve soldered a few times and liked the results does not make you qualified to disparage Ralph or his design. If you have a shred of integrity, you would have least listened to the class d Atmasphere amp before beginning your false sermon.

@atmasphere 

You may have already covered these issues earlier in this thread, but could you please explain a little more about the following two issues with regard to your Class D amps?

1. I noticed that the switching frequency for your amp is 500 kHz while several other GaNFET amps use a higher switching frequency. Did you decide that 500 kHz represented a "sweet spot" for switching frequency in your design? Does the choice of higher rates have unwanted side effects that can adversely affect sound quality?

2. What factors entered into your choice of a toroidal power supply rather than a SMPS? What number and size of capacitors did you use in the power supply and how did you decide on the amount of storage needed?

Thanks for any additional info you can provide!

It’s true the best measurements are those done by qualified and trusted independent parties.  Maybe that will pop up somewhere soon.  Meanwhile hope to give the Atmasphere amps a listen soon maybe at CAF. 

@kuribo 

You were doing a poor job earlier in this thread masking your Purifi bias. Now, you have removed all doubt.