Atma-Sphere Class D… Amazing

Like I said we all can’t be wrong. It’s not just my opinion. But some of the best spec’d gear sounds terrible. Anyway you slice it. Just not my opinion. At the end of the day…. It’s how does it sound when the switch is flipped. That’s truly the end game. At that point spec’s don’t mean squat. I have seen some specs from these amps. But not measured ones. And not to worried about that. As they eclipse any amp under $10,000 I’ve had in my system. I can’t say under $16,0000 yet because I haven’t been able to put the Pass Labs XA60.8 or a couple others. 
  And yes these are just my opinions.

First of all, there is no right or wrong, they are opinions, not facts. It doesn't matter if it isn't just your opinion. There isn't any strength in numbers when it comes to opinions- why? because there is NO RIGHT OR WRONG! Doesn't matter how many people agree with you- there will always be those who don't.

Yes, again, they are just your opinions. Get over the need to be "right". It doesn't matter how many more expensive amps you've had, how many class d or other amps you have tried, how many of your friends like them, how many magazines praise them, if your wife likes them, your neighbor's dog likes them, etc. It doesn't mean someone won't dislike them, and that is perfectly fine. You don't have to justify your preferences. They could be $99 Chinese clones and if you said they sounded the best in your system and beat out $100,000 amps, and all your friends hated them, it still doesn't matter. It still isn't "right" or "wrong". It's a personal preference, that's it.

 

I don't know why measurements were even brought up if it doesn't have anything to do with opinion, then why bring it up?

This is a never ending tactic - conflate comments in support of measurements as another tool to evaluate audio gear with their sole use in evaluating audio gear.

I have said repeatedly that measurements are useful to me in evaluating products as far as engineering, performance, suitability in my system vis a vis other components, etc. are concerned. I have also said repeatedly that the ultimate arbiter is how the equipment sounds in my system in my room. Yet over and over I hear the comments about how "I learned 50 years ago that measurements have nothing to do with the sound", "measurements are useless in determining how something will sounds", "go to ASR", blah blah blah. I can not help but conclude that several posters here have a reading comprehension deficiency and/or a fear and lack of understanding of things numerical and technical.

By the way, the designer of this class d amp surely used measurements to develop and engineer this amp. He also, based on comments he has made elsewhere, believes that measurements CAN indicate how an amp may sound, contrary to all those here who claim otherwise. Measurements and science play a crucial role in the design and development of audio products. They can be, if understood and properly interpreted, a very useful tool. BUT NOT THE ONLY TOOL.

@nonoise 

Kuribo is nothing more than a high functioning troll. 

The usual name calling when the intellect is feeble and struggles to produce any intelligent or meaningful counterpoint.

@nonoise 
Is that all you've got? Sad but as expected.

@nonoise 

What's it like going through life quarreling with those who don't see things your way? It must be all consuming for someone like you.

I couldn't say, why don't you enlighten us?

@holmz 

Ralph seems to have an amp that measures well and sounds great.
It seems like a lucky outcome to achieve both at once

Since he hasn't to my knowledge published the measurements I couldn't say it measures well or not. It seems to sound great to some, but every amp on the market sounds great in the minds of some people.

I don't think it is luck to have an amp that measures well and sounds good. I think it is the goal of many skilled engineers/designers. There are plenty of amps that measure very well and are very successful in the marketplace. There are also many that measure poorly in comparison, and yet they too find their supporters. If one didn't know better one might be tempted to believe that people's tastes vary quite significantly and that "good" and "not good" perceptions are relative to the individual, not the gear.

But I think the regulars have stopped feeding the trolls

Name calling when one doesn't agree with an idea or opinion is in fact the immature behavior being complained about. Too bad insecurity and ignorance ruined the thread.

@atmasphere 

Thank you replying....

There are the rules of human hearing perception (such as Fletcher Munson or the masking principle) and there is taste. They are two very different things and the two get conflated quite often! All humans use the same hearing perceptual rules- otherwise audio as an art would be impossible. What people do with that is different, which is why there is disco, rap, classical, tone controls and the like. Human physiology responds the same way to distortion, so it is something that is predictable and reliable within certain limits (there is individual variance on how the 3rd is perceived, depending on its phase for example).

Strictly speaking, Fletcher-Munson and the like are not rules or laws, but rather experimentally derived models of human aural perception. They are built on averages and generalities- in the case of Fletcher-Munson the results are said to apply to "average young people without significant hearing impairment". I doubt that describes many of those reading this thread... They have also been revised numerous times. While these rules of thumb are helpful perhaps to people such as yourself designing amplifiers aimed at as broad a segment of the market as possible, they are not "laws" or universally applicable "truths" like the law of conservation of energy or the laws of thermodynamics. As a result, they can not be relied upon on to be an accurate predictor on an individual basis. Thus, the guy shelling out $5K for an amp would be best advised to trust his own perceptions and tastes and to listen to the amp in his system, in his room, to form his opinions rather than rely on the perceptions, tastes, and opinions of others. Of course there are always those who love to gamble.

I see that you haven't made any comments addressing the patent that you received related to this amp, nor related why you have yet to publish any measurement plots, etc. Having this on the market now for a while, I would have hoped that info would have been forthcoming. Perhaps the transparency of Hypex and Purifi has spoiled me.

Again, thanks for your time. And best wishes on the success of your product.

@holmz

But if we assume that some amps were possible with a vanishingly low THD+N, then they would sound the same regales of topology

There are indeed those who claim once a certain level of performance has been reached, then products would indeed be indistinguishable from one another. I believe there have been rather rigorous tests done which seem to bear this out.

As I said, Fletcher-Munson and other such empirical studies have predictive power in a general sense but are weak on an individual basis. Additionally, personal preferences when it comes to audio gear is not based solely on sound, in any case. There are several other factors buyers consider when making a purchase which factor into a decision. It’s a complex decision that one needs to ultimately make for one’s self in the proper context.

Sure, a person could choose a proxy and take a chance. It all depends on risk tolerance and finding a suitable proxy. Me, I prefer to judge for myself as finding someone else with my tastes, the same gear and acoustical space, would be more difficult, time consuming, and risky than just trying the equipment myself. Besides, even if I associated myself with a "like minded group", the critical issues of component interaction and acoustical interaction in my space would make it impossible to find a realistically "safe" bet.

I don't believe your analogy is appropriate, either for those  "cable deniers" who base their argument primarily on an intellectual argument- it's a belief system, not a perception driven matter of taste, nor for those who simply claim that they hear no differences. That is more a pure perception argument rather than a matter of taste. In either case, it isn't a simple matter of taste at work, unlike the debates centered on amps, etc.

@holmz


I would have thought by now my point had been made.

Yes to both your questions.

No harm in using forums to learn of new gear. One needs to read critically and take the subjective opinions with a grain of salt. When it is all subjective opinion there isn’t much sense that can be made of it if you are a rational actor. Too many don't understand the difference between their subjective opinions and objective fact.

@kuribo You do know we have published specs right?

If you mean a rather thorough and complete set along the lines of Hypex and Purifi, no. Please provide a link if you have time...Thanks.

@soix 

There’s obviously much more to good sound than a lack of distortion.

"good" sound is a subjective opinion that depending on the listener, may have something, everything, or nothing to do with distortion or the lack thereof.

@fsonicsmith 

Here we go again-the old fallacy that the lack of distortion means more faithful sound reproduction.

How would you define/measure faithful sound reproduction?

If the output doesn't match the input, how can the result be called faithful?

Also, how humans sense sound pressure does not change from individual to individual; generally, the higher ordered harmonics are used. This is really easy to demonstrate using simple test equipment. Imagine a world where every individual used entirely different hearing perceptual rules! It would be a good basis for a scifi novel 😉

@atmasphere

thanks for the reply.

Of course I am not claiming that the "how" is different in every individual. What I am claiming is that there is enough natural variation among humans in reception, processing, and interpretation of external stimuli that one can not predict with certainty how any one individual will respond, all the more so when the amp is but a piece in a complex system full of external and internal variables. Clearly experimental results with a large enough sample can yield tendencies and generalities, but again, nothing that can predict with certainty on an individual basis. From your standpoint, that’s useful. From mine, not so much as I still need to listen for myself.

I am glad to hear that the feedback from your customers has been positive. It’s clear a lot of time, energy, and thought went into your product. I won’t hold my breath waiting for the measurements- you must have your reasons for not publishing them.

It might be interesting to consider that sound itself only exists in the head of the individual. It’s a back and forth from air pressure changes to electric signals. Our ears are transducers changing the air pressure pulses to electric impulses in our head. It is in our mind that these signals are perceived as sound. A lot of links in that chain that can cause differences in how the end result is perceived.

So I do not think that it is out of the question for Kurbio to ask for objective proof. Ralph has been talking about the distribution of the harmonics for a while, so to see it would be dandy way to objectively show some of what makes them sound good..

Indeed it would be nice to see the freq response versus load, the distortion spectra, etc....Too bad this info hasn't been forthcoming. Not sure how to interpret that...

One of the reasons I have bought Atmasphere's products is that Ralph can clearly and simply describe why his equipment works as good as it does.

I agree, it is nice that he takes the time to discuss his products. It would be even nicer if he addressed how his product differed from competing class d amps in performance and what a consumer gets with his product that justifies the price of 3-4 times that of competing products.

@juanmanuelfangioii

Maybe switch to decaff.....you seem way too stressed out about nothing.

Because it costs money to build a better mousetrap.

We have no proof it is indeed "better", whatever that means.

I am sure other manufacturers provide after purchase service and employ people as well...

Other than that, I would rather hear an explanation from the designer/producer himself rather than the ruminations of a 3rd party.

@juanmanuelfangioii

No one is forcing you to read my comments. You are free to ignore them.

Sorry if I am not cheering loudly enough for you fanboy. I deal in facts, not blind adulation. Show me the money.

He did state that he likes Purifi and Hypex, and that they also have published specs and graphs.
So I do not think it is out of line to ask for the graphs.

Being a fanboi of those brand does not automatically exclude one from liking, for instance, Atmasphere or Benchmark. It seemed more like “he has no objective proof that he should like them,” which if that is really what he means, then I cannot find a cogent argument to oppose that view. And I like them without an objective and rational reason to do so.

Hypex, Orchard, and Purifi are some of the current state of the art performance wise. The publish detailed measurements that give a great deal of insight into the abilities of the designer, the behavior of the product, and how the amp will play with other components. Additionally, they outline and highlight the performance envelope for users. Clearly these companies believe there is some value added by documenting the performance of their products and I for one agree. All properly engineered commercial amps are rigorously tested and measured by their designers so this is not asking for anything they haven't already done. I fail to see any legitimate reason to not share such data. Not everyone can or does find value in such information but that is no reason to piss and moan about those who do. I happen to appreciate products with state of the art performance and elegant engineering, both of which often go hand in hand with transparency from the manufacturer.

 

So we didn’t skimp on the power supply or the chassis. We just built it to proper engineering standards without cutting corners. IMO one of the reasons you see such variable comments about how Hypex and Purifi amps sound is because of how they are executed.

Thanks for the insight. Indeed, those marketing Hypex, Purifi, and several other class d amps using the modules of others can "tune" the sound through the input buffer op amp choices. I suppose it is a clever marketing technique to appeal to different tastes, rather than offering any color the customer wants, as long as it’s black. Of course most of them degrade the performance of the amp modules to some extent, but as we can see here, there are those who aren’t concerned with high fidelity to the input signal. Other such differences, like type and style of case, input mains filters, mounting configurations, etc., surely do vary widely, from head scratching to immaculate. No doubt these differences play some role in the final result as well-how much, I do not know.

No doubt with the weight of the transformer you would need a stout case. I suppose that can certainly add to the costs, though it is hard as a consumer driven by performance to justify spending 3-4 times as much as a competing product for things like a dealer network and a stouter case, neither of which in my opinion makes it "go faster". You might consider using a smps, a lighter, cheaper case, and offer your amp for half or 1/3 the price. Surely there is a sizeable market at the lower price point.

Again, appreciate the reply.

@twoleftears

If they can ’tune’ the sound just by changing opamps they are either using really terrible opamps or don’t know what they are doing!

These are the claims of customers- they prefer the "sound" of certain op amps over others, not mine!

I would think that a module with a high PSRR would reduce any deleterious effects of the smps, at least that is what Bruno claims with his modules. Based on their measurements, it seems to be true.

If that is so either the opamps were really terrible or the designer didn't know what he was doing! With any module you really don't need a lot of gain, so why would decent opamps affect the sound?? Answer: if the buffer is properly designed and if decent opamps are used, they won't.

Plenty of people have bought in to the "everything matters, everything has a sound" mantra. As I am sure you are well aware, audio people can be quite insecure and easily influenced by the siren song of other's wacky claims. Just look at all the audio voodoo on the market- if snake oil could only be refined into gasoline we would have $0.25/gal gas again.

 

Value picking seems to be easier when applied to established technology. Class D amp tech seems to in an evolutionary trajectory.

Current state of the art class d has performance with distortion at the limits of human hearing. Purifi, a leading class d amp company, is focusing their attention on drivers these days because in their opinion improving their class d amp has reached the point of diminishing returns. Speaker drivers are the weak link in the chain, thus I wouldn't worry about buying a state of the art class d amp only to have it materially improved in 2 years. Besides, one can get the state of the art for around $1000 these days.

@jjss49 

sell products to retail customers... you just get used to alot of random noise from purported know-it-alls

Clearly one need not be selling products at all to be subjected to a lot of random noise from purported know it alls.

Presenting an alternative view is not ok.

Name calling (troll, moron, etc.) is ok.

Nice.

@soix

Here you go:

"Conclusions
It was just a few years ago that people scuffed at class-D amps not being very clean or good for audiophile use. How the situation has changed. First with Hypex modules and now with the Purifi 1ET400A. Audiophile myths are shattered with use of large amount of feedback and high bandwidth to produce an amplifier which brings transparency to anything you throw at it.

Importantly, the 1ET400A does all of this while producing a ton of power and staying cool and efficient to boot.

There is a subjective aspect to measurements that doesn't come across in the graphs. When I run these tests with switching amplifiers, I often watch the analyzer struggle to get reliable reading, or there are jumps and glitches in measurements. None of that was here. The amplifier basically acted like a traditional class AB amplifier. Indeed, I measured it with and without my AES-17 40 kHz filter and the analyzer was happy both ways. This is when I know there is quality engineering that has gone into design of this amplifier.

Overall, it is my pleasure to strongly recommend the Purifi 1ET400A to DIY and OEM manufacturers."

Who’s the moron?

@pstores 

Point, counterpoint.
 

You've shared your opinion repeatedly: yes, you like the Atmasphere class d amp after not liking others, which to you is something significant. Yes, you like it better than some Pass amps, which in your opinion also means something significant.

Your opinions have been noted.

I have provided an alternative view: subjective opinions carry no factual information. We must each listen for ourselves to find our own truth.

I have tried to move the discussion to the objective arena where discussion on the merits can take place based on facts and debatable parameters. I have mentioned such things as design, cost, value, performance, etc., in an effort to draw logical comparisons to other class d amps- rationale, objective parameters that apply to all amps and all listeners- things that can be legitimately discussed and debated, unlike opinions on how something sounds.

As a result, we have learned several things- what was patented in the design, why the amp costs significantly more than other class d amps, why a linear power supply was chosen when many class d amps use a smps. Unlike hearing how fabulous and great the amp sounds, this is interesting and useful information. Additionally, the designer has been patient and comes across as an intelligent and thoughtful person. Also good to know.

I am disappointed however in the lack of transparency regarding the measured performance of the product. In today's market, with several companies backing up their marketing department with a wide battery of test results, I can't help but wonder why this company refuses to share such detail, nor even give any explanation as to why they do not publish a more comprehensive set of measurements. Ultimately the measurements will be made by a third party and shared, so again, hard to understand the secrecy, but clearly, it is the company's prerogative so it is what it is...

I wish Atmasphere the best of luck with their product.



 

@noske 


Figure 1 THD [dB] vs. Frequency @ 4Ω
Figure 2 THD+N [dB] vs. Power @ f=1kHz
Figure 3 Frequency Response @ Vi=2.83V
Figure 4 Frequency Spectrum (FFT) @ 1kHz, 1W, 4Ω
Figure 5 Intermodulation Distortion @ 18+19kHz, 1W, 4Ω
Figure 6 Frequency Spectrum (FFT) @ 1kHz, 10W, 4Ω
Figure 7 Intermodulation Distortion @ 18+19kHz, 10W, 4Ω
Figure 8 Frequency Spectrum (FFT) @ 1kHz, 100W, 4Ω
Figure 9 Intermodulation Distortion @ 18+19kHz, 100W, 4Ω
Figure 10 Output Power vs. VP @ 1% THD
Figure 11 Output Impedance vs. Frequency

@facten

Seems like you made a subjective judgment - at best similar performance - about the Atmasphere amp without having heard it. Nothing objective about that.

I said:

"I would not pay $5000 for an amp that offers me at best similar performance to one priced at $1000- it’s a non-starter."

What makes you think this is a subjective statement? I have been asking for measurements consistently and have said ad nauseam there is no value in discussing, debating, or arguing, subjective opinions about amp performance. Clearly if you had read and understood my comments you would have realized I am referring to objective performance above. Since the manufacturer has refused to produce the measurements, we can not compare the performance, thus my "at best" qualifier.
 

However, neither Ralph or any other designer has to be beholden to the design approaches that you favor. And, if they feel that their differently designed amps warrant a different price point that is their choice; they understand the market and their business objectives. No one is forcing anyone to buy anything. If you get musical satisfaction with Class D at the $1000 price point, great; if someone else gets Class D musical satisfaction at $3000, $5000 or whatever, great. There’s no right or wrong in that.

I don't believe I have said anything that contradicts the above, which is all obvious on its face. I have stated that the amp, from an objective performance standpoint, provided that at best it performs as well as the current state of the art, is a poor value at 4x the price. That's MY opinion, based on fact. As you astutely remarked, "There’s no right or wrong in that."

@csmgolf 

What measurement could be provided that would possibly change what is quoted here? You are already convinced it is a poor value and something that is a non-starter for you. So the question remains, why are you here other than to harpoon and tear down a product you have no interest in buying? It is blatantly obvious what you are doing. 

Simple, really. Take a look at the Hypex or Purifi web sites and download their measurements. It should be blatantly obvious.
 

I am not convinced of anything other than the poor reasoning faculties of so many who continue to make unfounded, knee jerk posts mischaracterizing my comments. I qualified my comment about value- without measurements, we can't rightly tell how it compares to the performance leaders, but assuming it is at least an equal, it would be a poor value. That's my opinion. You don't like it, that's your issue to deal with. If it performs better, then it could arguably be a better value. I am not tearing down anything except bias, misconceptions, and poor reading comprehension.

@csmgolf 

Did you bother to look at the suite of measurements published by Hypex or Purifi? Obviously not or you wouldn't keep chasing your tail asking me. Seek and ye shall find.

I have no interest in doing your homework for you. If you are too lazy to look and find the answers yourself, you don't deserve any more of my time. When you are ready to discuss the facts, let me know.


 

@ghasley

Not a lot of DIY- speakers are Tympani IVa, so it will be a matter of setting up the dsp crossovers, etc. No doubt it there will be a learning curve. Not sure yet about the amps, obviously. There is a plethora of options as class d has hit it's stride of late...I may look at the new Hypex Nilai500 modules due out soon as preliminary data is quite spectacular. Those would entail a diy build, which I have some experience with so shouldn’t be an issue....

@ghasley 

I assume @kuribo is a sincere potential customer

I have been using class d amps for more than 25 years. I have followed the tech with great interest over that period. I am currently putting together an active 3 way system and am indeed looking for 6 channels of amplification. With my long history using class d amps, yes, I am a sincere potential customer. I was originally drawn to class d because of its efficiency, form factor, and price/performance. While I can afford to buy whatever I like I still believe in price/performance and with class d amps with stellar performance available these days for incredibly reasonable prices, I don't think it unreasonable to expect to see performance measurements, especially for products that seem grossly out of line price-wise with other market entrants. Of course every manufacturer is free to provide as much or as little detail as possible, that's there choice. The consumer also gets to make a choice.

@aw-agd 




 

With all due respect, Silicon Mosfet cannot compete in performance nor on future FOM (Figure of Merit) improvement with GaN based semiconductors, it is not a matter of opinion, it is physics.

Really? Seems to me as a practical matter, silicon mosfet based class d amps by Hypex and Purifi clearly illustrate performance that not only competes with current GaN amps but in nearly all cases I am familiar with beats them handily in most objective parameters. One can argue that GaN devices offer inherent advantages over silicon mosfets, but unless the implementation exploits those advantages, it is all just a marketing scam. To date I have seen many GaN amp's brought to market, few that actualize these theoretical advantages.

@csmgolf

Um, the only one in this conversation that has their mind made up is you. What difference would it make if he published the measurements? How can I reasonably answer that unless he goes ahead and publishes them? As I said, if they are an improvement on the Hypex and Purifi designs, then arguably they have an added value that may justify the 3-4x great price. Why arguably? Because "value" is subjective and as I have also said repeatedly, the ultimate arbiter is how they would sound to me in my system in my room.

I have neither seen the measurements nor heard the amp, which would be the basis of any judgments. I have remarked that the amp, UNLESS it competes on an objective performance basis with its competitors (which we DO NOT KNOW), represents a poor value TO ME at its price point. This is called "a qualified opinion" and it is based on speculation, due to the lack of data.


 

@noske 


 

That is quite a slab of tests. I think that someone who owns one will drop-ship one over to Amir at ASR. Probably a couple weeks turnaround.

It's quite typical these days. I can assure you most bona fide manufacturers do much more than what I have listed.

My understanding is someone has already sent one for testing, or is in the process. We should know fairly soon how it "measures up".

Yes, I am aware of Atmasphere's recent entry into the class d market. I have already previously remarked that it is an impressive feat for someone who has previously been an exclusive designer of tube amps to make the leap to class d, which I know is a whole different ballgame. Bruno Putzeys once described class d amps as wanting to do everything but make music, or something to that effect, meaning, one must overcome their inherent nature and climb many mountains to tame them. No doubt it is a tribute to Ralph to produce something which on subjective grounds seems to have attracted a following on his first go around.

@juanmanuelfangioii

If one can get past the aethetics/gimmickry, this is what a reviewer had to say about the $20,000US version:

"output impedance [dashed trace, see Graph, above] rises steeply at HF, as does distortion, while the frequency response varies with speaker load impedance [unloaded/8/4/2/1ohm = grey/black/red/blue/green traces]. Put simply, if the impedance trend of your speakers rises in the treble then the Gran Vivace will likely sound brighter, and vice-versa.."

"a marked increase in THD into loads below 4ohm – typically >0.1% from 1-100W/2ohm versus 0.002-0.08% into 8ohm. Under continuous conditions, distortion increases from 0.004%/1W, 0.005%/10W and 0.09%/100W (all at 1kHz). Distortion also increases with frequency [see Graph 2, below] from 0.005%/1kHz to 0.07%/10kHz and 0.3%/20kHz (all at 10W/8ohm) in line with the response of the reactive output filter network."

The switching frequency is 800Khz, a bit higher than what most using silicon mosfets use (600Khz or so) but not really high enough to take meaningful advantage of the benefits of GaN mosfets. The Techniques GaN, for comparison, switches at 1.5mhz.

Load dependency is a non-starter for me. I wouldn’t call the performance "state of the art".

At $20,000US, for a shiny aluminum box and a fake tube, with performance bettered by amps at 1/20th the price, I can find little to attract me for a listen.

@aw-agd 

However as a matter of curiosity, is there a reason why in your peculiar selective cut&paste exercise you decided to omitt what in the same article the reviewer wrote about the sonic qualities and his personal experience about the sound?

I don't put any value in subjective opinions of third parties of audio equipment, especially when the associated equipment and listening environment are different than my own. In this case, the load dependent frequency response alone tells me that this amp will sound differently depending on the speakers used- all the more reason to disregard the subjective impressions.

@juanmanuelfangioii


I won’t apologize for having an appreciation for excellence, regardless of the source.

Perhaps you might try spending some time there. It would be a learning experience for you.

@aw-agd

@kuribo ...well...and that is my last comment on Audiogon, you may want to consider the fact that all amplifiers regardless the manufacturer/topology/technology will sound "differently" if one changes the load (i.e loudspeaker).

Well, that simply is not true. I have posted proof but for some unknown reason it was removed. An amp with a frequency response dependent on load will not only change character with a change in speakers but will change with the impedance changes of the speaker in use.

@noske 

 

I am very disappointed that the Gan guys have not taken an initiative on this. Gan is superior to silicon - so, prove it, as many others do in a variety of components and are sometimes subjected to criticism.  Everyone benefits.

110% agree. Exceptional claims require exceptional proof. Trust but verify, lol.

Here is an interesting take on the GaN device from the folks at Purifi:

Here is the opinion of the Purifi team on GaN as discussed in an interview:


Bruno: Well, with the sort of audio performance we’re getting I’d say that we’re asymptotically approaching “perfect”. One could argue that we passed the point of diminishing returns a few years ago already. I’m not saying that a next step won’t have any audible benefits, but in the grander scheme of things, the margin is shrinking.

Lars: That’s if you stick to audio performance alone. Otherwise we wouldn’t have bothered going to class D to begin with. You don’t do that for audio quality. You do that to get better efficiency, make the amp smaller and yadda. And then you get a new set of problems to fix, such as what it sounds like. And then there’s reliability, manufacturability and so on. I wouldn’t say that GaN is going to be the answer to those things, and neither is upping the switching frequency.

Bruno: Well for a given efficiency you could probably increase the switching rate, but if I’m going to shell out as much for a pair of FETs as what you’d normally pay for the whole amp, I’d rather benefit from that in terms of higher efficiency. Of course, not everyone is able to make that choice. I’ve spent my career honing control loops, most audio designers haven’t and so have to rely on simpler control loops. In that case, increasing the switching frequency is definitely helpful to reduce distortion.

Lars: We’re as fanatic about audio quality as anyone else, but because we’ve got feedback down to a T now we’re not forced to resort to higher switching frequencies.

Bruno: If we need to be geeky and I guess that the folks who are going to read this interview can handle that -eh Thomas?- lets grab the specs for the FET in our 400W Eigentakt module and its closest GaN equivalent. So that’s the FDP42AN15A0 (OnSemi) on our left and the EPC2033 on our right. Rdson: 36mOhm vs 7mOhm. Clear win for GaN here.

Lars: It’s also got a higher current rating (24A vs 48A) so if we want to be fair we should be scaling by about 2:1

Bruno: Oh erm well, that’s still a minor win for GaN because after scaling it’d come up at 14mOhm. Gate charge is of course magnificently low (30nC vs 6nC after scaling) so driver losses would be low and you can turn them on fast. GaN also has zero Qrr so you can do that if you want. But the main thing that sticks in my throat here is output capacitance. Our good old FDP42, which is from 2002 mind you, has an output capacitance at 100V of 70pF whereas the EPC device puts in a whopping half nanofarad (or 250 puff after scaling). That means your idle losses will go up, or you will have to increase dead time to allow the output inductor to recover the extra stored energy at its leisure. And isn’t it just idle losses that more or less determine real-life power consumption in full? And if power consumption isn’t something to care about, why not just stick with class A…?

Lars: And high dead time combined with high switching frequency sounds even less attractive. That just increases open-loop distortion.

Bruno: In applications like motor controllers and high density SMPS GaN and SiC devices are a breakthrough, mind you. It’s just that audio is this weird application where average power is very low and where dead time actually affects performance.

Lars: And GaN is going to mature so this picture is bound to shift at some point. Just not now.

Bruno: True. On the other hand, silicon is doing the same. More recent devices are getting frightfully close to GaN. Sadly they only come in SMD packages that require fairly expensive methods to get the heat out. Like most GaN devices. It looks terribly ancient, but the good old TO220 package is still a neat compromise in terms of performance for the price.

Lars: It’s just a game of tradeoffs. The fact that we’re using normal parts, and the reason why we chose to do so doesn’t make for a sexy story. We all like to believe in a magic bullet but when you’re an engineer you have to make choices based on tangible grounds. So the sexy story we’re trying to push about Eigentakt is that we think it’s a bloody clever design.



 

@nonoise 

Another negative attribute about zealots is they lack a sense of humor. 

Is name calling your usual response when people don't find anything funny about your sense of humor?

@facten

Nothing like high jacking someone’s thread.

If you try you will see the relevancy.

Why don’t you ASR guys start a whole other thread

Why don’t you?

@nonoise 

ignore what they refuse to listen to with their own ears.

Who has has refused to listen with their own ears or said not to trust one's own ears? All I have said is I refuse to listen with yours and other's ears. I trust mine just fine. More mischaracterization.

that tells me something about quality over quantity.

Actually your assumption is baseless as there is absolutely no proof whatsoever that lower power equates to higher quality. In fact, the AGD amp, the only GaN amp you mention that we actually have any performance data on, performs demonstrably worse than higher output class d amps from other manufacturers.

@nonoise 

More name calling. Seems you aren't clever at all.

@jerryg123 

wow best you have.

I tailor my reply to the intelligence and mental age of the recipient Jerry. Thus, when addressing rude and poorly educated people, I am limited in my replies lest they confuse things like "reply" and "retort".  I imagine this is frustrating for you but imagine how others must feel when they have to explain things over and over...

@jerryg123


A response is a retort. You are welcome.

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