Class-D amps - a different re view


Martin Colloms, the editor of HiFi Critic (ad-free mag from the UK) have recently published the review of several different Class-D amps, together with an in depth technical analysys and measurments.

His conclusions were not favourable, to say at least:

"I regret that not a single model merits unqualified recommendation. Price is not the issue; the poor listening tests speak for themselves. (...)
At present we have to take the prudent view that good sound might be possible from switching amps, but we haven't heard it yet."

BelCanto REF1000 (ICEpower) - score 10.5 pooints
"The ICE power module used has a dependable reputation, and the design is well built and finished as a whole. While I would not suggest that you shouldn't try this amp, on sound quality grounds alone I cannot recommend it for audiophile use."

Channel Islands D100 (UcD) - score 13 pooints
"While I have reservations about a number of aspects of sound quality, and advise personal audition, given the solid lab results (...) the overall performance and the moderate price, these CA Audio monos do make it to the 'worth considering' cathegory."

NuForce 8.5V2 (proprietary technology) - score 9 pooints
"Yes, the price is good for the power output. Yes it's pretty, light, small and runs cool. However, the sound quality simply does not justify recommendation." (on top of that the NuForce amp measured very poorly - Elb)

Pro-Ject Amp Box (Flying Mole) - score 5 points
"I'm sorry to say that Project (...) was a real disappointment in the listening tests, and can't be recommended."

Just as a point of reference, recently reviewed Krell 700CX scored 100 points, CJ Premier 350 - 110 points and ARC Ref 110 - 135 points.

At least someone have had the balls to say it. This is why HiFi Critic is THE mag to subscribe.
128x128elberoth2
Atmasphere...When transponders (radar response avionics for planes) were first introduced they were all transistorized except for the output device which was a traveling wave tube. The high RF frequency used by the transponder was cited as the reason for the TWT. The TWT was a frequent failure item. Thank God it has now been universally replaced by transistors.

The switching frequency of digital audio amps is well below 2 MHz, and solid state power devices have no problem at such frequency. My CI D200s (UcD) switch at around 400 KHz and my CarverPro ZR1600s (TriPath) are up to about 1.5 MHz.

I wish I could afford one of your OTL amps, which I believe exploit the benefits of tubes without their drawbacks (except cost).
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Muralman1, being one of those 'tube guys' I have to agree in part with you- this is something (at least for now) that I for one will not admit. IME, class D has a long way to go to beat what I see as the advantages to the amps that we make though I do not hold that out for my competition :) as our amplifiers are apparently unique even in the world of tubes.

I understand the cost, heat and size issues. However for the time being if the system is chosen based on those constraints rather than sound, then luck and luck only determines the sound of the system- no doubt why so many want to know which class D sounds the best!

If instead, the sound of the system is chosen entirely on the basis of sound quality, you get a different result altogether. Our amps were designed for performance/reliability as number one, all other aspects being secondary- we took a stand for quality in so many words. Class D was specifically intended to deal with heat/efficiency issues inside a cost model- consequently trying to overcome the issues that result flies in the face of its intention. Not to say this is wrong or bad- in fact, making the best of a situation has characterized a good bit of human behavior and consequent innovation.
"and luck only determines the sound of the system- no doubt why so many want to know which class D sounds the best!"

Good point Ralph, perhaps that's also why I would really like to know what solid state and what tubed amp sound the best, . . . because with all those technological constraints, compromises, and underlying limitations out there, regardless the underlying technologies, it is my own ever-so-limited experience that results are more often than I would like less than stellar. . . but then, I am admittedly a little hard to please. . . regardless of technology.
Atmasphere, you are entitled to your opinion. I did not know you are an amp producer. I have never heard a tube system, regardless of cost that can bring on the real performance better than my own class D system. Can you tell me what areas you think class D does not match your amp's performance? I have heard unspeakably expensive tube systems.
Muralman1 and Audioperv, I think the thing to look at is intention. If you start out with a given compromise, and then try to do the best you can, you wind up with something that is very good but with a compromise.

In the case of tube amps, compromise might start by choosing pentodes over triodes, as they make more power for their size. In fact if you look at transistors and the succeeding art, class D, that particular compromise of sound vs cost/size/weight/heat is one that as an industry we've been trying to beat for years.

So- what happens if you chose to do away with compromise? The intention is entirely different and so are the results. I agree that if you've heard a compromised (tube) amplifier, it might not best the class D amp that you have now, but the world of compromise has no meaning in the face of state of the art.

There is a common myth in audio that there is no 'best'. However, the English language tells us that it does exist- else the word 'best' would be meaningless. Usually we *believe* there is no 'best', since we have only heard that which is based in compromise. So we again come back to intention.


10-29-07: Muralman1
Atmasphere, you are entitled to your opinion. I did not know you are an amp producer.
Fairly well known.

I have never heard a tube system, regardless of cost that can bring on the real performance better than my own class D system. Can you tell me what areas you think class D does not match your amp's performance? I have heard unspeakably expensive tube systems.
Muralman1 (System | Threads | Answers)
A no-win proposition for Atmasphere, IMO.
Hello,
I would respectfully disagree with Atmasphere words, if not all then vast majority. Class D designers and manufacturers are not for iPod and such alhgough I will admit that Spectron, for example, is designing, now, amplifier with 50 watts rms power with size less then postal stamp - as one of the project in professional audio. On other end of the spectrum Spectron is developing (compact!) 8000 rms amp for Inter-M, where Spectron won the contact against Bang and Olufsen (ICE), Philips (Hupex) and others.

No, class D was not design to work against heat. Spectron chief designer John Ulrick designed it in 1974 (so its not so young technology either!) to drive bass modules in his (and Nudell's) Infinity speakers - which I believe were accepted rather well ay that time.

I am AND engineer (digital signal processing) AND professional musician (graduated conservatory class piano centruries ago) and I can't imagine any audio designer who build amplifiers that cannot handle speakers with huge phase shifts and yet cause the chill down my spine when I hear the real piano sound in my listening room ( not heavenly piano glorified by 2nd and other even harmonic distortions nor one made out of steel or other metal with all non -existing details).

All The Best in Your search of perfection
Vince, haven't you ever heard of Ralph's amplifier brand (Atmasphere)? :)

Ralph: my ICEpower based amps (ASP1000) have a bit aggressive and forward sounding treble. Do you know a cure for this? Will it sound better when I would use some kind of autoformer like the one from Paul Speltz (Anticable, Zero autoformer). Sorry, I'm not a techie so I can be totally wrong...
Btw, my current speakers are Dunlavy SC-V's.

Chris
"There is a common myth in audio that there is no 'best'. However, the English language tells us that it does exist- else the word 'best' would be meaningless."

Interesting Atma, I did not know you were a nominalist. . . . I thought that particular philosophy had been abandoned a few hundred years ago. By the way, I do not own a switching amp. My amps are 20 years old solid state class A/B JRDG model 7M monos.
Simontju, No, sorry, I am not familiar with most name brands of tube amps, since I am not shopping there.
Atmasphere, class D has, in fact, secured the boombox audio field for the very attributes you listed. That says nothing of the class D amps that have been designed for the 2 channel audio connoisseurs, anymore that the previous mass product use of tubes defines your products.

The most fussy tube amp I have heard is the Audio Note Kageki. As I understand AN takes pains to limit compromises for their upper shelf amps.

ICE makes the 500A amp module. This is a module that requires an add on power supply, unlike the ASP modules that have digital power supplies built in.

The 500A module is aimed at the tiny audiophile market. You'd think that would be it. No, they spent countless engineer hours improving the 500A module. You may consider this production in agreement with your reduced compromise ideal. Why did they do that? They wanted to limit compromises in their finest module.

Now, the 500A module's amp performance depends on that amp designer's talent and knowledge. And better sound doesn't stop there. That designer amp's performance depends entirely on it's owner's application. I have found the requirements of a successful class D system are stringent indeed.

The better of class D amps CAN be frightfully outer space transparent. The down side is any, whether it be electronic, like oversampling DACS, or physical, like hose speaker cables, the result can be disastrous. That has been my experience.

So y'all understand, just because I make tube amps, that does not mean I'm blind to what is happening in the world of class D. I think I made that clear on my first post to this thread.

Though Genesis did use a class D amp, it was a far cry from where the technology has gone today.

Can you tell me what areas you think class D does not match your amp's performance?

I think the area where we can show up a class D amp is in the area of soundstage presentation, the ability to be fast and detailed, yet relaxed in the highs, and last but not least bass impact.

The latter seems to be one of the least understood, but most people also do not realize that a tube can be direct-coupled to a speaker. DC response in the output section, coupled with the ability to separate the driver and output section power supplies, means that the amplifier can operate at sub-audible frequencies without modulating its own power supplies, something that plagues many transistor designs.

The issue here is: design according to the rules that the human ear uses, i.e. create circuitry that allows for the least offense to those rules.

Audioperv, I'm not a nominalist, I am merely dealing with what is. As an example, I think we can all agree that our ears are the most important part of our listening, not our amps or speakers or taste of music. With no ears we would not buy audio products. So why in heaven's name ignore the rules that our ears use?? Yet many of the accepted design, test and measurement concepts do exactly that. Negative feedback is an example: yes, it lowers overall distortion, but- it *raises* the slight amounts of distortion that our ears actually care about. These are the high order odd harmonics- the 7th and 9th, which our ears use as loudness cues.

Take a look at the distortion makeup of the typical transistor amplifier and the class D amplifier and the issue becomes clear. Without question this is one of the areas that defines the leading edge in semiconductor amplifier design. This is where the Pass 1st watt amplifiers gain their traction and where low or zero feedback tube amps get it too. Clearly this area challenges class D designers as well. Like it or not Class A still defines state of the art. But again, like I said earlier, any designer who ignores the advances and significance of class D does so at their own peril.
Nelson lives just up the road for me. What I would give for a visit from him. Seriously, he would be shocked. That from a former Pass Labs fan.

When I first got into class D amps, I immediately saw more promise than drawbacks. My amp builder cut his audio teeth designing no feedback class A amps. There is no looking back for him or I.

My own system has been criticized over the last three years. I was told just the other day by a fellow audio enthusiast class D sound has an overemphasis of the leading edge, and a lack of depth. There was no question in his mind my system championed sound-stage presentation and detail.

Much to his surprise, on a visit just a few days ago, there is no hint of a hot leading edge. Depth leaps into the distance. Place of the music's origin superimposes my own walls.

Why the change? It is the learning curve I wrote about. The choice of caps, of speaker cables, and of source made all the difference.

Atmasphere, if only you could hear this.
Muralman1, here indeed is one the bigger issues of forum use in high end audio! We use a lot of the same language in description of system attributes, yet have no way of knowing if we actually mean the same thing with the same depth. So there is no way that I would know what you have, just as there is no way that you would know what I have without us hearing each other's setup.

The learning curve is without a doubt a serious concern. What I have seen of class D amps confirms your own findings- proper setup pays huge dividends (regardless of the technology). We deal with the same issues all the time with our amps too. I do wonder about some of the comments seen in the press that started this thread- how much was said based on setup issues?
I have to pay closer attention to Class D amps. I've read a lot about them but really considered them. I looked at the Nuforce speakers and Nuforce nine amps at ces. It sounded good but didnt move me. I just returned from RMAF and wow! What a show. Im considering the Acoustic Zen Adagios as my next speaker. I talked to Robert Lee of AZ and I told him the Halcro/AZ combo was awsome at the show. He said for the price range i want to be in, that i should consider a pair of moded belcanto 1000 or red dragon amps to go with those speakers. He said they sound as good and in some eyes better than the halcro/az combo. The same goes for the national sales rep for joseph. Im very familiar with joseph speakers. He mentioned that the Belcanto 1000 amps were mind blowing amps with the new RM 33s speakers. Now i want to hear them.
Atma, I am glad you are withdrawing from "it can be expressed in words, therefore it must be true" kind of logic. As for distortions, I hear a lot of distortion in most systems, regardless of underlying technology and -- I should add -- regardless of price point. Yet, whereas my ears may be 'bleeding' when listening to a particular system -- or conversely I may be dying of boredom -- I notice audiophiles as hardened as I am, experiencing true rapturous epiphanies around the very same setup. Am I unable to grok true audioheaven? Or are those other audiophiles getting a little case of 'The Emperor's New Clothes"? Or should we perhaps accept somewhat soberly that we all may be seeking subtly differing things in our private quests for audio Nirvana?
Chaz801, in the same general price range as the Nuforce and Red Dragon, you should consider also having a listen to the Spectron Musician 3 Sig, the H2o, and to the Rowland 501 monos. You may find they sound somewhat different from one another. You may love one or more of them. . . or you may very well hate them all. If I am correct, some form of at home auditioning may be available at least from Spectron.
Atmasphere,

I take issue, just a bit, with the notion that there is one technology that represents no compromises, based entirely on sonic considerations. I know that all triode, no feedback, and no output transformers have a lot of theoretical advantages, but, some would argue that paralleling multiple tubes to increase output and to decrease source impedance has its drawbacks. I am not arguing that that is the case, but, just pointing out that every technology has its theoretical disadvantages.

That said, I personally like very much what I hear from your amplifiers. There is nothing like a good OTL when it comes to liveliness, energy and sheer fun (something so many designs seem to suck out of music). But, there may be purely subjective reasons to favor another form of amplifier, even if that amplifier is not "objectively" as accurate.

I have only extensively listened to one Class D amp myself. I heard a Rowland (first generation amp which sold for something like $15,000 for the pair) in two systems, in one driving Sonus Faber Anniversarios, and in the other, the same amp driving a custom horn system. I personally did not like the sound, but not because it sounded edgy, as some have commented. To me, that amp, in both systems, sounded shut in on top (lacking "air") and devoid of natural sounding hall cues and realistic decay of notes. The soundfield just sounded artificial and "dry." There was something else "odd" and "unnatural" about the sound that I cannot quite describe, but it was immediately bothersome to me. This was a drop-into-a-system audition with no attempts to find complimentary components and optimize setup, but these same characteristics were evident in both systems which makes me wonder if this was an inherent trait of the particular amp.

I know any one example cannot possibly represent all applications of a particular technology, so I hope to hear other switching amps in good systems.
Hi Larryi, I concur with a lot of your findings on the 1st generation Rowland 302 amp. I heard it twice at some length at a dealer, but it was not stirring my imagination at all. . . polite to a fault. Totally different experience with the 2nd generation 312 amp from Rowland. I heard it at RMAF both last year and in 2007 in the fabulous Soundings / Rowland / Sumiko suite, driving a pair of Vienna Mahlers. I have enjoyed the sound of the whole system sooo much. . . I have ordered a pair of Mahlers. . . can't afford a JRDG 312, at least this year [chuckles!]. By the way, the system configuration was identical this year and last. . . but last year the system was set up in a much better suite at least twice as large as this year's. Yet, in spite of their acoustic challanges, this year's two little suites of Soundings (of Denver, Co, 303- 759-5505) still were in my opinion two of NOT TOO MANY RMAF suites where I met music that unconditionally moved my soul . Guido D. Corona
Larryi, on second reading, the 302 is a stereo amp. You seem to be describing monoblocks. Do you remember their very approximate physical size? JRDG has 3 monoblocks in its 1st gen ICE offerings: 201, 501, 301.
Tubes and Class D. I have heard all solid state systems with class D power amps. Larryi gave a good description of the sound. I have a tube pre and a class d power amp. I think the sound is both highly detailed and warm. Clean, clear, tight, and warm. No solid state "cold". No class D "thin". To get the best out of class D, IMHO, combine old (tubes) with the new(class d). Just as the tube vs. solid state or CD vs. vinyl debates go on and on, so will this new debate in the audiophile world. Muralman, good listening from "Prairie Class T".

The Rowlands I heard, were huge monoblocs (what happened here to compact size of Class D?). I have not heard the later iteration of this design. I am not surprised that it is much better. Typical of any relatively new technology is that the learning curve is pretty steep at the beginning.

The issue will be where that curve tops out and how long will it take to get there. It is really impossible to know now what the ultimate capabilities of any technology will be. Take phono reproduction as an example. To me, there is NO question that modern cartridges keep getting better. On other fronts things are not so clear. Some of the best speakers I've heard use drivers and other components from the 1930's and so very old amps are absolutely amazing when hooked up to modern front end gear (Western Electric amps, Brooks, etc.).
Thanks Audioperv
For the recomendations.
I will check out those amps listed a little closer.
I am glad you are withdrawing from "it can be expressed in words, therefore it must be true" kind of logic.

From my own perspective I have merely been dealing with what is.

I notice audiophiles as hardened as I am, experiencing true rapturous epiphanies around the very same setup. Am I unable to grok true audioheaven? Or are those other audiophiles getting a little case of 'The Emperor's New Clothes"? Or should we perhaps accept somewhat soberly that we all may be seeking subtly differing things in our private quests for audio Nirvana?

I think 'The Emperor's New Clothes' is a powerful issue in audio, perhaps because humans are more visually oriented than aurally. We get told that something is state-of-the-art (like a Yamaha receiver) and we pay the money and are so investing in the belief. But knowledge and belief are not the same thing despite how as humans we persist in trying to live our lives as if they *are* the same!

So the result is a disparity, I think the result of one individual listening with their ears as opposed to another listening with the filter of 'status symbol'. How many times have we been sold 'new' as 'better'?? I am not saying that because class D is new that it is worse, nor am I giving it a whitewash: just from reviewing the comments of this thread, there is quite a range of experience. I think in the end that fact that an amp is 'class D' will not be enough for one to judge what it sounds like. Ultimately if an amp is sounding really right, it should sound like any other amp that is also sounding really right, shouldn't it?
Thank you larryi, the only larger class D monoblocks Rowland makes are the model 301. Here are the dymensions:
10.6" x 15.5" x 18.3". Weight is 80Lbs each.  
One probs they have is to have a relatively low damping factor of only 60, which is likely to create problems on low impedance speakers. Model 312 has damping factor of 1000 instead.
Does this size sound right. . . not exactly huge. . . actually less than typical full size amps. They are rather narrower than the typical amps. Cost is $30K for the pair. I have not heard them so I can't comment on their sound. JRDG makes much more compact models like the 501 and 201. The little ones are built to a price point and are not in the same league as the 312. I wish I have heard more switching amps than I have. For the moment my favs are the 312 and the Spectron Musician 3 Signature. It is also worth pointing out that I heard only a very unbroken Spectron this far on a system that had a few other challenges. As such I can't make a real comparison with 312. . . but what I heard was extremely PROMISING and is DEFINITELY worth further serious auditioning.
Guidocorona, I have a custom made 12au7 pre amp and an Audiosource Amp Seven T. This is a Tripath based amp, 200watts at 8 ohms. Got it off E-bay. The rumor is Audiosource had problems with FCC and radio interference. I hear nothing but black quiet from mine, even with the tube pre. It has a large torridal transformer and probably the Bel Canto Evo would be the closest well known equivalent. I wanted to try the Class D technology after reading reviews that one could have SET sound with high power output. All I know is that my combo of tube and Class D produces a musical experience that is excellent. I can not comment on the differences between Nuforce, ICE and Tripath as I have not heard them compared head to head. I have heard Class D systems without tubes and my system with tubes and IMHO, mine provides a superior sound. I have no interest in having a system using Class D that doesn't have a tube pre-amp and I can not imagine a system now that doesn't have a Class D power amp. Rest of system:Harmon Kardon CD player, Scott Nixon DAC and custom speakers using the full size Heil ATM, Peerless Mids and sub-woofer using KEF bass drivers. Good listening.
I also have a tube pre-amp paired with my class d Spectron Musician III and the combination is very,very,nice. Smooth,detailed,spacious,and natural sound.
the problem with most solid state amps is the unrealistic presentation of detail. the sound of an instrument is usually represented as highly timbrally inaccurate, compared to some of the classic tube designs.

there is something very unnatural about solid state.

yes, you get the speed, control and resolution, but there is no bloom and the sound seems forced, rather than liquid.

it would be nice to meet some audiophiles at ces, visit soem rooms and compare perceptions.
Guidocorona, FWIW there is no audible difference between a damping factor of 60 and that of 1000...
Ralph. . . I typically dispense with visual frivolities [chuckles!] does that make me a 'purer' kind of audiophile who is inherently better capable of grokking the ineffability of true sonic beauty? But here's the rub, some fellow audiogoners that start from my very same sensorial premises, end up with very different equipment choices

"Ultimately if an amp is sounding really right, it should sound like any other amp that is also sounding really right, shouldn't it?"

I can't see why the above should be the case. . . there are nearly infinite forms that a beautiful sound can take. Even after excluding extra musical consideration, our individual personal experience often causes us to make subtly different value judgements, equally valid in their own right. . . or invalid, if you so prefer. If what you posit were correct, not only all truly top flight amps should sound alike, regardless of underlying technology, but a Steinway piano should sound exactly like a Bosendorfer, a Stradivari should be indistinguishable from a Guarneri, Anne-Sophie Mutter should play exactly like Salvatore Accardo, and a Karajan performance should be carefully patterned on Toscanini. In other words, yes, greatness exists. . . but True Truth in art? I doubt it.
And -- needless to say -- mediocrity in art is very much like greatness, quite alive and well.
Guidocorona. dyslexia appears. Heil Amt, not a Heil automated teller machine. Snopro, I know what you are saying, vis a vis the sound. I am hearing instruments I have never heard before on my familiar albums. Yes, I am old enough to remember the introduction of 8 track (59). Classical and bop jazz are my musical favorites. I am afraid my old rock recordings will not suffice if I want to do some serious listening.
Mrtennis - your perception of solid state is largely correct. We are talking about class D. Some bloke wrote yet another personal opinion piece based on guesswork equipment matching.
"FWIW there is no audible difference between a damping factor of 60 and that of 1000..."
Thank you Atma for the information Much appreciated.

"the problem with most solid state amps is. . ."

Right on MRT. I should also like to add:

"the problem with most tubed amps is. . ."
"The problem with most OTL amps is. . ."
"the problem with most switching amps is. . ."

Or in other words:

the problem with most amps is. . .that in every technology, there are inherent problems, and not all engineers know how to address them.
hi audioperv:

the objections i raised are reasons not to want to listen to solid state amps. what ever faults lie in the design of tube amps do not deter me from wanting to listen to them.

subtractive coloration of some tube designs does not bother me. additive colorations of solid state amps is annoying.

i have heard class d amps at ces many times. i have no desire to listen to them on panel speakers.

ralph, what say you ?
Audioperv:
that in every technology, there are inherent problems, and not all engineers know how to address them
Hmmm, may I paraphrase? "In every topology there are inferent problems, and all engineers (worth their salt) have adressed them, choosing one compromise over another." Cheers.
That's interesting MRT. . . roaming the halls and suites at RMAF I was actually dismaied by how so many tube designs at all price points were trying to out-solid-state solid state designers. . . and succeeding admirably, tizziness (additive flaw presumably) and vanishing harmonic structure (subtractive flaw I presume) included. The difference apparently is that. . . if such flaws are heard on classic solid state or switching technology--which I did hear in spades as well--the problem is with the technology or the design, but if any apparent 'solidstatification' of tubes is perceived, the culprit is supposed to be only the wild and utterly uncontrollable acoustics of the suite. . . go figure!
Oh yes, let's not forget that flabby bass, or conversely that magic vanishing bass, or that sudden hard clipping: these are apparently more artifacts that plague room acoustics where some tube designs are featured. . . Yet, if switching amps or solid state amps are present instead, 'tis always safe to point an accusing finger at the designer.
Mrtennis, Class D should not be confused with solid state. They don't even sound similar.

You would not like to hear class D on panel speakers? You obviously have not heard my panel speakers.
If a room sounds good at a show, I pay attention, but if it does not sound good, I don't let that deter me. I've had my own room sound lousy plenty of times... its really tricky to come into a room, set up a high end stereo and have it sounding convincing in a day or a day and a half (which is the timing that the shows give you).

If people keep coming back and wanting to hear more tracks I take that as a good thing, but I've never had a room sound as good as my system at home, nor have I heard *any* system at a show sound as good as what I have at home. I'm pretty sure I have a lot of company!

So we're back to the same deal- you have to audition this stuff. I've had the opportunity to do just that, and tweak the circuits as well. From that, and the feedback of customers, come my comments. My conclusion has been that while class D lacks many of the traditional solid state artifacts, that they do have artifacts of their own, but not ones that are common to class D in general (IOW very unlike traditional transistors in that regard; every transistor amp I've ever heard has identified itself as a transistor amp, class D does not identify itself as 'class D'), instead the artifacts seem to associate themselves with the specific product. That, by itself is a very good sign- it suggests that as the technology evolves, a truly neutral implementation could emerge.

Our auditions and customer input show that its not there yet, that we (as Atma-Sphere) have some breathing room for now. By no means has our own line of work been exhausted- the circuit is always suggesting new ways for it to be improved. So it will be interesting to see where things are in say, five years.

One thing that I have been intrigued with is that it is possible to build class D amps that lack the traditional style of feedback loop- a deadly sin as far as the human ear is concerned (and part of the 'traditional' transistor sound). That suggests that the amplifier can be designed around the rules of human hearing rather than the arbitrary standard of 'constant voltage' output. From what I have seen though, the open loop distortion is going to have to go down a bit yet...
hi muralman1 what panel speakers do you have ?

as i have said , i have heard several class d designs. my friend owns an expensive pair of piega speakers. i have heard them driven by a class d amp. i was not impressed.

class d is not the sound of classic tubes, or many set amps.

we all have our preferences. i prefer the vintage tube sound. many current production tube amps sound too sterile for me.
Mrtennis, I have Apogee Scintillas. Of all the systems in my area, mine sounds closest to a $150,000 SET system, with mine certainly leading in real size, and in everything else IMHO.

Like another SET owner told me, "You and I are climbing the same mountain. We are just taking different paths."

Are you into vintage tube amps, or vintage tubes?

My DAC is an Audio Note DAC. That is as much tubes as I want to fuss over. I see what my tube gear cohorts go through testing one vintage tube after another for every component. Egads! :)

My system is listed here.
high muralman:

i prefer the vintage tube sound. the conrad johnson mv 125 is my favorite amp. no class d amp will resemble the mv 125.

a class d amp will never sound like a vintage tube amp.
I suppose it would be blasphemy to bring up the Carver Conrad Johnson shootout of the 80s...
>>10-31-07: Mrtennis
a class d amp will never sound like a vintage tube amp.
Mrtennis

10-31-07: Dazzdax
Mrtennis: And a vintage tube amp will never sound like a class D amp
Dazzdax<<

Wow, this is really deep thinking. Maybe you guys should take the MENSA test.