Who tried Class D only to return to S/S or Tube

And what were the reason you did a backflip back to S/S or tube.
As there are a few pro Class D threads being hammered at the moment, I thought I'd put this up, to get some perspective.

Cheers George
Excellent idea for a balanced thread George... I have happily gone back and forth from class A/B to D over the years. In chronological order, here are my amps since 1998....

Rowland M7 -- An uber-currented class A/B mono released around 1987 with a golden sound.

Rowland M312 class D stereo -- My first venture into class D.... Much more nimble and present than M7. Is both more linear, and has greater exposure of harmonics.... Beutiful transparency, and sweeter than M7, although it does not have the euphonic midrange glow of M7. Yes, overall, I much prefered it to M7.

Rowland M625 (V1 (early production actually) class A/B stereo -- Harmonically just a little denser than M312, but did not have the same amazing transparency between notes that M312 had. But the main issue with it was that it was not quite powerful enough for my Vienna Die Muzik... As a result, during fff passages or loud transients, it gave me the impression that it was "working for living". I heard later production units at RMAF, and they were quite superior to my early unit.

Rowland M725 monos class A/B -- These guys had all the power I needed, and had several circuit and materials enhancements that made them really wonderful amps... Yes, I did prefer them over M312.

Rowland M925 monos class D -- My current amps. These are uber amps that use NCore NC1200 modules buried in the output stage. By far the sweetest and most musical amps I have ever owned, as well as the most powerful and resolving ever to be in my system.

What's my future... Not sure yet. I suspect that for my next amp, I might want to simplify a bit.... One option might be to go to the class D Rowland Daemon superintegrated, which will also serve as DAC. The other possibility is to keep my Aeris DAC, and to adopt the new M625 S2 stereo, which instead runs in class A/B. Not sure in which direction to go... I probably will want to listen to the two contenders before making an eventual decision. I have heard from people in the know that the class A/B M625 S2 might be the finest amp that Rowland has designed... But I have also heard that the class D Daemon makes wonderful music in its own right. I am a pragmatist... There is marvellous music and sound possible with any clas of amps. Final decision will be determined by audible satisfaction, and... Budget.

Saluti, G.
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Excellent post as usual Guido.
I'm another who has been in and out of class D for the past 7 or 8 years. My first foray was with the inexpensive PS Audio Trio A-100. This little amp blew me away with it's small size, no heat, and most of all relaxed and engaging sound. How much of this positive impression was based on the excitement of the new product is a question I still ask myself.
I liked the amp so much I bought another and used them to bi-amp. After a few months though, I couldn't say I preferred bi-amping to a single amp.
Without going into the different types of modules used in the different amps, I'll just say the Trio A-100 did not use what were considered "audiophile" quality modules. As that was the case I went searching for better class D.
There were several attempts at bettering the little PS Audio amp without success until I bought a Bel Canto Ref 500S amp. This amp seemed like the absolute "straight wire with gain" amp, in other words, perfect sound. Should'a quit then? Not on your life.
As like most of us, I had several amps to switch in and out just for the heck of it and to keep audio boredom at bay. Mostly standard class A/B amps; none of which were better than the Ref S500, only different. One day, on a whim I placed $100 ebay bid on an old Harman Kardon PA2200 amp. As luck would have it, I won the bud and a few days later I hooked this amp in to my system. Was it better than 20 times more expensive Bel Canto? No. But there was something about this amp I really liked. It stayed in my system for about a month and I couldn't find reason to remove it.
I did remove it to recap the amp and do some rewiring. I also adjusted the DC balance and bias on the amp. After all my fiddling the amp still sounded wonderful. I sold the Bel Canto.
A few years and many amps later, (including a few tube trials) I wanted something very compact for my system. I ended up with a Wyred4Sound mAMP mono blocks. This amp uses the same module as the Bel Canto I found perfect so I figured it would be perfect for me. I found a good deal an a pair and hooked them up. Clean, quiet, perfect(?), but somehow lifeless. Unfortunate as they really fit my space perfectly.
I'm now using an Aura Vita integrated amp as it also fits (barely) my space. I think I'm done trying the class D thing. Although I understand the allure, I also understand, it's not to my taste. And that's really what it's about.
I owned Gilmore Raven stereo amp for a few years, then upgraded to the Raptor monoblocks. Was happy with them for several years as well.

Then I built a pair of two stage, direct-coupled SET monoblocks, with 6E5P driver and 833C power tubes, producing 200wpc. These are so much better from bass through treble that I was stunned. More real-sounding, more musical, and more authoritative. They make me want to listen to music as often as possible. I'll not go back.
Oh, and prior to the Gilmore Class D amps I owned Flying Mole Class D monos. The Gilmores were better than those, but the FMs were still nice sounding. I also auditioned NuForce Ref9 SE monos and thought they sounded awful - harsh and screeching are the descriptors that come to mind.

I don't see myself with anything but my 833 SET amps from now until I will them to my son.
I have 2 Class D setups currently.

My main system with Bel Canto ref1000m amps and ARC sp16 tube pre-amp that run a variety of speakers and my second family room system built around a Bel Canto C5i integrated.

I added the C5i recently to test the waters of a digital /Class D amp versus the tube/Class D hybrid approach.

My take is on Class D is that the technology delivers again perhaps the most neutral, dimensional and seemingly "perfect" sound.

Will that alone float everyone's boat?

Not likely. I suspect no one particular sound will.

But I will say I think building around a Class D amp to tailor the sound to what one will like is perhaps the most versatile and prudent approach out there today.

Reason is Class D is so clean neutral and dimensional. It's the best place to start, kind of like starting with vanilla ice cream. From there, no way to know what "flavor" will be preferred.

My two Class D setups sound nothing alike, even when using the same speakers essentially with both. But each is musical and enticing in its own unique way. If I had to choose just one, it would a very tough choice.

I have auditioned many tube amps in teh process but have never owned one. The Ci did replace Tube Audio Design Hibachi monoblocks which were SS amps designed by a tube guy as a reasonable alternative and those very quite nice in their own way as well.
I have gone back and forth about once a week for the past year. The only Class D I have owned is my current NC1200 Acoustic Imagery Atsahs. I also own a McCormack DNA-2 LAE that received Steve's Signature Edition upgrades (the best) in 2014. Before that, solid state with Clayton Class A M300s and M200s, Lamm Hybrid M1.1s, and top SS amps from Cary, Herron, BAT, and McCormack (DNA-500).

It has been difficult to decide whether I like the McCormack or the Atsahs better and I am set up so I can easily switch between them, which has been interesting. From a purely sonic standpoint, the Clayton M300s were the best I have owned but the Atsahs and McCormack are close, and have ergonomic advantages over the Claytons. The McCormack and the Atsahs have slightly different sonic presentations but the differences are not large and both sound great. I would say the McCormack sounds a bit cleaner and more extended while the Atsahs have a touch more tonal density. Both have great bass and, again, the differences are small.
Hi Tim and AIT, I more than sympathize with your shell-shocking experience with class D.... AIT you summarize it best when you describe the NewForce monos as "awful - harsh and screeching "... That was exactly my impression.... Let us not forget cardboard-like bass and completely lifeless treble... That is whenever treble does not screech to high heaven instead. As for Wyred4Sound, Tim you are being kind IMO... I tried to listen to the brand several time at RMAF, and the things were yowling like bobcats with ingrown claws... I typically resist a couple of minutes in the suite... As for Flying Mole... Meh!

It is funny how exactly the same module will make fab music in one amp (Bel Canto REF1000M), and screech in another amp. But after all, we should not be surprised... There is quite more than bare modules in Bel Canto amps... Those little boxes are designed by John Stronczer, an engineer/designer who has a profound understanding of what music sounds like.

Besides, Mapman is 100% correct... No matter how wonderful some class D amps might sound to some of us, their relative neutrality will make them inherently unpalatable to the lovers of much warmer sound... And... Vive la difference, n'est pas?!

I've owned Densen B-350 Class A mono-amps, Classe Audio (Class AB), Parasound A21(Class AB), Peachtree Audio(Class D), Jeff Rowland M525(Class D) and have tried the Bryston 4bsst2 (Class AB). I currently own the Jeff Rowland Class D Continuum S2 and submit it's the most musical amp that I've owned. In addition, I love the fact that I can leave it on 24 hours a day and it doesn't get hot. I'm currently debating the Jeff Rowland 625 S2(Class AB), not because of my dissatisfaction with Class D, but my own stupidity. Unfortunately, I keep trying to go to the next level and incremental improvements are expensive!
It's interesting to follow the development and different incarnations of Class-D amps, and lately Devialet and in particular the NCore-based solutions have caught my attention the most - sadly not via auditions in my own setup.

To me though the choice of amp comes down to the choice of speakers first and foremost, and being that I favor speakers of high(er) sensitivity (not necessarily as a means in itself, but as a function of their design/principle and the sound this produces), I'm not sure generally high-power Class-D is the best option. Here the first watts or less are what counts, and Class-D topology seems to be "more happy" going beyond these lower thresholds.

Interesting as well is reading the notions of the supposed "neutrality" of Class-D amps, which appear to be influenced to some degree by an array of their measured performances as an "objective" criteria. The criteria essentially can only be what is actually heard, and if what is heard distances itself the most from any mechanical, dynamically restrained and tonally inauthentic imprinting, the more natural and "neutral" it is in approximating a live, acoustic sound, to my ears.

The development in my setup, as per before mentioned desirable sonic traits, has lately gone from Class-D to SS Class-A, and who knows whether a 3-4 watt SET would take the reign in the near future to come. Certainly not a "modern" development, indeed it's rather old fashioned, but why should one care? On the other hand, should a Class-D based iteration cross the way and level the Class-A/SET alternatives with high sensitivity speakers of choice, well then, it's a hassle-free and greener solution for sure.
I played with the Devialet amps today. It was very enlightening for me to hear what a great class D amp can do. It was warm, smooth, very clean and tight. In other words, I couldn't find any faults (except the price).
This is the first time I've liked Class D when compared to class A or tubes.
My goal is to eventually have a top tier tube amp , a/b, a, and class D . Switch things up as i feel so inclined . They all have there sonic flavor and who likes to only eat vanilla ice cream .
Hi Phusis, your bring up an excellent point.... The problem of paper listeners who evaluate the musical experience basing themselves on printed graphs and figures... You find these types spread all over the tubed / ss / class D continuum.

Admittedly, I am fond of a neutral sound with a bare smidjin of warmth.... But my only criterion for judging if a particular device is to my liking is.... My own ears.

I returned briefly and now I`m stumped.

I can hear a very thin additional layer of sound/decay on the BACKSIDE of the front to back image of the tube amp that just..JUST eludes the Class D amp.
I`m talking onion skin layer, barely perceptible if that makes any sense, the width and height of the Class D is really nice no issues there at all.

I THINK I may be able to bridge the gap with a tube phono stage and maybe recover that added/perceived dimension but my ASR Mini Basis MKII sounds so good to me that I`m scared to think what a tube phono stage might cost to better it.

My speakers need some power and I`m not sure I`m willing to spend the money needed for a tube amp that can provide the needed power that the Class D has on tap.

For once I agree with ebm...this thread is dead in the water....who gives a rat's a$$
Interesting thread, I've been wondering what the deal is with class D and have learned a fair amount already from this young thread already.
Me. Three times. Treble quality was atrocious. Roland, Job and one other. This was up until 4 years ago. People say they've gotten better. On each try, they were out of my system within 2 days. (Yes, they were broken in).
Jeffb28451, while the Class D amplifiers may have been "broken-in," it is possible that a two-day warm-up was not long enough for them to reach their full potential. I would have previously called BS on this notion but, after living with NC1200 monos for the past year, and switching between those and my Class AB amplifier, I found that both need to remain powered up all the time or the amp that is warmed up sounds better every time. Particularly with the Class D amplifiers, it seems they need to be powered-on up to a week for the treble to sound its best.

I also admit that the treble is one area where my Class AB amp beats the Class D amps. Both seem fully extended but the Class D amps seem comparatively a little "shelved-down" in the very upper frequencies, which seems to affect ambient cues more than how instruments/vocals sound directly. I get just a little better sense of venue and infill of the background sounds between players with the Class AB amp. However, there are other areas where I like the Class D amplifiers better, which is why choosing between the two has been difficult for me.
Jeffb28451, while the Class D amplifiers may have been "broken-in," it is possible that a two-day warm-up was not long enough for them to reach their full potential. I would have previously called BS on this notion but, after living with NC1200 monos for the past year, and switching between those and my Class AB amplifier, I found that both need to remain powered up all the time or the amp that is warmed up sounds better every time. Particularly with the Class D amplifiers, it seems they need to be powered-on up to a week for the treble to sound its best.

I also admit that the treble is one area where my Class AB amp seems to beat the Class D amps. The Class D amps sound comparatively a little "shelved-down" in the very upper frequencies, which seems to affect ambient cues more than how instruments/vocals sound directly. I get just a little better sense of venue and infill of the background sounds between players with the Class AB amp. However, there are other areas where I like the Class D amplifiers better, which is why choosing between the two has been difficult for me. Maybe I should just keep both.
As has already been stated, the pre-amplifier is as important to the sound of class D. One cannot simply swap out an AB amp for a D. The system must be coherent and matched. I'm fine with my Bel Canto and Wyred monos driven by Modwright tubed pre-amplifier.
My Rowland 102 sounded the best after about 400 hours. Class D amps are very revealing and often don't work well with some "bright" components. I cannot say if class D works better when powered for a while since it is always on in my system. It doesn't even have on/off switch. Yes, trebles are different, more natural IMHO. Cymbals sound fuller and brassy and not "splashy" as it was with class AB amp. It requires some time getting used to. Midrange is just wonderful.
11-28-15: Kijanki
My Rowland 102 sounded the best after about 400 hours. Class D amps are very revealing and often don't work well with some "bright" components. [...]

The exposure goes both ways; what's at the end of the signal chain (i.e.: speakers) can also be ruthlessly revealing as well as, conversely, reveal their limitations. When people describe SET's as possessing "lush, warm [i.e.: meant as warmer than strictly "neutral"] midrange" and generally "loose bass," it could be descriptive of speakers lacking mids resolution/speed and of (bass-)ported designs with poor damping and overhang. Connect well-implemented horn speakers instead (themselves far more revealing than most direct radiating designs) with non-ported bass of higher damping and the "math" can suddenly reverse into match-bliss: here the mids are no longer warmish warm, but attain a "bloom" and naturalness that's ultimately freeing of any containment resembling "hifi" in the usual sense, and a bass enriched with an organic imprinting more about texture, immersion and cohesion (traits of true horn bass as well) than oomph, attention-seeking and depth.

If one were to insert a Class-D amp here instead (many iterations though they are), and the sound suddenly became slightly bleached, bass-thin and lacking fullness (that's a guess), my take would be to assess the amp lacking harmonic richness and being over-damped in this particular setup rather than aiming the search light towards other components - not least the speakers. Though speakers (and their acoustic environment) are by far the most coloring and limiting factors, their potential to put into perspective on what to use earlier in the chain is significant.
One cannot simply swap out an AB amp for a D. The system must be coherent and matched.
This seems to be in response to my post so I will bite...and ask what do you mean by "coherent and matched?"

I didn't mention that I tried the amps with three different preamp options, two of which were made specifically for the amplifiers, by the same manufacturer that made the amplifiers. Because two of the preamps have low impedance outputs, those two matched well with either amplifier wrt impedance. The highest gain preamp was +6dB and the other two have zero gain, while the source is 4V. These numbers work well with either of the two amplifiers. Are there other parameters that need matched? Regarding coherence, what attribute or parameter would make one preamp more "coherent" than another when used with a Class AB or Class D amp, and couldn't the same preamp be "matched and coherent" with both of those amplifiers?
The Rowland was, I believe, a 500 series. (301"s?) It went from Atlanta in my car to my home after audition where the previous owner claimed he had owned it and it had been in his system for 2 years. Definitely broken in. It had the same sonic signature as the Bel Canto 500 References that I had such high hopes for.

The highs on all of these amps did have the "unbroken in" sound of limited extension, chunky mids. It was the upper mid distortion that drove me crazy, sort of like original cd players had. 4-12 khz was just a mess. Resolution, yes, due to a really good noise floor, but a harsh and not so musical sound. Maybe I'm not being fair, since I did not own any of them long enough to "tune" cables to their particular needs, but I didn't hear anything promising me that it would be worth the time and money.

It's for sure that technology has progressed way beyond the days when everyone used ICE stuff (and it all sounded the same). I remain curious and it still amazes me that SS amps of any sort work as well as they do (and I've owned a lot of them).

However, I just turned 60 and settled into a Mac 275. I have owned so many amps, etc. that I'm just going to listen to music for a change.
Yes ,the class D amps from a few years ago were unlistenable to me as well. I do
not think many of us are touting past class D designs as being musical and
competing with other class amps .Only in the latest implementations are they
competing with other classes these days .
Hi Jeff, I suspected as much... The amp was probably a pair of M501 monos or M201 monos... Unlikely to be the M301 monos, unless each chassis weighed about 95Lbs. Each M501 chassis instead might weigh some 20Lbs, and is about 7.5 inches wide only. is

M501 was a basic implementation using the ICEpower 1000ASP module. Very powerful and clean, but.... Subtlety and high musicality were not its main features. I heard the M501 several times at RMAF.... I deemed its sound not to be involving at all... ANd yes, treble can have a rather cold quality to it, which also means that if complex treble passages go through M501, you might hear more than a bit of harshness.

For the ICePower 1000ASP to sound good, it requires either the fine work done by Stronczer with the REF1000 Mk.2, or the PFC rectifier and custom power supplies that Rowland used in its higher end amps based on the same module, such as the M312 that I had for several years.

Rowland does market an external PFC rectifier called PC-1 which is compatible with M501. People who used PC-1 on M501 report the sound to be completely different, and to have approached M312.

Regardless... All of this is in the past.... M201, M501, M312, M301 are all 3 or four generations old. Class D has made significant strides since these 4 legacy Rowland amps, the only one whose sound I consider excellent for today's standards
is the M312, which shows up very seldom on Audiogon.... Its owners tend to keep it for a long time.

Regards, G.
In my main system now I use Class D amplification. I do rotate between the different kinds of amps to just get different flavors of sound. Right now I have my Jolida JD502P with Tung Sol KT150 tubes powering my Ohm Walsh MicroTall SE. The Jolida does fine with powering them and is a nice space heater in these cold days. With the system/speakers I have I found Class D works best.
I recall that Stereophile put the PS Audio HCA-2 in the 'Class A' 
category... kind of curious how they would rate it today ??

I had one and although my setup has changed a bit...my acoustic memory would have the Class D Audio 470C showing the HCA-2 the door !
For the money spent this amp reminds me of the NAD 3020 that I used with my DCM Time Windows, both of which I bought new at the time.

This amp could easily hold you over till the 'dust settles' a bit in the class D wars...and for next to nothing (relatively speaking) !!  
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The way people talk about the older amps from just a few years ago not sounding anywhere near as good strongly suggests that a few years from now class D will sound a lot better than it does now.

This has entirely to do with technology performance curves; if only a few years separates the good from the bad then its simply a fact that the technology is not yet mature and further improvements are already in the pipeline
I am interested to see/hear how much better the technology might sound in a few years.  It already competes with the best in some opinions, including my own, to the extent that I think I will only know it can be a lot better when I hear it. 

I’m waiting for the Class D component technology to advance enough so the switching frequency can be much higher, only then will the switching frequency artifacts be abled to be filtered out away from the audio band.

As of now it’s too low and when filtered, effects the audio band HF with phase shifts and or roll off’s when filtered out.

But I believe it will come soon, then it will be only way to go, and linear amps may all become door stops or boat anchors.

Cheers George

Atma, I extend to you the invitation to get out of the house more often. Believe it or not, evolution or not, there is already "Wonderful Life" out there to behold. Oddly enough, it is not even based on tubes, OTL, or classic SS topologies.

To quote the immortal words of our Rodman99999...

"Just don't fall into the category of those whose minds, like concrete, are thoroughly mixed up and permanently set"

Regards, G.


^^ 'out of the house' by that do you mean visit customers, go to audio shows, visit dealers and manufacturers? I do that already! We even experiment with class D in house; we heard the Bel Canto class D amps before they were even released to the public; we've been actively observing the evolution of class D for nearly 15 years.

Its **really** obvious that that you misinterpreted my prior post- go back, and read it again.

Atma, sadly, I had read your post very carefully... I was hoping to avoid pointing out to you that your logic is painfully flawed.

Essentially you are stating that while class D persists on an evolutionary curve, at any particular point of the curve, it is inherently not good enough to yield a top quality listening experience because a "better" experience is just around the corner. Trez bizarre, n'est pas?! 

As for Bel Canto, it is a brand, not an amp... In their history, there are a few dozen models, ranging from their first units several years ago, up to the Black. Did you experience them all? And what about other brands?

From a logic point of view your process is called a false induction. It has the form :

If set X contains at least one element without property A, than the entire set X lacks property A.

Besides, demonstrating a negative remains a futile quest.

Thus I renew my words of encouragement... Do get out of the house more often... Or at least, leave your preconceptions home when you do so... You might be surprised about what you end up discovering!


Atmasphere made no big logical mistake - his assumption is valid, though the result of the technological evolution is by no means guaranteed. In other words, class D amps might get a little better and then exhaust their potential, or they might keep improving more and more with no end in sight.

guidocorona, if you were any linear amp designer and saw on the r&d bench test a square wave that looked like this.


You would say this amp is broken, do not put it into production yet till we get rid of that ringing.

This is what all Class D’s look like, and if they filter the s**t out of it so it doesn’t look half as bad, then you would have an amp that is rolled off at -3db at 5khz (no highs).

You been told now by a few, that the technology is not there yet to get that (ringing saw tooth) out of the audio band.

Once the technology is there and they put that switching frequency way up higher, then and only then will they be able to filter the s**t out of it away from the audio band and leave a nice clean square wave, and only then will Class D have become of age.

Cheers George   

Funny you mentioned that.  I was just at a comparison today between one of my previous favourite amps the Arion HS500 monoblock digital amps with Duelund Cast capacitors that I own.  Its valve input with digital output.  I personally prefer my upgraded Prima Luna Dialogue - but its a close call - at comparisons with others it was about 50-50 which was preferred.

Well today I was at a comparison of the Arions with the similarly priced new BHK 250w amp I just purchased.  Its valve input - mosfet output.  It was a joke - here is what others said:

'We did a back to back comparison with the new BHK amp and the old Aurion 500 D class that Mike was using about 3 years ago. Well it was night and day.I was kind of hoping it was just all hype, then I could crawl back into my hole and forget all about it!! A lot of the guys were commenting on the lack of balance in the Aurion amp, but listening to the BHK was like a live performance and the Aurion was more like listening to the radio with a blanket over it. If I was looking for an amp in this price range, then I would definitely audition this one!'

'The only amp the BHK was compared to was the Arion mono blocks, and as others have mentioned there was no competition. The Arions sounded boring in comparison, in this setup.'

'Yep the Arions had the same work done, (added by me - referring to that the Arions have Dulund Cast capacitors) I thought they were still nice, but the switch back was instantly amazing and by then the late comers were in and virtually all turned or twitched in wow factor'

My comments - the Arions were dull by comparison - they lacked life and verve.  The BHK was simply sweet liquid life.

I hate to say it guys but at the moment digital has a LONG way to go.



Firstly, let’s get a major misconception out of the way: class d amps are not digital, they are analogue.  And not all class d amps have square wave performance as shown above, though listening to square waves doesn't seem too common...Hard to place any real value in the opinions of those who do not even understand the basics of the technology or misrepresent the performance of high quality, state of the art class d.

Secondly, amps are part of a system. They don’t perform or sound the same in all systems. Some may be great in one system and not so great in another. This is true not only for class d but for class a, a/b, etc. Sweeping generalizations based on limited experience or use are worthless.

Thirdly, the objective performance of many class d amps is better than nearly anything any tube amp is capable of, and in the case of Hypex ncore, better than nearly any ss amp one can buy. Subjective performance can not be argued as it is a matter of individual taste. There are many many people who have dumped their ss or tube amps in favor of class d. Claiming the technology is "not there yet" is a bit behind the times and ignores the fact that not only is it "there", but it is replacing class a and a/b ss and tubes amps in large numbers.

Enjoy whatever works for you. No need to put down what others enjoy.
+1 Kuribo

At the risk of sounding like a broken record - switching amplifiers are simply another major amplifier class to choose from. 

Consider the list of major amplifier designers who currently offer a switching amplifier along with their traditional designs. As well as the list of powered speaker designers that use switching amplifiers. 

Thank you Kuribo, could not have said it better myself!

To be honest gents, most amps leave me cold, regardless of underlying topology... Be it triod, push pull, OTL, SS class A, SS class A/B, analog class D, or digital. On occasion, there are a few amps in almost each class that I love for what they do for music. Some of these happen to be class D.

Eventually, I am pretty sure I will even hear an OTL that does not make my head shake in perplexity. Who knows, may be such ATMA amp already exists today, even though OTL is not on an accellerated evolutionary path per se... I am an optimist, and I know I have heard but a small minority of OTL amps in existence... I have not even had the opportunity of hearing every ATMA amp: until the target set is known to be filled with "NO" on each member, I am hopeful that a "YES" exists somewhere in the extant set.

As for square waves.... Love that clarinet sound, but I do not waste my time confusing paper and an individual graphs with music from a thousand different amps... I much prefer listening to music through my own ears one amp at a time... After all my ears have served my passion quite well since 1957 -- the time I was first mesmerized by music coming from LPs through my Dad's Grundig.


Have to agree with "georgelofi" - the "ClassDAudio" (brand) SDS-470C is superb and rivals any "hi-end" amp... after burn in and left on and warmed up.  

Though, I do vacillate a bit between my JC-1's, Atma-Sphere M60's, and the SDS-470C.  Depending on the speakers I'm using... I think I find... that one, or another may sound a "wee bit better" than the others.  

But... think... I may end up settling on the SDS-470C... since... they all sound so similar... and the SDS-470C... is small, low-temperature, and hassle-free.  Not to mention - that at it's price it is a "huge bargain!"

The thing is... there is not a big difference in the sound of any of them - so, I really couldn't recommend any one over the others - except in the context I note above.  And... I tend to think that's likely true of several of the class d amps and hi-end amps - that there are only very subtle differences in the sound of any of them that one person or another will find make one better than another.  But, in reality such subtle differences are not really so significant as to definitively determine that to be true -  "Beauty is (only) in the mind of the beholder."
"Once the technology is there and they put that switching frequency way up higher, then and only then will they be able to filter the s**t out of it away from the audio band and leave a nice clean square wave, and only then will Class D have become of age"

Stereophile picture is about right:  1% of about 50V switched at 400kHz.  I’m not sure why it bothers you - you cannot possibly hear 400kHz.  Speaker will respond to average value.  There is distinctive possibility of tweeter modulating this wave with other frequencies, but this would be true only if tweeter’s membrane could move at 400kHz - not likely.  Also any effective radiation from speaker cable would require about 1/10 wave antenna that is 750m/10=75m.  I wouldn’t worry about that with few meter cables.  There is still possibility of cable to cable capacitive coupling but, because of shielding it would me minuscule amount further filtered by amp’s input filters.  There is some phase shift at 20kHz (about 20%), but it is usually the case of any amplifier bandwidth limited to 60kHz (my Rowland 102). Improvement in Mosfets speed will allows better initial linearity that is right now pretty good to start with.  Class D amplifiers suffer less delay (being one stage only) than multistage class AB amps reducing effects of TIM (resulting in softer sound).  Output impedance is also low by design, even without feedback.

Second generation of class D amps was better but I’m not even sure why.  Bel Canto’s Ref1000 got additional power supply caps and inductors.  That possibly reduced noise on the power cable (Power Factor Correction) but Icepower module used in both generations of this amp has line and load regulated power supply (uncommon in class A or AB amps).  My Rowland 102 is plugged into Power correcting Furman conditioner (big cap and inductor plus filters). Second generation of class D amps served one important task - it allowed some critics to remove foot from their mouth.

If top designers like Jeff Rowland, who is very sensitive to noise issues, don’t see any problems in class D or SMPS (that he uses in class AB amps), then I wouldn’t worry about it either and would judge it only on the merit of sound - it is the only thing that counts.  If it sounds good then it is good.
I think it comes down to the simple reality that audiophiles are in general a very insecure group. Many like to think that whatever components they have are "the best" and will go to great lengths to put down the choices of others in a senseless and futile effort to somehow prove the superiority of their choices, blind to the fact that there are no absolute "right" choices in a quest that is entirely subjective, and thus personal.

Most high-end audio manufacturers cater to this insecurity in a market that thrives on "mine is bigger, better, more expensive (thus sounds better) than yours"...

Class d seems to be the red haired foster child for those with deep insecurities, or perhaps, vested interests, as it gets kicked around all the time. Perhaps because it offers a level of performance to the masses at a previously unavailable low cost, taking away much of the snob appeal many of the insecure so value...For those without vested interests or insecurities, it has proven to be an exciting and fulfilling option for amplification. Excellent measured performance, high performance to cost ratio, small, light, energy efficient, plug and play without any finickiness, the list goes on and on. Never mind the fact that many have dumped their tubes and high dollar boutique ss for class d...No wonder people feel threatened!

Clearly, the reason there are so many different types of speakers, amps, dacs, etc., successful in the marketplace is obviously because tastes and priorities differ. There are many roads to audio paradise, none more valid than the next; we shouldn’t be so concerned and critical with the route others take but as fellow travelers, wish them well in their journey.

My assessment is the technology continues to improve in regards to power supply and switching frequency so even better sound is possible but when done right it already is hard to fault so how much it will matter practically remains to be seen.   I will keep mine for a long time I think and when time to replace technology will only be even better. Much like computers and other forms of digital technology. 

Well said Mapman, I myself am not ready yet as I outlined, but once the new (let's call it 2nd generation)  far higher switching technology happens, I'm jumping in with both feet, compared to my setup at the moment the bass/upper bass of todays good class D amps is already better.

I just have to time it right when I'm ready to make the jump as my two biamped power amps can re-coupe enough $'s s/h before they become boat anchors to get a pair of good 2nd generation class D's, and the same to a degree will happen to the 1st generation class D's as everyone will want to dump them also.

Cheers George    

Hi George, what would you deem to be a sonically safe switching frequency for future class D modules?

Do you know of any such "Upcoming Attractions" with higher switching rates preparing their entry to market?

Meantime, Yesterday I checked the NCore NC1200 switching frequencies... It ranges from 440Khz to 520Khz., which is almost 5 octaves above theoretical human hearing range.

Honestly, I cannot perceive any artifacts or shortcomings from my amps... But there may be some audible artifacts that I am not aware of. 

On the other hand, I freely admit that I would be just as happy with a wonderful Solution monoblock, or a major AudioResearch tubed amp... I mean, apart from the heat dissipation, and reliability anxieties from ARC amps.

PS... My class D monos are not light... 160 Lbs per side. They are not furnaces by any means, but are relatively toasty to the touch during Austin summertimes.

Saluti, G.

The switching frequency guidocorona, may be 520khz, but it’s the amplitude as well of it not just the frequency and has to be filtered at the end with all that rms power by low order filters that have to take that power. 

From what I’ve been told by those in the know of Class D technology this has to be shifted up 5 to 10 times higher so the filtering of it on the output of a Class D amp can then also be shifted up higher, and therefore not be affecting the audio band, with audio band HF phase shifts or audio band HF roll-offs.

On most of todays Class D amps that try to get the highest frequency response they can get, you may hear a sizzle from a high bandwidth tweeter if you put your ear to it, if it’s not muted eg: in-between tracks on a cd.

Then there are those Class D’s that want to get rid of that sizzle which filter it even more savagely, then those ones can be starting to roll off the audio HF already at 5khz.

The sounds of the two can be then different in the upper-mids and highs, one being hard or harsh because it lets through some of the switching noise. The other sounding opaque or soft in the upper mids and highs.

Therefore to cure one or the other the switching frequency needs to be much higher so the filtering has little or no effect within the audio band.

Analogy: is to remember the early days of cdp’s with their brick wall filters, which on paper looked ok but sounded shocking, just because they wanted to show a flat 20hz-20khz frequency response. But in Class D amps this filtering is low order and happens at the end of the power amp at full rms wattage power levels, and the filters need to take all that power handling.

Then there's the SMP power supplies another problem again, that some Class D manufactures try to get around by powering with more expensive to make Linear power supplies.  

Cheers George