Class D = Trash?

madavid0,

  I just finished reading this entire thread. You've described your experiences using class D amps in your system as:

" Mid-range GONE.
Soundstage depth CRUSHED.
Euphonics DISAPPEARED.
Yes, resolution went up. Driver control went up, allowing me to play compressed rock/pop and orchestra with the speakers being able to render it all. But enjoyment in the sound is basically gone. Using my best power cable (LessLoss Original) improved performance, but didn't fundamentally change the amp's nature. I ran back to my headphones (Focal Utopias) to detox my ear canals."
" I can definitely detect that element of...whatever it is. Dryness? Poor blending of upper- mids into highs? Lack of weight? There's a SOMETHING to the sound that hints to listener fatigue.""Also....am I crazy or is this amp casting an unstable image? Like sounds don't want to focus and stay there."
Like....the vocalist says a word that happens a little to the right, but the trailing consonant finishes a little on the left.""Damn, 24 hours later and this amp sounds like trash -- rolled off / recessed mids again, soundstage depth almost gone...wow. I guess this thing with wired class D burn-in is true. "

     You seem to attribute all of the above to the class D amplifiers and you've received replies affirming these perceptions of the poor quality of class D from the herd of Audiogon usual suspects of class D naysayers that reliably chime in on most threads mentioning class D.
     Of course, the naysayers chiming in their aspersions was not surprising but, not being aware of you being similarly afflicted with their knee-jerk anti-class D bias, I was very surprised to read of your negative results.  I have no experience or knowledge of the Teac class D offerings but I do for the D-Sonic and several other companies' class D offerings. 
    As a user of 3 different class D amps over the past 3 years (The ClassDAudio SDS-440-CS and the Emerald Physics Ep-102 stereo amps as well as a pair of D-Sonic M3-600-M monoblock amps) in my system driving Magnepan 4 ohm speakers, I find it hard to believe the D-Sonic M3-800-S amp is performing so poorly in your system.  

   Even straight out of the box, I would expect the main attributes of the D-Sonic M-800-S amp to be immediately and obviously apparent; very good bass response and control, extremely low noise floor, very good dynamics with a smooth and neutral mid-range and treble that is also very detailed without any hint of brightness or harshness, In my experience with the D-Sonic monos, that use  Anaview/Abletech modules rather than the Pascals in your amp, there was a reasonable break-in period but I recall them sounding very good immediately and then proceeding to improve mainly in the mid-range and treble detail and smoothness over the first few weeks.  
     You not getting similar results in your system suggests to me that there may be another culprit or culprits responsible in your system.  There are several possibilities:  your left and right speakers may not have been properly matched at the manufacturer, you have 1 or more drivers blown/not performing to original spec or your D-Sonic amp is not functioning up to spec.

     There are a few methods to narrow down any issues that may exist:
1. Bring your D-Sonic amp to a friend's or dealer's and test it out with their speakers/system.
2.  Borrow a friend's or dealer's amp that you can verify is working properly and determine if the sound differs.
3. Take your speakers to a friend or dealer and connect them to their amp ,that they can verify is functioning properly, and determine if the sound differs.
  #1 will identify whether your D-Sonic amp is the culprit and #2 or #3 will identify whether your speakers are the culprit.
  I think trying #1 and then #2 sequentially would likely be the most efficient, least laborious and sufficient method to identify exactly what is causing your system's poor performance.
     If the amp continues to under-perform, I'd suggest contacting D-Sonic's owner, Dennis Deacon, about your issues.  He's very knowledgeable, reasonable and fair.
     If you go through this method, please post your results. If you're accepting wagers, please put me down for $5K straight-up on your speakers being the culprit.

     A final friendly tip: If you try your D-Sonic in a friend's system, don't expect it back without a struggle. 

Thanks and good luck,
       Tim 

Hi Henry,

     I respect your knowledge and experience as well as your H2O amps.

     I realize you utilize large analog power supplies in your Icepower based amps, rather than the more typical switching power supplies, and your amps are known for their excellent bass response.

     I own three class D amps that have all been used to drive my Magnepan 2.7QR speakers at separate times.  The first two were both stereo amps that have analog power supplies/toroidal transformers, a Class D Audio SDS-440CS and an Emerald Physics EP100.2.  My current class D amps are mono-blocks that have built-in switching power supplies in their Anaview/Abletec power modules, D-Sonic M3-600-M mono-blocks.   

     All three class D amps produce the best bass I've ever heard from my Magnepans but, IMO, the D-Sonic monos with the switching power supplies have significantly better bass response than my other class D amps with analog power supplies.

   My former class A/B  Aragon 4004 MKII amp also used an analog power supply that included 2 very large and heavy toroidal transformers. Both of my stereo class D amps, with much smaller toroidal transformers, and my class D monos, with small and lightweight switching power supplies, all have much better bass response than my former class A/B amp had even with its very large analog power supply.

    Of course I realize you don't want to give away any trade secrets, but I'm curious on your thoughts about whether there's a direct relationship between an analog power supply and good bass response in an amp.  My personal experience implies there is not a direct relationship but I sense the truth is likely more complex and think it is best heard from an amp designer such as yourself.

Thanks,
  Tim

Hi Henry,

     Thank you for taking the time to respond in such detail to my question and stating that you do think there's a direct relationship between an analog power supply and good bass response in an amp. Given your praises of regulated amp output voltage, which the switching mode has but which the analog power supplies typically lack due to expense,  I would have thought the relationship between an analog power supply and good bass response would be less direct. However, I'm fairly certain it's best to defer to your knowledge and experience on this matter.

     It's very interesting and encouraging to know that you're continuing to explore the potential of the somewhat newer class D power modules such as the Hypex NCore 400 modules along with corresponding Hypex switching mode power supplies.  I would be very interested to know if you discover varying performance levels between these modules paired with the various Hypex smps (NCore 1200 and 600 smps) and the NCore 400 modules paired with your own analog power supply.

     Strictly from my subjective viewpoint,  the most obvious differences I've noticed between using class D and various class A/B amps(Adcom, McCormack and Aragon) in my system are improved bass response, a reduced noise floor,  increased dynamics (especially on content recorded in hi-res 24/96 format), increased detail and a more neutral sonic character in general.  
     These benefits were clearly noticed on the first 2 class D amps I owned (Class D Audio SDS-440-CS and Emerald Physics EP-100.2) and these qualities are even more clearly noticed on my current class D amps (D-Sonic M3-660-M).
      Just to be clear, I was not offended with anything you said and agree that there is no absolute in this hobby.

Thanks Henry,
 Tim   

Hi Henry, 

     Thank you for clarifying your findings: "from what I have implemented and heard is that an unregulated analog power supply seem to always sound better than those with SMPS. And this is strictly in the context of class D Icepower."  I understand you're in the midst of experimenting to determine if the same holds true for Hypex NCore 400 modules.

     I'm not really surprised that Hypex didn't allow you access to their top NCore 1200 module. I've read that Hypex had a predetermined sales strategy to  reserve the NCore 1200 module for the larger OEM market while offering the NCore 400 module for sale to the DIY market and amp assembly market.  I believe Hypex is considering H2O a segment of the amp assembly market even though we, and likely many others, realize H2O  actually more closely resembles an OEM than an amp assembler.   
     
     I assume you're aware of the newest Hypex module, the NCore 500, which supposedly is very similar to the sound quality of the NCore 1200 but not quite as powerful.  There is even a U.K. company somewhat similar to H2O, Nord, that offers stereo and mono-block amps based on the NCore 500 module that use Hypex smps but have discrete class A input buffer boards that allow a choice of op amps (Sparkos SS3602 or Sonic Imagery 994).  Maybe this will be the future of class D, with op amp rolling rather than tube rolling.

     There are also many very good alternative class D power modules such as the Anaview/Abletech ALC-1000-1300 (used in the D-Sonic M3-600-M mono-blocks) that utilize Phase Shifting Modulation (PSM) rather than the Pulse Width Modulation (PWM) that Hypex NCore modules utilize and the Pascal modules (used in the D-Sonic M3-1500-M and M3-800-S, Red Dragon S500, Jeff Rowland Continuum S2 integrated and 525 stereo amps) that feature their proprietary and patented UMAC  technology.  I believe these modules would be available to you and could possibly be enhanced with your custom analog power supplies.

Thanks,
  Tim

georgehifi,

      Yes, Nord does cut costs and prices to customers by selecting op amps for their input boards that they like the sound of rather than the much more expensive method of designing and building their own.
       Class D power module manufacturers typically utilize the more expensive but high quality discrete MOSFET transistors in their output stages.  I've read that there's recently been a lot of effort in the transistor industry going into developing even faster switching MOSFET transistors expressly for use in class D switching amps.  Are class D amps becoming so popular and mainstream that their manufacturers' needs are now influencing the direction of transistor r&d?  I believe the future of class D certainly looks very promising.

Tim

georgehifi,

     Here's a link to what I was referring to in my last post about reading of faster switching mosfets:

http://audiophilereview.com/cd-dac-digital/why-well-soon-be-living-in-a-class-d-world.html

      This transistor technology is called Gallium Nitride (GaN) and is poised to uproot the high-end audio world.  There's even mention of your favorite subject, higher PWM switching frequency, and how these new GaN FETS will enable it.

Tim

Hi George,

    So, you're saying it may be a year or two before you buy your first class D amp?
     If you're going to wait until class D is absolutely perfect, the good news is that it'll probably be the last amp you'll ever need to buy.  
Good strategy.

Later,
 Tim

Hi Henry,

       You know, if I said "Hi" and used your last name after, I'd be saying:"Hi-Ho".  Mind if I say it twice and add: "it's off to work we go"?
      True story from my college days:
       I worked at a Chinese restaurant and a new guy was hired.  He was a Chinese exchange student whose 1st name was "Ho".  When he came to work the next day, I instinctively said: "Hi Ho".  After I realized how goofy that sounded, I told him his  new American name would be "Henry".  Honest.

       Okay, sorry for my side track.

      You're correct, the Abletec modules have a built-in smps, auto European/North American power sensing circuit and a regulated input power circuit.  D-Sonic also uses a custom input buffer to raise the low input impedance to 60K ohms so it's compatible with almost any preamp; so my former tube VTL preamp (output impedance of 200 ohms) matched very well with the D-Sonic M3-600 monos.

     I believe the Pascal modules also incorporate the smps and other circuits on the same board, so these are likely ruled out for your purposes as well.  At least the Hypex NCore 400 and 500 modules remain as good candidates.  

     So, please knock our socks off with that thing that you do with your analog power supplies!

Thanks for your participation,
              Tim 

georgehifi,

     From the comments of your fellow mates on www.stereonet.au,
it seems you've been posting about the need for an increase in the switching frequency of class D amps to the 3-5mHz range for years to the point of their apparent consternation.  

     I'm not certain, but I'm fairly sure you've been stalking threads concerning class D, and posting similar messages about the dire need for class D amps to raise its switching frequency to 3-5mHz, for years here on Audiogon.  If it hasn't been years, then I apologize, but it sure seems like years to me and I'd hazard to guess to other frequent readers of class D related Audiogon threads.

     Please excuse me while I flash my 'Literary License Badge' and briefly pontificate: Georgehifi is like a stealthy panther, desperately hungry for the definitive answer to the eternal delicious question of the optimal switching frequency for class D amplification that, due to his being a magnificent beast of nature possessing extraordinary feline aural senses,  he alone having the capacity to ever so faintly detect when that frequency is set a few kHz too low.  
     He persistently lurks and stalks through the wild plains of the audio forum hunting grounds until he spots a class D thread and then he suddenly pounces with an uncontrolled fury upon his allegorical prey and maliciously metes out his vengeance by predictably, mundanely, and rather annoyingly, launching into another repetitive attack/statement concerning his bloodthirsty quest for the elusive optimal class D switching frequency.  

     Okay, I think we've all had our fill of whatever that was.  

      I'm apparently to the point of consternation myself.  Unfortunately, I  must admit I lack the complete expertise of  mathematics, electrical engineering and class D amp circuitry and design that I believe may be required to definitively determine whether your claims of the necessity of a higher switching frequency utilization in class D amps is justified.

     Therefore, the only current recourse that came to mind is to directly quote the acknowledged guru of modern class D amplification as well as the inventor of class D UcD and Hypex NCore technology, Bruno Putzeys.  The quote below is a relevant portion of an interview conducted by Peter Roth (PR) of Bruno Putzeys (BP) done on March 1st,2014 and posted on www.sounstage!ultra.com (I'll link the entire interview at the end of my post):

"PR: At Hypex, obviously, you continued development and implementation of the UcD modules for OEM clients -- but tell me about the much newer NCore class-D devices. Is NCore a further extension of what you’ve been doing with UcD, or is it an entirely different class-D scheme?

"BP: I think it would be fair to say that it builds on from UcD. Certainly the fundamental math is the same. The really crucial part of NCore was to figure out how to improve the loop gain even further from what we had -- UcD had substantial loop gain up to 20kHz of 35dB or something -- and I wanted to go beyond that. As I said, there is no such thing as too much feedback, so I was looking for a way to add 20 more dB. That’s actually a very hard problem to crack, because once you start doing that, you have to remember that a class-D amplifier has a limited bandwidth. A reasonable switching frequency for a class-D amplifier is just under 500kHz or so. If you go much above that, you run into efficiency and headroom problems. That, in turn, implies that you have no more than some 200kHz of bandwidth to play with -- actually, less than that. And if you want to cram 50 or 60dB of audioband loop gain into that bandwidth, you have to think completely differently from the way that linear amplifiers are usually designed.

Linear amplifiers typically have what we call single-pole compensation; some of them have two-pole compensation, but nothing much beyond that. UcD has four-pole compensation, and NCore has five. Once you reach into the four- and five-pole compensation, you have this problem that the amplifier can be operating in perfect stability until you clip it, and then it will suddenly start oscillating at a frequency that will immediately damage the amplifier and the loudspeaker -- so you want to avoid it like the plague. And not just that, but you actually want to return the amplifier, once it comes out of clip, to its normal operating regime so quickly that you don’t hear any glitches. The whole NCore patent revolves around the practical solution to that stability problem, the way that it actually catches the feedback loop at the moment that it’s thinking of going unstable, and then lets it go when it is safe to do so.

Apart from that, of course, I did learn some more tricks as concerns driving the output stage. If you have 50dB of feedback, and you are aiming for -100dB of distortion, you’ll still need to manage to get -50dB of open-loop distortion. In that respect, you are right in your previous question: You have to start out with something that’s good, because there is always a trade-off. If you’ve got yourself 50 or 60dB of negative feedback, but if you can also get 10dB improvement in open-loop distortion, why not do so? So the actual power circuit has also changed between UcD and NCore, and obviously, then, the later UcD modules actually use an improved power stage that was borrowed from NCore. The core of NCore is the feedback circuit, but the actual product contains some more improvements that are now trickling back into the UcD range."

     georgehifi, Putzeys states that a switching frequency of 500kHz or so is reasonable and you're claiming 3-5mHz is necessary for optimal class D performance.
      I'm not actually claiming that he's right and you're wrong.  For all I know, he may believe 500kHz or so is reasonable but may agree with you that 3-5mHz is optimal.  I just don't know if my class D monos would sound better with a higher switching frequency since there's no method to currently compare unless I compare my amps to the $30K Technics amp with the new eGaN FETS.  It's honestly hard for me to imagine how my amps could sound better but I'll be keeping an open mind until I can try a more reasonably priced alternative to the Technics.
      I'm thoroughly pleased with my experiences with class D amps so far and likely a permanent member of the class D Fan Club;I've already got my official club card, big club ring with the diamond studded 'D', club jacket, beanie, "Class D Stands for Delicious" t-shirt, "Class D or Die" bumper stickers , matching underpants and, due to years of practice, now have the unbelievably elaborate secret member handshake down pat.  

     Anyway, my main point is that I know Bruno is a friendly and accessible guy via email and will answer your email inquiries on class D switching frequencies.  Wouldn't you rather receive answers straight from the horse's mouth than constantly raise the subject on Audiogon Forums?  Speaking for myself, I know I'd sincerely enjoy not hearing about this subject again until you, hopefully, post on what you discovered in your discussion with Bruno.  


Complete Putzey Soundstage interview:
http://www.soundstageultra.com/index.php/features-menu/general-interest-interviews-menu/455-searchin...


Thank you,
   Tim  

Hi atmasphere,

      I'm very interested in checking out your take on the first Atmasphere class D amp.
     Too early to share any insider details like modules chosen. type of power supply adopted, any customized components, target price and expected release date?  

     As to the Audiophile Review article describing class D amps as 'digital' amps, I think the author, Skip Taylor,was a bit inconsistent in the entire article. I think you're right, he was  all over the place on terminology and his knowledge base seemed outdated:

.1. He generically states "Class D Audio amplifiers" which is very close to the name of a class D company, Class D Audio.

 2. He talks about "Class D amplifiers" having to use high levels of negative feedback to compensate for poor open loop performance and meet target levels of TIM, not seeming to realize that the inventor of many recent class D breakthroughs such as UcD and Hypex NCore power modules, Bruno Putzeys, believes there's no such thing as too much feedback in his amp designs and considers TIM to be an irrelevant and meaningless measurement as far as class D amps are concerned. 

 3. The author states:"   By definition, large amounts of feedback introduce transient intermodulation distortion (TIM), which introduces a 'harshness' that hides the rich subtleties and color of the music that were intended for the listening experience."  
       His concept of feedback and TIM have more relevance for traditional linear amps than class D amps as far as 'harshness' is concerned and he doesn't appear to understand that high levels of feedback at all levels of the audible frequency spectrum are the key concept /tool that allow Hypex Ncore modules to sound so good over the entire spectrum, including a lack of 'harshness' and its high levels of detail that enables the rich subtleties and color of music to be reproduced so well.

4. I think the author's 'digital' experience is not primarily in home audio and it was reflected in his article.  
     His discussion about keeping the signal in digital format as long as possible, without converting it back and forth between analog and digital, is a concept I remember from the earlier days of class D when the confusion between switching and 'digital' amps seemed to begin.

     I think it's a good concept that kind of lost focus once it became clear that the adoption of the other system components that could make this concept a reality lagged considerably behind the adoption of class D switching amplifiers.  Components such as completely digital sources and preamps, that would allow digital signals to be inputted into the audio chain, remain in the digital domain while being routed by a purely digital preamp and sent along to a class D switching amp still in the digital domain, where it would be converted from a digital signal to an analog signal before being amplified and sent along to the speakers.

     Most of the early examples of class D amps were actually switching amps that were interchangeable with traditional linear amps but could easily accommodate the above with just the addition of digital inputs.

    The author made absolutely no mention of any of this.
     However, I should point out that, while I think keeping an audio signal in the digital domain as long as possible would likely be a good thing sound wise and with the possibility of enhanced functionality, I believe it also creates a boatload of issues that could be fairly complex, challenge manufacturers' flexibility and budgets, would require industry wide agreement/guidelines and negatively affect the number of customers willing to adopt this new technology/paradigm.   At this point, it may be more trouble than it's worth.
Tim                  , 

Hi atmasphere,

     Proprietary power modules and supply?  Wow!  Very cool and very interesting.


Good luck,
   Tim

georgehifi,

Over six hundred years ago, adventurous explorers were looking for financial backing to sail west on the Atlantic from Europe to see what was out there and ,hopefully, discover new lands. At the time, early explorers limited their explorations to sailing around the coast of Africa always keeping the land in sight and never venturing out to open uncharted waters.
This is why these first explorers didn’t discover much beyond the trade routes from Europe to the East and back. The reason they were reluctant to venture out to uncharted waters and truly discover new things was because of the ’Flat Earth Theory’. The Catholic church was very influential around this time and it, along with other misguided opponents of scientific discovery, propagated the ancient unproven theory that the earth was flat and, if you sailed too far west, your ship and everything in it would eventually reach earth’s edge and fall off into God only knows what.
I mentioned the above because your ’Low Class D Switching Frequency Theory’ reminds me of the ’Flat Earth Theory’ in many ways:

1.Just as the ’Flat Earth Theory’ (FET) postponed some early explorers from discovering new lands, your ’Low Class D Switching Frequency Theory’ (LCDSFT) could possibly postpone some of the more gullible audio explorers among us from discovering new audio fidelity in their systems.

2.Just as the FET promotion kept explorers close to the safety of the shore for awhile, your LCDSFT promotion could keep some of the more gullible audio explorers among us close to the safety of traditional linear amps for awhile.

3.Just as the FET proponents used repeated claims of the false affects of an unproven theory to mysteriously prevent the advancement of scientific discovery, you use repeated claims of the false affects of your unproven LCDSFT to mysteriously prevent the advancement of system discovery.

4.There’s obviously more allegorical meat on this bone but I’m stuffed.

You never responded to my earlier questions, possibly from this or another thread, about whether there’s any scientific basis for your theory that current class D switching frequencies are too low and negatively affect the sound of class D amps in the audible range. You also failed to respond about whether or not you have personally heard any sonic anomalies in the sound of class D amps you’ve listened to.and, if so, whether you could describe what these sonic anomalies sound like.

When I first read about your theory, I perhaps foolishly listened to several very familiar and very high resolution (96kHz/24 bit) music files I have trying, as best I know how, to be hyper-critical of the sound quality in an effort to hear if there was any subjective evidence I could actually detect to determine whether your theory had any merit.
Well, after a few hours of failing to detect even a hint of a whiff of a scintilla of even a possible twinkle in the eye of even a single sonic anomaly, I decided it was safe to relax in the knowledge that my class D amps had no sonic anomalies in the audible range, at least that I could subjectively detect with my possibly tin ears.
Subsequently, I searched the internet for any scientific or even any subjective or anecdotal evidence in support of your LCDSFT and discovered there is zero scientific evidence to support your theory and the only subjective or anecdotal evidence I discovered was numerous google references of your thread postings here and on various other audio forums.
I find it hard to fathom why you have repeatedly made false claims of the false affects of an unproven theory on Audiogon and other audio forums.about class D amps. I tend to doubt you do it for some twisted personal version of fun and believe there must be some hidden motivation for someone to so diligently,consistently and repeatedly put forth the time and effort required, as you have, unless they personally judge achieving their mysterious goal as sufficiently motivating.

Don’t worry George Hi-fi, I doubt anyone expects you to actually reveal your hidden motivation or agenda.
Fortunately for current and future class D amp owners, repeated suggestions of non-existent sonic anomalies produced by their amps are not audible to any human I’m aware of.
Even in the infinitesimally small chance you’re theory actually has an iota of merit, the truth is if the thousands (millions?) of current class D amp users cannot hear these elusive, currently not to have been heard by human ears. very suspect and apparently extremely quiet sonic anomalies then they, by definition, do not exist.

Class D=Trash, my Ash!

Later,
Tim

georgehifi,

I never set out to write long winded posts but I admit they tend to be overly verbose. I’m going to strive for more brevity starting now.

Your last post goes over information already discussed on this thread.and totally avoids answering both relevant questions concerning your theory asked of you in my admittedly long winded prior post:

1. Does any scientific evidence exist that in any way supports your theory that the current class D switching frequencies are too low and result in sonic anomalies that are audible?

2. Have you personally ever heard these sonic anomalies listening to good class D? If so, please explain what these theoretical sonic anomalies sound like. Apparently, you currently may be the lone known human believing in, and claiming the audibility of, these sonic gremlins.

Tim

georgehifi,

     Let me get this straight:

     When  I initially asked you:

"1. Does any scientific evidence exist that in any way supports your theory that the current class D switching frequencies are too low and result in sonic anomalies that are audible?

2. Have you personally ever heard these sonic anomalies listening to good class D? If so, please explain what these theoretical sonic anomalies sound like. Apparently, you currently may be the lone known human believing in, and claiming the audibility of, these sonic gremlins."

  Your response, is to post quotes from a very forgettable 10yr old roundtable discussion that actually is more concerned on the relative merits of class D amps than on the existence of audible affects caused by the switching frequencies utilized?  And the panel consists of 9 traditional linear amp (both tube and solid state) designers and a single designer actually designing his amps around class D amp power modules that he did not design but purchased from another company?

 Come On, Man!  You didn't come anywhere near answering either one of my clearly straight-forward questions  by quoting from the comments of a stacked deck panel of traditional linear amp designers, 90% of whom have absolutely no experience designing a single class D amp  

    Who's the genius who picked out this ridiculously unbalanced panel of participants?  Is he the same one who selected the participants for that infamous 'A Remarkably Unbiased Roundtable Discussion on Christianity' that consisted of those 9 adamant atheists and that single choir boy?
     I would have found that Class D Roundtable a lot more informative, interesting and worthwhile had the genius invited an actual class D amp designer, such as Brruno Putzeys, the inventor of both the Ice and Hypex NCore class D amplifier technologies.
     Due to the complete absence of ANY evidence that even vaguely supports your theory, the complete lack of ANY description of what these theorized sonic anomalies  actually sound like,  you're reluctance to state whether or not you've ever actually heard them yourself and my personal experience of never hearing even a hint of sonic anomalies from my class D amps,  I think you understand the reasons you need to come up with a new fake theory/boogieman to further your mysterious agenda.
     How about claiming they spontaneously combust?

Later,
 Tim 

Hi atmasphere,
     Thank you for your explanation.  I know your credentials and trust your comments have no hidden agenda.  Unfortunately, I don't know georgehifi's credentials and whether he has a hidden agenda against class D.
     Okay, so you're stating that there can be intermodulations between the scan frequency and the signal being amplified in class D amps.  Amp designers call this 'inharmonic distortion' and its affects may be a cold and sterile sound.  I just have a couple questions about this:

1.  Is there a consensus among amp designers that current switching frequencies (what I believe you're calling 'scan frequencies') being too low is the primary cause of 'inharmonic distortion'? If so, is there also a consensus that raising switching frequencies to the 3-5 MHz range would reduce 'inharmonic distortion'?

2.  Can you explain why I, and apparently many other class D amp users, do not perceive our class D amps as being cold or sterile?  Do you think the ability to perceive  the affects of 'inharmonic distortion' differs among individuals or do you think it's more likely the degree of 'inharmonic distortion' varies by amp?

3.  Are there any current methods of measuring 'inharmonic distortion'?

Thanks.
  Tim

randy-11,
     You stated:
"of course, you can measure all sorts of distortion products - inharmonic means non-harmonic."
    Well golly gee, Randy, I would have never thought that 'inharmonic' means the same as 'non-harmonic'.  Of course they mean the same thing, but that doesn't mean that either one is an accepted scientific specification and it definitely doesn't mean either one can be currently measured.
    Despite your claim of certainty, I am going to wait until atmosphere replies before I believe that there's a current specification for 'inharmonic distortion' and whether it's measurable.  I know there's a specification for 'harmonic distortion'  and 'intermodulation distortion' as well as standardized methods of measuring both. 
    But this is the first I've heard of 'inharmonic distortion' and I doubt it's even currently a valid scientific term and, even if it is,  whether there's a standardized method of measuring it.  From atmasphere's earlier post, it seemed to me that the term 'inharmonic distortion' was an informal term used by some amp designers to distinguish it from intermodulation distortion and he made no mention of whether it could be measured.

Erik_ squires,

     I'm in complete agreement with you and I hear absolutely no sonic artifacts/anomalies when listening to my class D amps, either.  I know from personal experience that all of my class D amps outperform my former class A/B amps by a wide margin in every area that I care about, although my A/B amps may not have been as highly biased as yours.
     However, I try to keep an open mind about things and listen to the thoughts and opinions of others, especially from well respected sources such as atmasphere.  Hopefully, he'll impart some more wisdom on this subject soon.

     Ultimately, I realize I'm not concerned at all about whether the theory that current switching frequencies are too low and cause audible artifacts/anomalies is true or not, other than curiosity.  If the theory is proven not true, it will just confirm what I have not been hearing since I began using class D amps in my system.  In the unlikely case that the theory is proven true, I will be admittedly shocked for a few moments but then I'll just continue on enjoying my class D amps as if nothing had changed because nothing will have changed; I will continue to not perceive these sonic artifacts/anomalies that are proven to exist just as I did not perceive these sonic artifacts/anomalies before I even heard of the theory of their existence.      
     Sure, I'll listen to a class D amps in my system that claim, either by employing better passive filtering or higher switching frequencies, to eliminate all  theorized sonic artifacts/anomalies if they ever become affordable just to test if I perceive an improvement in performance. 
    I'm just having a hard time conceiving of how the absence of something (sonic artifacts/anomalies), that I didn't perceive in the first place, is going to improve my system performance.  
     I'm not planning on selling my excellent performing class D amps anytime soon, perhaps ever.

Tim

atmasphere,

      Thank you for replying to my questions.

    Your confirmation that current class D amp switching frequencies are not causing 'inharmonic distortion', along with class D Ice and Hypex NCore power module inventor Bruno Putzeys' statement that current class D switching frequencies in the mid-500kHz range are "completely reasonable", refutes the theory that they need to be raised to the 3-5mHz range (to not affect frequencies in the audible range) as far as I'm concerned.
     These confirmations make sense since they mirror the more subjective perceptions many class D users have, including myself, of the total lack of sonic anomalies and very high quality performance levels of class D amps..

    I'm looking forward to hearing the results of your first class D amp design effort.
   I suspect your class D amp will be transparent, detailed, with a very neutral overall quality while also having the extreme low noise and distortion levels that all seem to be common characteristics of good class D amp designs.  
   I believe you'll also find that an amp with the above traits will be a great match with high quality tube preamps since the amp will operate as the audio ideal of 'a straight wire with gain' which  will allow the sound qualities of your tube preamps to be amplified faithfully without any alterations. 

Tim
    

Hi George,

From my technically limited layman’ s perspective, the quote you posted from Optoma USA actually seemed logical and made some sense to me. If I didn’t know better from years of personal experience, I’d probably just accept what they stated as the truth, assuming they knew what they were talking about.

However, I find myself still resisting this theory that current class D switching frequencies cause sonic artifacts/anomalies in the audible range for several main reasons:

1.Two well credentialed and well respected amp designers whom I also respect and trust, atmasphere and Bruno Putzeys, have made statements that there’s no need to raise the switching frequencies for class D amps from the current mid-500kHz to the 3-5 mHz range.

2. If these proposed sonic artifacts/anomalies and supposed phase shifts actually do negatively affect the sound quality as theorized, I would think that a certain percentage of the currently thousands (millions?) of class D amp users, including myself, would be capable of detecting any peculiarities in the sound quality in their systems. I would also expect a certain portion of these users would be alarmed enough to post their observations on this or other audio forums seeking explanations and advice.
Oddly, the only comments I’ve read questioning the sound fidelity of class D amps were made by you, George.
To be fair, I have read comments by others claiming that they thought class D amps sounded cold and sterile but I’m not sure if these perceptions are related to sonic artifacts. I always made sense of these comments by questioning the quality of the class D amp they heard. After using 3 different class D amps from 3 different companies for soon to be the past 3 years, I’ve never perceived any of them to be cold and sterile and have never heard anything I would classify as a lack of fidelity.
I’ve asked you numerous times whether you’ve ever personally heard these elusive,quiet and apparently very difficult to notice sonic artifacts from a class D amp and if you could describe what they actually sound like but you never responded.
I wanted to keep an open mind and know what to listen for when I actually spent a couple hours listening to some very familiar music trying to be hyper-critical and detect anything that didn’t sound quite right. I didn’t hear anything amiss.

3. There seems to be a serious lack of any scientific studies or research concerning the affects that particular switching frequency ranges utilized in class D may have on the the actual audible musical signal frequencies being amplified. I’m referring to carefully controlled tests and experiments, with the results required to be consistently and reliably achieved when conducted by independent scientists before results can be verified, conclusions reached and a knowledge base on the subject can begin to be established.

The absence of a solid knowledge base allows individuals such as yourself, George, to put forth any theory that serves their purposes without being constrained by anything as silly as needing to support their theory with actual evidence such as facts or at least agreed upon truths.

But enough of this scientific mumbo jumbo, the simple truth is that I would have sent back my first class D amp for a ’no questions asked’ full refund, and bought a more expensive traditional linear amp, if any of these theorized sonic artifacts or phase shifts caused an audible lack of fidelity in any part of the audio spectrum.
The only thing I heard was a small, lightweight, efficient/electricity sipping, cool running, $630 Class D Audio SDS-440-CS class D amp significantly outperforming my large, heavy, inefficient/electricity gulping, hot running, $2,400 former Aragon 4004 MKII class A/B amp in almost every amp criteria that I care about: much better bass response, a much lower noise floor, better dynamic range and a much more neutral and detailed presentation. Both amps had a roughly equal ability to present a solid, stable and realistic 3D sound stage illusion while both had similarly very good mid-ranges and trebles that were well extended but not fatiguing.

Tim

Hi George,

    You asked:"why do you think Technics have gone to the trouble to advance the class!"?

   Most likely to sell them at $30k each to gullible buyers. that believe higher switching frequencies amps actually sound better than the $630-$3,000 competition , and have more dollars than sense.

If you get a few more dollars, this could be you.

Later,
 Tim

Hi George,
      I think you're seriously under-estimating the performance of the many current good class D amps using switching frequencies around 5oo kHz.  I say this based on my personal experiences with 3 different class D amps over the past 3 years. 
      Since you've repeatedly refused. or are unable, to answer my pertinent questions of "how many current class D amps you've listened to?" and "What are the telltale audible signs that result from switching frequencies being too low and affecting the audible range?", I now have a new theory about why you continually make this claim without anything close to scientific or even subjective or anecdotal evidence:

   I now believe you are the sort that enjoys reading and learning about audio technology and equipment but also one that has very little to no actual experience of listening to audio equipment employing newer technology.  This is the only conclusion I'm able to reach given your apparent lack of knowledge about how good some current class D amps perform utilizing supposedly switching frequencies that are too low and your total lack of responses concerning what your theorized affects on the audible range actually sound like.
   There's also the matter of you seriously over-estimating the improvements that will result from using higher switching frequencies in the 3-5 mHz range.  I think the new faster switching FETs are more likely to improve class D performance than higher switching frequencies.

Later,
  Tim   

    George,

You stated:  "All your doing at the moment is trying to protecting your investment so it won’t take a monitory nose dive when this new technology becomes mainstream and finally puts Class-D into the hi-end Audio bracket, with today’s great linear amps
Keep that finger on the sell button and press it before they become obsolete."

     Protecting my investment?  I've never considered my amplifiers an investment since I began buying them a few dozen amps ago.  As I recall, the vast majority of "investments" I've made in my history of buying amps have been of the 'buy high and sell low' variety.  Hardly a recipe for success.

     Fortunately, every "investment" I've made in the many amp transactions in my lifetime were made with an expected ROI (return on investment) of improved sound quality in my system, not a financial one.

     Since I consider improved system sound quality as my ROI when buying an amp, my 3 "investments" of about $3,500 in class D amps have already been extraordinarily successful, with Sonic Gains already greatly exceeding my expectations. 
     The Sonic Gains continue to flow freely from these amazing, small, light, great sounding, neutral, low noise, powerful, highly dynamic, detailed  and affordable "investments".  Due to the very low levels of heat they produce, they'll likely continue to reliably provide their sonic dividends for many years to come. 
     Regardless of whether higher switching frequencies and faster/better FETs are able to even further improve class D amp performance,  my current class D mono-blocks are providing remarkable performance, with absolutely no detectable sonic artifacts/anomalies in the audible range, at switching frequencies in the mid 500kHz range. I, therefore, have no need to await affordable higher switching frequency class D amps to enjoy their promised benefit of not negatively affecting performance within the audible range since I've already been enjoying this for the last 3 years.
     While I already know and appreciate how spectacular class D sounds without the switching frequencies having affects within the audible range, out of curiosity I'll likely still audition a pair to hear how the faster/better FETs affect class D performance.

Later,
 Tim

" Not one mention of the output filter that has to address the switching noise of the switching frequency, which is the Achilles Heel with present day switching frequencies."
George,
     I understand the importance of having a good well matched passive filter in class D amps to remove the ultra high switching frequencies from the signal path after their Pulse Width Modulation job has been completed. I agree that this is a critical component in the process since this is where your theory states these switching frequencies can affect the audible range if not completely filtered out.

     Perhaps I just got lucky and only bought class D amps with exceptionally good passive filters. If they weren’t so good, maybe I could catch a trace of the switching frequencies affecting the audible range that you mention so often. Thank you, George, I think you just might have solved the mystery of the missing sonic artifacts/anomalies in my, and likely boatloads of others’, class D amps. No wonder nobody believes your theory; All the evidence is being filtered out effectively just as designed.

     Please tell me the class D amp brands and models of class D amps you were able to detect some audible artifacts from. We can compare all the specific filters operating flawlessly in our class D amps to the specific filters obviously working so poorly in the class D amps you listened to that inspired your infamous and discredited theory.

Thanks again for your help,
Tim

teo audio,

I haven’t heard the affects of music described like that before but I liked it.

Well said!

Thank you,
Tim

stevecham,

     You asked:
"I'm not reading consistent sonic and utility praise for the format. Why is that?"

     I can only speak for myself but I think many class D users will probably agree with my answer to your question.   I don't specifically praise the sonics, or mention any of the usual terms used to describe the sonic characteristics of amplifiers in the past, in any of my posts on this thread or whenever I've attempted to convey  the overall sound of my several class D amps  for a very simple reason that is very obvious to anyone listening to a good class D amp in their system:

     Good class D amps are extremely neutral, have no consistent sonic signature that is imparted onto the music and therefore there are no sonic qualities to criticize or praise.
     Criticizing or praising the sounds one hears through a good class D amp is essentially just an evaluation of the music since there is nothing  discernible that is added or subtracted from the original signal.  In my experience, good class D amps behave just as many have consistently described how an ideal amp should behave; like 'a straight wire with gain'.

    As to consistent utility praise for the format, I think you need to reread  this thread and pay closer attention because the practical advantages of class D amps when compared to traditional amps has been well covered in this thread. I'll summarize the utility advantages of class D amps have over traditional amps, however, to save you the time:

 Class D amps are much lighter, usually much smaller, are significantly more efficient, produce much less heat and generally are less expensive than traditional ss and tube amps.  I also believe class D amps will be proven to cost less to maintain and operate  while determined to be more reliable than traditional amps as data is accumulated and analyzed.


Tim  

 
        
 R

     

stevecham,

     You asked:
"I'm not reading consistent sonic and utility praise for the format. Why is that?"

     After rereading your post from 8-28-2017 at 1:00am, I now realize I may have misunderstood your exact question just prior to posting my reply on 9-19-2017 at 8:36am.  I originally understood your question to be referring to why all posters on this thread, "that posted favorable experiences listening to class D amps",  were not consistently reporting sonic and utility praise for the format.  I currently understand your question to be referring to why all posters on this thread, "that posted either favorable or unfavorable experiences listening to class D amps", are not consistently reporting sonic and utility praise for the format.
      In other words, I think your intended question was basically:
 " Why do some posters on this thread report positive experiences, while some report negative experiences, listening to class D amps?" Please let me know if I'm incorrect.

     IIn any case, this is a very interesting and insightful question that I believe gets to the very heart of the issue concerning why some really like the performance of class D amplification and others really do not.  This difference of opinion is currently reflected in 2 diametrically opposed current forum threads:
  
This one titled "Class D= Trash"  started by madavid0

versus

The opposing viewpoint titled "Class D is just Dandy!" started by erik_squires

 This dichotomy of opinion on class D performance has also confounded me since I first learned of class D about 5 years ago and began reading Audiogon and other audio forum opinions on their performance.

     I recall the opinions on class D from this time alternating between glowing reports and those that claimed the sound was "thin", "strident", "shrill in the high frequencies" and comments like "it just seems like something's missing".  The only consensus of opinion I remember from about 5 yrs ago was that the bass performance, noise levels, distortion levels and detail levels were considered by almost all to be very good along with the obvious utility advantages of small size , low weight, low heat and relatively low cost.  My perspective is that the conversation hasn't changed much over the past 5 years.

     I can sympathize with your confusion since I recall being equally perplexed at the time about why there were such a differing opinions on class D performance.  Also at this time about 5 yrs ago, my high powered class A/B Aragon 4004 MKII amp's power supply capacitors leaked and it went dead.  I had to make a decision on whether to have the amp repaired for a quoted $1,800 or buy a new amp.   This was a pain at the time but, in retrospect, I now consider this amp failure as very fortuitous.  
     I decided not to spend $1,800 to repair my nearly 15 year old amp and instead viewed it as an ideal time to audition a class D amp in my system and just determine for myself how well or poorly class D performed.  I considered this option as low risk (as it remains today) since many class D amp sellers offered generous in home trial periods with 'no questions asked'  full refunds if you were not completely satisfied.  I wanted an amp that at least matched the power of my now deceased class A/B Aragon amp (400 watts @ 4 ohms) that was stable into low impedance loads to drive my fairly inefficient ( 86 dbs/1 watt) Magnepan 2.7QR spkrs that I know sound best with lots of power.  

     So I chose an SDS-440CS stereo amp from ClassD Audio that had numerous good reviews, a 4 week in-home trial period, was powerful ( 440watts @ 4 ohms) and very affordable ($630 5 years ago and still $630 today).  This amp sounded very good right out of the box and I was thrilled with its performance.  It outperformed my former Aragon amp in every area I cared about; power, dynamic range, quietness, imaging, distortion, accuracy and musicality.  Oh yeah, it was also about 1/3rd the size and weight of my former amp, ran cool to the touch, consumed significantly less electricity and there were zero detectable EMI or RF interference issues in my system.  

     Needless to say, I kept this amp and it has now been operating faithfully in my system for over 3 years (currently driving my in-ceiling surround spkrs).  I've subsequently purchased additional class D amps (a stereo Emerald Physics amp to drive my Magnepan CC3 center ch and a pair of D-Sonic M-600 monoblocks that currently drive my Magnepan 2.7QRs).  All have performed equally well or better than my original ClassD Audio SDS-440CS amp and completely outperformed the very good class A/B amps they replaced. My combo HT and 2-CH music system is now completely class D amplified and I've been completely satisfied with the sound of my system for both for a few years now.  

     Now, this is just 1 person's honest opinion of the performance of good class D amps.
     I would urge you, and any other readers of this thread considering class D amps in their systems, to not take my or anyone else's word for how good the better ones perform.  Just audition one or more in your own system and discover for yourself how class D sounds to you.

     I say this not only because it's the best method to determine how any component affects your system, but also because it seems as if class D may not be the best solution for everyone.   I've been admittedly and repeatedly confounded by how class D has performed and been perceived to be so exceptionally good in my system while others claim to have issues with its perceived performance in their systems.

     Is it possible that some individuals have an 'allergic' reaction to class D produced sound or are more sensitive to certain affects introduced by class D amplification?  Can it be true, as georgehifi has adamantly and repeatedly claimed, that the Switching Frequencies currently used in most class D power amps (about 500 Khz) are too low and cause sonic anomalies in the audible range (about 20-20,000 Hz)? 
     I tend to doubt both theories because there is absolutely no scientific evidence I'm aware of to support either.  However, if actually true, it would go a long way in explaining the rather wide spectrum of reactions thus far concerning class D performance.  

I'm going to try and keep an open mind,
     Tim  

Hi George,

    You're probably right, my old Aragon likely died a slow death with its performance dropping so gradually I failed to notice it was ailing til it seized up. 
     However, I also noticed the exact same improvements when switching my decent quality and healthy class A/B center and surround channel amps for good quality class D amps.
     I've also  continued to leave my amps on 24/7 barring severe weather.  I've noticed a significant ($30-40) reduction in my monthly electric bill ever since.
     Good point, never the less.
        Tim