WOops... You are correct George: Theta Prometheus is indeed based on full NCore1200, not on the lower end NC500 module... My bad!!!!
G.
Class D Technology
So I get the obvious strengths of Class D. Efficiency, power output & running cool which allows for small form factors. I also understand the weaknesses somewhat. 1. Non-linear & lots of distortion that needs to be cleaned up with an output filter.
So my question is, if it weren't for efficiency & power, would there be any reason to own a Class D amp? Do they beat Class A in any other categories that count for sound quality?
So my question is, if it weren't for efficiency & power, would there be any reason to own a Class D amp? Do they beat Class A in any other categories that count for sound quality?
527 responses Add your response
Hi seanheis1, as far as I know, preamplifiers cannot be implemented in class D... I have been told that their topology is the equivalent of class A. However, Preamps with regulated SMPS do exist... ANd the ones I have listened to are rather wonderful: e.g. Rowland Corus and Criterion, Rowland Capri and Capri S2, and the preamplifier section in the Continuum S2 integrated. G. |
Speaker cables would be a very poor antenna. Since wavelength of 500kHz switching frequency is 600m a typical 2m cables would be 1/300 wavelength antenna. Usually antenna becomes rapidly ineffective below 1/10 of the wavelength.That's true, but in order to meet EU directives, UL and a host of others, the speaker cables are effective enough that the issue has to be addressed by any classD amp producer. In fact it is speaker cables that are mentioned when the issue of HF radiation is brought up in the design papers. However, its so easy to address that I regard it as a non-issue. As I do the switching noise of SMPSs. The only reason we don't use the latter in our OTLs is the cost of custom SMPSs- its a lot cheaper to use traditional supplies! |
I think were already seeing digital/Class D integrated amps make significant headway. The technology is so good already (low noise floor and distortion compared to separates) that I see no need for a separate pre-amp these days anymore quite frankly. When time comes to replace my current pre-amp I will likely just go with a Class D integrated of some sort based on my experience to-date with digital Class D integrated in my second system. |
Well nothing’s perfect but in all honesty gotta say that Class D done well comes about as close in all ways that matter as anything I’ve experienced in home/high end audio. Even without breaking the bank in some cases. If I were competing with it these days rather than benefiting I would definitely consider it a threat to my existence and take actions accordingly.Maybe we will start seeing Class D preamps then... |
Well nothing’s perfect but in all honesty gotta say that Class D done well comes about as close in all ways that matter as anything I’ve experienced in home/high end audio. Even without breaking the bank in some cases. If I were competing with it these days rather than benefiting I would definitely consider it a threat to my existence and take actions accordingly. |
You said it booboobaer. I haven't read the entire thread, but have followed its progress, and I know there are lots of smart people here talking about Class D switching noise, and zombies coming out of the power supply, and modules and cats and dogs living together, and basically the the worst parts of the Bible. I don't know about any of that...and I concede that due to my lack of technical knowledge, it's possible that my Peachtree integrated is secretly plotting the overthrow of mankind right under my nose and I don't even know it. All I can tell you is that there's beautiful music coming out of my speakers, and that my Audio Research integrated with new set of KT120 tubes has become a very nice rack ornament. |
Thank you Tim and nyame.... I try to report what class D amps I have experienced in the last decade in as unadorned a way as I can. One more class D amp worth looking at below $10K is the Theta Prometheus... I believe it is an NCore NC500 implementation which uses custom toroidal transformers instead of the standard NCore SMPs or a custom SMPS... Perhaps you Statman can tell us more about your unit.... How long has break-in taken to complete... What amp is it replacing.... And what audible characteristics are most salient on Prometheus? Regards, Guido
|
I've observed part of the maturing of Class D technology in recent years is that noise as Atmasphere mentions is a valid concern that may have been a more common issue earlier on in some cases when not handled properly but should not be and is not in practice an issue normally anymore with newer well designed and properly functioning Class D amps. |
I'm no scientist but I understand the difference between theoretical noise and actual verifiable noise and that, empirically, only the actual noise can actually be heard. by us humans. Noise needs to be heard to exist.Class D amps are nearly immune to any noise they (or their SMPS) might make. The switching occurs at the output of the amp to which speaker cables are attached, which might make a suitable antenna. Its the other gear in the system that is really the concern (not to mention pacemakers and the like in the area)- they might pick up the radiated RF noise and might react poorly to it. However, neither of these are really issues with any competently designed amp or power supply, and while I get the concern, its mostly a red herring. You would never be able to ship an amplifier (or power supply) out of the country if it made any appreciable noise! So I don't think this is anything to be worried about. |
bcgator and mapman I am with you guys all the way. I had the GT200 mono block tube amps from Tube Research Labs. They were by far the best tube amps I have ever heard. Does that make me an authority? Absolutely not. But when I replaced them with H2O 250 SE mono blocks my world was turned up side down. Were the 250s as warm in the mids? No! But guess what.I used a tube pre-amp (the TRL Dude) the Ayon Skylla 2 DAC and I was 90% there in the mids. What I did NOT have was distortions (even order nor odd order) that was obviously missing since replacing the tube amps. I have the Sound Lab A3 PX speakers and as you say " full range" with a vengeance. Unfortunately components add their own color. That is the nature of the beast. So system matching is always the challenge. Just bringing the Sound Labs 4 inches closer to each other dialed the sound right in. I hear the arguments and look at the measurements and guess what the sound contradicts those arguments and measurements. Not one of my audiophile friends has not been floored with the sound. They too have heard the class A tube monos and said these thing eats them for lunch. I think it was you Mapman that said you changed a cable. There you go, system matching. If you are ever in Columbus, Ohio stop in for a listen. |
Hi Guido, Very good summary of the evolution of class D over the last few decades. I've become familiar with your thorough knowledge of most things class D over the last few years and I'll take your word for it that early class D amps did suffer from some of the ills that the op and george have discussed.. Luckily, I avoided the early disappointments by not using class D until the last 2-3 yrs. I've experienced no high frequency harshness, brightness or any other negative treble qualities and thought they were referring to more recent class D amps. I'm not a fan of bright sounding amps of any type and, if any of the class D amps I currently use shared any of those qualities, I would not have kept them and definitely would not be recommending them to anyone. Guido said:: "Please note that exactly like proclaiming that all class D amplifiers are inherently flawed constitutes a logical fallacy, so would be the assertion of the opposite... Reality is, that with all topologies, some amps will meet our particular taste in music reproduction, some will miss by a country mile, and some will be somewhere in between." I agree with your summation completely.I think you're correct, the reason I enjoy my current D-Sonic M3-600M amps so much is because they match my taste in musical reproduction so well: Very good bass response that is deep, solid but also nuanced when required. Very low noise floor that enables details to be heard. Powerful for good dynamics and a relaxed and effortless quality on all content that allows music to sound very natural and life-like. Dense, solid and stable imaging that allows for the illusion of a 3-D sound stage both laterally and front to back. A smooth mid-range and treble that also manages to be highly detailed. A generally accurate and neutral presentation that is capable of conveying warmth when it's contained in the music and captured on the recording. This is a summary of what I hear when I listen to my class D amps. It is a combination that suits my tastes well but I realize may not suit others tastes and I realize not everyone will even .hear the same qualities from these amps in their system and room. as I do in mine, it's to be expected. Tim |
| Post removed |
modules and device designs have evolved enormously in the land of class D amplificationI say more of a gradual upwards evolvement, with tweaks and band aid filtering, no real technical breakthroughs. The only one I know who is stretching out for real progression is Technics with their SE-R1, with the supply finally of newest technology to double the switching frequency, with this latest device from EPC Corporation Inc. Who invented the Mosfet Power Transistor years back. This is where the real evolvement for Class-D will come from the manufactures of the components, not the manufacturers of the amps. In a way it’s up to the audiophiles to get them to use this new technology then the price will come down for something like the $30k Technics through demand of those components and other device manufactures copying them. http://epc-co.com/epc/GaNTalk/Post/13752 http://www.technics.com/us/products/r1/se-r1.html Cheers George |
The concerns of the OP and of George are correct, at least from a historical point of view.... When I first started looking at class D amps, in the middle of the last decade, there were many examples of class D amps which were either sounding dark, or limited in the harmonics of the upper frequencies, or harsh, or high-fiish, or a combination of several of the above undesirable characteristics.... For Example: * Flying Mole -- All the delicacy of music reproduced with 150grit sand paper! NuForce Reference 9 SE V2 monoblocks -- Clean but quite climical, even after 1K hours break-in... And treble was clinky and limited. Red Dragon monos -- Both harsh and dark at the same time... Quite an achievement! Wyred4Sound monos -- Listened extensively at RMAF several years in a row... Harsh and fatiguing to the point of non-listenability. Rowland M501 monos Powerful, but lacking subtlety. Bel Canto Ref1000 Mik.1 -- Better than the above, but still somewhat rough in the treble... Note that the problem simply does not exist on the Mk.2 version. Rowland M302 stereo -- Sweet and delicate, but will little macrodynamics... And just slightly cold. But... The World has moved along... A dozen years have gone by, and modules and device designs have evolved enormously in the land of class D amplification, starting with the Rowland M312 stereo, and the Bel Canto Ref1000 Mk.2 monos: products that simply... Make real music. Today, amps like the Bel Canto REF600 monos and the Merrill Teranis stereo based on Hypex NCore NC500 modules, once appropriately broken in -- yes I insist it is needed -- make extremely fine music for their quasi entry level pricepoints, without pretending to achieve the ultimate subtlety of reference level amps. But if one were keen in hearing what musical refinement has been achieved by current reference-level class D amplification without audible compromises, please have a listen at least to some of the amps that have captured my heart over the last few years: * Merrill Veritas monos based on NCore NC1200. * Rowland Continuum S2 integrated -- Based on Pascal M-Pro2. * Rowland M825 Stereo -- based on NC1200. * Rowland M925 monos, based on NC1200. * Bel Canto Black -- based on customized NCore modules. And there are more marvellous class D devices, which I have not had the fortune to audition at all price points. Are all current class D amps today superb music makers? That is unlikely.... For example, last time I heard W4S -- admittedly this was 3 years ago -- the sound of my music camples: piano, string sextet, Diana Krall, orchestral, and vocal + sax was still so harsh to give me an "ear bleed".... But by now, W4S may very well have matured as well. Please note that exactly like proclaiming that all class D amplifiers are inherently flawed constitutes a logical fallacy, so would be the assertion of the opposite... Reality is, that with all topologies, some amps will meet our particular taste in music reproduction, some will miss by a country mile, and some will be somewhere in between. G.
-- |
no human has ever claimed to hear these affects or even describe what these affects would sound like.Plenty have with saying, hard sound, soft sound, lacking in harmonic structure, dead gaps between notes (no harmonics) like the amp has been turned off. There are many that hear these effects, myself also, but like I said before I "could" live with the Belcanto Ref600's, with their in house special filter for the switching frequency, but they were driving an expensive two way with a very benign 8ohm Raven ribbon tweeter load. Cheers George |
Question: If a tree falls in the forest, but no one was there to hear it, does it still make a sound? Answer: Yes, the theory being the tree hitting the ground moved the air and created the sound. Because someone was not there to hear this sound does not mean the sound did not exist. Question: If a class D amp is playing in a system, but no one could hear anything other than finely reproduced music, does noise still exist? Answer: Who cares, although there are theories that state the SMPS and a low switching frequency has affects on the sound in the audible band, no human has ever claimed to hear these affects or even describe what these affects would sound like. Thought this might be helpful, Tim |
Noise needs to be heard to existNot correct, EG: take an opamp for instance, it can oscillate (if not implemented well) at VHF, too high to hear, but it will make a known opamp with smooth sound, sound hard/bright because of the oscillation that you can’t hear. And if the noise is filtered out afterwards then the opamp is compromised and can sound too bland, better off not having the oscillation to start with in the first place. Cheers George |
Hi Tim, I believe someone explained it best when they said that there were two ways that amp makers deal with the noise produced in the audible band due to the switching frequency being too low. One way creates an overly smooth top end with missing detail and the other way creates a hard sound. Either way, both are forms of distortion. |
I've read about all this supposed noise produced by my class D monos due to their SMPS rather than a typical analog power supply and all the noise produced in the audible band due to their switching frequency being too low. However, the only noise I can actually hear is from claims of all this class D noise that no one can hear. I'm no scientist but I understand the difference between theoretical noise and actual verifiable noise and that, empirically, only the actual noise can actually be heard. by us humans. Noise needs to be heard to exist. In my experience, and apparently many others experience, class D amp noise is being exposed as a myth. I have yet to hear from any class D amp listener or user hearing any noise issues. In fact, I have yet to hear any descriptions of how this theoretical noise would audibly manifest itself. I'm trying to keep an open mind but I'm not going to believe in dragons without at least 1 charred sheep or human. Tim |
THD numbers, while appearing to be unusually good, may be partly the result of using too much negative feedback. I’ve never heard this amp, but too much negative feedback and you can end up with a soulless amp.You’ve got that right, anyone who’s had an amp that’s had feedback level control, knows that too much can lead to worse sound, minium is best if you can keep the bass tight extended. I put them on all my tube amps that I made, to do it on s/s can be dangerous. Cheers George |
New class AB amp from Benchmark ABH2 also utilizes SMPS resulting in 132dB dynamic range.They had to cut costs somewhere to hit that $2995 price point. The dynamic range and THD numbers, while appearing to be unusually good, may be partly the result of using too much negative feedback. I've never heard this amp, but too much negative feedback and you can end up with a soulless amp. |
You should do a study to see if class d amp sound quality correlates strongly to switching frequency alone.I have, done numerous bench/listening tests, and tried to come up with my own cascaded output filters like Belcanto I believe did with their 600ref monos, but doing filters this way has a other set of problems (interactive ringing) if your familiar trying cascaded filters for speaker xovers. Mark Levinson with their no53 also tried it but that fell a bit foul with a Stereophile review/measurements. Cheers George |
So much noise about nothing of real consequence. I will of course look forward to improvements in switching frequency under the assumption that things will get even better overall down the road at least on paper. How much difference it makes practically is TBD. George I do think you are too obsessed with this one technical issue. You should do a study to see if class d amp sound quality correlates strongly to switching frequency alone. To hell with all the rest that goes into these things if that is all the story. |
Well, most of people on this forum (including you) think that SMPS is noisy and linear power supply is better. This believe comes from bad rap of noisy crude computer SMPS applications. They don't even realize that "Linear" power supply is a primitive unregulated switcher. I addition, many believe that when something is smaller and more efficient something else has to give (that's human nature). They apply this believe to both SMPS and class D amplifiers (that are basically controlled SMPS). In view of that amplifier manufacturers would be stupid not to keep using "Linear" power supplies. Only few true pioneers like Jeff Rowland had courage to develop state of the art SMPS supplies that are extremely quiet (noise very easy to filter out at 1MHz operation). Even 50kHz SMPS executed well are far better than "Linear" supplies IMHO. |
The main reason manufacturers of high end audio (like Rowland) use SMPS is low noise and line/load regulation. You can find it in FAQs on his (or Benchmark) website. He uses SMPS in preamps where size or efficiency play no role. Yes, top manufacturers still use linear power supplies, but main reason is demand from people who, mistakenly, believe that if it has to be heavy to be good. |
3 of the main reasons manufactures choose use smp (switchmode) power supplies. Size/weight, efficiency, and cost to manufacture. Well designed linear power supplies, are still the supply of choice for performance/noise and reliability. But they are costly and inefficient. If/when I go to Class-D amps, I would also prefer to have a well designed linear power supply powering it. Just quickly two that I can think of that use linear supplies for the best result they believe to power their Class-D amps are. Mark Levinson and Rogue Audio, there are many more from the upper end of town. http://www.stereophile.com/content/mark-levinson-no53-reference-monoblock-power-amplifier#OXQH9C1XSJuv27p5.97 http://www.rogueaudio.com/PDFs/Pharoah.pdf Cheers George |
This is a huge step in the right direction getting rid of another point of noise (the smp), with the added lift of future higher switching frequency/filters and the benefits it brings, would spell the end of all linear amps. And Srajan's tubes below. Practically all supplies are switchers. So called linear are very primitive -switching at 120Hz when voltage is the highest, creating a lot of high frequency noise. Current is drawn in narrow spikes of high amplitude. SMPS on the other hand, when done right, is far better in many respects. It is quiet, switching at zero voltage/zero current. It operates at high frequency that is easy to filter out (much easier than 120Hz ripple) and is line and load regulated (vs. unregulated linear supply). It has fast response to load demands - vs. slower response caused by inductance of huge electrolytic caps. It tolerates DC on the mains (It even operates from DC). Rowland switched completely to SMPS using them for class AB amps as well as for preamps (to lower the noise). Benchmark improved S/N ratio by 10dB by replacing linear supply in their DAC with SMPS. New class AB amp from Benchmark ABH2 also utilizes SMPS resulting in 132dB dynamic range. Why then, designers still use linear supplies with huge transformers and capacitors? For two reasons: First, it is very difficult to design good switcher. Second, they follow market demand - many people believe that it has to be "linear" and heavy. |
They have Ice modules in them minus the power section. The amps have huge analog toroidal power supplies. And massive caps for reserve power.This is a huge step in the right direction getting rid of another point of noise (the smp), with the added lift of future higher switching frequency/filters and the benefits it brings, would spell the end of all linear amps. And Srajan's tubes below. What Srajan Ebaen of 6 Moons said about the H2o M250's In conclusion, I love these amps for different reasons than my tube amps. The emotional connection is still stronger with the valvesCheers George |
H2O Audios' M250 Special Edition Mono Block Amplifiers I saw a question on the forum about Class D amplifiers. Following the question was a comment about how class D amplifiers have distortions and lack of low level detail. I am not here to debate or disagree with anyone but just to tell of my experience with my H2O Audio M250 Special Edition mono block amps. My previous mono block amplifiers were Tube Research Labs GT200s'. My pre-amp was and still is Tube Research Labs "The Dude". The sound was very desirable and I had that sound for a couple of years. During those years they were matched with JM Labs Nova Utopias and then Martin Logan Summit Xs'. The tube amps had the qualities that most tube lovers desire. They have rich harmonic textures, great 3D imaging and are very dynamic. They are triode amps with zero negative feedback rated at 200 watts. I must mention that I also have owned Sonic Frontiers Line Three SE amps, several Krell behemoths including the 650 mono blocks. I am a big electrostat fan and now own the Sound Lab A3 PX speakers. Let me tell you Sound Labs are lightning quick and have tons of inner detail. But to really hear what they are capable of doing they really need an amp that just laughs at the load. Because these speakers are so revealing, any amp that has issues will be brutally exposed in seconds. That is where the H2O mono blocks come in. Boy you talk about power, grip, extension, lightning fast transients, inner detail, low level detail, it is out of this world! These amps just kick butt and have such grace and beauty. They took a long long time to break in but boy when they broke in! Never have I been so pleased with the music these things recreate. They have Ice modules in them minus the power section. The amps have huge analog toroidal power supplies. And massive caps for reserve power. I have a pretty good front end on this system. I have the Ayon transport, Ayon Skylla II DAC, Dude pr-amp. I have WireWorld power cables, interconnects, and speaker cables. My power conditioning is by Triopoint Audio it is called the Orion. Also I have the Tripoint Troy grounding system. The room is very carefully treated with sound treatments. I am just saying there is a great new world out there and most are blown away with what they hear from these amps. A friend of mine that has been in the recording industry for years said "never in his life has he heard solid state amps so free from harmonic distortions" as the H2O amps. In fact he said never has he heard ANY amp sound so beautiful period. I know I am biased but I must agree. Bottom line is do your home work about class D amps. Just like cars or anything else for that matter not all are created equal. |
Nobody can hear 500khz, it the filter that has to deal with it and what’s left over and the byproducts of it that is the problem.What is left over is 500kHz. Byproducts are possible (modulation), assuming nonlinearity of motion, if tweeter can move membrane at 500kHz - no chance. Filter or frequency have very little to do with quality of the sound, IMHO. It is related to quality of the modulator, slew rate of output devices (accuracy of the duty cycle), ringing caused by inductance and capacitance of output devices etc. Actually, increasing switching frequency can make it worse because it will reduce accuracy of the duty cycle - calling for deeper NFB. As I showed before (using 50kHz Lamm amp as an example) phase delay in audio band has nothing to do with extension and, if anything, might be beneficial since most of the speakers accelerate phase (much more) at these frequencies. Also, increasing switching frequency will reduce amount of residue on the speaker cable but at the same time it will make it radiate much better. |
Erik, I agree with you that, if I can't detect any issues in the audible range on my current class D amps due to their switching frequency being not high enough, than there is no need for concern and I should just enjoy them and my music. Actually, this is what I've been doing since I installed the amps, I just tried to intently listen for any issues for a short period when I first heard of this theoretical issue. Once an affordable class d amp with a switching frequency in the 3-5 mega hz range is on the market and there are any objective or even subjective reports that it sounds significantly better than current amps, I'll audition one. I believe this is a more effective approach than not using class D until the theoretical performance benefits of a 3-5 mega hz switching frequency becomes a reality, since the numerous benefits of class D amplification will not be utilized and enjoyed between now and then. I would think just 2 of class D's benefits, sound quality and electricity cost savings, would be sufficiently convincing for many to switch right now. If it's only going to get better, upgrade to class D now and then upgrade again whenever you determine future improvements are worth it. The cost of world-class amplification has never been less expensive,as long as you're willing to be open minded, a bit more adventurous and let your ears guide you. Enjoy, Tim |
I cannot hear 500kHzNobody can hear 500khz, it the filter that has to deal with it and what's left over and the byproducts of it that is the problem. Read the link and carefully try to absorb it. http://epc-co.com/epc/GaNTalk/Post/13752 Cheers George |
I've been living with ICEPower based amps for six months, I don't hear any of the issues being discussed, and my speakers have extension beyond 30kHz. Some folks hear the issues and others don't. Some folks are really sensitive to phase/point source issues or maybe they focus on the image across the soundstage. If someone told me that the image was off, I would just shrug and keep enjoying my gear/music because it's not something that I notice. |
Is there no need to advance in this direction in raising the switching frequency then?? Too many myself included think it is. Quote from manufacturer of these new transitors, who btw invented the Mosfet power transistor. " Higher PWM switching frequencies allow for a higher audio bandwidth, and hence higher-frequency output filters. As a side benefit, this higher-frequency output filter allows for smaller output filter components (especially, the Inductors) without compromising the sonic performance. Cheers George |
What I’ve been trying to get across re the Class-D’s switch noise and it’s associated output filter, trying to eliminate that noise without effecting the audio band. This is a page by the actual component manufacturer that allows the new mega expensive Technics SE-R1 to double the speed of it’s switching frequency, which in turn allows the filter to do a better job, and be less destructive to the audio band. They still need to double it again before I’ll dip my feet into Class-D. http://epc-co.com/epc/GaNTalk/Post/13752 Cheers George |
ultimate transparency / cleaness / hifi is no more their goal these daysThose never were my goals. Although resolution and a quiet background (similar to what you may mean by transparency/cleaness) are expected attributes in higher end gear, excellent tone, dimensionality and dynamics are more important to my enjoyment and, in my experience, it can be hard to find all three in a component. |
Tim, If you can't hear the difference, stop! :) Unless you are a QA professional, learning to tell the difference in equipment you couldn't hear before doesn't lead to better enjoyment. I traded in my class A/AB amps after evaluating class D and finding them inaudibly different. I could not tell blindfolded which I was listening to. I DO see potential for tweeters with rising impedances or high capacitances being too much of a challenge but that's not how I make my speakers. :) Best, Erik |