Ah I see now glofi . Let us know when you get it right.
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
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 |
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 |
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. |
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 |
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 |
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 |
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.
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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 |
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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 |
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. |
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. |
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. |
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
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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. |
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. |
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... |
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. |
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! |
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. |
atmasphere, Good points about class D amps being immune from noise due to their modules or the smps but that RF radiated noise could be a problem for other equipment nearby and even pacemakers and other electronics either within or separate from one's system. I was warned of possible RF radiation about the same time I purchased my first D amp. I read a tip that a portable am/fm radio could be used as a crude detector for any RF radiation emitted by a component. The instructions were to tune to a spot on the dial that is between stations that is relatively quiet, turn the volume control to about 3/4 and move the portable radio slowly around all sides of the tested component. The point being that if the component is radiating any RF signals/interference it will be indicated by the portable radio producing a change in sound once it is in the proximity of any component being checked. I did this test on my D amps on the am and pm bands (since the tipster didn't specify a specific band) and I noticed no changes in sound coming from the portable radio but I hope this was a valid method for RF radiation detection. Seanheis1 stated: " Maybe we will start seeing Class D pre-amps then... " My understanding is that class D pre-amps would not have any significant advantages over traditional tubed and ss pre-amps, that I believe all operate in class A. This is mainly due to the signal amplification being so small in class A pre-amps that heat and energy efficiency are not significant issues as they are in tubed,class A and class A/B amps. Tim |
I read a tip that a portable am/fm radio could be used as a crude detector for any RF radiation emitted by a component. Yes for smps leakage, should also work not that I tied it for Class-D switching frequency leakage. Tune down low and try at different frequencies between 500-800khz on the am/band, so it’s off station not getting a station signal just white noise (some portables mute these are no good to use), then switch on the smps/class-d, and go close to it with the radio, and see if you get a change in sound or level. Cheers George |
Hi all, in olden days, with the NuForce and M312, RF leaks were of some concern... My old FM tuner did pick up hash from the amplifiers if when held less than 2 feet from the power supply of the amps. However, newer amps like the Merrill Veritas and my current Rowland M925 do not radiate at all.... AM and FM bands are not affected at all, not even if the tuner is placed on top and is in direct contact with the amps. Without making a broad generalization, I suspect that FM leakages might today be less common than in the past. Perhaps more of historical interest than anything else. Worth checking out though, particularly when testing older class D amps. Regards, G. on the |
There is about 1% of switching voltage noise on the speaker cable since filter is not perfect but, as I said before, 1/300 wavelength antenna won't radiate. In addition, electricity in speaker cable flows in both directions canceling the most of RF (if any). When you place radio directly on the wire you might get some capacitive coupling, but I doubt it. Many speaker cables are twisted making it completely inefective (better than shield) for electromagnetic radiation or capacitive coupling (both ways - from cable or to cable). |
When electricity flows in two wires in opposite direction it tends to cancel radiated EMF or capacitively coupled noise. Same goes for receiving - the closer two speaker wires are - the less susceptible they are to pick up anything. Twisted pair exposes both wires symmetrically to external fields making them almost immune to coupled or radiated noise. That's why in any circuit design signal and return should always go closely together to avoid any loops. The point of my post was that cable (two wires where electricity flows in opposite direction) is a very poor antenna for radiating and receiving. Twisted pair is practically no antenna at all. |
There is about 1% of switching voltage noise on the speaker cable since filter is not perfect but, as I said before, 1/300 wavelength antenna won't radiate. In addition, electricity in speaker cable flows in both directions canceling the most of RF (if any). When you place radio directly on the wire you might get some capacitive coupling, but I doubt it. Many speaker cables are twisted making it completely inefective (better than shield) for electromagnetic radiation or capacitive coupling (both ways - from cable or to cable). You may find this of interest: https://www.maximintegrated.com/en/app-notes/index.mvp/id/3977 scroll down to: Minimizing EMI with Spread-Spectrum Modulation |
There is about 1% of switching voltage noise on the speaker cableYou need to rethink this. Look at the switching noise ringing on the test square waves Stereophile show when they don’t use their special Audio Precision’s auxiliary AUX-0025 passive low-pass filter to hide the switching noise ringing from view. This is what’s on the speaker cable on the $7K Anthem Statement M1 monoblocks, and it more like 20% of the wave form. Without Audio Precision’s auxiliary AUX-0025 passive low-pass filter http://www.stereophile.com/images/1212AM1fig02.jpg With Audio Precision’s auxiliary AUX-0025 passive low-pass filter http://www.stereophile.com/images/1212AM1fig03.jpg Cheers George |
Stereophile test shows about 0.5Vp-p - that is about 1% since switched voltage is in order of 50-80V. It comes from the fact that output filter is 2-pole making it -40dB/decade while switching frequency is about decade above filters cutoff frequency suppressing noise by 40dB. -40dB is 1% As I posted before, speaker cables have no chance to radiate for many reasons. Tweeter won't play 500kHz, not only because of membrane inertia but also because of its impedance rising extremely high. |
Sorry your wrong kijanki, the switching frequency to signal ratio follows the signal level in a proportional manner. and that 20% pod SF noise in the links I provided above, the SF noise does not disappear at certain levels of playing, it stays proportional to the level your playing. And I didn’t ask you about tweeters playing 500kHz, but seeing you mentioned it, ask the poor sod I had to replace both the Wilson 8’s tweeter diaphragms on, because they were blu’ed with heat abuse from this 500kHz noise. They still worked but never sounded quite right, but they did when I replaced them. BTW he won't use a Class-D again, until he's convinced that the SF noise won't harm his tweeters again. Cheers George |
You might damage membrane from overheating, but most likely not from 500kHz switching frequency. As for switching frequency level following signal level - your understanding of class D output is poor. Amount of switching noise is constant independent of the signal level and in your Stereophile example equivalent to power of 4mW (of inaudible frequency) on 8 ohm speaker. This switching noise is only dependent on the switching frequency and the filters cutoff frequency. Amplitude of the music signal has nothing to do with it!!! If anything, switching noise at extreme duty cycles will be lower. Signals of 10% or 90% duty cycle represent lower amplitude (in comparison to no signal represented by 50% duty cycle) of the root frequency (500kHz) and a little bit higher harmonics. After filter amplitude of 500kHz will be lower (and not higher) at high music levels. |
I’ve seen it on the scope, with Nuforce 9se V3, you need to see it for yourself. Lower or raise the signal level at the same frequency, then increase or decrease the scopes sensitivity to the same visual appearance, and you’ll see the SF noise remains the same. Forest and trees sunshine. BTW it was this amp that gradually cooked the WP8’s tweeter voice coils, and the owner (a reviewer) was never abusive with high level, if anything he was anal about playing too loud, he now ones Gryphon Antillions, and has not looked back at Class-D. Maybe in the future when they can rid this SF noise demon totally without any effects down into the audio band, even he concedes to this after what he went through. Cheers George |
I'm not sure what NuForce are doing. It is possible that they adjust supply voltage to signal level, but that would only mean much lower noise (than for instance Icepower) at low signal levels. Noise level at max loudness would be the same as for the amp that doesn't do that (assuming same switching frequency and the filter) - equivalent to about 4mW on 8 ohm speaker. Icepower doesn't adjust the rails and I'm pretty sure Hypex uses constant supply voltage. With constant supply voltage amount of switching noise at 90% or 10% duty cycle would be most likely 1/2 or even 1/3 of the one at 50% duty. |
