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?
You mean allowing the listener to feel the musical emotions? Like how the Atma-Sphere amplifiers and pre-amps does in spades :-)
Class D has never given me those intimate feelings during musical playback however for Studio recording, tracking and mixing on large studio speaker it can work, for Large Pro Audio Speakers it works even better. For Audiophile level setups i am not yet sure but i have not heard them all.
I have Class D Quested Amps setup for Home Theater use, powering up my Quested Rear channels all 12 of them with out a hint of strain, and it does a fine job. However my main front LCR Speakers use Active setup Class AB Quested Amps.
I Would like to Hear a Class D amplifier paired with a 300B Tube pre-amp.
Try to sell everyone, I'm sticking to cars and subs, been in this game a long time, I also worked as a stereo salesman, this means nothing, been in this game too long, between my brother and I, we have probably had every brand which is worthy under the sun. a good a/b amp is by a country mile, just better. I will keep my ears open for a good class d sound, but so far there are several missing components of the sound they make, and yes, on multiple speakers/sources, preamps, missmash of components, cables, name it , my brother has probably owned it at one time.
Sure, they are cool running, gobs of power, small footprint, etc etc, but the sound............it is just, not there. There is no sparkle, rapture, goosebumps, whatever silly names which are used.
If YOU, like them, awesome, enjoy them, I know they are not for me
and as far as the belittling names, sterile, heartless, soulless, etc etc, so not the case in ANY amp I have listened to.
Recently acquired the NAD 12, which uses the NCore technology, along with M22. Best sound I've ever heard. Clean, focused, powerful, clear as a bell. As an aside, I use some powered PMC monitors for recording and read somewhere that they use similar power modules. That would explain the similar clear and detailed sound I heard through those.
Might not be as much fun for you audiophiles, but I think this may be the technology of the future.
I usually don't have the time to read these much less chime in on these things but I can't resist here. Those that say D amps are for Cars and Subs don't know what they're talking about (sorry). I have been in the hobby for 25 years and been a dealer as well. I have owned many amps throughout the years and have reached audio nirvana with a Red Dragon pair of M1000 monoblocks and a Prima Luna preamp. I have two other friends that have been dedicated hobbyists for many many years (one of which was also a dealer for 15 years) who have become believers too. One owns the AVM MA3.2's and the other owns H2O monoblocks. Both pair them with tube preamps. Two others class D amplifiers that I know are incredibly musical.... the Peachtree Nova 150 and 300. Another friend of mine owns the 150 and he's never been happier. I heard the 300 at Axpona last year driving a $20,000 pair of Martin Logans and was creating one of the best sounds at the show. The other brand is Primare. Only heard it at a show but again a sound that no one could say wasn't incredibly great musical sound that was hard to pull yourself away from. Class D was for cars and subs only five or ten years ago but they ARE up to par NOW. Set up properly they will exceed your wildest audiophile dreams. At the end of the day there is more than one way to skin a cat my friends. It's what can make hi-end audio so fun and also very frustrating at times. Happy Listening!
OK Guys, I have a whole different approach to this Class D issue. While I have a beautiful sounding stereo setup, I like variety. So I recommend you buy the Topping 80W per channel amp on Amazon for $200. It uses Class T technology (Tripath) that is used in the evo versions of Bel Canto. Looping technology is the key to making class D work today, and this little amp is stunning and is cheap enough were you can hear something different while waiting for the ultimate realization of Class D.
And for those of you who care, I use Soundlabs U-2 (6' electrostatics) with custom modifications normally powered by custom 6C33C based mono-blocks, Audioquest Sky interconnects, Custom pre-amp with OTL and transformer selectable switching and variable capacitor loading in OTL mode, Wadia DAC, etc. And yes, I do use the tube amps in the winter here (Denver) to warm the room as it cuts don on the time the forced air heat is running, which causes a bit of annoying background noise.
The P49 has been designed to leapfrog the competition with a massive 200 watts per channel into 8 ohms and 400 into 4 ohms. It delivers 50 watts in pure class A mode while allowing for huge extra power reserves from our latest generation class G topology that is both clever and efficient. During normal operation, distortion is measured in less than one part per million so that this massive power is deliver with total control and finesse.
There have been great strides made in improving audio sources and loudspeakers in recent years and the time is right to match them in the field of amplifier design. This ground breaking amplifier is a must audition amplifier for music lovers who understand that power is nothing without control.
Interesting discussion. Can someone suggest a low-cost "bettter" Class D amp for use as a 'mid-fi' system with consumer-grade speakers for elderly parents who like to listen to music, but don't "LISTEN" to music as we do?
I own NuForce mono block class D amps. They were cited by Absolute Sound as "amp of the year" several years ago. Combined with a tube preamplifier and old Dalquist DQ 20 speakers, the sound is remarkable. I listen mostly to Classical music and find the rendering more lifelike than with any other amp I've owned.
In my personal opinion, I think the very best sounding Class D amp out there right now are the Classe Sigma Mono's. However, I still think a Class A, a Class A/AB, or a Class AB amp will still at this point in time beat sound wise any Class D amp, but I'm talking Class A amps of the high end order vs Class D amp also built by a high end manufacturer. Of course a high end manufacturer's high end Class D amp will beat a mid-Fi companies Class AB amp. I don't think any mid-Fi or low-fi company builds any pure Class A amp's as I'm sure all of us already knows that.
I have a couple of Class D integrated amps: Peachtree Nova125 & NAD Master M2. They are very different in quality IMO.
The Peachtree soundwise is pretty good. Perhaps, it does have a little harshness some associate with Class D when compared to good Class A amps. However, I may have a unit specific problem with the DAC portion, which may be to blame for this (I will have to sort out with Peachtree). It also can get slightly congested with complex passages (bands & orchestras) at higher volumes. At it's price point, it does an excellent job. There would not be many/any Class A amps at this price, unless you bought some older, used ones. It also does have a great feature set for digital inputs (only one analog).
The NAD M2 is a very, very, fine amplifier. It is not a typical Class D amp, more of a powered DAC, using a relatively new technology. It is very musical, which is not typical in Class D amps. It is absolutely dead silent when no signal is played, which makes it extremely dynamic. Very detailed, excellent bass control, mids are rich and authentic. Makes high quality recordings sound exceptional. Given that it all you need is a source, the M2, and speakers, it is extraordinary value. (See glowing reviews in Stereophile and Absolute Sound that explain the technology)
Main drawback of the M2 is that it does not have a USB input, so a S/PDIF bridge is required in that case. It does have both RCA & XLR analog inputs if required. The analog signals will undergo an A/D conversion because everything is digital in the amp, so purists may object. Personally, I don't notice any degradation when fed an analog signal.
IN summary, the Peachtree is good value for the price, but (with my unit) may not satisfy those willing to spend big dollars on high-end Class A or Class A/B amps. The NAD M2 (costing several thousand more than the Nova125) is a good challenger for Class A & A/B amps costing quite substantially higher. Definitely worth auditioning. I believe it is no longer manufactured, but newer NAD products will use the technology.
Class D amplifiers are good at delivering lots of clean power, that's true , but you listen to speakers driven by them . From my perspective the best sound has a seemingly limitless low level resolution and quickness where you can hear very far into the distance with what I call " the breath of life ".Everything sounds so real . High sensitivity loudspeakers do that the best and don't require tons of power . You choose your power amplifier to suit your loudspeakers , not the other way around . There are two new David Berning ZOTL amplifiers from Linear Tube Audio at 10 and 40 watts that offer enough power if you have the right speakers . I've only heard an older ZH270 and that's got the best sound I've yet heard . Would love to hear the newer designs.His designs are not class D , using tubes operating at radio frequencies , extracting the music signal from the carrier wave for dynamic , effortless sound .Reviews can be found .
As far as I'm concerned the best Class D amps made today are the Mola Mola Kaluga Monoblocks, which I own. They have ZERO of the nasty sound behaviors people always seem to cry about when ever the topic of Class D technology comes up. It wouldn't surprise me if 99% of people who always crap on Class D base their opinions on hearing sub $2k examples of B&O ICE tech of yesteryear or even worse, are just parroting what they read elseware of other oblivious folks who fall into the previously mentioned 99%.
At the end of the day, you get what you pay for. Those mentioning issues with switching frequencies have no idea what they are talking about. Can you really tell me with a stright face that you can hear a 500Khz switching frequency and that you have a speaker that can reproduce such a sound? Come on people!
A drunk ran a stop sign and T-boned my car, totaling it, back in July. I had a lower back injury that was really painful (bulging disk into my sciatic nerve); its only now healing to the point that I can dress and move in a normal fashion.
Oh, wow! Sorry to hear about this, Ralph. But of course I’m glad that it wasn’t even worse, and that you are progressing toward normalcy.
We practice pragmatism, not ideology.
No wonder we usually agree about things in the discussions here. In a past thread I recall describing myself as neither a subjectivist nor an objectivist when it comes to audio, but rather as a pragmatist with a technical background.
As far as the subject matter of the thread is concerned, I have no experience with class D, and nothing in particular to offer in the way of comments.
Ralph, I’m glad you making progress in your recovery. ThankGod for seat belts and air bags. I’ve witness people make significant improvement with physical therapy (and time) following a major MVA. Charles
Tube amps generally require certain speakers that are an easier load and more efficient to shine.
This is true of all amps including class D. You can see it in the specs. If high end audio reproduction is your goal, there is no argument for a speaker that's hard to drive. The last thing you want to do with **any** amplifier is make it work hard!
Ignore the pronouncements of any manufacturer who is committed to any particular topology -- Hello Atma, how doing?
Fine, thank-you. A drunk ran a stop sign and T-boned my car, totaling it, back in July. I had a lower back injury that was really painful (bulging disk into my sciatic nerve); its only now healing to the point that I can dress and move in a normal fashion.
In case you were not seriously asking about my health, it might interest you to know that we've been studying and working on class D for some years now. So you might want to re-think your notion that we are 'committed to a particular topology'. We practice pragmatism, not ideology.
My experience is similar to some others here and well-stated by timrhu,
I stopped with the almighty NCore amps. They almost always sound impressive at first listen, clean, quiet, and cool running. For me though, they begin to show their true sound after a month or so. I've given up on them.
In my case, it was a fatal flaw similar to that described in the review of the Mola Mola Kaluga by Mono & Stereo. I had no problems with high frequencies and for me it was more about inner dynamics and the presentation sounding whole instead of like a grouping of individual sounds...sort of like the difference between a band playing live and the same band creating a recording by dubbing one player over the other until finished. Sorry it is hard for me to explain, but the Class D Ncore just didn't sound as musical or involving, although they were clear, quiet and had excellent bass. I really wanted to like them best but kept thinking something was missing.
So, what sounds better? The Class D I owned for over a year was the Acoustic Imagery Atsah, which is the Ncore NC1200 modules in CNC-milled aluminum boxes, very similar to the Merrill Veritas. At that time, I owned four amps. What I liked better were; Lamm M1.2 Ref - Class A McCormack DNA-2 LAE with full SMc modifications - Class AB Clayton M300 - Class A
I still own the last two and in my system playing Aerial speakers the Clayton monos (300/600 wpc all in Class A) were easily the best sounding of the bunch IMO.
Guido, I understand your practical advice. However, companies such as Bel Canto & Rowland don't make Class D amplifiers. They take Hypex or Ice Modules and make mods to them so they can add their house sound. So, I think that Class D can be discussed as a topology. There is general agreement that the sound of Class D is improving, which is to be expected since this is a high tech product.
Guido, thanks for the very practical and level headed advice. I suspect you have more experience with more Class D amps among others than most anyone, plus as far as I know you do not have any particular financial interest in any particular product line or type, so together that all means a lot.
I agree amp type alone means little. Its all in the execution as usual. Not just of the amp but matching system as a whole. There are many options of all types, some better than others and all surely somewhat different. Its best to understand something about them all and then decide. No one type will likely ever own 100% of the pie. But I suspect Class D will continue to own an increasing larger slice over teh next few years anyway. Who knows what might come next after that?
To the O.P.... Whether or not class D amps are inherently better or worse than any other topology is a false problem.
Rather, with class D amps, like with any other topologies, you are bound to find amps that are of your liking, and others that you will hate with passionate abandon.
The key is... Set your budget, and then... Use your own ears to evaluate and determine what you like!
Ignore the pronouncements of any manufacturer who is committed to any particular topology -- Hello Atma, how doing?
Ignore those who attempt to denigrate a class of operation as a whole, be it D, A/B, A, or tubed, particularly when they are basing their pronouncements on measurements, graphs, and specs.
Like any other technology, class D amps range in price... From less than $1K, to at least $60K... Some amps -- -- might sound a little non-denominational, and might sound even sterile, without much sublety. Other ones, even modestly priced, are amazingly subtle and musical.
One thing to bear in mind, is that class D amps are bears to break in... The wonderful old Bel Canto Ref 1000 Mk.2 took a relatively modest 600 hours to deliver its best, but my NCore-based Rowland M925 monos took about 1500 hours to achieve thier top magic.
I adore my class D Rowland M925 monos without reservations for everything they do... In my opinion, their resolution and seductive grainless musicality is in the same league of the big Solution class A/B amps and the ARC 800 tubed series.
I have no interest in "upgrading" to anything else at this time, as what I heard this far would be, at most, a lateral move... On the other hand, at some future, I might indeed "upgrade". But whether this process will take me to a class D device or a class A/B device remains an open ended question.... I will evaluate, and will decide which gives me "magic" close to my heart, and which manufacturer offers me confidence.
But I admit... in spite of class A and big tubes being as capable to deliver sound that I would adore, There will probably be no pure class A amps in my life... I have no symphaty for inefficient heat generators... Nor will there be big tubed amps, because I have no intereest in tendeng and swapping sagging or burnt-out tubes.
Admittedly, I have limited experience with Class D. About three years ago, I bought a Peachtree Nova 125. At first, I loved the 'sparkle' that it produced at the high end. But shortly thereafter, I kinda got tired of it. I felt like I was listening to music much less than before. When I replaced my speakers with BW CM10, the brightness was too much to bear.
I replaced the Peachtree with a Parasound A23 (I now own A21 BTW), and the difference, at least to me, was night and day. The music was much more balanced all the way. I listened longer and enjoyed my music more than before.
Perhaps other brands, or higher price points, yield better results. I don't know. But I was not all that impressed with Class D.
I recall when I was in college I could hear well to 20khz. I know because I ran tests.
I also found it much harder to get sound that was not fatiguing. This is back in analog days even.
These days I know I cannot hear to that extent which is normal for ears my age. I find listening not fatiguing at all and can listen enthralled for hours and not want to stop. With most any kind of music or recording. Well except the occasional really bad modern loud pop mp3. That’s what its all about. Maybe there is some advantage to getting older after all.
Any young cubs out there still with golden ears out to 20khz? I’d like to be able to associate what people like to listen to with their age and measured hearing which becomes less extended for all as one gets older. I suspect a big correlation there.
Again, switching noise is inaudible, unless anybody can hear 500kHz. Even bats won't hear it. I'm not sure why is it so difficult to understand. I addition tweeter's membrane won't move at all. Personally, I have problem hearing 20kHz. As for the bandwidth - in my amplifier it is set to 60kHz -3dB. Different sound, more tube like, of class D amp can be explained by low TIM distortion, often responsible for the sharp splashy sound (added higher order odd harmonics). Class D is in fact so clean sounding that sibilants, for the first time, still strong are very clean and wonderful sounding on every record.
Somehow people cannot comprehend that class D amp is purely analog and switching itself is inaudible. Switching is present all the time - even without input signal. Place ear against the tweeter and you will hear very low typical amp's hiss - likely much less than with any class AB amp. From the sitting position nobody will be even able to detect that amp is ON.
I'll cast a vote with mapman re a D with a Walsh driver. Although it's just a 'dinky' driving two pairs of my smaller DIY versions, it's a good fit. As long as I don't get exuberant and crank it to clip, it's amazing to me how well it 'fits' them.
They'll improve as time goes on. Pretty soon the electronics will shrink to near invisibility and we'll be left with just the interfaces and the radiators. I'm working on the latter, myself. *S*
Cymbals, for instance, sound more "brassy" and less "splashy". To me it sounds more natural, but it might create false impression of limited extension.
If the switching noise output filter is set at a higher cutoff so to make the amp look to be flat to 20khz on test this will sound hard. If it's set lower to try to rid most of the switching noise, this will already be rolling of at 10hkz and therefore rid any cymbal harmonics, this will sound more natural but not very extended. So your compromised either way, the only solution is a much higher switching noise so it can be cut out totally with the output filter without effecting the audio band at all.
Mapman, high frequencies are different for sure, but not for the worse. Cymbals, for instance, sound more "brassy" and less "splashy". To me it sounds more natural, but it might create false impression of limited extension.
George not much buzz on the new technics gear yet. Maybe to come. I was in their room at Capital Audifest but they kept talking about the gear and did not play it while I was there. I wanted to hear and was disappointed. Nobody had it in their best of show list that I’ve seen.
No doubt higher switching frequencies done well is better. How much better practically in regards to what can be heard is TBD. I will say that each newer generation of Class D gear does seem to only improve so not at the end of the road yet.
I try to hear these high frequency artifacts in my Class D amps that I’m supposed to hear and have not heard it yet. So if it exists it is not blatant. At least to these 57 year old ears.
Again there is often more noise at the highest frequencies human ears can hear than music. So perhaps its an error of omission mostly to the extent present at frequencies that really do not matter much for listening to music.
Take a look at the audio frequency chart and you’ll see what I’m talking about in regards to at what frequencies music mostly all occurs.
Nuforce/Nuprime appoaches Class D differently and is most appropriately called an analogue switching amplifier. I have tried many class D and the Nuforce/Nuprime designs beat them all plus all Class A and AB that I have listened to. They are the most musical in my opinion and that is with a rig with 60K speakers and other fine equipment - give an audition. MY Nuforce Reference 20's are liquid, fast, controlled and natural in the highs
Correct, and Technics are showing the way with the SE-R1, why strive for higher switching frequencies by deleloping their own components, if what we have off the shelf is "good enough". Technics knows and are doing something about it, they can see the forest through the trees.
And like I said when they do get the technology to make it much higher I will be the first to change over, till then I’ll stick with linear for hiend amplification.
George , I did put my ear to the tweeter and I can hear almost complete silence - much better than class AB amp I had before. I'm not surprised since tweeter membrane has no chance to move at 500kHz.
Modern SMPS are much quieter than linear power supplies that, in reality, are very primitive noisy switchers operating at 120Hz. Modern SMPS switches at zero voltage/zero current while much ripple is much easier to filter out than 120Hz, that requires huge amount of capacitors (that produce unwanted inductance that is in series with the speakers). In spite of all capacitors linear power supply in power amps is unregulated. Because of that Jeff Rowland does not use linear power supplies at all. He uses SMPS even in preamps to lower noise floor. Benchmark replaced linear power supply in their latest DAC with SMPS lowering noise floor by 10dB.
Mapman is right - you're not sold on class d yet. I enjoy my class D amp immensely. Efficiency is not that important to me (but it should), but is always welcomed as added benefit.
I am going to chime in here in favor of current class D amps, with a big thumbs up! I have been in the tube amp camp (both SET and others) for 20+ years, and now I am happy as can be with my Red Dragon S500 amp. No, it's not like a tube amp, but it's not SS sounding either. It does so many things right, and hardly anything wrong, that I can easily live with it. All topologies have their pros and cons. Throw a tubed preamp in front of a Class D, and there you go!
Ok George we get it. You aren't sold on class d yet. Others are. Mine sound great and no faults I could point to when listening. They just make sweet music as said.
Great thread. I'll add that Class D amps are extremely sensitive to power source and power supply. To hear the best the technology can offer, you would have to pair it carefully with a matching quality power cord and possibly a power conditioner. This took my NCores to a whole new level (refinement, bass, micro detail, etc) and brought out the musicality that had been lacking.
Just a couple of quotes from other Stereophile measurements personel.
I dislike measuring amplifiers with a class-D output stage. This is because such designs can throw out enough ultrasonic noise that you can never be quite sure that what you’re actually measuring is the input stage of your analyzer being driven into slew-rate limiting. What I do, therefore, is to insert, when appropriate, a sixth-order low-pass filter set to 20kHz or 30kHz between the output of the amplifier and the analyzer. But you can see from this graph how the amplifier’s ultrasonic output rolls off rapidly, presumably due to the low-pass filter necessary to minimize the HF noise produced by the switching output stage
Here is just one of many that Stereophile tested, not using their test filter. It’s more than 1%. And this Class D had a linear power supply as well, most use smd now which creates even more other noises as well.
Let me add that while I do concede that my engineering knowledge falls short of what many of you possess, there's still a lot of bat guano peddled on these forums. I like it here, and there are some very smart, very cool, very interesting people that I've learned a lot from, but oftentimes this forum is to audio knowledge what Fox News is to global news coverage. Sometimes after I visit I have to remind myself that I didn't just spend 10 minutes on Shutter Island.
This small residue (about 1%) has no effect on the sound
Put your ear to a wide bandwidth tweeter, you will hear it’s poluting artifacts. If not the filter effects is set very low to cut way down to 10khz or even less, creating all sorts of other problems.
George, I looked at the link you provided. Yes they use filters for the purpose of measurements to eliminate residue of switching frequency that is otherwise completely benign. This small residue (about 1%) has no effect on the sound. Speaker membrane will react (move) to its average value only.
I don’t buy the "gas guzzler" A/B vs. "green" class D arguments for the latter. Kilowatt hours are cheap and relatively clean until you pile up a WHOLE lot of ’em. With typical audiophile usage patterns, and the fact that we’re a VERY small segment of the population, there’s no significant ecological impact here.
According to this pouring used car engine oil to kitchen sink is OK (does not have environmental impact) since very few people do it.
And as far as ecological impact, class D probably makes things worse overall, due to the fact that audiophiles ship ’em over, decide they don’t like the sound, and then ship ’em right off again
I have two integrateds, an Audio Research VSi55 running KT120s and a Peachtree Grand X-1 (Class D). Through both pairs of speakers I own, Wilson Benesch Arc and BMC PureVox (both retail for $6500, whether these qualify as low-fi, mid-fi or otherwise is a matter of perspective and budget), I'd choose the Peachtree every day. It sounds every bit as nice as the Audio Research, but runs cool, keeps the electric bill low, and takes up very little space while putting out huge power. I guess admittedly there are a few cold days each winter where it's nice to use the Audio Research to both play music and heat the room, but otherwise it collects dust. So I guess in my case, the future arrived 3 years ago when I bought the Peachtree.
All that stuff about switching frequencies and flux capacitors and quantum math, I don't know anything about that. I just press the power button, hit play, and sweet music comes out. For all I know there's a team of hamsters inside the Peachtree playing little tiny violins. I leave all that stuff to you engineers...if it sounds good, that's all I need to know.
If you want to be eco friendly, and be a little compromised at the moment, then sure get a ClassD. Or pay the bucks and get "maybe the new Technics SE-R1 Class D". http://www.technics.com/us/products/r1/se-r1.html#overview Cheers George
I don’t buy the "gas guzzler" A/B vs. "green" class D arguments for the latter. Kilowatt hours are cheap and relatively clean until you pile up a WHOLE lot of ’em. With typical audiophile usage patterns, and the fact that we’re a VERY small segment of the population, there’s no significant ecological impact here.
The extreme case would be a 100+ Watts pure Class A amp user, who leaves amps on 24/7, switching to a class D amp. Then yes, you’re going from a $1,000+ yearly power bill to like 100 bucks. But that’s an outlier. With more sane usage patterns -- e.g. a class A/B tube amp that you turn on/off as needed -- the difference is close to negligible. And as far as ecological impact, class D probably makes things worse overall, due to the fact that audiophiles ship ’em over, decide they don’t like the sound, and then ship ’em right off again.
I agree with George that switching frequency should be increased, since 50-60kHz bandwidth limitation introduces around 20deg phase shift at 20kHz (causing wrong harmonics summing), but I’m not even sure I can hear such nuances. There are many highly praised amps that have similar bandwidth, I’m sure.
Switching frequencies are up around 600-800khz at the moment, except for that Technics above. The problem is the switching noise output filter has to handle the full power of the amp and can only be low order, otherwise it will burn out. And being low order it has an effect down into the audio band. If the switching frequency is 3-5MHz then it can do it’s job well away from the audio band without having phase, fr, ect limitations effects .
Just look at the ringing artifacts in Stereophiles 1kzH square waves of Class D, they now test with a inline heavy filter to make this (ringing) disappear, that Audio Precission’s filter they use makes the test wave look clean, but it’s a con job as it’s done at very low power so it doesn’t burn out, in real use it would last a microsecond. I have asked JA to include both unfiltered (normal) and filtered square waves, just so readers can see the real deal. Read comments at the bottom of the page, no answer from him. http://www.stereophile.com/content/bel-canto-eone-ref600m-power-amplifier#G7miwIhm5pj5EDlK.97
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