Class D Technology

Power supply is no less important with class D than with other amps.   A lot of vendors focus on optimizing it and it is a common theme among better reviewed and received designs. 

Atmasphere why does 200khz bandwidth matter if there are no sources practically (record or CD res digital) that can even come close to delivering it today?

I did explain this in my post but here it is again:

In order to reproduce phase correctly bandwidth is a requirement. Put another way, if the bandwidth is not there phase shift is the result. You are correct that digital doesn't have bandwidth and that is one of the reasons that the LP sounds better and is still around after all these years of being 'obsolete'. Nevertheless, to prevent phase shift in the amp you need bandwidth even it its not there in the recording. In fact the recording doesn't matter.

To put this another way: phase shift components can be heard to 1/10th of the cutoff frequency. So if you are cutting off at 20KHz there will be phase shift to 2 Khz. 100KHz cutoff means that phase shift will exist down to 10KHz. We older adults don't hear so well at 10KHz so you can sort of get by with 100KHz bandwidth but if you really want to do it right you better have 200KHz so your kids will like the stereo (unless you're the type that just wants them off your lawn...).

What prominence does the heft of the power supply play in the sonic performance of Class D amps relative to SS or tube amps?

The supply should be clean else IMD components related to the noise in the supply and the scan frequency will show up in the output. IMD is pretty audible to the human ear (shows up as brightness and grit or 'grundge'). Since the scan frequency is pretty high the power supply had better be properly bypassed to be effective at the scan frequency! But it can't have any sawtooth going on either. Otherwise the supply has to be able to support the operation of the amp at full power, even though most of the time the supply will see a fraction of the current draw that a traditional amplifier supply would see, so most of the time the power draw from the wall is minimal.

Traditional power supply design or SMPS is irrelevant so long as the supply is quiet (SMPSs have the advantage of being easier to regulate...).

Assuming nothing is there to start with isn't a phase shift of 0 = 0?

I did not know vinyl has frequency bandwidth so high.    Most home hifi always talked of 20-20K frequency response.     Is this in practice or theoretical?   I'd agree theoretically vinyl could do more but practically its news to me.   The best digital (higher res) sounds as good as most vinyl to me these days.    RTR is better but look where that got us practically.

Also what is the math relationship between bandwidth and phase shift? Where does 10X bandwith number come from? is there something akin to Nyquist that is used to determine this? Did the engineers making high end Class D amps miss the boat on this somehow? it does not sound like they did in practice based on listening, at least the good ones seem to know what they are doing.

From my perspective there is understanding the theory which is useful and how things sound, for which there is no mathematical equation to properly represent that. Pundits focus on the strengths of a supporting theory and skeptics the weaknesses. No approach is perfect and holds all the cards. That’s clear by the variety of successful amplifier designs out there today.

Ralph sounds like you are actively prototyping your own class D designs? that tells me you think there is in fact something worthwhile there if done right.

Dear Audio Friends,
I write this as one who is rather un-technical but possessing excellent 'ears'.;-)
As one of the few who have all 3 main amp designs in house and active in-system, and who owns 6 pair of priastine and extremely detailed Apogees, including a purely1 ohm Scintilla pair completely rebuilt by Rich Murry of True Sound Works, I am making a rare post here to clarify a couple of things re my experience with amps of all persuasions:
In my room as I write this I have 2 of Henry Ho's H2O SE amps driving my Scintillas, and the staging, imaging, frequency response and range are world class. I gave up a pair of beloved Class A Nelson Pass XA100.5s for them, as I could tell very little difference whiule getting some serious power benefits for my room and speakers. Please note that Henry Ho first made his name as a successful and well-reviewed Class A amp builder, and his Class D amps have Class A grade power supplies. They weigh 60lbs each, and mine have some extra-fine caps, to boot.
I also have a pair of custom Bob Carver built-for-me-by-Bob-Himself KT120 tube amps that he designed specifically to drive 1 ohm Scintillas. They have a 1 ohm tap, and sound exquisite, with a slight wider stage and image than the H2Os, but not as tight a control over the transducers, of course. These are NOT like my Kronzillas which, though superb and with unrivalled detail and finesse on my other Apogees, can NOT drive a 1 ohm Scintilla - nor would I ever try!
I have other amps, hybrid Vincents, Wyred4S SX500s, a fine Class A Coda 3.2 Stage, and the H2O and Carvers out-do them all by a wide margin in every particular.The only exceptions at all are the T1610-tubed Kronzilla DX MkII monos.

I hope my personal and ongoing experience with these amps might lend a bit of boots-on-the-ground substance to an otherwise thorny and subjective discussion.

My final and main point, really is this: From my experience it seems - and I have discussed this in detail with both Bob and Henry - that each style and design philosophy has its strengths and weaknesses: HOWEVER, as the designs and designers progress to the pinnacle of what is possible to each, the differences become a matter of diminishing returns. They each become less distinguishable in a blind test, with almost equally transparent and less 'visible' between listener and music.

That is and has been my experience.
All the Best

shibui,

Sounds to me like you pretty much nailed it in all regards based on actual experience seeking the best sound possible with some of the most challenging speakers to drive well ever.

That a Class D design can even compete in that arena says all that needs to be said really. There is no reason to categorically reject the approach. From there it comes down to personal preferences and case by case details that vary widely most likely. Plus things can only continue to get better as/if needed as bandwidth continues to increase over time. Better performance always tends to come for additional cost. class D is no different there except it lowers the price barrier for what most would consider good performance especially when more power is needed to get the most out of less efficient speakers. Ability to get the most out of more challenging speakers is the primary value added use case for Class D these days I would say though I find the newer ones to be top notch as well with easier load speakers I own. Class D has kept me from pulling the trigger on a tube amp now (and associated speaker changes that would be needed) for several years.

Also what is the math relationship between bandwidth and phase shift? Where does 10X bandwidth number come from?

Hi Mapman,

If I'm not mistaken class D amplifiers typically use an output filter consisting of a series inductor and a shunt capacitor.  Together with a primarily resistive load that will form what is known as a second-order low pass filter.  "Second-order" meaning a filter that increases the amount of attenuation it provides by 12 db/octave (12 db per doubling of frequency) above the frequency at which it has rolled off by 3 db (that frequency usually being what is referred to as the bandwidth of the filter). 

The equation defining the phase shift introduced at various frequencies by a second order filter is complex, and is shown (approximately!) as equation 3 on page 2 of this reference.

To provide some perspective, however, it may be helpful to consider the much simpler case of a first order filter (6 db/octave rolloff), which is what would be formed by the combination of a series inductor and a resistive load, without the capacitor.  A first order low pass filter will shift the phase of a given frequency f by an amount equal to:

Phase shift = arctangent (f/bandwidth)

So a first order filter having a 3 db bandwidth of 200 kHz would shift a 20 kHz signal by arctan(20/200) = 5.7 degrees.

The 10x figure is a rule of thumb, as Ralph indicated, chosen to limit the phase shift introduced at frequencies of interest (e.g., at 20 kHz and lower) to amounts that are presumably inaudible.

It should also be understood that while for a pure sine wave at a single frequency any amount of phase shift will be inaudible, a musical note consists of a combination of many frequencies that are simultaneously present.  And the goal is to achieve proper alignment of the timing of all of those frequency components relative to each other.

Best regards,
-- Al
       

Assuming nothing is there to start with isn't a phase shift of 0 = 0?

Nope! The point is that if you don't have the bandwidth in the amp it will cause phase shift at lower frequencies- down to about 1/10th the cutoff frequency is then its considered negligible (of course, 'negligible' by whom is a different story; obviously some designers don't care about that so much). IOW the ear might hear 20-20KHz but to reproduce that in an amplifier without phase shift you need 2Hz to 200KHz if you really want to do it right (the same rule applies on the bottom end; otherwise the bass loses impact due to phase shift). For this reason Stuart Hegman, who designed the h/k Citation 1 and Citation 2 was a big fan of wide bandwidth. 

I did not know vinyl has frequency bandwidth so high.   Most home hifi always talked of 20-20K frequency response.     Is this in practice or theoretical?   I'd agree theoretically vinyl could do more but practically its news to me.   The best digital (higher res) sounds as good as most vinyl to me these days.   RTR is better but look where that got us practically.

Its not just theoretical.

Its true that most LP systems don't spec past 20KHz but you would be very much mistaken if you think it stops there. Most phono cartridges and phono sections made since the mid 1960s go much higher than that (although it does not show in the specs as at the time there was no thought that it made any difference). Our cutter head is an early Westerex 3D, made about 1959 and it has no worries cutting 30KHz which can then be played back by a 1970s Technics on a 1970s h/k receiver (the Westerex mastering system has a filter that cuts it off at about 42KHz). By contrast RTR does not have this sort of bandwidth; about 25KHz or so is the best you're going to get at 15 i.p.s. IOW LPs have wider bandwidth than tape and its been that way since the inception of reel to reel. 

Every time a new system has come into the scene the previous knowledge of the prior engineering often goes by the wayside for a while until the new technology gets its pants on. This happened with digital; its only been recently that its begun pressing bandwidth past 20KHz and we're seeing the same thing with class D right now.  In time this will all get sorted out as the technology improves to the point that such bandwidths are routine; until then essentially what you will see is the industry collectively placing its head in the sand as if these facts don't exist. But this is not rocket science and we've known that bandwidth is essential going on half a century now. But people have short memories when new technology comes in... Look how long people put up with unruly fuel injection while carburetion was pretty figured out and actually performed better. But fuel injection was 'new' so people put up with it. Now days its sorted and no-one would consider a carburetor. But literally it took 3 decades to get there!

Al, thanks for that.

I was aware of the phase shift concerns and recall looking at measurements and reviews prior to buying to get a feel for what is going on.   Knowing no gear measures perfectly in all regards I decided to give it a try and was glad I did. 

I have to say to whatever extent my amps and gear may be imperfect or not, listening enjoyment is not affected.  I can listen for hours and never grow fatigued or tired.   That's not something I could lay claim to with my system prior to Class D. 

So as we know  in the end it always comes down to what one hears and can enjoy or not.    Measurements help scope out the likely candidates in advance, and their technical strengths and weaknesses but never tell the whole story regarding how things actually sound.

So while nobody including me has argued that more bandwidth done right is always a good thing, I do still think its unfair to dismiss Class D technology and products as a whole these days based solely on that.   The benefits will far outweigh the disadvantages for many  but probably not so much for those who are put off for whatever reason.

Shibui,
Thanks for your real world experience driven insight. I will always place more weight on actual use and listening experiences than the hypothetical/theory argument. Ironic given the contrary opinion of some on this threat that tube and class D amplifiers are superb driving your 1 ohm load Apogee speakers.
Charles

My good buddy Glen (shibui). A fantastic friend, an all-around great guy, and an ardent and experienced audiophile/music lover with a superb-sounding system. What more could anyone ask?

Phase shift and wrong summing of harmonics argument might look plausible (I claimed it myself) if not for the fact that my speakers already limit bandwidth to 22kHz creating larger phase shifts in comparison to 65kHz amp's bandwidth.  This 65kHz amp's bandwidth is responsible for about 20deg phase delay at 20kHz (that I cannot hear) and about 10deg delay at 10kHz (that I can hear).  One can argue that this phase delay might be beneficial since many speakers have positive phase shift at these frequencies.  I don't have data for my speakers, but I picked one of the speakers reviewed by Stereophile.  As you can see on the phase diagram (dotted line) speaker actually accelerates phase at the highest frequencies.  Phase delay caused by the bandwidth limit of my amp would improve summing of harmonics (Al, am I missing something?).  
http://www.stereophile.com/content/monitor-audio-platinum-pl300-ii-loudspeaker-measurements#Oze7AYHq...

There are many class A or AB amps that have bandwidth much lower than 200kHz (including Krells that have -3dB at about 100kHz) but nobody makes claims about  bad sounding highs.  It is a little of negative placebo effect - if you really believe that class D cannot sound good it will not.  

As for the hefty H2O power supply - it is unregulated and as such requires huge bank of capacitors to keep voltage steady and to filter out 120Hz ripple.  Jeff Rowland uses only very quiet SMPS, line and load regulated that operate at 1MHz switching frequency that is very easy to filter out.  In fact, he uses SMPS in preamps (Capri), where efficiency is not important, to lower the noise.  SMPS got bad rap from crude computer applications.  Either way works but traditional "linear" supply generates a lot of switching noise.  Also low inductance capacitors (like slit foil) are very expensive.  Why only a few companies use SMPS?  Perhaps because it is not easy to design good switcher and also because of market demand.  Many people believe that it has to be very heavy to work right.  Tiny ferrite transformers can carry at high frequencies as much power as huge transformers operating at 60Hz - not to mention wide supply voltage range and DC operation.  SMPS in mapman's amp can deliver 36 amperes for a full second!

BTW has anyone ever noticed a reviewer complain about phase shift when reviewing gear at a show? They can find all kinds of faults but seldom if ever that. Are they not listening right or is it just not there? Gotta wonder.....

It is a little of negative placebo effect - if you really believe that class D cannot sound good it will not.

I suspect some truth there as well. I went in not totally sure but willing to believe anything. I think.

SMPS in mapman's amp can deliver 36 amperes for a full second!

And....loving it!

I had a fellow agoner over to listen to my gear a while back. He is a fan of David Berning ZOTL amps. I heard these at CAF last summer and liked those very much as well. He indicated he really liked my setup running off the C5i which is latest and greatest Icepower and pure digital integrated amp as well with both phono and line level analog inputs. I do not know the bandwidth. Its a non issue in regards to what I hear personally so I haven’t even given it a thought. But I still gotta know so need to look it up. The ZOTL tube amps I heard and the C5i had quite a bit in common in regards to the sound IMHO. More evidence its the overall execution that matters more so than the technical approach of individual quality parts.

Kijanki 11-21-2016
One can argue that this phase delay might be beneficial since many speakers have positive phase shift at these frequencies.  I don't have data for my speakers, but I picked one of the speakers reviewed by Stereophile.  As you can see on the phase diagram (dotted line) speaker actually accelerates phase at the highest frequencies.  Phase delay caused by the bandwidth limit of my amp would improve summing of harmonics (Al, am I missing something?).  

No, I don't think you're missing anything, Kijanki, and that's an interesting point.  As is frequently the case it's possible that non-ideal behavior in one part of a system can to at least a loose approximation offset or compensate for non-ideal behavior in another part of a system, and turn out to be subjectively preferable.  And it is true that dynamic speakers in particular commonly have impedances in the top octave or two that are inductive, meaning phase angles that are positive.  On the other hand, though, there are of course many other factors besides impedance and bandwidth that contribute to a speaker's overall time domain performance.

Best regards,
-- Al
 

BTW has anyone ever noticed a reviewer complain about phase shift when reviewing gear at a show? They can find all kinds of faults but seldom if ever that. Are they not listening right or is it just not there? Gotta wonder.....

You see them writing about it all the time. Don't look for them to use the expression 'phase shift' though. Look for them to talk about the soundstage, how deep and expansive it is. That's one indication (but not the only one).

The thing is, you can build an amplifier that only goes to 20KHz or so that can still sound pretty good (lots of SETs only go that high). The effects of phase shift are more subtle but they do exist. So you might be happy with what you have (which is good) but ultimately its all in comparison to what, and if you've not heard that 'what' then you just don't know how much better it can get. That's why many people listen to boom boxes. They just don't get how much better it can be.

Companies such as Devialet are creating hybrid AD Amplifiers. In theory, that could be the best of both worlds with sound & efficiency. Are the hybrid amps subject to the same issues with phase & bandwidth?  

Wading through this discussion, I found myself reminded of the late neurologist, Oliver Sacks. He was, as I’m sure you all know, hugely interested in music and how we experience it. He was an enthusiastic devotee of the music of Johann Sebastian Bach, and was pretty indifferent to the music of Beethoven. He volunteered for a brain-scan to see how he reacted to the music of each composer, and the results showed that Bach noticeably increased his brain’s activity, while Beethoven showed no such effect. http://mentalfloss.com/article/23288/inside-oliver-sackss-brain-he-listens-music

I mention this because what I’m taking away from this lively discourse (apart from the technical details which is mostly beyond me) is that we all have our innate preferences. A sound that lights one person’s candle might have no effect at all on another, and some of these sounds might be actively irritating to a few. Our ears and our brain-wiring are all different, so what appeals to one group of us won’t appeal to another. Hence our differing preferences for and reactions to various classes of amplification.

Personally (and I’ve alluded to this subject in my review of the Wyred4Sound reclocker, q.v.), as a professional musician, I like to be "inside" the music, that is, to be able to discern its details and building-blocks, but I still want the overall sound to be pleasing (musical) enough to be enjoyable. It’s a balancing act. As stated in my previous post in this thread, my ARC STi200 achieves this for me. It might not for you, though, which is fine. I’m not a tube-person, but I certainly can see (hear) why this sound appeals to so many of you. Would be very interesting to see what MY brain looks like on music.

atmasphere, I’ve pretty much heard it all , including Atmasphere amps.

phase shift is just one factor that might acount for an expansive soundstage. You can’t equate the two or infer a large soundstage necessarily means phase shift being heard. if its truly phase shift that is there and not being mentioned then the reviewers need to go back to school perhaps.

For example, my setup has expansive soundstage only on recordings made a certain way conducive to that. on others it is quite the opposite. So there is no evidence there of artificial effects of phase distortion that would persist constantly. Certainly nothing that I can hear with any of my speakers large or small. You might measure something but I doubt anyone could single it out listening.

Maybe young pups with 20-20khz hearing and speakers with awesome bandwidth, but frankly there is a good chance that other forms of noise and distortion are what’s mostly occurring at the highest frequencies for various reasons, phase shift being one of many nasty things that occur there predominantly. Very little music does. Mostly just "air" at 20khz.. See the reference here:

http://www.independentrecording.net/irn/resources/freqchart/main_display.ht

So based on a combo of facts and experience I still see it as one of theoretical things that exist but do not add up to much if anything in practice for most.

So based on a combo of facts and experience I still see it as one of theoretical things that exist but do not add up to much if anything in practice for most.

Are you going to be producing an amplifier anytime soon?

If an amp cuts off at 20KHz then expect phase shift artifacts down to 2KHz. If an amp cuts off at 60KHz then its 6KHz. If the cutoff has a steep slope the artifacts can be more severe. The trick, if you can't get bandwidth the way you want, is to not have a severe rolloff.

You'd think this stuff is inaudible but it isn't. Many factors add up to how a given amp sounds and its plain foolish to attempt to focus on any one factor by holding it above others **or** below. They **all** affect the result.

So you are right in a sense. But I'll give you an example of how phase shift can manifest. Years ago a dealer brought an MFA Magus preamp to me with the complaint that it was really bright in the phono section. In fact I had heard this problem in the preamp myself. I put it on the bench and  found that in the RIAA equalization there was a circuit that caused the equalization to go to flat at 50KHz. This is a ways above human hearing. Normally the RIAA curve would be rolling off at 6db per octave.

So I took the circuit out, thus restoring the RIAA curve (FWIW the RIAA  did not spec the curve past 20KHz but it usually designers assume that it will continue with its 6db per octave rolloff as frequency goes up). The **very audible** brightness was eliminated! The dealer was thrilled, and MFA changed their production so that this circuit was omitted. Apparently they didn't like the brightness either, but had not made the phase shift connection. They said it was there to "improve square wave response". I'm sure it did that!

If your amp does not have lot of bandwidth then you are in the same boat as a lot of SET owners and they seem to like their amps just fine. The fact is that its not the most important thing in the world. But don't confuse that with it not being audible at all! In a class D amp, most of the artifact that its going to have is coming from the input circuit and in that regard whatever amplification it has (probably an opamp) which imposes its own signature. That's a lot better than the signature that many transistor amps impose; opamps if treated right can be pretty musical. If the bandwidth is limited then the amp might not seem very bright and a lot of audiophiles (myself amongst them) cringe when things get too bright. You like your amp a lot so if your hearing isn't too off than I have to assume that the designer chose a reasonable set of compromises in the design. I guarantee though that the designer would prefer to work with greater bandwidth if possible. When they come out with the latest greatest replacement for your amp (which will happen sooner or later), take a look at the bandwidth spec and see if they didn't improve on it. 

Are you going to be producing an amplifier anytime soon?

Nope. Not my lot. I’m just a critical listener reporting what I hear and trying to understand why.

I already have two generations of Bel canto Class D amps. I have yet to hear any hint of brightness ever with the newer one. Even with Dynaudio Contour monitors known to lean that way with the wrong amp. It is an all in one integrated the C5i so less to get wrong or right when matching . In fact one of the reasons I bought it was to be able to compare and contrast with what I had. And guess what, better bandwidth and improvements in general with a newer and still evolving technology is exactly the thing that leads me to keep testing the waters.

As I said I do not doubt the relevance of bandwidth in theory, only is it an issue of enough magnitude in practice that most people would care these days when things are done well otherwise.

Some people report brightness in some Class D amps. Same true with other SS amps. Probably even with tube amps to a lesser degree. But I am not hearing it at all ever, in fact less than ever, with my latest and greatest Class D amp. So I do not find the fears bandied about with the technology in general to be warranted at all in practice.

Nor am I saying all Class D amps perform equally well either. Only the ones I own and know well for sure. That just proves to me it can be done now and today. I am not alone there I would say. YM always varies.

Its nice to hear a maker of tube amps and another of passive pre-amps gives the competing technology some credit. Its only fair to point out where the achilles heels lie. Every product has one. All good information for the educated consumer to mull over when making a decision.

Here is part of Lamm Industries ML3 Signature amplifier by Michael Fremer in 9/2013 Stereophile.

The ML3s produced the most glorious, palpable, airy, detailed midrange I’ve ever heard from reproduced music. That part is easy. They pushed that performance envelope without going all greasy and congealed over time, as some tube amps do after the initial appeal of warmth wears off.

The ML3’s standout features were its natural re-creation of instrumental attacks, generous sustain, and lifelike decay—all as close to live as I’ve heard, if nowhere near the real thing. It was quiet, fast, detailed, dynamic without reservation, transparent, airy, and extended on top. No sharp edges unless the recording had them, and no boredom-inducing global softening. The pair of them produced an enormous sense of space when that was appropriate, and, within that space, images of exceptional delicacy, three-dimensionality, and body.

It should be good for $140k/pair. This amplifier has measured -3dB bandwidth at about 50kHz - which is 15kHz less than my class D amp, that supposed to suffer from wrong harmonics summing. Please notice words "airy, and extended on top". Imaging also did not suffer.

He also stated:

Most startling, though, was the ML3s' effortlessly clean and airy high-frequency extension. 

Full text:  http://www.stereophile.com/content/lamm-industries-ml3-signature-monoblock-power-amplifier#HxPd7KZt3...

I will try Class "D" when it get's as common as "bacon and eggs". In the meantime I will maintain my staunch prejudice against Class "D".

Did you know that the vast majority of people who hate "Black" people have never seen one up close and personal. If that can be accepted, I'm sure my stance on Class "D" amps can be accepted; in both cases there is no logical or rational reason for such a stance.

But seriously, I have already "verified" that computer sonics, and analog sonics, are impossible to tell apart, if the computer is done right; evidently it depends on the level of switching; but there are many indistinguishable differences that "audiophiles" claim to hear; such as six 9's copper; 99.9999% pure.

While there is a difference in the quality of interconnects, and it is due to the composition of the wire, the composite of silver plus copper for example, but that also has a scientific variable in ohms. When so many minute differences are carried to such great extremes, accompanied by extreme prices; without any scientific merit, I for one am quite dubious, as in the case of interconnects. I strongly suspect that almost any difference is interpreted as better; how else could you explain a 1K price for a 6 foot piece of copper wire?

Some of these differences are at a "subconscious" level; tube, and solid state for example. I think SS is best for rock, and tube best for "smooth sounds and female vocals"; but I am speaking of a tube pre and SS amp, where the difference is even smaller; when both are SS, then it's audibly obvious.

There are many dubious things on this forum, that I "strongly" suspect are no more than opinion, but "placebos" are good for one's mental health; that is, if the health of one's bank account can accommodate this feel good luxury.

I suspect I have become an "Audiophile"; it snuck upon me when I wasn't looking.  

Oh no, o!  Say it isn't so! What about the sonic influence of various dielectrics (smearing of the sound due to signal "absorption and release" time-misalignment), the winding geometry (reducing RF/EMI noise and phase shift), the use of active shielding (accomplishing the same as the first two to an even greater extent), and Graphene (improving conductivity), not to mention optimally matching capacitance and inductance to the input/output sweet spot of your equipment and speakers?

I don't know what cabling you are using, but I hope that some good ones "snuck up upon you when you weren't looking" for the sake of your excellent preamplifiers (and your ears). 

Best to you o,
Dave 

Dave, I think it done snuck up on you too.

The cable I use to make my own, was once sold by Belden in 100 ft rolls to radio and TV stations; that lets you know it's some good stuff; they both demand the highest quality at the cheapest price. Belden no longer sells that cable to the masses. I asked for some replacement cable, and if it was food, the dogs wouldn't eat it.

Fortunately, I'm working on my last major improvement, and thanks to your excellent ideas, I know it's going to be a success.

Hi o,

I know the early Belden cable, very good for XLR runs due to the inherent noise-cancellation characteristics of differentially balanced circuitry (not applicable for SE circuitry).  Once you get your room acoustics in order and you can really hear what your equipment/speakers are capable of doing, I predict a new interest in your quest: cabling and power.

Best to you o,
Dave 

I power my Maggie's with a D-Sonic Class D amp and this cold and dry sound I read about here is foreign to me. I suggest posters put aside their assumptions and give one a trial, you may be quite surprised

^^ Or not. You can't put them all in one basket. That's why this thread is as long as it is.

Class D amps vary in sound due to the fact that some have higher scan frequencies than others, some have more 'dead time' than others, some have more distortion in the input circuit than others, some have cheesy power supplies and some don't, some have feedback and others don't!

Companies such as Devialet are creating hybrid AD Amplifiers. In theory, that could be the best of both worlds with sound & efficiency. Are the hybrid amps subject to the same issues with phase & bandwidth?  

Devialet was one of the best I heard till date. Yes they are AD Hybrid. Someone mentioned that they are overpriced, however, my experience was completely opposite. I actually saved some money by selling my preamp, dac and previous amp. Many existing Devialet owners are swapping their existing units with the Pro line, which was released last month. You can buy one cheaply on Agon and try it at home. If you don't like it, you can sell it at small loss or break even. They are definitely worth the home audition. If you can get your hands on D250 at a good price, go for it.

Agreed! They save money. I owned one and sold it however once I heard the Lyngdorf 2170 in my system. I liked the Devialet, but the Lyngdorf sounded better on my Harbeth 40.1 and Accoustic Zen Cresendo speakers. The room correction in the Lyngdorf really put it over the top once it read my room and speakers. 

Both are great options for sure. 

Just my opinion, but all you guys out there claiming audible switching noise are a little misguided.

Speak for yourself Kimosabe.

You probably missed the part where I mentioned we have a class D amp in the works, right?

Seanheis 1,

If you're only interested in sound quality and nothing else, you're likely missing the finer points of a good class D amp.  IMHO, the ONLY good point of a class A amp is its sound quality.  If you would list all the pros and cons of a class A amp, the only pro would be sound quality. ALL the other factors  you could think of when buying an amp would be on the con side, and I mean EVERY SINGLE factor you can think of:
Most expensive to buy
Most electricity consumed to operate
Most of the electricity inputted is converted to heat and wasted.
Nuclear reactor type heat  produced in your listening room
Huge due to huge heat sinks required to try and prevent nuclear fusion from occurring.
Constant high heat reduces reliability and life span.

Put it this way: would you only pick a life partner based on looks? Would you ignore the fact that she required a very large payment to even consider you? Required expensive gifts to keep dating? Raised the temperature 20 degrees every time you were near her? Occasionally pooped in your bed blaming the high heat that she was the cause of and requiring expensive 'repairs'? Grew to enormous size and weight in an attempt to dissipate her excess heat through an increase in surface volume like a hippo?  Okay that's enough, I can't think of many more analogies or are they metaphors? I think you get the picture.

Sure, looks/sound quality is important but I suggest you might be happier with a woman/amp that is only one of the most beautiful in the world but not quite THE most beautiful but is your best friend,  low rather than high maintenance, a toned and healthy size and weight rather than extra large and heavy, generally has many more pros than cons. Besides, the higher quality class D amps currently sound strikingly similar to the higher quality class A amps.  I think you'd be pleasantly surprised if you gave a good one a try, I know I was.

Okay, that's the gist of it but I wrote more specifically about my experiences with class D in the book below:  

  
I've become  a big fan of class D amps for several reasons:

1. They are extremely quiet, having THE HIGHEST S/N Ratio and THE WIDEST DYNAMIC RANGE of any amp type, with almost no audible background noise and highly detailed.  I can turn my volume control to maximum without any source playing, put my ear an inch from the tweeter panel of either speaker, and there is absolutely no sound. Is this possible with a class A amp?  This is very important because it enables sound to emerge from a dead silent background which enables very fine details to be distinguished, including the all important spatial cues required for good sound staging. I believe the quietness of these amps is the root cause of their excellent detailed nature; this is my theory but it has been proven to me repeatedly through my actual listening experiences.  I know my music well and I can easily discern a redbook CD from a hi-resolution 96/24 digital recording mainly based on the low level of background noise, high level of detail, lack of the 'loudness wars effect' and the very life-like attribute of having THE greatest dynamic range of any amp type. 
I also found it is now much easier to discern audible differences between different speaker, interconnect and power cables and other upstream issues with these class D amps than with any of my previous class A/B amps I've used.
Contrary to comments by previous posters, I have never heard any 'switching noises', they are the quietest amps I've ever heard (not heard?).     

2. They are very powerful and good ones are very stable into very low impedance speaker loads.
My main speakers are relatively inefficient (87 db at 1 watt)  Magnepan 2.7qrs. that can dip a bit below 4 ohms.  I'm currently driving them with a pair of D-Sonic M3-600 monoblock class D amps rated at 1,200 watts @ 4 ohms.  These amps are rated as stable down to 1 ohm.  All tube amps, and many class A and A/B amps, are not capable of driving speaker loads that dip to a dangerously low 1 ohm (almost a complete short) as some more exotic speakers do at specific frequencies.

3.  They are very neutral in their overall tonal characteristic, not adding or subtracting anything audibly that I can perceive.

I had previously always paired decent class A/B amps (McCormack and Aragon) with a good tube preamp (VTL 2.5 with NOS Mullards) to achieve the slightly warmer sonic characteristics I favored.  Initially, I paired my class D monos with the VTL and it sounded very good.  But, after extensively comparing my system's sound with and without the VTL, I decided my music sounded just as rich, sweet and dimensional  without the added tube coloring so I sold my beloved VTL to a friend.  I don't want to portray the sound of these amps as 'tube-like', but the natural sweetness and richness of good music and instruments played well is definitely conveyed if the recording is well done and the recording captured it. 

I think it's important to note that most of the newer class D amps rely heavily on feedback circuitry that constantly compares the signal accuracy at the input stage to the signal accuracy at the output stage going to the speakers, making adjustments as needed to ensure the accuracy prior to releasing the signal to the speakers. This is likely a major factor in the generally neutral nature of the best class D amps.  Those using tube preamps need to choose carefully since the tube preamp's sound will be passed through faithfully without any alteration and the differences in sound qualities between preamps and tube swaps will be readily apparent and distinct.  

In my listening experiences, tube and class A amps tend to have a sound more to the warm side of neutral, which I previously thought I preferred to neutral.  Class D amps are closer to the classic audio amp ideal of a 'straight wire with gain' than any amp type I've listened to.

4.  They excel at dynamic range so much I feel the need to mention it again.


My system is a combination 2-channel and 5.1 HT surround system used about equally between both.   I use an Oppo BDP-105 as a 2-ch preamp, 5.1 surround processor and as a wireless DAC.  I run JRiver on a laptop that wirelessly streams music files from a Synology 20 TB NAS to the Oppo DAC. My entire CD collection, along with numerous 96/24 hi-res digital WAV files are stored on the NAS.  All amplification is class D:

D-Sonic M3-600M monos power my front Magnepan 2.7 mains
A bridged Emerald Physics 100.2SE powers my Magnepan CC-3 center
A stereo ClassDAudio CS440 powers the Infinity in-ceiling rears.
A Dayton Audio class A/B amp powers 4 Audio Kinesis subs configured in a distributed array bass system. I'm currently searching for a good class D amp that can handle 4 subs @ 4 ohms to replace the Dayton that came with the distributed array sub system.

The video connections from the cable box to the Oppo to the tv are all HDMI. The audio cabling is all run directly from the Oppo to the amps, XLR for the D-Sonics and RCA for all others. All of the class D amps have the same neutral, ultra quiet, detailed and highly dynamic sound quality that seems to be charactaristic of good class D amps. The ability of these amps to go from quiet to loud for both music and HT audio is very good and can be even startling on well recorded content, an obvious improvement over my previous class A/B amps.

5.  They are space and energy efficient.

My previous main amp was an older class A/B Aragon 4004  that was very big (19"W x 14.75"D x 6.75"H), weighed 76 lbs, got warm-hot to the touch, was inefficient and put out 400 watts @ 4 ohms. This amp had to be replaced due to leaking caps in the power supply section.  My current D-Sonic monos are small (7.25"W x15"D x4"H), weigh about 10 lbs. each, never get more than mildly warm, are very efficient and put out 1,200 watts @  4 ohms which has had a very positive effect on the performance of my inefficient panel speakers.
After switching my previous 3 class A/B amps for class D amps, I would estimate my monthly average monthly electric bill decreased between $30-$40 varying by the season.  I've always left my amps on 24/7 for both types unless I'm away for a day or more. I think that's fairly significant savings, especially projected over a full year.
The switch also allowed my audio gear to be streamlined due to the new equipment occupying roughly half the space. The top shelf of a new much smaller rack containing just my Oppo straddled by both D-Sonic monos on small maple isolation stands with all remaining gear located in an enclosed shelf below. Aesthetically a breath of fresh air with less gear, less visible gear, with a more pleasing symmetry, better air circulation and minimal heat.

In conclusion, I think we can all agree that there are many tube, class A, and even some class A/B, amps that achieve a stellar performance level when properly matched to quality speakers.  I have no doubt because I've personally listened to many examples.  However, I also have no doubt that high quality class D amps can achieve similar stellar performance levels when properly matched to quality speakers but I realize everyone is not ready to acknowledge this quite yet.  Resistance could be due to deeply held beliefs in the superiority of certain amp design types or perhaps a reluctance to concede a relative equal status to such an upstart newcomer.  But, after reading this thread and listening to some of the comments, it seems increasingly obvious to me that many have simply not heard a high quality class D amp driving a pair of high quality speakers and how closely it approaches the sound quality of even the best of the class A amps.  

And you don't need to believe me when I proclaim my opinion that class D is the likely wave of the future in high end amp design not only due to its excellent sound quality but also due to its many ancillary benefits such as lower weight, smaller size, lower heat, higher reliability, lower maintenance costs, lower R$D costs due to amp module designers/manufacturers taking on this responsibility and lower production costs caused by completed amp sellers simply buying the amp modules they prefer from 3rd parties.  All you need to do is look at the many stalwart amp manufacturers (Jeff Rowland, Theta, Mark Levinson, Audio Research, Rotel, NAD, Technics, Yamaha, Marantz, Cary, Halcro, etc.) that are now offering class D amps.  They're doing this because they've compared the sound quality of their traditional amp designs to the ever increasing and improving class D amp module typologies and decided they offer high quality sound along with many ancillary benefits:

Amp module designers assume many R$D costs=Lowered internal R$D costs
Lowered heat=Increased reliability=lowered warranty repair costs and increased company amps'  reputation as being reliable 
Lowered weight/size=lowered shipping costs
Higher efficiency=lowered customer electricity usage=a 'greener' product
Increased amp module suppliers=freedom of company amp designers to tailor sound to their preference via amp module selection and design of custom input stages
Other likely benefits I'm not thinking of right now because I'm tired

It is evident there is a slew of benefits to traditional amp sellers increasing class D offerings with minimal associated risks that could result in a class D wave of the future and the proverbial win-win situation between amp sellers and amp buyers that I believe has already begun.

Sorry my post turned out so lengthy but I was trying to be as thorough as possible,
    Tim
 
      

     



 

 



















i

One heck of a lot of information, too much for my poor head!
I am in the market for new amplification, moving on from my trusty Krell KAV250 and was considering giving class d a try again. I say again as about 3 years ago i tried a pair of bel canto 500m mononblocks and found them to be so cold and sterile that I could not stand them.
So have class d moved on since these or should I stick to a monster class a like a bat vk500 or ml product?

@uberwaltz

Keep your Krell KAV250 (nice amp) for a while yet, read my reasons here.   
https://forum.audiogon.com/discussions/class-d-technology

Cheers George

A standing ovation to Noble100 ’s post . Claps !

Great post Noble100.

I am in the market for new amplification, moving on from my trusty Krell KAV250 and was considering giving class d a try again. I say again as about 3 years ago i tried a pair of bel canto 500m mononblocks and found them to be so cold and sterile that I could not stand them.

History is quite interesting for Class D. If you believe the reviews, Class D has been state of the art for lets say 10 years. When the Tripath amps came out they were declared to be superior to prior class D generations that sounded poor in the higher frequencies. Boutique companies such as Red Wine audio made reference gear using Tripath and the reviews were glowing. 

Next came Ice Power generation 1. They were claimed to be superior than Tripath and the boutique amp makers and Stereophile reviews claimed their superiority as reference grade.

Next came Ice Power generation 2 same story. Then Hypex NCore, etc.  

A snippet of a 2009 Stereophile review is below. 
"The Bel Canto Ref1000 Mk.II can be compared with the cream of the other amps I've had in my system: the Classé CA-3200, Mark Levinson No.433, and Ayre Acoustics V-6xe. Each of these distinguishes itself in different ways, and particularly with different speakers. Because of this, I think I must keep the Bel Canto Ref1000 Mk.IIs as a reference amplifier—an easy decision even when based solely on its sound, but also: in my living room, none of the others can be so easily hidden in plain sight."

Thank you maplegrovemusic and Kijanski,

    I'm glad you thought it was a useful post.

   I  did a lot of research on class D amps and technology before buying my 1st one about a few years ago.  Guido Corona, mapman and atmasphere   helped me a lot on this site and I really appreciated it.. I now own 3 different brands and have gained some personal experience with them over time.  

    I'm glad I have some somewhat decent knowledge to pass on to others looking for similar knowledge.as I was.  I also have learned along the way that class D is a great choice for myself and many others but not right for everyone. 

Thanks,
  Tim

      

Bel Canto Ref1000 Mk.II

The newer Bel Canto e.One Ref600M monoblocks (that had the newest Hypex modules) with Belcanto’s own designed "series" output filters, these so far have sounded the best Class-D to me, and I thought, yes I could live with this.
They were were driving a speaker that had a very benign 6-8ohm flat load tweeter with minimal -phase angle which was one of the Raven Ribbon tweeters, once we used another speaker, with not such a nice benign load in the top end my opinions of it were dashed somewhat.
http://loudspeakershop.eu/glosniki/images_dane_750/raven/linesource_imp.png
Cheers George

My D-Sonic M3-1200S 2 channel amp is a dual mono design using Pascal modules which I believe is still Dennis's module of choice. It powers my Maggie’s with ease. I can tell you, Dennis’s amp came highly recommended and I was skeptical but decided to do a trial. My McIntosh amp was quickly pulled from the rotation and put on the block, it’s that good and meshes well with my Modwright LS100 preamp.

1. They are extremely quiet, having THE HIGHEST S/N Ratio and THE WIDEST DYNAMIC RANGE of any amp type, with almost no audible background noise and highly detailed.  I can turn my volume control to maximum without any source playing, put my ear an inch from the tweeter panel of either speaker, and there is absolutely no sound. Is this possible with a class A amp?

Yes, and with tube amps too.

The reason? Your volume control setting is saying something about your preamp and sources but nothing about the amp. We make tube amps that have to be quiet on speakers that are 107 db... try putting your amps and preamp on a set of speakers like that and see how much noise you have then. Low noise is not a weakness nor advantage of class D amps.

Dynamic range isn't a particular strength or weakness either- it is the same as any good amp.

The real strengths of Class D are low cost, high efficiency (about 85%) and because of the latter, smaller size as large heatsinks are not as important. Class D was first proposed in the late 1940s and can be done with tubes. Its a fairly simple technology which is why its also inexpensive to build. **Those** are the strengths; what an individual designer brings to the table and how well its executed is going to have a big effect on how the amp sounds and performs. There is nothing inherent in the technology otherwise that make it inherently better. The reason its showing up in spades is the semiconductor industry is really wanting to make switching transistors right now instead of linear transistors, so audio manufacturers hare having a much harder time getting linear devices as easily as they did in the past and can read the writing on the wall.

If you want to demystify what class D is all about, I recommend reading this article, which really demonstrates how simple class D really is:
 https://hackaday.io/project/4369-class-d-subwoofer-amplifier-out-of-scrap

Yet you, Mr. Designer, dismiss Class D as nothing more than midfi.......

That's general idea, but simple it is not. None of current class D amp modulators uses triangle waves.  If anything it is more sinewave and closely resembles modulator use in Delta-Sigma converters, that produce similar output.  SACD is also a product of such Delta-Sigma modulator and it is basically class D output signal (PWM).  In addition to modulator alone there are different configuration of output stages, output filters, multiple feedbacks etc.  Let just say that it is so "simple" that it took whole PhD work of Karsten Nielsen (Icepower) at University of Denmark to describe theory behind it - much less actual implementation.  Once you take FPGA approach to class D you will find that it is very, very complex.

 

The real strengths of Class D are low cost, high efficiency (about 85%) and because of the latter, smaller size as large heatsinks are not as important.

Lower cost for manufactures, which seems to result in higher margins instead of reduced retail prices. Manufactures have to of course be careful of cannibalization.    

Yet you, Mr. Designer, dismiss Class D as nothing more than midfi.......

Apparently you've not read this thread or you would not have said that; IOW this statement is false.

Lower cost for manufactures, which seems to result in higher margins instead of reduced retail prices. Manufactures have to of course be careful of cannibalization.

This is true- and is a time-honored technique in the world of audio going back a good 60-70 years. First I can recall is when they went from electro-magnet speakers to permanent magnets. Permanent magnet speakers are cheaper to make but we didn't see the price go down way back then. After that it was the transition from high efficiency loudspeakers to lower efficiency types as transistors came in; lower efficiency speakers are cheaper to make but we didn't see the price go down all that much. Then there was the transition from tubes to solid state. Solid state amps are a lot cheaper to build- no filament circuit and no output transformer but the price really didn't go down.  Then we went from LP to CD and CDs are lot cheaper to build but we didn't see the price go down (instead we saw the price of LPs go up after the record industry sorted out that there was still a demand...). Now we're seeing class D supplant traditional solid state in many ways but for some reason they aren't particularly cheaper even though they are cheaper to make.  

I have no dog in this discussion/fight/whatever, but FWIW I believe the statement Mr_m is referring to is the following:

Atmasphere 11-3-2016
Right now the technology is to the point where the amps have become practical for mid fi, but they still have a ways to go before they can challenge a good class A transistor amp or a good tube amp. There is no question that this is a technology to be watched.

FWIW I do not interpret that statement as "dismiss[ing] Class D
as nothing more than midfi......."  As I read the statement it does not by any means exclude the possibility that the best present day implementations of class D may be much better than mid-fi, while nevertheless not being as good as what well implemented class A solid state or a good tube amp can presently offer.

Personally I take no position on this, having no experience with class D.  But that is how I interpret Ralph's statement.

Regards,
-- Al

 

Yes, I have read this thread in its entirety. You could not have made it anymore clear. Go back to the beginning of this thread and read your own post. Not a false statement.

Obviously I could have been more clear or this conversation would not be happening!

Al’s got it right. Note where I say ’good’ twice in the statement Al is quoting.

As I have mentioned before, we’ve been playing with Class D for about the last 15 years. While I think they have gotten much better (15 years ago they were a joke) I’ve yet to hear one that keeps up with a ***good*** amplifier of conventional design (note emphasis; FWIW I’m used to listening to some pretty ’good’ amplifiers...). High end audio is pretty variable and I know of amps that are considered high end that I personally don’t think are all that good. I know of one such amp that has balanced inputs yet its CMRR (Common Mode Rejection Ratio) is about 18 which is pretty terrible if not outright criminal.

So I can see the interpretation issue. Most class D amps have specs and sound that are similar to many midfi amps (take a look at a Kenwood car stereo’s specs and compare to many ’high end’ amps and you will see that there’s not a lot of difference). Some don’t; they’re better. And they will continue to improve.

For example the scan frequency is continuing to rise. George makes a pretty big point about this. You can’t scan at 100KHz and get good high end resolution. 250KHz is in fact marginal if you really want to do it right.

As I mentioned before, you can get high power high speed output devices that switch at the speeds needed, but they cost so much right now that the resulting amplifier would be a lot more expensive than a tube amp of the same power would be (tubes are usually the most expensive form of power). So as a result no-one uses devices like that. In fact many designers simply use chip sets so they’re locked into the performance of whatever the semiconductor house provides (who rarely have audiophile interest at heart).