Class D Technology

Hi George,

     I didn't intend to twist your words, sorry.

     I reread your posts and I get that you are waiting for the switching frequency to be significantly raised before you'd be willing to 'switch' to one.

   I understand the theory that the current class D switching frequency is too low and affects the sound in the audible range but I can honestly say I don't hear any irregularities when listening intently to my system.  You may be completely correct but I'm just having a hard time faulting what I hear.  When I listen explicitly for switching frequency issues I mainly concentrate on the highest frequencies to make sure they are well extended and to make sure that spatial cues are present and the sound stage is well defined and stable both laterally and front to back.  

     Am I listening for the wrong things?

     Is there a simpler method to determine if the  switching frequency is too low and is  affecting anything in the audible band?

   I'm not really disputing the theory that a higher switching frequency  would upgrade class D amp performance.  I was just hoping to gain a better understanding of exactly how.

 Any assistance is greatly appreciated,
     Tim

























i honestly I  

noble100
Georgelofi acknowledges the benefits of class D but mentions its low cost in a manner that suggests it’s not a further benefit,

Now that’s twisting words.
I suggested that future technology in higher switching frequency will be of great benefit to class-d, so then the output filter can do it’s job properly without effecting the audio band.

We’re trying to band fix the switching noise problems with some innovative (ML below) (Belcanto my last post) but not completely successful filter ideas.

Just look for one at the $50k Mark Levinson No53 Class-d monos. 4 x massive inductors for the output filter probably cascaded to get rid of the switching noise. Speaker designers know that doing this with filters has it’s own set of interaction problems. Didn’t get a great Stereophile review/measured performace.

http://www.stereophile.com/content/mark-levinson-no53-reference-monoblock-power-amplifier#kXGk3Vi1RAApjFoi.97

Like I said before, I’ll be the first to get a Class-D once the switching frequency is around 3-5mHz so the filter can do it’s job properly, but at the moment nothing save for the very exclusive $30k Technics SE-R1 with a higher (double) but not high enough switching frequency, then my linear amps will become boat anchors.

Cheers George

Guido have you heard ref1000m amps respond similarly to power cords?  In what way specifically?  Thanks.

Congratulations geekboy!

Be patient with your new BC Ref600S before evaluating them seriously.... Unless they were completely broken in before you got them, it will take anywhere from a few hundred hours to about 1000 hours for them to reach their full potential.... Try leaving them powered up 24/7 and let them crunch a signal at medium lowish volume... E.g. the interstation hash from an FM radio tuner.... That should clear their musical throat quite nicely. Full break-in on class D amps is essential... The difference is quite staggering.

Once they have stabilized, the careful selection of PCs will bring them to even newer hights. For PCs that are not super-expensive, I would suggest Shunyata Alpha

Regards, Guido

ee

" Mid fi has a negative connotation in these parts. That’s all. One can either laugh or be insulted. Best to not use the term unless that is the message intended."

     Well said, mapman.

Ralph (atmasphere) stated:

" What I'm seeing in class D is something I've not seen in audio before- amplifiers that use the same parts as a mid fi amp as in a high end amp. In fact its safe to say that class D has lifted mid fi performance to what many would have called 'high end' only a decade earlier."

Georgelofi acknowledges the benefits of class D but mentions its low cost in a manner that suggests it's not a further benefit, implying that sound quality and low cost are mutually exclusive and that we should, therefore, look down upon this technology that dares to sound so good and be so affordable at the same time.  

     I'm a fan of all good class D amps and admit it's a bit annoying to hear them described as 'mid-fi'. But it is true that class D amps today are in a wide range of products that do cover a wide spectrum of sound quality: from 'mid-fi' applications such as car audio, boom boxes, home receivers and powered full-range speakers/subs (that enabled better sound for less cost than the previous amps used)  to  'high-end' applications  such as the state of the art line of modules from Hypex ,  Anaview/Abletec and Pascal modules that are used in world-class amps from Jeff Rowland, D-Sonic, Mark Levinson, Marten, Merrill Audio, Audio Research, Halcro and possibly even Atma -Sphere in the near future.
     .
     These are just some thoughts from my perspective from the outside as a consumer looking in.  I have no amp design experience or knowledge and wish all amp companies, regardless of the amplification type employed,  continued success.

Tim    

   
 

Pass labs 250 INT - but while I am sure they are really great - are HUGE and serious $$$.

In Australia the Belcanto Ref600’s are $8k around the same as the Pass 250 int.
The new BC Ref600 monoblocks use the latest NC500 Hypex modules with moded from what I was told output filters (cascaded?) by BC. They sounded very good to me with a certain Raven ribbon tweeter that presented a very flat 8ohm load in the uppermids/highs. Read my post here.
https://forum.audiogon.com/discussions/class-d-technology/post?postid=1372318#1372318

Cheers George

Folks - really enjoyed reading this long thread. Very much appreciate the education and the discussion!

Just bought a pair of Bel Canto Ref600m on the Gon and found this thread after doing so.

I opted to go this route while trying to upgrade my amplification - which is currently a Supernait 2 driving PMC Twenty 26s. While the sound can be quite nice at times I’m thinking I’m underpowered - the Snait 2 is only 80 watts and the speakers are not an easy load - sensitivity of 86 reported (though probably lower based on some of my reading) and can go down to under 4 ohms. I’m hoping for a more dynamic range for orchestral music which sounds a little congested/strained currently. Plus I’d just like to hear the Bel Cantos.

I landed here after finding other options (with an eye to Class A) for getting more power to be a challenge - and thus not able to pull the trigger on something. I looked quite seriously at a demo Pass labs 250 INT - but while I am sure they are really great - are HUGE and serious $$$. I’d also have to get a new rack to hold them - even more $$$ and space.

Basically, Class D appealed due to cost and size. Reviews have been solid. The pair was under 4k less than a year old. And if I don’t like them they can go back to the Gon and I will be out a small amount of $$$ to test them in house! Pretty good deal (says the recent purchaser!) The new Bel Cantos is the new chip or whatever - different technology used than all their other units - so I am hoping for good things. this is going to cost me as I skipped the monos from Wyred for Sound cyber monday special - could of had those 1000sx pair for around $2200 - hope I made the right call!

anyhow - Really glad to have found this thread!

I’ll be sure to post how they sound!

I had the Ice Amp 125ASX2 and it was awful. 

I had a Bel Canto Class D amp a few years ago and it was awful. However, I heard the Channel Islands Audio Class D mono block amps a while ago at an audio show and judged them to be outstanding.  Class D amp technology has progressed and I don't doubt it will be the wave of the future for audiophiles.  

Why do the people who say they don't like class D mention the class D amps they have heard?  One guy slammed the H2o's that he had obviously never even heard.....how ridiculous is that?!  No not all class D amps are great but there are plenty that are EVERY BIT AS GOOD (and better) than any other design.

Mid fi has a negative connotation in these parts. That’s all. One can either laugh or be insulted. Best to not use the term unless that is the message intended.

Some amps of any type can be labeled as mid fi compared to others of same type, SS Class D, tube, whatever based on whatever criteria one chooses including the sound quality.

The point is not all of any type are created equal. Some of each type these days compete in the big leagues but play the game differently. Some in the minor leagues.

Also safe to say Class D competes well in all leagues at most any price point these days.

Its generalizing and labeling all products of a particular type equally for better or for worse that causes problems just like labeling all persons of a particular nationality or religion negatively causes similar confusion and problems, just of a lesser importance in the case of hifis.

The BelCanto C5i in particular has shocked me in that my quite tube amp friendly Triangle Titus speakers sound the best ever with it. The 60 w/ch are Ok but not the best with any of my OHM or Dynaudio speakers though I have had visitors from Agon still compliment the sound with those even. Which just goes to show it all depends. Class D amps play the game radically different than OTL tube amps do. But both can deliver big league results (Class D for less perhaps especially when cost of speakers factored in) based on my listening experience perhaps both even with easier load speakers that are required more for the OTL or tube amps but easier load in general tends to benefit all amps to some extent when done right.

Also I would note that modern OHM Walsh speakers (especially the larger models) are a good bit more efficient than Magnepans and not as tube amp unfriendly as one might anticipate. I found Magnepan to need power (though not so much current) to a much greater degree than OHM when I owned both.

Whatever Ralph meant the mid-fi comment did make me laugh knowing that the sound I hear from practical Class D amps today (like the ones I own which are neither the least or most expensive) is not mid-fi by any reasonable listening standard.

@mapman  Do you think that because we've taken this technology very seriously that at the same time we don't?

If I can point out some things without people trying to put words in my mouth, first- tube amps are rarely mid-fi. The term 'Mid-fi' refers to equipment generally sold in box stores like Best Buy (not including their in-store Magnolia dealerships); stamped out to make money. Tube amps are usually too expensive for that (tube power is generally expensive, which is why there were many high efficiency speakers on the market when tubes were the only game in town decades ago).

The thing about most solid state is that the specs really haven't changed a whole lot since the late 70s or early 80s. Like I said, compare a Kenwood amplifier a Krell and you will see what I mean. The big difference is power (on paper). Bandwidth and distortion are almost the same. Of course a Krell is built better, has bigger heatsinks and bigger power supplies. And its not sold in box stores.

Class D has almost entirely taken over at the bottom end of the audio market. And the middle part too. You can't buy a boom box now days that isn't class D. For the number of class D amps in total on the market, only a tiny minority (the ones that generally have our attention) are considered high end. Many of them use the same modules found in mid fi gear.

Think about that for a moment before railing on me? I'm only working with the facts here so don't shoot the messenger. If you look at a high end tube amp or a traditional solid state amp, **NONE** of them use parts/circuitry/assemblies also found in mid fi gear.  This is something different about class D and has entirely to do with how inexpensive the technology actually is.

(To give you an idea of that, I have a module on my desk that was sent to me by a customer (who happens to be the vice president of Phillips Semiconductor). This was one of their best modules built about 12-13 years ago. It makes 100 watts per channel and is a stereo module that is complete except for the power supply. It even has connectors on the board for easy hookup. The specs are quite good (Phillips TDA8920B, scans at 317KHz!; not bad for decade-old technology; faster than some amps made today and features no 'dead time') and it sounds alright too. In quantities of 1 it cost $25.00. I know of at least one 'high end' amp that uses this module that cost $2500.00. This module is the size of a pack of cigarettes complete with connectors and heatsink.)

So when I talk about mid fi and class D, you **should** know why now. I think a lot of posters here are attaching a negative meaning to the 'mid fi' term that does not exist; Just because its mid fi does not mean it has to sound bad and I can point to plenty of examples (we could start with the Radio Shack Lineaum speakers). What I'm seeing in class D is something I've not seen in audio before- amplifiers that use the same parts as a mid fi amp as in a high end amp. In fact its safe to say that class D has lifted mid fi performance to what many would have called 'high end' only a decade earlier.

So you might like your amp and I'm not disputing that! OK, I'll say it again, you might like your amp and I'm not disputing that. But if you think that the amp does not share a lot with mid fi gear you are ***really*** mistaken.

There is one other thing that keeps getting left out of this discussion. Its a simple fact that no matter what the amp is, if you make it work hard for a living its not going to sound as good because its distortion will be higher. This is easy to hear and easy to measure!! You can see it in the specs of any amp. Tube amps in general are best experienced when driving higher impedances 8 ohms or more. All output transformers are more efficient driving higher impedances and also will have wider bandwidth (its not unusual for an output transformer to loose an octave of low frequency bandwidth going from the 4 ohm tap as opposed to the 8 ohm tap). For this simple reason, Magnaplanars and Ohm Walsh loudspeakers are not the best candidates to really tell how good a tube amp actually is (the tube amp will sound better on a load that's easier to drive, and so will any solid state amp). My speakers at home and here at the shop are both 16 ohms and very different designs; both extremely transparent. When both amps are on a level playing field their differences are more easily assessed.

At any rate, if you are happy with what you hear than that's really what's important. If you have audiophile nervosa, which is a deadly disease (I've had it for decades and its no picnic) you are always left wondering what's around the next bend, how you can arrange things to get better sound. I've outlined already how class D has to improve (FWIW, some of the complaints I have apply to regular amps as well), which we hope to address in our design.

You guys are right! Please do not forget the Lyngdorf 2170 which is just amazing and class D. It is a dac, int amp, and room correction all in one. The room correction is SOTA and what makes it one of the best options out there. 

Neal at Sound Science sells them. See his ad here on the Gon. It is replacing, and besting, $30,000 plus of separates. 

The newer Class D integrateds I have heard like BC C5i and Rogue Pharoah and Sphinx are game changers for me. Prior to these, I would not have thought to ever replace separates with an integrated amp, but I would strongly consider that with any of these. The only downside is my Class D monoblocks are 500w/ch and all those go to good use in my larger system. In my smaller system, especially with more efficient speakers, the 60w/ch C5i comes very close to doing everything ever needed though a few more watts/ch would still likely only benefit.

60w/ch Class D and truly digital C5i has phono and line level inputs in addition to all the usual digital ins. Plus an outstanding headphone amp as well. Just add speakers and a digital source and you may be set with everything most would ever need sound wise.   In a single easily handled and manageable package smaller than the size of a shoe box.

I decided to try this (latest and greatest Class D and digital technology from Bel CAnto) prior to trying a tube integrated amp in this system and guess what its not going anywhere.

@seanheis1 Of course you can compare the two. And your answer tells me that you are falling into the same trap I did. 

Yes, the Emotiva had more power, switchable Class A, etc. It also doesn't sound all that great.

I was making a point that you can buy that or for $103 more, you can have an awesome amp. We are talking retail to retail new.

I purchased the Emotiva gear during one of their sales. I purchased the Rogue in 9/10 condition preowned here. I actually paid less for the Rogue than I did for the Emotiva gear. And it's not a fair fight at all. The Rogue sounds so much better.

The Rogue Pharaoh is an integrated though? Emotiva Monoblocks running 600 watts of power with their best preamp compared to a 185 watt Rogue integrated?? You can’t compare pricing on monoblocks plus preamp with an integrated that has a fraction of the power. It’s 3 pieces compared to 1.

Those Emotiva monoblocks will also run in Class A mode. If Emotiva were to sell a 185 watt integrated, it would be priced around $500 and of course couldn't compare with a $3500 Pharaoh.

@seanheis1 Emotiva and Rogue is more compatible price wise than you stated. If you are looking at top of the line seperates, the monoblocks are $2398 a pair, and the preamp is $999- excluding holiday sales. So you are looking at $3397, a whopping $103 less than a Rogue Pharoah.

Performance wise? The improvement with the Pharaoh is staggering.   

I keep reading the negative comments on class D amps here and then listen to my Devialet 1000 to Maggie 20.7 setup for flaws. I know the Devialet is a class D hybrid design..... but the system just blows away all the other amps I have tried.

For 35k I would hope so. I believe that this hybrid is unique in that it doesn't require an output filter....it's kinda like a thread where people are debating if class B amps can compete with tube amps and someone chimes in that their Class AB amp sounds brilliant and they don't get why folks rag on Class B.

I keep reading the negative comments on class D amps here and then listen to my Devialet 1000 to Maggie 20.7 setup for flaws.  I know the Devialet is a class D hybrid design..... but the system just blows away all the other amps I have tried.   

Fast forward 6 months and I can truly say the Emotiva gear was mid fi. The Rogue gear outclasses in in every way. I don't care that Magnepan says to avoid Class D. They are wrong for making such a blanket statement, and I was wrong for heeding the advice.

I am finally very happy.

Magnepan recommends high current Class AB because they know their panels work well with that. Class D doesn't have a consistent track record and they don't want that to cost them in sales and returns. They also don't want to bad mouth Class D because their dealers sell it. I believe that their most recent advice is listen to their panels at the dealer with the amplification that is going to be used.   

Emotiva gear is mid fi for sure. Their most expensive amp is $1000 and Rogues cheapest amp is $1300. Hardly a fair comparison ;-) 

Arc and Rogue have been on teh bandwagon for a number of years now knowing Class D is the ticket to get the sound their customers might like

It's called maximizing profits, as Class-D is many x cheaper to produce.

Cheers George 

@mapman I totally agree with the above statement. I'll also point out that Magnepan themselves say on their website to avoid Class D. 

That's why i purchased TOTL Emotiva seperates. I was confident that the dealer where I purchased the Maggies carried and recommended Emotiva as well. It sounded good when I purchased the Maggies.

Fast forward 6 months and I can truly say the Emotiva gear was mid fi. The Rogue gear outclasses in in every way. I don't care that Magnepan says to avoid Class D. They are wrong for making such a blanket statement, and I was wrong for heeding the advice.

I am finally very happy.

Whatever Ralph meant the mid-fi comment did make me laugh knowing that the sound I hear from practical Class D amps today (like the ones I own which are neither the least or most expensive) is not mid-fi by any reasonable listening standard.

I suppose mid-fi is in the eye of the observer or the ear of the listener.

Nevertheless respected tube amp makers like Arc and Rogue have been on teh bandwagon for a number of years now knowing Class D is the ticket to get the sound their customers might like with most of the speakers out there today that are not overly  tube amp friendly. My local dealer sells Arc and Rogue (mostly tube amps for many years) and has jumped on teh Class D bandwagon even saying that the Rogue models he sells are the best sounding with the speakers popular with his customers (Magnepan and Sonus Faber).

Just to ad to Ralph, why would Technics (SE-R1) strive to develop twice the current going switching frequency, if there was no point to it.
But you pay for this first off development $30k! But the price will come tumbling down when others adopt it. But it also still needs to be higher again.

Cheers George

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).

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

 

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.  

 

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.    

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.

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

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

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.

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

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

      

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."

Great post Noble100.

A standing ovation to Noble100 ’s post . Claps !

@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

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?

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

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?

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. 

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.

^^ 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!

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