The Hifi Trajectory Of Class D Amplifiers


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I bought my first digital SLR camera back in 2005. Film SLR cameras were still king back then. Longtime film camera hobbyists and pros thumbed their noses at digital. Ten years later, film cameras have been surpassed by digital cameras and are nearly extinct. Millions of people use cameras. The market was already in place for anyone that would advance the technology of digital photography.

With Class D amps, you don't have a marketplace the size of the camera marketplace. There doesn't seem to be enough economic incentive to spend the necessary research dollars to advance the technology to get the same sort of improvement trajectory that digital photography has enjoyed.

Anyone care to speculate how long it will take for Class D amps to consistently rival the best tube, Class A and Class A/B across the board....and do it without resorting to the stratospheric prices that current non-Class D amps are priced at.
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I bought my Sunfire 300 amp in 2005...
One can argue that we're already there except that Class D technology will likely continue to improve and become more affordable still for the foreseeable future.

I've heard many amps and systems over the years. I could not be happier with my Class D amps. I expect only even better things down the road.
+1, Mapman
Mapman...what class D amps do you have?

I gave up on class D a few years ago after trying several different ones. At that time, I wouldn't have put any of them into my garage system. Not a fan so far, but do see the potential.
I have Bel Canto ref1000m mono blocks and c5i integrated amp.
Class D has completely taken over the bottom end of the market. The amps in your cell phone are class D.

Class D has arrived insofar as its ability to challenge conventional solid state is concerned. I use a Crown class D amp for amplification of my keyboards in my band. It has two channels each of about 500 watts and it weighs 22 pounds. The amp I had before had half the power and weighed nearly twice as much. That can be a big deal when you have to lug heavy equipment around every time you play.

When it comes to challenging tube amps there is still a ways to go however. I like to relate the story of a show we did with a number of other bands a couple of years ago. Our bass player uses a 400-watt vacuum tube Peavey amp which we offered to backline (the term refers to the amp staying on stage so other players could use it, reducing the setup time that the band needed to go on stage). However one band had a bass player using a 500-watt class D amp made by Orange. He thought the Peavey would not be able to keep up with the sound that he needed. I told him there was no way a 500 watt class D amp could keep up with a 400 watt tube amp- he was quite shocked.

So we had him audition the Peavey- what he found was it made far more energy than he could get out of his Orange, so much in fact that he felt it might be too much to handle so he went with his Orange anyway as the bass from the Orange was less prodigious.

Just so you know, bass amps are far less likely to get overdriven than guitar amps are. IOW this was not just a matter of distortion due to overload or anything like that.

My experience with class D in high end audio is similar- and is why I made the comment to that bass player. I've not seen a lot of change in the years since, so I suspect that if class D is able to surpass a good tube amp, that day is still a ways down the road.
Couple of people reported on another thread, that Rowland's new $38k class D integrated had the best sound of NY Audio show. Feel free to keep discussing bass guitar applications.

Class D is still growing and coming out from it's infancy.
The technology isn't here YET to get the switching frequency for Class D far higher than what's available at present.
Once this technology is developed only then Class D may get to be considered real high end.

Doesn't matter how much is spent today like the above $38k Rowland, hifi manufacturers can't make the switching frequency technology happen, this can only come from big component manufacturers, like Burr Brown, Analog Devices and such.

Once this Technology is developed, and it's coming, all linear amps tube or solid state, will become worth less boat anchors, and Class D will become the norm for hiend instead of being just a good bass amp.

Cheers George
hifi manufacturers can't make the switching frequency technology happen, this can only come from big component manufacturers, like Burr Brown, Analog Devices and such.

George, is this because hifi mfgs pockets aren't deep enough to finance the research to advance the technology?

What's the incentive for Burr Brown, Analog Devices etc to advance the technology of high end Class D? That market is sooo small.

Why wouldn't a guy like Nelson Pass or Bob Carver look into Class D? Are the best brains in hifi amplification stuck on linear amplification? I believe if they put their minds to it, they could advance Class D.
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Screw the technical theories and assessments.

Listen to some and make your own assessment.

You might like them better than a tube amp or not. There is a chance. It all depends. There is a lot of top notch performers out there of all types to consider.

Class D is a bigger threat to Class a and A/B I think than to tube amps. Class D and Class a/b amps will tend to work best in similar systems whereas tube amps are a different paradigm that requires other differences as well to work their best.

No doubt in my mind a $35K 1500 w/ch Class D integrated amp by Rowland will hold its own own with most anything and possibly even win head to head if all is done right.

But,if its loose, warm euphoric tube amp sound specifically you are looking for, Class D amps will not give you that.
Although technology is much different, I think it a good analogy that Class D eventually will do to other amp designs what digital cameras did to film cameras. it may take another 5-10 years of market growth still to totally dominate in most common applications. The reason will be because the technology is "greener" as well as being capable of doing the same applications as older amp technologies better and for less in general.

Tube amps have enough unique properties though I think to stick around even longer as a niche technology, much like phonograph technology.
Obviously you guys haven't heard the SPEC Real Sound amp. Best, Rob

11-19-15: Mitch4t

George, is this because hifi mfgs pockets aren't deep enough to finance the research to advance the technology?

It's up to the massive component manufacturers, that HiFI manufacturers purchase their components off to advance this technology.

As for guys like Nelson Pass and such, they will also in the future use Class D when this technology is reached.

Others manufacturers who have already invested in Class D, are getting into it because it's already a financial viable product to make
As the components that are around now will make an amp that costs half the price of linear amps to manufacture, even though the technology is not yet matured enough.

Cheers George
Yes, the semiconductor industry really doesn't want to make linear devices if they can help it. Switch mode devices are easier and more profitable.

Kijanki, in case you didn't know it, most decent bass guitar amps are built along hifi lines. They have to be in order to sound right. If you get a chance, look up a schematic of an amp called the Marshall Major and you will see what I am talking about.
Atmasphere, Bass amps were and often are made as cheap, crude implementation of class D, where you can get a lot of power in inexpensive portable package. Because of that many think of class D only as a crude inexpensive way to get lots of power. I'm not sure why you even brought the case of 500W class D not being able to keep up with 400W tube amp, since it is irrelevant to our discussion and refers to particular design and the way power was specified (only 6.7% difference in perceived loudness between 400W and 500W). In addition, in last decades bass amplification in larger venues got into PA system, making raw power of the bass amp relevant only for small theaters. Class D can be designed with any headroom, often has line and load regulated power supply, that doesn't sag under big loads and soft clipping similar to tube amps (whole Icepower family). In contrast, class A SS amps have very limited headroom, mostly unregulated power supply and hard clipping, but they are great example why suitability of given amp class for bass head says absolutely nothing about sound quality in home stereo system.
My Class D amps at home are top notch.

At the gym, they use inexpensive pro Crown Class D amps with large horn loaded speakers and instructors use their Apple devices as source. Not audiophile material in there with lots of echo and speakers in corners near ceiling but gets the job done nicely.

Very versatile technology!
In terms of sound good Class D amps I have heard and good tube amp setups I have heard differ not just in components used end to end but soundwise as well. Tube amps often provide some degree of warmth through the midrange. Class D amps I have heard deliver more of a "liquid" midrange but not warm at all. You have to add that somewhere else if warmth is what you seek. A good matching tube pre-amp does nicely.

I have one mostly digital (with phono and line level analog inputs plus various digital) integrated amp (Bel Canto C5i) and my main rig with BC CLass D amps and ARC tube pre-amp. They are both excellent performers but have their sonic differences, mainly the touch of warmth the ARC preamp delivers. I can listen to either happily for hours.
Mapman, there are some highly praised class D bass heads (like Ampeg micro or Gens-Benz Shuttle series) and some really bad ones, like with anything else.

To me liquid midrange of class D, that you mentioned, is closer to tube amp than SS amp sound. Other than that my class D amp is pretty neutral sounding. You like a little bit of warmth, that tube preamp gives you and I get the same from my warm sounding speakers. Either way, Icepower is a very good amp, for the money.

Class D progress, in my opinion, is related more to switching speed of output Mosfets that would allow to lessen phase shift by extending audio bandwidth. Companies like Fairchild or International Rectifiers announce new faster, higher power Mosfets every year. That is bottleneck IMHO. Everything else is only matter of integration level. It is also worth mentioning that modern class D modulator is not a simple ramp and comparator but resembles more Delta Sigma A/D converter. In fact PWM is a byproduct of Delta Sigma conversion, that appears alone as SACD. SACD is pretty much class D output (PWM) at high carrier frequency (2.8MHz) before filtering.
Kijanki, agree.

Neutral liquid midrange is a good thing.

I have insufficient data points to say all class d sounds that way but ice power does seem to.
I disagree with the premise that class d has not yet arrived.
I also disagree. Class D amps have arrived. I was a skeptic until I borrowed a pair and used them in my system for a week. I am very happy with my system's overall presentation now. Fantastic low end, dynamics, and smooth articulate midrange. Not to forget a silky smooth and extended high end with such a low noise floor, it makes the music sound that much better. The issue is more being able to admit that fact and hanging onto past prejudices to satiate the ego. The digital camera comparison is a great analogy.
I have two integrateds, one a Peachtree Grand X-1 (class D) and an Audio Research VSi55 running KT120 tubes. Through first Proac D2, then Wilson Benesch Arcs, now BMC PureVOX speakers, I can't tell the two apart other than that the Peachtree is more powerful and will play louder. At volume-matched levels, I cannot distinguish between the two. The only time they sound different is if I engage the tube buffer (running two upgraded Cifte 12AU7) on the Peachtree, then it's actually a little warmer than the Audio Research. But with the tube buffer off, it's apples vs apples. It's my opinion that the ARC VSi55 puts out more than acceptable sound quality, ergo Class D has officially arrived, at least in my house.

I'm not sure why you even
brought up the case of 500W class D not being able to keep
up with 400W tube amp, since it is irrelevant to our
discussion and refers to particular design and the way power
was specified (only 6.7% difference in perceived loudness
between 400W and 500W). In addition, in last decades bass
amplification in larger venues got into PA system, making
raw power of the bass amp relevant only for small theaters.

A smaller theater was exactly were my example occurred. It was not the overall power that was the issue- it was that the Orange lacked the bass impact and the player had grown used to that. Not all bass amps are cheaply made BTW- in order to sound right the demands are exactly the same as in a good home audio power amplifier. **That** is why I brought it up.
Kijanki, Ralph (Atmasphere) is well qualified to talk about guitar amplifiers. He won't mention it, but he's the designer and manufacturer of a superb OTL guitar amp based on the circuit in his Atma-Sphere amplifiers. See:

http://www.renditionaudio.com/evolution.html
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Rushton, I don't question anybody's qualifications but rather particular example. I'm pretty sure we can find 500W tube amp that doesn't keep up with 400W class D bass amp, but again it wouldn't be relevant to the issue we discuss (class D sound in home stereo system). If anything, class D amplifiers keep extremely well with music peaks (mentioned in many reviews) when equipped with regulated power supply (SPMS).
Most pro audio applications call for high efficiency easy to drive speakers in order effectively fill large rooms. That helps assure tube amps will be able to do a good job as can good SS or Class D. Most will opt for the lower cost and maintenance solution out of practicality as long as results are good. So few would choose a tube amp these days even though I have no doubt some might sound very god.

HOme audio is different as Kijanki points out. Tube amps are not suited for many home speakers designed to deliver more bass out of a smaller package. A god Class D amp will have little problem with most any home speaker.

What sounds best in each particular case will obviously depend on a lot of things.

So I agree pro use or benefits of tube amps is not really useful for this discussion.
I'm pretty sure we can find 500W tube amp that doesn't keep up with 400W class D bass amp,

Good luck with that. While I do think that day is coming, its still a long ways off and that amp simply does not exist yet. I've no intention of arguing back and forth about it- this is simply how it is.

Has Class D arrived? Sure. But do they beat tube amps? That's an entirely different question!
But do they beat tube amps? That's an entirely different question!
...and one with no answer here, because you will never achieve consensus on the definition of "beat"
Not only has Class D arrived but their making a big splash and the ripples are being felt through out the audio community. For some of you dyed-in-the-whool Class A or Class AB fans, there is a technology that threatens your existance, well maybe not yet but they are getting there. Even those cheap little Class D amps by Lepai sound better than a lot of midfi conventional amps when properly set up. Even so I will keep my McCormack amp because it just sounds different but in a damn good way! But I will continue to listen to some of those Class D amps just because they are diferent but sound good!
Atmasphere,as much as a lot of folks here love the sound quality of tube equipment [me included] your assessment and comments on SS class D amps just doesn't sit well with me.

We know that you make great sounding tube equipment,but this thread is about solid state class-D amplification. You really do not have to defend your business every time someone speaks about liking SS kit better than tube kit.

I may be going out on a limb here... but I would presume that you never sat down and gave a serious listen to the likes, of say, a Merrill Audio Veritas mono block amp. If you can ever get the opportunity to hear them,I think you will be picking your jaw up off the floor...
11-23-15: Phd
"Not only has Class D amps arrived but ... there is a technology that threatens your existance ..."

No, the rise of Class D amps doesn't threaten my existence at all - not even by a teeny bit.
You really do not have to defend your business every time someone speaks about liking SS kit better than tube kit.

I may be going out on a limb here... but I would presume that you never sat down and gave a serious listen to the likes, of say, a Merrill Audio Veritas mono block amp. If you can ever get the opportunity to hear them,I think you will be picking your jaw up off the floor...

Your presumption is incorrect- believe it or not what is actually " defending my business" is actually done by auditioning products like these and then assessing the threat. If you think about you will see that no business in high end can really exist in a vacuum (if you will pardon the expression...). We assess a lot of technologies to try to understand how that might affect us in the future- I would think anyone in it for the long haul would do just that!

Further, its my opinion that you didn't read my posts all that carefully. No worries- but read this one, because it explains in greater depth what I am actually thinking.

First- Its not like we can't make class D amps; we've been looking into it for over 10 years.

But more to the point I've not seen Class D threatening conventional tube amps let alone ours (which are less conventional)- **so far**. What I **do** see (or hear, as the case may be) is that class D has effectively supplanted the traditional solid state design in all but the very best of the traditional designs (which might be a misnomer, as the best solid state amps I am thinking of are leading edge and really are not that traditional). Otherwise what it still boils down to is still just about the same old tube vs transistor argument which has been there all along, although the goal posts have moved about somewhat.

Those of you who are familiar with price performance curves will understand why this is so, and thus is likely to be so for quite some time. What the question really becomes is what part of the price performance curve (for more understanding, google 'technology S curve') class D is on right now.

Its my surmise that class D is nearing or at the top of the most vertical part of the curve. This suggests that the technology is reaching maturity. This is certainly what its advocates would like us to believe! If this is so, then what follows are incremental improvements.

FWIW, transformer-coupled tube amps are a very mature technology so improvements over the last few decades have been fairly slight.

Now if you have been following along, if my surmise is correct than this debate will be on-going possibly for decades. If my surmise is incorrect, then class D is a bit lower on its ascendancy of the technology S curve. IOW, breakthroughs are still possible, causing the technology to achieve much greater performance than is available right now.

So which is it? The answer is we don't know. But its been around for a while and its clear that class D is much much better now than it was even just 10 years ago.

So I am sticking to my position, which is not based on a personal bias or some need to 'defend my business' that it is possible for class D to surpass not only traditional solid state but also tubes, **but the latter day has yet to arrive**. But I'm not ruling that out as one can see from my prior posts.
Cleeds, please sir don't take that particular statement literally, no one is being threatened. Just to draw attention to Class D's formidable sound quality and it's getting better as time goes on.
Atmasphere.

"Has Class D arrived? Sure. But do they beat tube amps? That's an entirely different question!

So I am sticking to my position, which is not based on a personal bias or some need to 'defend my business' that it is possible for class D to surpass not only traditional solid state but also tubes, **but the latter day has yet to arrive**."
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I understand your position of necessity on the matter but,to my ears, class D has and does surpass tube amplification,for many,many reasons... Key being,it just sounds like a real music... in real time... in a more believable way. Of course,horses for courses...
I'm a class D guy. Tube amps are fine but have not lured me to the dark side. 🌚
Is it a rocket!!!
Ten years later, film cameras have been surpassed by digital cameras and are nearly extinct.
Mitch4t, I'm not sure I agree with your on this statement. Yes, digital cameras are everywhere & millions of people have gotten into "photography" as a result but IMO the film vs. digital camera is the same argument as .WAV vs .MP3 music files. The high compression of music files has made the file size smaller, totally wrecked the sonic quality but has afforded great convenience to the public to the point that 100s of songs can be stored on your portable device & played back at will. Digital photography too has made it very convenient to take photos without thinking much about the photograph to be taken because it's so convenient to delete the bad photos & keep the better ones. People are mindlessly taking photos because they can & the quality of photos (in terms of composition, lighting, artistic content), in general, has gone down just as fast. It's a great stride forward in convenience but many steps back in art of photography.

Take a look at these photos - they are all take by a FILM camera (no digital). In fact, it is my understanding that Arizona Highways magazine does not accept any digital photos as their resolution is not good enough for even an 18X10 print! The photo quality is superb & very much like what the human eye sees - all boundaries are gradual; not stark/abrupt as in a digital camera....

http://www.arizonahighways.com/photography/photo-archive
Bombaywalla, comparison film vs. digital SLR is very unfortunate here, since class D is purely analog with unlimited resolution.
Still, you can take equivalent quality pictures using medium frame size film camera for much less money than digital, but in case of 35mm frame film camera has no chance. Digital cameras have better resolution, lower noise, bigger dynamic range and much higher sensitivity (ISO) not to mention overall convenience.

http://petapixel.com/2015/05/26/film-vs-digital-a-comparison-of-the-advantages-and-disadvantages/
The premise that class d amps haven't "arrived" is flawed. Many people love them, in fact many have dumped their Pass, Bryston, ARC, etc. amps in favor of class d. All one needs to do is read through the various Hypex class d threads all over the internet to see this. It isn't a question of if, or even when, class d will take its place at the table, it has already been accomplished. The objective performance of class d amps is now significantly better than most ss and surely all tube amps. Of course there will be those with vested interests who will poo-poo class d, and there are those who prefer the distortion profile of tube amps. Ultimately, it comes down to personal preference and subjective tastes, and as has been demonstrated in the market place, class d has shown it has not only arrived, but displacing traditional ss and tube amps everywhere one looks...