Perhaps not for Class D.
Are future improvements in Amp/PreAmps slowing to a crawl?
https://www.stereophile.com/content/nelson-pass-circuit-topology-and-end-science
Is Nelson Pass Right?
Is Nelson Pass Right?
402 responses Add your response
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I liked the closing of the article. He mentions without saying bluntly, that most of the designs out there today are spinoff’s. Dashes of this or that thrown in, and a new something is born. This is what I took from it anyways, right or wrong. Yes, this happens all the time. Most of the topologies out there now are repeats. I mean, how many ways do you think you can run a tube? Transistor? Wouldn’t one think those kinks were ironed out years ago? I sure do.... I knock people’s heads off quite regularly with a few of my restored 30+ year old amplifiers. Yes, they are solid state, and they sound nothing like the type would suggest, nor do they sound like tubes. They sound like music. If something sounds solid state or like tubes, it is not right IMO. I have not heard any revolutions in amplification/preamplification with anything new, to be honest. "Who is this clown?" you say? Who cares. Let’s just say I have been in this hobby all my life, and I have had a ton of gear, with a good set of musically trained ears. Now, DAC’s are another story. Cables are another story. Electrolytic capacitors are another story. Everything else however, not so much..... All of course, JMO. |
I think, he is both right and wrong. He is right that there doesn't appear that much more can be done with either tubes or transistors. Breakthrough will come when something different is invented. Whether it is ever invented or not is another question. I hope so. Let's be clear about it - neither tube nor transistor is good enough. He knows it but he sounds quite resigned. |
As noted already, type D is still in its' relative infancy. So there's perhaps a new 'kid on the block' that's yet to hit the ceiling in terms of it's impact.... I keep seeing 'type T', which I suspect is referring to the Tripath units which appeared awhile back. Is this a reference to a form of D class amps? Can anyone expound on this for the record? Curious minds, all that...*G* |
@asvjerry you are, indeed, correct. Class T are built using the Tripath chips and are a subset of class D amps. From what I understand, though, Tripath chips are no longer manufactured and haven't been for a few years, so anything advertised as Class T is probably not going to be a great example of cutting edge class D. |
No - the future is already clear. The new switched Mode Power Supplies are reducing 60Hz hum and lowering noise floors further than ever before imagined with a linear power supply. Look at the specs on a Benchmark ABH2! Can anyone find an amp with better performance specs? Only a few years ago world class was around -110 dB SNR, THD etc... these improvements are nothing less than staggering and YES you can hear the extra definition, clarity or blackness that such performance brings even though the best speakers are only -70 dB in performance. (I was doubtful about whether this level of performance can actually be heard but my ears tell me otherwise) |
Class D is a poster child example of modern day innovation in audio amplifiers. It is indeed SOTA in some spectacular designs and will only get better. I suppose many manufacturers, Pass Labs included, are a tad offput at the fact that great sounding amps, amps that cost and weigh a small fraction of theirs, are becoming readily available. The fact is we are in the midst of disruptive amp technology. It is pretty much the opposite of the article’s suggestion in amplifiers. Class D is still in process, but great sound is already out there. How can we dismiss this reality? Strange to me how when in the very midst of innovation and change some still miss it. Some that should, and probably do, know better. Tommorows’s Class D amps will be wonderful, but some will still prefer a tube amp or this other amp etc... This will always be the case as choice is so very important as we all hear differently. However, dismissing the Class D evolution/revolution is startiling. Combining Class D with high quality DACs (powered dac) is another fascinating innovation hot bed. |
The Map is Not The Territory. A wanky and side shifted statement might be that Class D is about solving a problem that no one in the world of high end audio was interested in asking. Further... in the world of stately posturing (why back down when you can double down!): For me, an innovation has to exceed what I know, almost from the get go, not spend 20 years in the middle of a fistfight argument about barely equaling it. Like Digital vs analog. Human spheres of communication and awareness/sharing, social grease, clannishness and so on. Marketing..being a thing that works..speaks to the eternal shame of some of humanity's complex integration(s). |
Our amps are really not spinoffs of anything. And they are tube. So I don't agree we're at the end of the line by any means... But to make it more interesting, we've been working on a class D amp of our own for which we're also working on a patent. Not going to reveal too much, but we solved one of the major sources of distortion in class D amps. And we have proof of concept. Now if we can do that on no budget and without any prior *recognized* expertise in the field of endeavor (people tend to think that just because we only do tubes that we can't know solid state as well, as if solid state is not taught at the University of Tubes or something...), what does that tell you? That perhaps there is still more to be done? One area that is a problem for all amplifier designs is that most are designed to have specs that look good on paper and are not really designed to also sound good. Now this is a simple engineering problem (understanding the rules of human hearing and designing to those standards rather than the existing set of arbitrary rules); the bigger problem is tradition- the tradition of how we say what are good measurements and what are not is at the heart of the issue. How do you get the industry to move off of standards set in place 60 years ago?? Until we fix *that* problem, progress will only be had by the outliers who are willing to buck the tradition and pay the price. And they are out there. Some years back I had some troubles when some people tried to steal my company. I remember getting a call from David Berning, who simply called to offer moral support; he told me (paraphrasing) that 'the industry needs people like you that bring diversity to the field'. I really appreciated hearing that from him and who better to say it as he is exactly one of those individuals: a brilliant designer and no-one makes amps like he does either! There are brilliant designers in this field and there are those that recognize that if their amp is simply competent, someone will buy it even if it is a rehashed 1950s circuit. I don't see that progress has slowed down at all- if that is what Nelson (whom I see as one of the world's top designers) is saying then I disagree! I do think that we see a lot of derivative circuits but we're always going to see copycats. |
Hey Ralph, the liquid metal cable is all about re-writing the ground that electricity walks on. As fundamental a mental shift as can ever be. From the molecular and quantum levels, on up. Hardcore and real. However, it’s a difficult thing for most people to understand has even taken place. It’s a dancing bear that dances a lot like wire but is not even remotely the same. At all. Can it do better than wire/solidus in it’s application in audio signals? Most definitely so. Can people relate to those changes and upturns in qualities they desire? (the human question is more complex than that, though) Some do, some don’t. Top people in various fields ’get it’, immediately. Pundits on forums?... sometimes...not so much. |
Hey, todd, thanks. That's more or less what I'd assumed....I remember Audio Control or a company of a similar name had fielded a line of T amps; one could buy one standalone or a group of them that could be mounted into a common chassis (which was more or less a rack to encase them). They came and went rather quickly...I guess they were either too far ahead of their time to be taken seriously or just got hammered by the pundits. I was attracted by the concept, but wasn't in a situation to pull the trigger on them. I may have been lucky or broke at the right time. *L* But I hear and see the feathers being rustled by the factions already here....*wince* C'mon, y'all. Tubes and the 'typical solid state' are not going to vaporize any time soon. The alphabet soup of amp types will be around for quite awhile, certainly long after the bulk of the readers here will have gone off to greener pastures...under grade level, but that's another issue for another sort of forum. Any and all adherents will have their 'favs' tweaked to the nth degree. D at some point will get superseded by E, F, and whatever quantum audio will look and sound like. As was said by a wag sharper than I: "The Future: Live it, or live with it." It ain't going to go away, and it'll be here soon enough. ;) Be patient, or ignore as best you can. *G* |
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'The end of science' bit in the title is mostly journalistic license in designing a hook for the article. Nelson speaks on some of this via: The other fundamental thing—number 2—is that I am centrally aware that all this is just entertainment, mine and yours. The objective needs of amplifier users are largely solved on a practical level, and as [Marshall] McLuhan perceptively noted, when that happens, we turn our technology into art. For me, the art lies in making simple, unusual amplifiers that sound great and measure fairly well. They aren't for everyone, but if they appeal to even a narrow segment of audiophiles, I'm perfectly happy. I'm equally happy if they are reliable.Thus not quite the end of science but an established science can head into being used in or as - art as commentary. |
@kosst_amojan The gold standard is class A and nobody has come close to building a class D amp that touches the qualities of class A. Even the very best draw very mixed opinions. Amplifiers are art. Every amplifier imparts distortion with some character. For those of us accustomed to low order distortion imparted by simple topologies using as few gain stages as possible, class D isn't even on our radar.It may interest you to know that our tube amps are class A with only one stage of gain. It can't get a whole lot simpler than that. And I've yet to hear a class D amp that can keep up. But it would be a mistake to simply write off class D. Its still on the steep part of the price/performance curve. |
I think in General, Nelson is exactly right... when it comes to the traditional designs of A... A/B anyway. I look at an old Sumo or Gas Amp that Mike Bettinger mods. He changes caps & resistors to newest & best as well as switching a bipolar to a Jfet, the results are that you have a 30 to 40 year old amplifier that competes with modern amps or Take an old PS Audio 200C.... from 1985. Yes it can be beat, but if comparing apples and apples, it still stands up with modern amps. So what I see is better devices, better parts, not necessarily better design. I think really that was what Nelson was referring to is that He jumped in a big way to LISTEN to Input/output devices to build the best components that he could muster, based upon the best parts that he could find and how those individual parts sound, it wasn't necessarily a revolutionary new design. With that said. I agree that we have newer technology that will matter. Class D output Is pretty amazing... I've taken abletec modules and built some of the light weight little amps that don't get hot, yet are very musical amplifers. So, I see both sides and suspect that some new input or output part will come along for Nelson or someone else to make the Next Best Thing. |
Anyone who thinks the best Class D is the lesser technology or always inferior sounding when compared to Class A is just not paying attention. "Will it sound like what you like?", That is a completely different discussion to have. If anyone can make a _better_ amplifier than the best linear and Class D for normal speakers I cannot hear it. However, lots of ways of making amplifiers sound different, juicier and more colorful. As someone once told John Coltrane (I believe): "You can't make it better, only different." Peace, E |
Speaking of Pass, it is important to note that the model for a high quality SS amplifier was first really codified in the late 1970's by the work of the late Dr. Marshall Leach Jr. Using bipolar transistors Dr. Leach's proposal set the blueprint for every SS design going forward for decades. Almost 40 years after this paper, I would love to have a panel discussion with Pass, Curl, Carver about how far we have come from then, what Leach got right, what he got wrong, or what they think Dr. Leach would have done better with the parts we have today. Best, E |
Want to give a shout out to Carver, the concept for his magnetic field amplifier continues to be used by Yamaha, NuForce and possibly even NAD (D 3020). Carver's design used a linear amplifier of relatively small power handling and hooked it up to a power supply of varying rail voltages. This minimized the power dissipation required in the output stage. Carver sued (and won) against Yamaha, but the Yamaha Pro line is using the EEEngine which seems derived. NuForce is using the idea in their hybrid amps, Class-D providing the voltage rails, with a linear amp sandwich, and maybe... the NAD D 3020. Still, how old is this tech? We can definitely argue against calling it all that revolutionary. Is any of it better sounding? Not sure, but Yamaha and Nuforce are free to send me samples.... :) Best, E |
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Eric I built the low TIM Leach amp from Audio magazine, and followed through with the next year of 100+ circuit changes in the following issues. I also owned Leach’s L S R&D amps from his company. He did not believe in matching transistors, and his amps were "average" sounding for their time! His article just re-hashed what was known in amplifier circuits at the time. No breakthroughs IMO. TIM was just "frequency overload" in fancy talk. |
I never said the amps were exceptional, but that the paper put together the formula. I am unaware of any other document before his paper that put together all the components that would become known as the SS formula. If there are, please share. High distortion SS amps were no longer passable as hi-fi. I have no idea what "frequency overload" means. Explain? |
@inna Why would a respected tube amp designer want to play with something very different?To see what is possible. Nelson Pass sold a kit very briefly that employed an output transistor known as a Static Induction Transistor or SIT. This was and so far is the only transistor type ever made that had the linearity of triodes and even had a soft clipping characteristic- so it should be possible using them to make a solid state amp that sounds exactly like a tube amp. Sony made them back in the 1970s for their Vfet amps. Nelson made a kit using them and you can bet that I wanted to know what that sounded like so I bought a kit. Why would you not? is more the question! |
Ralph, I love your innovative attitude as well,And greatly look forward to your class D design. I really enjoyed the Sit2 amp but I like my Diy sit that is push pull that uses nos Sony Vfet's.How could I not. What we need is some new transistors directly designed for audio amplifiers and not other applications.I have no Idea what that would be but I'm sure Nelson would. Kenny. |
Ralph, I love your innovative attitude as well,And greatly look forward to your class D design. I really enjoyed the Sit2 amp but I like my Diy sit that is push pull that uses nos Sony Vfet's.How could I not. What we need is some new transistors directly designed for audio amplifiers and not other applications.I have no Idea what that would be but I'm sure Nelson would. Kenny. |
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Yes in "some" cases they are engineering the musicality right out of them because too many audiophiles are demanding more detail from their gear. Excluding Class D amps how much more positive advancements are left to improve upon both in preamp and amp designs? I know there are different topologies applied to some designs and when you purchase a certain piece you are agreeing with the designer on what he thinks sounds good. Just maybe twenty years from now people will searching to buy the gear you own right now because what they are currently dealing with sounds like crap. |
@sean_heis1 Musicality is a meaningless term that can’t be measured. Improvements like SNR, channel separation, THD+N, and power into various loads are measurable. This amp does not use negative feedback to achieve improved performance over competitors. It has a carefully designed switched mode power supply that pushes all power supply noise completely out of the audio band. Benchmark had been making world class Analog devices for pro TV production for years before they embarrassed the audiophile world by building far better devices. I would say that competitors are catching up to their DAC technologies but this new amplifier is another leap in performance and another embarrassment to the long established amplifier providers churning out their mediocrity year after year! Perhaps it takes someone from outside the establishment to make major advances. |
@sean_heis1I find SNR & THD+N to also be meaningless. Same with THX certification. However, I agree that the best switch mode power supplies are really good these days. Benchmark is a very good company. They take pro gear and package it for hifi buyers. If your flavor leans towards the clinical side, they could be an excellent fit. They won't embarrass anybody that shouldn't already be embarrassed. Only Schiit can do that. ;-) |
Dragon_Vibe, "maybe the Future is already here and we are at the very end of technology breakthrough regards to audio?" This reminds me of the patent office wanting to shut down decades ago because "everything has already been invented" Breakthroughs happen every day. As far as designing amplifiers with the express goal of having a particular sound to me is a waste of time. It means the designer has given up on the notion that "perfection" is not attainable. Take a look at this viewpoint of distortion... http://h-cat.com/images/H_CAT_White_Paper.pdf Roger |
@sean_heis1 If you find outstanding (better than anything else on the market or ever mass produced) measured performance to be a meaningless achievement then how do you propose to measure what you find important? I would put it to you and everyone here that if you can’t measure performance then there is no way to track improvement. Perhaps this is the fundamental problem in the audiophile industry - it has become a fashion clothing industry that suits people’s tastes and follows trends with no goal to improve anything because "good enough" in clothing materials was achieved 30 years ago - so now it is about color and style in an endless circle of ever fluctuating fashionable trends. |
