I have recently paired an Audio Research DS225 Class D amplifier with an Audio Research tube preamplifier (SP8 mkii). I cannot believe how wonderful and lifelike my music sounds. The DS225 replaced an Audio Research SD135 Class AB amplifier. Perhaps the SD135 is just not as good as some of the better quality amps that are out there, but it got me thinking that amazingly wonderful sonance can be achieved with a tubed pre and Class D amp. I have a hunch that as more people experience this combination, it will likely catch on and become the future path of many, if not most audiophile systems. It is interesting that Audio Research has been at the forefront of this development.
No one has provided a logical, technical counterpoint to kosst's argument regarding class D other than experiential vignettes.
No one has proven the measurements Kosst has alluded to are audible on the other side of a speaker.
All Kosst has done is noticed 1 measurement.
There are plenty of ways in which Class D is as good or better than many SS and Tube Class A, Class A/B amps.
Noise and frequency response and low output impedance in the audible band among them. Why don't we count those 3 as better than Kosst's single measurement?
Why do you think Stereophile uses an output filter in the first place? Because it is more meaningful that way. What makes Kosst such an authority that he can disregard it? Puhleese.
Congratulations on the Nord. I too have the LM508IA and largely prefer it over the W4S ST-500 mkii class D. The W4S had great lows and mid bass but sterile mids and hard highs. Heck I even liked a 20 year old parasound HCA-1200ii better. I can see how a tube pre could work wonders instead of my DAC-2 pre on a class D amp.
What get's me is how much a positive difference quality room correction makes. How many commenting on Class D vs. A/B, SS, tubes have made these comps with room correction and separates? My experience was that class D was stark, bleached, just plain fatiguing. I'm sure a better/new class D amp would sound better.
The exacting results of RC may have synergy with one amp and not another and knowing the differences RC makes, I never A/B compare without it. Could the Lyngdorf 2170 buzz be largely attributed to room correction?
I for one have owned the gamut of amplification (including several class D variants with multiple iterations of Hypex and a DIY amp from Class D Audio). Class D was pleasant enough (with a tubed pre-amp), but failed to hold my attention and seemed vaguely flat and bleached for lack of a better description.
This common even with those that persevere with it as above. But some don’t hear it, and because they can’t hear it, they say those that do are full of it, even if measurements are backing them up. Bet you thought there was nothing wrong with the bass though . I still believe it is the future, just not yet, I think the Technics and Merrill ones with GaN technology, are going to lead the way, and take Class-D where it needs to be to compete with the hiend linear amps. The others at the moment are great bass amps, but not hi-end yet elsewhere in the audio band..
so Kosst, are you saying all class D has audible distortions? What about A and or A//B? Don't they as well?
I have a 20 amp dedicated line, Core Power 1800 PC for front end . I bought it for my amp/s too, but they sound better plugged direct to wall. I use both WireWorld PCs and a couple from Tekline Audio, which sound better, but are 2+ xs the price, although WW has more expensive PCs too
Kosst. You have repeated your stand about specifications on distortion, overshoot of square waves, etc,etc. But you have eluded the simple question many of us have asked you, "have you listened at length, (weeks, months) to any viable Class D amp in your own system. I have no problem with class D not being your cup of tea, just you and other nay sayers believing it is junk and should be dismissed. To many well trained ears here have had wonderful experiences with class D, myself included. Tim
I don’t recall the amp model, but Pass installed a pot on the front of the thing to dial in the distortion character ranging from a few hundredths % positive phase second harmonic to a few hundredths negative phase.
Pass makes the opposite argument you are making. Your argument is: I can see it has more distortion so it’s bad.
Pass’ arguments are that MORE distortion is favorable.
Further, he’s adding distortion which is in the audible frequency spectrum. Your claims Class-D switching noise (i.e. distortion) are in the RF frequency range.
So, we are back to : Is switching distortion from Class D amps audible or meaningful? In fact, none of the claims of sonic inferiority here even point to that. The only counter points I hear are of sterile sounding, or lacking dimension or engagement. Which of these problems do you think come from switching noise and distortion?
George insists that high speed is where it's at, based on no particular evidence. I mean, what exactly is high speed? What is too low? What is high enough? You have to buy into the idea that you have an audible problem to begin with.
For years I poo poo’d Class D in the same fashion as Kosst has here. But, because of curiosity and a sense that a company I trust, PS Audio, wouldn’t be spouting off about how good these amps are if it couldn’t be backed up, I decided to try a pair of their class D monoblocks.
They sound better than ANY of the MANY of non-Class D amps I have owned in the past, not only to my ears, but to several of my audio buds who have now listened and who are both tubed and solid state (non-Class D) amp owners. They ALL agree that my system sounds significantly better than before with these amps.
I took a chance and am now convinced that the technology has arrived at level consistent, and exceeding, the sonic perfomance of ANYTHING out there.
Also, this nonsense about caps burning up early due to the switching technology is a lame attempt to scare people in an era where fear reigns supreme. Good electrolytics last a long time. Enough of this fear mongering.
Horseless carriages were deeply despised and 'destined for failure' when they started out too. Any car owners out there?
I said in a post that I could not hear switching distortion in my amp and believed that most, if not all, of said switching distortion wasn't audible. Ralph Karsten said to me, and I quote:
Also, this nonsense about caps burning up early due to the switching
technology is a lame attempt to scare people in an era where fear reigns
supreme. Good electrolytics last a long time. Enough of this fear
mongering.
In the amps or speakers?
I think there's been a great deal of improvements in cap technology over the last 20-30 years. Low inductance, and low ESR electrolytics are a lot more common.
Maybe the question we really should be asking Kosst and George is this:
What, exactly, are the audible effects of switching distortion in a Class D amplifier, and can you give specific examples, with speakers, that you have heard this from?
Like all amps, I don't think Class D is right for every speaker, so I am open to the idea that certain speakers will perform worse than others. So, George and Kosst, ball is in your court. Please share with us your experiences.
Wrong!!! look at it and think again. It’s Stereophiles, there’s your
hint, they’ve NEVER EVER given a Class-D 20khz square wave, as it would
look unrecognizable as a square wave.
You are correct and I was in error- that is a 10KHz squarewave.
So that makes the scan frequecy in this example only 200KHz(!), which means the class D in question had to have been built in the **1990s**. By the early 2000s, everyone was doing well over 300KHz. That means that the bump on the leading edge is the phase shift caused by a filter that is likely at only 40KHz. So using this as an example of **all** class D amps is still a Hasty Generalization and like any logical fallacy, is false.
20kHz is hard for any amp to do, much less well???
Look
at page 17 where the FW F5 absolutely nails a 200KHz square wave at 1
watt. A lot of amps are designed to roll off at or past 20KHz more for
purposes of self preservation than technical limitations. You’re always
going to have that guy who wants to try Litz wire ICs and create a high
power oscillator.
I agree- but the Pass amps IMO are some of the best solid state amps made :)
Our OTLs are quite good at 1 watt 20KHz squarewaves too. And they don't care about the Litz wire; I'd be shocked if the Pass amps do!
Regarding distortion- I agree wholeheartedly that small amounts of particular kinds of distortion are easily heard. This is why I've avoided feedback in our amps; while feedback suppresses distortion in doing so it adds some of its own, and its all IMD and higher ordered harmonics which are easily heard. But it is also true that you can build a class D with zero feedback and there are a number of them around. At that point, the limit of the distortion becomes the precision of the encoding scheme. For example if you use Pulse Width Modulation using a triangle wave to set the switching frequency, the distortion is all about how precise the triangle wave is and the speed and offsets of the comparitor circuit used. It happens that with that sort of circuit, as the amp approaches full output, it can have a form of soft clipping as the encoding scheme starts to fall apart. So the resulting amp can have very low distortion and a lack of higher ordered harmonics over most of its range.
So that makes the scan frequency in this example only 200KHz(!),
Wrong again when have you seen an amp that can do 200khz, have a slewing audio frequency square wave like this, the sides are collapsing in like the leaning tower of pizza
Our OTLs are quite good at 1 watt 20KHz squarewaves too.
And that is where you should stay linear and with tubes, otl, even add trany coupled, so your not hamstrung to certain speakers. You built your rep on them and now your going to destroy that?. Not a good move, it will come back and bite you on the arse, your just another respected amp manufacturer saying "give me some of that class-D action"
So that makes the scan frequency in this example only 200KHz(!),
Wrong
again when have you seen an amp that can do 200khz, have a slewing
audio frequency square wave like this, the sides are collapsing in like
the leaning tower of pizza
I think you misinterpreted this. The amp at the link you provided was an older amp that was only switching at 200KHz. Nobody has been building amps with switching speeds that low in a long time, unless its for subwoofers only. Also, we don't know why the risetime is as slow as it appears since the data on the amp itself is lacking. That can be caused by measurement errors, but it can also be caused by analog signal processing before the encoding scheme.
So its erroneous to apply the results of this nearly 20-year old circuit to newer amps.
I think you misinterpreted this. Nobody has been building amps with switching speeds that low in a long time
Geez Ralph other way around, get with it, in this case I wasn’t talking about 200k switching speeds, I was talking band-width and the slewing of this square wave I posted up, with and without switching noise embedded in it.
Ralph, you are more capable than anyone on this thread to explain why class D is the future from a technical standpoint. Lay it on us. Also, have you (as George is implying) had a religious conversion to the world of class D to the point of implementing it in your products?
I know I shouldn't weigh in on this, because I've never heard a Class-D amp, but I am an electronics tech with a First Class license.
Back in the 70's, me and Julian Hirsch declared that we could determine what any amp sounded like by it's specifications.
Julian Hirsch, bless his honest deceased heart, did not have 20-20 hearing, and I had faith in our belief.
In the late 80's, I wandered into a high end emporium in order to discover why people were paying so much more money for stuff that was inferior to mine according to the specifications; did I get an ear full.
I didn't know it, but I could hear a lot better than Julian Hirsch; there was a world of difference between my SS amp, and ARC tube (price as well). There was a big difference between everything I owned, and what I heard. What I heard was worth the difference in price.
Specifications are not as important as they are laid out to be; we can hear what can not be measured; you would be surprised at what some people can hear. In the military, my hearing was measured as exceedingly high. No need to pay for more than you can hear, but I could hear more than what my rig delivered.
I said that in regard to the SS versus Tube amp debate; although I have never heard class D, not only have I heard, but I was religiously devoted to SS amps; that is until I heard a tube ARC. I'm not pushing ARC amps, but I am pushing tube amps.
While a tube pre, and a SS amp power amp will pass; when you go SS all the way, it's a no show for me. I said that to say that I "believe" a class D amp will sound the same as a SS amp, and that's why I know I should not have weighed in on this discussion, but I did; so forgive me for commenting on something I've never heard.
I’m using all tube preamp and amp gear, Class A/B. However, at several audio shows, I heard relatively decent Class D amps. One that stood out was from PranaFidelity. http://pranafidelity.com/index.php/reviews/ Using my CDs in an EAR player and his electronics and speakers, my jazz and classical sounded very enjoyable and I could listen for an extended period of time. It wasn’t as good as my home systems or more expensive systems I heard, but it was musical. More than I can say for any Magico speaker demo I’ve heard in five years. If Class D ever became as good as my big tube amps, I’d be interested but not as of today.
I’ve heard tube preamps (e.g. EAR 912) with big SS amps (Bryston 28 cubed) sound very good, even excellent on demanding speakers. I don’t know if I would like an all SS system though. The ones I’ve heard over the years just lacked something. The PranaFidelity was using a tube (and warm sounding) CD player which may have made the difference using an SS preamp and Class D amp.
Ralph, you are more capable than anyone on this thread to explain why
class D is the future from a technical standpoint. Lay it on us. Also,
have you (as George is implying) had a religious conversion to the
world of class D to the point of implementing it in your products?
My apologies for a long answer to a short question.
No religious conversion. Its just engineering. We've been watching the development of class D for 20 years; the early amps were a joke, like the one under test that is represented in the little graphics George likes to post.
About 3-5 years ago they started to really come around. I've been using one for about ten years for my keyboard rig in my band, mostly because its light and powerful, and I have to move that stuff myself when we do a show. Its a Crown, and doesn't sound that bad. But for high end it falls short, although it is an older amp.
About two years ago I realized that Atma-Sphere had something to bring to the table so we investigated and it turned out that was the case. As a result we have a patent pending.
So my experience is by listening to our class D side by side against our regular production OTL amplifiers. They are remarkably similar. I have to assume that if Merrill has their ducks in a row, their amp should be very nice also.
As Kosst has pointed out, with any amplifier its all about distortion- what the amp has and what it doesn't have. Traditional solid state has always had a bit of low level higher ordered harmonic distortion, which is the source of the brightness and hardness for which solid state is known (and the basis of the tubes/transistors debate). Class D does not have the mechanism to create that sort of distortion. The higher-ordered harmonic structure of traditional solid state is partially the result of non-linear capacitive aspects imbued in the junctions of most transistors *and* also the feedback needed to linearize many transistor circuits.
Class D relies on switching and so eliminates that capacitive problem- and they can be linear enough that its nearly as easy as using tubes to build one that runs zero feedback.
So think about that last paragraph- the two main reasons transistors sound bright and harsh (which, make no mistake, is a coloration) can be eliminated with this technology. Of course, in solving that problem other problems are created; distortion in class D amps is increased by low switching speeds, deadtime circuits and the precision of the encoding scheme.
That is why we've seen the steady march to higher switching speeds- to reduce distortion and increase bandwidth. The problem has been shoot-through current (this is where both output devices are partially on at the same time, allowing current from the power supply to shoot through both devices at the same time, heating them up quite quickly). We can get the encoding schemes to work pretty well, but some modules employ opamps or other amplification at their inputs which can color the sound. But they are not mandatory and some circuits have the audio proceed directly into the encoding circuits without any processing whatsoever.
Oddly, the thing that most class D amps get attacked for, switching noise, isn't a thing because you can't have a noisy amp channel sharing any kind of circuitry with another noisy amp channel. They will find a way to talk to each other and it gets ugly (oscillations, hetrodynes, intermodulations, etc.). So any commercial design has to have that problem licked and they do. This is actually a requirement to meet international radiation standards.
So there are a **bunch** of variables! But if the following criteria are met, the amp will have low distortion and in particular will be lacking the higher ordered harmonics and IMD, which means they can sound very 'tube-like', 'organic', 'musical' and so on:
1) High switching speed with low residual 2) no deadtime introduced (deadtime increases distortion) 3) accurate encoding 4) no feedback
Regarding feedback, unlike regular amps in which there are things like phase margin and the like that can cause phase shift issues with feedback (and possibly result in oscillation), class D amps employ switching, which introduces *propagation delay*. This means that the output of the amp is occurring time-wise always slightly behind that of the input. Its a tiny bit, and so gets treated by many designers as a phase shift issue, but in essence the feedback **over the entire bandwidth of the amplifier** is going to always be slightly late. This means it will make distortion; such amps IME will have amusical properties. IOW I don't think applying feedback in a class D amp to be a good idea.
hello brotw Sorry for the late response, this thread has come to large and techincal. I find it hard to follow. Well, my Nord NC500 One UP is just burning, but even out of the cage it sounded better than the LM508, to my ears and in my system. I also have to say that the Nord only has about 30 hs of use and it has a long way to go before reaching its best. Nevertheless, during this period I know it will sound sometimes better and sometimes worst. For instance, I found it yestarday a "little bit" thin and harsh, more than at the beginning. I'm sure that it will get warmer and more delicate with time, as it happened with other owners. I also have to say that I really like my LM508 and I would like to compare both amps again, once the Nord has settled down, in a few weeks. But I also have to mention that I was expecting subtle differences, if any, but I found out noticeable ones, mostly in texture, noise and 3D image. FInally, I don't think Digital Room Correction has something to do with the amp and the speakers. For me it makes the sound much transparent and plus I have the option to set it to my taste, rising some frequencies and lowering others.
Zero-feedback Class D would seem to be a unique twist.
Bit late to the party Merrill already did it using the GaN transistors, I believe the SE-R1 does also.
Merrill Quote: Merrill Audio claims that this is by far their most ambitious design mostly because they are using open loop, zero feedback, and zero deadtime with GaN gallium nitride transistors, which are better than most transistors used in other solid-state amplifiers because that have close to zero capacitance, which allows fast switching. Plus, the gallium nitride transistors can operate in the GHz range. Gallium nitride transistors offer a fast, clean, low distortion power capability", and so Merrill Audio claims that are "natural and smooth in their musical capability".
And after doing this, since the distortion was eliminated, there was no reason to use any feedback at all. He went on to tell me that he is very proud of not having to use feedback.
Eliminating feedback has two distinct advantages. The speed capability is increased significantly and a remarkable gain in the clarity of musical information is achieved. Since there is no signal loop-back, all the feedback loop distortions as well as the attendant time delays are eliminated.
There are two reasons I will be keeping my Class D amps for a long time:
1) they work and sound great
2) the longer I wait the better (and more affordable) this still evolving technology will continue to get in years to come for many many reasons.
Same reasons I tend to hold on to most good quality digital gear (and cars) I buy for as long as I can as well.
BTW I believe it was Merrill Class D amps I heard driving German Physiks speakers at CAF 2017 and loved what I heard, not unlike what I hear with my Class D amps and OHMs at home.
piaga, for some reason I do not see your post which starts out ...
01-03-2019 2:42pm
EST
hello brotw Sorry for the late
response, this thread has come to large and techincal. I find it hard to
follow.Well, my Nord NC500 One UP is just burning, but even out of the cage it
sounded better... View
full response →
Zero-feedback Class D would seem to be a unique twist.
It would, since feedback is how the switching is controlled, without feedback, there can be no switching.
The Technics model is different though. It uses digital signal processing to compensate for the speaker load, and then is a pure digital amp with no feedback ( I believe )
Our experience with class D includes Nord’s and Mola Mola.
While Nord’s are good at their price point there is absolutely no comparison with the Mola Mola Kaluga’s sound quality. There’s an audiophile on YouTube that has a wonderful high end set up that sold his very high end Swiss class A amplifier (£50k) and moved over to Mola Mola Kaluga’s. Lansche, Manger and Vivid speaker manufacturers use Mola Mola amplification at the Munich High End Audio Show, not without good reason. The designer, Bruno Putzeys, has been at the forefront of class D design. While Nord’s and Mola Mola Kaluga’s both use Bruno’s Hypex class D modules, the sonic results are quite different.
I don't think anyone here is suggesting that Nord, or most sub $4K class Ds compare to some of the super expensive class Ds, BUT
* we all don't have trust fund accounts
* it seems no matter the tech (Ill use racing engines) getting that extra 10% performance increase usually doubles... triples, and more the price
Having owned 4 different W4S + PS Audio, Emerald Physics and now the older Audio Alchemy DPA 1 stereo amp, it is by far the most natural sounding (MUCH better than my Parasound A23 A/B amp), and speaking personally, $2K MSRP isn't chump change, and neither is the used price < $1000 to many of us
I was going to upgrade to the AA monos, but this thread has me doubting any future value on the used market. In just 3 short years these $4k MSRP the pair can be purchased for < $2k and have stellar reviews from 2016
It would, since feedback is how the switching is controlled, without feedback, there can be no switching.
There are three main types of encoding. One is 'self oscillating' which requires feedback and the feedback sets the switching frequency. So for that type the above statement is true but for Pulse Width Modulation and Pulse Density Modulation the statement is false; the latter two can be operated without feedback.
The
Technics model is different though. It uses digital signal processing
to compensate for the speaker load, and then is a pure digital amp with
no feedback ( I believe )
Saying Class D is as good as Class A is like those hyping Digital is a good as Vinyl. Are your ears truly that bad? Does a digital piano sound as good as an acoustic? No. End of story.
Saying Class D is as good as Class A is like those hyping Digital is a
good as Vinyl. Are your ears truly that bad? Does a digital piano sound
as good as an acoustic? No. End of story.
Someones feelings are hurt. NO no no. I meant to say that good Class D is better than several Class A amps.
Please stop comparing it to such inferior technology better suited for cold climates and drafty hallways.
I find Brunos definitions kind of useless. Most Class D have no Analog to Digital Conversion (ADC) stage, but do have comparators. Hence the feedback required.
The Technics on the other hand, really does have an ADC, and once calibrated, the output behavior is deterministic. Best, E
Eric you've tried numerous threads to get this Class-D "praising thing" on a roll, never to keep going, because of the "non acceptance" by way too many for you to counter.
Give it up be happy with yours, that you say you can't hear any problems with it. And let those that can, and have been down that path go the way they want.
The only ones that are really backing you, are manufacturers that are making, going to make, or selling them in retail supply, they all have a monitory interest in doing so.
It almost sounds like sometimes you asking for acceptance for owning Class-D and listening to it.
I've always said Class-D will be the top dog one day, just not yet, all the detractors (designers and audiophiles) of it have the same common complaint, it's the upper/mids and highs that are the problem, never the bass, this is a done deal showing where it needs to improve.
I would say it's the other way around, Erik has proven his case while George has failed to do so. Erik has sided with experience while George has sided with the lack of. Erik is being open minded while George is not.
George (assuming the are the same George who reviewed the Hattor passive pre with a Nord) you should read your own review as you praised the combination
Eric you've tried numerous threads to get this Class-D "praising thing"
on a roll, never to keep going, because of the "non acceptance" by way
too many for you to counter.
Give it up be happy with yours, that you say you can't hear any problems with it. And let those that can, and have been down that path go the way they want.
It's the other way, George. Every time anyone says they like Class D you jump in with as many posts as you can explaining why they must be wrong, but (based on zero evidence) the next big thing will surely fix it!
I think an objective read of my posts, whether about Class D or other will show which of us has a point to prove, and trouble making it.
Seems to me, in most of the class D threads I have read, there are more positive reads than naysayers. I'm fine with it if you don't like class D for whatever reasons, just don't tell me it is garbage and has no place in HEA! Reading between the lines, it seems many of the naysayers have NEVER had a class D amp in their systems. I said "many" not all....
assuming the are the same George who reviewed the Hattor passive pre with a Nord
Sorry you need to do your homework there sunshine, you've got the wrong George I'm afraid on that one.
I'm fine with it if you don't like class D for whatever reasons, just don't tell me it is garbage
No one said it was garbage, I said it doesn't compete with hiend linear amps "yet"!!, one day it will with the likes of the Technics SE-R1 and the Merrill Element 118 now using the new GaN technology that it needs to be rid of it's achilles heel to get there.
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