So, wanted to make things a little more full.
One of the spec’s commonly sited is S/N (signal to noise) or related THD+n (Total Harmonic Distortion + noise). The problem with Signal to Noise is that it is often cited at full power, and not at a more reasonable amount, like 1 watt.
So, a 1000 watt amplifier can claim 10 dB more S/N than say a 100 Watt amplifier that sounds exactly as noisy. The full power S/N ratio becomes useless for comparing amps and how quiet they are. What I wish reviewers and manufacturers did more consistently is rate the S/N at 1 watt or 10 watts. Something small so we can compare what we’ll actually hear.
Distortion is also something that tends to go down as power goes up until the limit of the amp is reached. This is why these figures can be misleading. This is something stereophile does a little better, in showing graphs of THD vs. power output. Now we can at least look at charts to compare noise and distortion as more usable power outputs.
The other thing, I think that the amplifier community is having a hard time keeping it’s prices up to make boutique manufacturing possible. This makes it necessary to have big differentiation. For instance, having a 1,400 watt amplifier is cool and all, but in my living room, at my listening levels does it mean my sound is better than my 250 W amps?
I don’t really know all the answers to these questions at all. I’m just sharing where I start to scratch my head. :)
Best,
E
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Hi Guys, The biggest issue with input/output impedance is the change in frequency response. This is especially bad with tube pres as they usually have a high output impedance. Driving a low impedance input amp can affect the overall response and deviate from ideal. With purist tube pre's even the volume control setting can affect things because they lack additional buffer stages that would prevent this. Good ways to see this is to look through the Stereophile archives and look at tube preamps. In the measurements section you will see the frequency response driving different simulated amps. Here is a link: http://www.stereophile.com/category/tube-preamp-reviewsIf you look at this particular preamp, youll see the FR changes a great deal when driving a 100k load vs. 600 Ohms. http://www.stereophile.com/content/vtl-tl65-series-ii-signature-line-preamplifier-measurements#aVQTI...High impedance inputs also tend to be noisier (I think). Solid state preamps or op amp based preamps can easily be completely flat down to 600 Ohms. |
You know, I was just thinking of something. It would be really fun to marry a Nelson Pass First watt Class A amp to Class D voltage rails via transformers.
Sigh I wish I had more energy. :)
Best,
E
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I am a big a fan of excess as anyone, but at this point I'm going to have to wonder if big power matters ? I mean, come on! :) :) :)
I also worry, like Nelson Pass, if big amps are worse performers in the first watt.
What do you guys think? Have you heard "better" in digital as you got "bigger" ?
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Guys,
I'm so very happy with all of the participation on this thread, I'm also learning a lot, since I don't get to go to shows and dealers and listen as much as I would like to.
Would it be worthwhile to put together a web site JUST for class D amplifiers? It might give me the chance to listen to a lot more gear as a regular review feature, and break the mega-linear-amp stronghold.
It's just an idea, a lot of work if I chose to.
Best,
E
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@samac
I looked at the NuPrime pages VERY briefly. NuPrime’s tech sounds a lot like the Yamaha EEEngine. Small class A amplifier sandwiched between Class D voltage rails.
Again, kind of goes back to Carver’s Magnetic Field amp and NAD’s switching rails technology.
Sure gets grate reviews. I would love to give them a serious listen to see what the benefits really are.
I mean, it’s quite different from Hypex/Pascal/B&O but I have no idea if it’s much better.
The challenge with this kind of hybrid approach is again, you rely on feedback to tell you everything about what you should do from instant to instant. With the voltage rails swinging at the same time the Class A amp is swinging it is like shooting an arrow from a moving boat.
Best,
E
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@madavid0
I don't have to be nice to people who are being nasty, so I'm not being nice to you anymore. You are the most transparent hater in the long list of transparent haters, and I know haters.
You previously stated you know almost nothing about Class D but now you claim to be an expert and want to bashing all the contributions of almost everyone else in
this thread. I take offense at you coming in here and deliberately
starting trouble. I trust the contributors. I value their input, and
clearly you want to ignore all of us or call us poor judges of music and
sound, which I find a personal insult to me and everyone here.
I have two questions for you:
1 - What is your income source? Are you in the audio industry or do you own a store or sell audio equipment online?
2 - Why don't you just come out, make peace with whatever point you want to make and leave us alone. You have put a tremendous amount of emotional energy contributing nothing but hatred and bashing a technology.
What happened? Did a class D amp fall out of the sky and kill your dog as a child?
E
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randy,
See if you can connect with @h2oaudio he makes Class D with linear power supplies. They sound pretty sweet.
Erik
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I’m afraid I’m guilty of saying "Digital" vs. "linear" when I should stick to Class D instead, so my bad. :)
And yes, those quotes and tech are stale as hell. No wonder George can’t enjoy digital amps, all the stories he reads about them are a decade old and he can't trust his own ears.
Erik
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So, to those confused by Class D vs. Digital, to be "digital" you have to convert or have the signal as an integer to describe the waveform. Like the digits in a CD track. This is "digitization" or converting an analog signal into a series of digits. Class D does NOT do this conversion, but the amplifier IS switched on and off. :) It’s confusing because what happens is that the comparator keeps the switch ON or OFF more or less in proportion to the incoming signal. This is why feedback is so important and completely different in a Class D amp vs. linear. The feedback IS essentially the only way the amp has to control the output signal, however this feedback takes different shapes. The more global the feedback, the more accurate the output. It’s a subtle but important distinction. Here is a list of Bruno's papers, I encourage you to read them, as I am sure I made mistakes, and the guy is one of the celebrated Class D amp designers of our time. https://www.diyclassd.com/p/application-notes-white-papers/Best, E |
@georgehifi Interesting article, full of inaccuracies. One I may have helped propagate. Class D vs. Digital Amplification The article claims, erroneously, that Class D amps all have an A/D converter at the front. They do not.
It is actually more of an Analog to Analog converter with a switching voltage amplifier in the middle. :) Somewhere there is an article or paper by Bruno Putzeyes chafing at the use of "Digital" to describe his amps, which I can't find right now. Worth a read if you can find it Class D amps (ICEPower/Hypex) generally rely on feedback to control the switching, which uses a linear comparator. There's no A/D conversion in the chain, it's not needed. Here is a good short article on the subject: https://en.wikipedia.org/wiki/Class-D_amplifier
Interestingly, George, the Technics Class-D amp you are looking forward to IS more of a digital
amp than most Class D in that it DOES have an A/D front end, followed
by a DSP engine to do the calibration and frequency/phase adjustments to the original signal
before feeding the amplifier section. You are really trusting the amplifier with a great deal, because it will chew the signal up and digest it before spitting it out again. This is an approach not entirely unlike Theta and Meridian have undertaken. Best, E
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Randy,
I trust todd's ear. :)
I would go with the Ghent Audio kits.
Best,
E
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HI @jrunr
Yeah, Theta is owned by ATI, btw!!
The Prometheus AFAIK uses custom linear supplies also, which explains the huge size. :)
Best,
E
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@kdude66
The interest in this thread has been brought about by the positive participation of it's contributors like yourself.
Best,
E
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Thanks @wtf I appreciate it, I had not noticed who that thread starter was, but I could tell the attitude was that of a brawler.
Re: ICEedge There are probably already products out there with this technology we just don't know about them yet. From B&O's point of view I think the main focus is on custom power and integration into receivers, all-in-ones, etc. not really us uber-audio-geeks who want to be seduced with stories of custom capacitors with dielectrics made from the excretion of a rare Himalayan beetle. :)
Honestly doing digital right is not easy, which is why Pascal, Hypex and B&O have been so successful. I think that in the high end, manufacturers are going to have to get VERY lucky to find talent who can bring on enough experience and insight to complement it.
This is all pre-game BS though. :) Can't wait to see what the future holds.
Best,
E
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ICEPower went through several incarnations. I can attest that the AS (or ASP if powered) is superb.
ICEedge is the chipset without the amplifier. :) Just the brains. So I think that we’ll start to see a lot more product differentiation among vendors.
The normal ICEPower module is 100% complete and tight in space. There’s no place to modify anything. At best, you can put in your own input buffer stage, and you can do lots with that. Transformers, tubes ets. but the ICEedge is the place where you can go really bonkers with part selection and circuit design.
I have no personal experience with these amps and linear supplies.
Best,
E
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madavid
I use bare ICEPower 250 ASP modules. They beat a lot of premier class A amps.
Also, you bring a lot of attitude. Not everyone on this list has mentioned uber pricey class D amps. Some were quite affordable.
If you are looking for a place to start a linear vs. class D argument I really would be happier if you took it elsewhere or started your own thread. As posted, this thread, which is one of the most popular on right now thanks to the readership as well as proponents who are participating is for people who like Class D. :)
Thanks,
E
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madavid
I strongly wncourage you to read this threa. At least skim it. It is filled with glowing recommendations for Class D.
You can disagree, but there are other threads for trashing class d and I would appreciate it if any detractors took their coments there.
Best,
E |
madavid0
Every moment of every day |
@autre
Thanks, and thanks for being among the first to spell my name correctly.
Best,
E
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It's also important to say, differences are not better or worse necessarily. Maybe two amps sound different. Is one better or worse, is it worth caring about? Are you trying to make your ears more sensitive or enjoy music and movies more? :)
We get all confused in our goals (Me too!) so it's important to be clear. Audiophiles too often think the next different thing is "better" when it's not. I think even John Coltrane was guilty of this, and would make endless takes until someone told him "You can't play it any better, just different."
Best,
E
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@jrunr
I would listen to them. :)
Bridging is a tricky thing, possibly involving slightly more circuitry at the front end, and possibly lower damping factor (Higher impedance). How much is audible? Is a higher 8 ohm power rating going to help you drive speakers better? (unlikely)
The real question for me would be whether you need 500 Watts / Channel. :) The basic 200W/ch models are overkill for almost everyone. In a modest configuration (< 8 channels) you could have a lot of reserve power.
Depending on the costs involved, you might also want to play with the 400 W/Ch nCore kits available from Hypex. I’m not sure how they compare to the ATI multi-channel amps.
Best,
E
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Hi @jrunr
Regulator or not, the question is whether they all share a transformer, that's where the money/size/weight is.
If I were designing them, I'd stick to 1 power supply model, and add or remove amp modules as necessary.
Best,
E
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Here is the relevant part:
The AT52XNC amps are rated at 200W RMS per channel at 8 ohms
with300W
RMS at 4 ohms and are available with 2 to 8 channels.
The AT54XNC
amplifiers use two N-Core modules per channel in a differential bridged
output configuration delivering 500W RMS per channel at 8 ohms and 900W
RMS at 4 ohms. The AT54XNC amplifiers are available with 2, 3 or 4
channels.
It seems the 54xNC series are bridged, and therefore have half the
channels of the 52xNC models.
Since the power supply is linear, ATI is limited in what they can put in a single chassis. A 1,600 watt linear supply is BIG and HEAVY and EXPENSIVE. This wattage / size limit is driving everything else. If you limit the channels to half, you can double the per channel output (more or less). Personally, I'd rather go with a pair of unbridged 52xNC models, but limit the channels. 3 or 4 channels in each would give you a lot of power supply capacity/channel and ensure you had the best low-impedance drive possible. Best, E |
So I just checked out ATI's multi-channel nCore amplifier. It looks really interesting, except packing that many channels (8) into a single chassis limits the total simultaneous output.
If you only have a pair of hard to drive speakers, this should not be a problem. Also depends on what you mean by "hard to drive". This is a big range.
Still, 8 x 200 watts = 1,600 watts total. That is a lot of output!!
Best,
E
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@jrunr
No, not necessarily. :)
Usually you can tell by how low a speaker impedance it is rated for (8 --> 4 --> 2 --> 1 Ohm) and how well the power doubles each step down in impedance. So for a 50 watt amp the best should put out 400 Watts at 1 Ohm. :) :
50--> 100 --> 200 --> 400
This is how Krell go their fame, with a 50 Watt class A amplifier that output 400 Watts into 1 Ohm.
Of course, these amps are beefy, but also usually ridiculous. :)
It's also important to understand exactly where your speaker is hard to drive. Digital amps tend to do better in the bass than the treble, which is good because most conventional speakers are hard to drive in the bass. nCore modules are famous for being less sensitive to where your speaker is hard to drive.
Best,
E
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@kdude66
Sounds like something I've said, about other things though. :)
Best,
E
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Ah, fine. :) That's fancy.
All we really need is a signal generator, and voltage meter at a couple of frequencies.
Best,
E
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By the way, I just ran the numbers on that.
Based on output impedance, and assuming a 1 Ohm speaker impedance the ICEPower 250 A would droop around 2.2 dB at 20 kHz. That’s not unacceptable, and in line of what a tube amp would do to a lot of normal speakers.
Pro: A gentle glare reducing effect.
Con: Removes air, dulls top end.
A bigger concern to me would be the speaker efficiency and output power of the modules used.
Also, one not well known thing about these modules is that their cooling matters a great deal. The power rating increases with better heat sinks. Some manufacturers stick these in sealed speaker cabinets but the power gets derated.
Best,
E
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If it were possible to measure, I'd ask for these amps to be measured with a 1 Ohm resistor at 2.83 Volts. :) About 8 Watts. Let's see that first.
REW is great, but measuring the speakers adds a ton of confounds. I say this as a speaker maker and integrator. And that's fine, but what I'm personally after is to understand how well these amps do electrically, as that will be the most clear.
If we try to measure just the speaker/room we won't have any idea what is due to the speaker, and how much is due to the amp/impedance interaction.
If I remember where my oscilloscope is I may do this with mine.
Best,
E
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Hi @h2oaudio
Oh, agreed. In many cases a top octave roll-off may be much better sounding than a flat amp.
Also room dependent.
Best,
E
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@h2oaudio
No reason to get elaborate. Too many words make misunderstandings even easier. :)
I'm just curious if you have measured the electrical frequency response of those amps hooked up to the Scintillas. I'd love to see those charts. :)
Best,
E
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@h2oaudio
What you do with your amplifiers is between you and your part supplier, but these are high current outputs. Unless specifically rated for such low loads I would never encourage anyone to attempt this without further input from the manufacturer. :)
Um, as a guy who makes loudspeakers, no, I don’t know what you mean, but measurement and experience trumps theory. It would be interesting to examine what happens to the output response on those scintillas, as they are pretty much the worst case scenario. :)
Honestly, those speakers were absolutely brutal. If ICEPower modules can drive them as well as you say they do that’s pretty astonishing, even for me, an obvious fanboy. I think the biggest, most lasting impression they have left on the audio industry was to give Krell a raison d’être. I think without Apogee loudspeakers the history and viability of Krell might have gone a different way.
Best,
E
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To sell a new product we must sell the problem first, so I can see where a lot of this is coming from.
I don't have a problem with listening to the new when it comes out.
I'm not easily swayed by naked kings though.
Best,
E
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@h2oaudio
That's fascinating, for two reasons:
1 - I did not know any ICEPower modules were rated for 1 Ohm
2 - The output impedance is quite high at the top octave
Have you measured the speakers with those amps?
Best,
E
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@h2oaudio
VERY interesting. :) Please elaborate on the amps you are using, and how the speakers are configured (bi-amped? etc.)
Thank you!
Erik
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My own take on high efficiency speakers and flea tube amps:
People LIKE the sloppiness.
That is, the high impedance outputs of the amps make the electrical frequency response much more variable, and .... that's what some people like. :)
I don't think it's from "damping" or over-controlling the drivers at all. But hey, no matter. Buy what you like.
Best,
E
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@kdude66
No worries at all. :) I think that the participation of so many here who have been pleasantly surprised and are enjoying Class D amps speaks for itself.
We also went a little deep into theory without measurement. :-) We should stay away from that. My bad.
Best,
E
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Hi Phusis,
Not sure why high efficiency would be a bad combo. The issue with different Class D designs, as covered, has more to do (in my mind) with impedance drops of exotics.
They are dead quiet.
When I first heard digital amplifiers it was with a pro monitors based on pioneer metal-dome compression drivers. OMG that was painful. :)
But that was in the 80's.
Class D amps are also dead quiet, so that's not a big deal.
Still, I don't have recent experience, so I hope some one who does will chime in.
Best,
E
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A little confirmation bias there, George.
The phase shift in the nCore, if ONLY due to the output coil is minor, about 10 degrees, and almost none from 10kHz or below. We don’t actually know the output phase shift without a direct measurement. We can only estimate what a 10 uH coil would do.
The size of the output coil is in the same order of magnitude of most SS amplifier output coils. Maybe 2-3 times bigger.
Also please note the effective nCore 400 output impedance is not 1.25 Ohms at 20 kHz but around 0.003 Ohms. Probably due to feedback being outside the coil.
These are minor quibbles. In fact, the interesting part about the Technics amplifier is that it solves this not by a better output section but by measuring the frequency and phase differences with the actual speaker load and then compensating for it at the input. This is pure frequency and phase equalization. You could do this with any current Class D amp plus a miniDSP if you chose to.
The ICEpower amps on the other hand have much bigger phase shifts. No idea what it’s attributed to.
Of course, time marches on, and progress will be made but what we have now is really very very good.
Best,
E
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Hi Kdude,
That output coil is perfectly in line with the output coil in many SS amps.
Based on my simulations, this ends up being no more than about 10 degrees of phase shift at the top end. Far better than ICEPower. :)
Best,
E
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One thing I'd like to see for the nCore modules which I can't find is output phase angle. If anyone can point me to a doc which has this I would appreciate it.
I notice that the ICEPower units do have some phase shift involved. It is minor compared to what your average multi-driver speaker and crossover will do, but it's significant. This is something the Technics SE-A1 compensates for in the input.
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@kdude66
Thanks and welcome! :)
Erik
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Hi @guidocorona
Thanks for the suggestion. I feel bad asking for a loaner pair with no intention of buying. :)
To everyone else, it is really the contributors on this thread, even those i don't agree with, who keep it interesting and welcoming. :)
Best,
E
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Hi @guidocorona
I wish I had a way to listen to an nCore pair without spending money. :) I would be better able to discuss the sound quality honestly.
What I can repeat, is that compared to Parasound Halo A23's which are heavily class A biased, I cannot hear a difference.
Best,
E
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Hi Tim,
I just tested it. It actually is a PDF download, so check your download files. :)
Best,
E
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