Class D is just Dandy!
"The only negatives to class d is driving the exotic speakers,the ones that drop below 3ohms." Kenny, I believe it is all about system synergy and listener's preferences. I have class D driving the Apogee Scintillas just fine. The Scintillas's impedance is 0,8 ohms from 20Hz to about 2 KHz, and about 2ohms from there on up to 20KHz. Henry |
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 |
Class-D that can finally equal or better hi-end linear amplifiers, tube or S/S. It's closer than you think. Why We'll Soon Be Living In A Class D WorldCheers George |
I can easily comment a little about the pairing of class d with efficient speakers.I have been using d with Zu definitions for 4'yrs and also a pair of Crites cornscalas that I built for 2 yrs.Basically if the first watt of any amp is no good I don't want x amount more of them.There has been a lot of people say that high damping factor of any class of Amp is'nt a good match too full range drivers which cause over damping of the cones and don't sound as natural in a musical note decay.I found this not true too my ears,I have owned lots of tube and class a amps over my time and my preference in the music presentation leads me back too the class d amps I currently own.I had a pair of the Janzen Valentina hybrid ESL speakers recently for 6 months and drove them with class d very well.But I like the Zu's better in my room and kept them.I have a pair of Tekton double impacts that will arrive this wed and I will see how they sound with class d. The only negatives to class d is driving the exotic speakers,the ones that drop below 3ohms. Reproducing audio in the home has and will always be highly subjective and system synergy has tremendous benefits. Erik, I'm not a Amp designer but I have been a Avionics tech at a major airline for 28 yrs,so I have a fair understanding of electronics in general.It is very cool and also very interesting too learn as much as we can about our gear but you are going to hurt your head just like I have trying to fully grasp class d.I prefer to just kick back and enjoy the music.I recently caught myself analyzing my double impact speakers before I even get them,crossover points and driver configuration.There is a lot of positives for class d now and in the future. Kenny. |
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 |
It would seem many here hold their own share of beliefs and agendas either in favor of or against Class-D for a variety of reasons - certainly predictable and all too common to have some sort of investment in a particular design principle, sometimes based more in theorizing than drawn from actual listening sessions. Perhaps in an effort to counterbalance my own inexperience and skepticism, or even prejudice against Class-D designs in regards to successful implementation with very high efficiency loudspeakers (+100dB’s), does anyone here have practical experience in this regard and how this combo plays out? Typical "wisdom" seems to have it that Class-D designs are less favorable within the first watt of usage compared to Class-A designs - not least SET’s/SIT’s - and are therefore considered the poorer match with very high efficiency speakers. Is there any merit to this in the eyes (ears) among those with actual experience here, or is it a field laden predominantly with theory as to how things ’should’ (as opposed to how that actually ’do’) pan out? |
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 |
+1 kdude66 This equates to an output impedance of 1.25 Ohms at 20kHz and SIGNIFICANT phase shift within the audio band. Just what I’ve been saying all along, would be great if you can post a link to this. This is why it important to increase the switching frequency by hopefully x5, which then takes the filter up higher by the same amount, away from the audio band. And why the above transistor development (in my last post) is so needed to get it up there. Cheers George |
George, They can’t yet, as that technology needs to be taken up by the major semiconductor manufacturers Motorloa, Sanken, Fairchild, Toshiba ect. Then the small Class-d manufacturers will be able to get them as well at a decent price. Remember the guy http://epc-co.com/epc/Applications/ClassDAudio.aspx that invented these special Gallium Nitride transistors that Technics use in that amp, also invented the Mosfet years back, and look where that ended up, every big manufacturer makes them now. So hopefully it won’t be long, then all other Class’s of amps will become defunct, and there’ll just be Class-D. Cheers George |
Erik, Buried on page 5 of the NC400 spec sheet is the figure relating to output coil inductance. Typically, 10uH. This equates to an output impedance of 1.25 Ohms at 20kHz and SIGNIFICANT phase shift within the audio band. Page 8, graph 9.1 is particularly telling. -0.5dB @ 20kHz is nothing to write home about. It also suggests serious phase shift problems well down into the audible spectrum. I remember seeing more info somewhere about this,but I did'nt save it. This is related to the nc400 only but I did'nt stress about it too much I just continue to enjoy them.I do like my 600 m's more than the 400, but I'm using my nc400 right now. I hope this points u in the right direction,I way spend some time later looking for more info. Kenny. |
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. |
George, I have looked at at the technics,very interesting,now we need other designers too go in that direction and evolve. I had one of the very first technics CD players in 1983,touting perfect sound forever,I now have a ps direct stream.Look how far digital has evolved but it has taken a long time.With me it's not about the money,I can buy just about anything I want,If I like it I will Buy it.A good example of me is auditioning a set of demo magico q3 at a dealer with money in hand but I really wasn't that impressed because they really didn't better what I currently own in speakers. Basically there is a lot of hype in this industry and I really don't have time for it,I just want too everyday enjoy the music. My most recent purchase is a set of tekton double impacts,I get them next wed.I read about them and then I called Eric and asked a few questions that he quickly answered which sold me instantly to purchase.I respect his talents as a speaker designer and I will see if I like them or not.I know he makes some very bold statements about his speakers and has even gotten a patient for his design. Kenny. |
@georgehifi whatever dude, you're just a hater, get out of here. Just kidding. You've proven yourself to be a topnotch human in this thread. We know you're not enamored with current class d and you've very respectfully and clearly outlined why based on theory and experience. So I can respect that and do. What I find annoying are the people bashing class d (or anything, really) without having given it a listen. Don't speak on what you don't know. If only Mr President would follow that advice.. |
and not the usual negatives.Some love them some don’t, and on a forum this is where it should be discussed, not limited to just the "pro sector" usually from owners, but the negatives also from those who’ve listened/owned but don’t like their sound, and then technically the reasons why this maybe the case. and class d does it for me,not looking for class a or tube amps anymore.That’s good, if you believe you’ve reach your holly grail with the Class-D. I’m still waiting for it to mature with future advances in technology that are coming, as Technics have started in very expensive limited supply. Then we’ll all be happy Class-D campers. I see it a bit like the first hard sounding brickwall filtered CD players, which I also didn’t like, took a while but the newer technology especially in filtering and I/V conversion now makes great music, even with using those same old d/a chips, of that era with pcm redbook replay. Cheers George |
Sounds like you guys are getting a little too technical for me,but keep the thread going because it's so nice to read positives about class d and not the usual negatives. All I can say about class d is it has come a long way but will probably continue improving as time goes by.I started into class d about 4 yrs ago with a set of diy nc400 and I own a set of bel canto ref600m and I have a new red dragon s500.I have been in this hobby for 30 yrs and have been blessed with all kinds of nice gear.I practically gave away a pass labs xa30.8 and first watt j2 on the used market just because they did'nt better any of my class d amps. At the end of the day it is still all about the music and the amount of emotion and involvement that I can receive,and class d does it for me,not looking for class a or tube amps anymore. Kenny. |
I love this thread. Thanks again Erik, for starting it and Guido for being such a solid foil. +1 .. it’s a pleasant change from the normal bashing class d takes. I have 3 class d amps, an older PS Audio Trio A-100 (ICE based), a Fleawatt TPA3116D2 integrated, and a Dayton Audio DTA-120. I really enjoy all 3. |
Hi Erik, have you considered asking my friend Merrill if he would let you audition a well-broken-in pair of NCore NC1200-based Veritas monos at your home? Here is Merrill's contact info: Merrill Audio Advanced Technology Labs, LLC Saluti, Guido
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I am with you Erik, I have not experienced yet an amp based on ICEpower technology as mesmerizing as NCore NC1200.... THis includes my old beloved Rowland M312 based on ICEpower 1000ASP. See my review of Merrill Veritas on PFO: http://positive-feedback.com/Issue68/merrill_audio.htm On the other hand, not wanting to mortgage the future.... I have hardly heard heard all ICepower amps on the market, nor I can venture what ICEpower might do in the future. For one thing, I have heard very good things about the little Rowland M125.... I It is based on a current generation ICEpower, and delivers 125W per channel in stereo mode, and 500W bridged.... Apparently super sweet... But I have not heard it yet. Best, G.
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Following on, at 200 Hz the output impedance is 10x better with nCore, but the absolute figures are tiny. The difference in output between a high and low impedance speaker is less than 0.01 dB. Most "normal" speakers get very difficult to drive in the bass, not the treble, so for these owners, I think nCore and ICEPower are equivalent and subject to personal preference. If you have an ESL though, I would really expect the nCore to over perform. Best, E |
So, let’s get into some meaningful spec-manship. Let’s compare the frequency response, and output impedance (8 / output impedance = damping factor) of ICEPower and nCore to see about what could matter with different speakers. Here are the source docs I start with: Ncore docs: https://www.diyclassd.com/documenten/download/860 ICEPower : http://www.icepower.bang-olufsen.com/files/solutions/icepower250aspdata.pdf I’ll use a couple of examples. My own custom built speakers which have around 9 Ohms of impedance at the top octave, and ESL’s which are basically giant capacitors, and murderously low impedance at the top octave often near 0.3 Ohms. I should point out most SS amps have coils at the output to protect from hyper-sonic oscillation. This coil acts as a low pass filter and will cause the frequency response to droop at the top octave. This is not by itself unusual or ONLY about Class D amplifiers. Using a "normal" speaker like mine let's examine how the output impedance changes response at the 20kHz mark: nCore: -0.003 dB ICEPower: - 0.3 dB 0.3 dB isn’t inaudible.... but VERY subtle. Below this, in the bass where many speakers get difficult to drive, there’s only tiny differences in response. Certainly better than most tube and zero feedback SS amps. This is a small difference which fits well within the idea of "system matching" an amp to personal preferences, speakers and room tuning. But let’s take an extreme case of an ESL which has around 0.3 Ohms in the top octave: nCore: -0.08 dB ICEPower: -6 dB This is a case where the nCore could make a very significant, audible difference when playing the same speakers. My point to this is, based on specs, both modules will perform very well with normal loads. Any differences in the top octave may be inaudible, or useful. This is one example of where I think specs and technology can help us understand how to match an amplifier with our system better. Best, E |
I wanted to describe an additional benefit of good class D amps that I quickly discovered after switching from my former class A/B Aragon 4004 MKII amp to my first class D amp, a ClassD Audio SDS-440-CS stereo unit and is a quality of all 3 class D amps I’ve owned thus far: the latest 2 are an Emerald Physics EP-100.2 and a pair of D-Sonic M3-600-M mono-blocks. It’s a benefit I never read about in my prior research on class D, still don’t read much about and that I believe is common to all good class D amps and not unique just to my 3 amps but I’m not currently certain. As many of you already are aware, humans generally perceive bass and treble frequencies to be attenuated relative to mid-range frequencies when listening at lower volume levels. This means as volume is reduced, the less we perceive the bass and treble frequency extremes and the more the mid-range frequencies predominate; which flattens out the perceived sound since the mid-range frequencies are accurately perceived but the bass and treble frequencies are perceived as under emphasized. Some of you are old enough to remember ’loudness buttons’ on receivers from the 1970-1980s. These controls were used to boost the bass and treble frequencies when listening at lower volumes to compensate for this known deficiency in human hearing. Okay, enough preamble. I’ll describe the class D benefit now even though I haven’t yet thought of a better short description of it than ’a consistent and continual loudness contour’. I began carefully listening to my first class D amp at a lower volume and immediately noticed the sound was much different than I was accustomed to with my class A/B amp at lower volume. There was no flattening of the frequency range, I perceived the entire frequency range of the music with seemingly no under emphasis of the bass and treble. This struck me as amazing since it was the best I had ever heard my system sound when listening at a low volume. After a few days of listening I decided it was safe to experiment with higher volume listening levels closer to the levels I formerly listened to music at with my class A/B Aragon amp (probably in the 70 db and up range). As I began slowly increasing the volume, I was pleasantly surprised to notice the frequency range balance or perspective of the music remained constant while everything within this perspective just gradually increased in volume. The music sounded well balanced and enjoyable from low volume to high and all points in between. This well balanced frequency perspective was also consistently maintained even at volumes well above my normal listening level. Some of you with higher quality systems are probably thinking ’what’s the big deal’ about turning the volume up and the music just gets louder without the fidelity or overall frequency perspective within the sound stage changing but this was revelatory amp quality behavior in my experience. My former Aragon didn’t sound near as good at low volume levels and required volume levels in the 70 db plus range to sound its best in my opinion. Music at low volumes seemed to flatten out with attenuation in the frequency extremes. I’m a bit embarrassed. As I’ve written this post, I’m thinking the quality of my former Aragon class A/B amp may have been lower than I thought or it was gradually aging and sounding worse just prior to the power supply caps leaking and it going belly up. Perhaps I was just hearing the difference between an older amp on its last legs and a brand new class D amp of good quality. Well, at least I consider the good sound quality at any listening volume a class D benefit and hopefully others who may enjoy listening at lower or very high volumes will find this attribute useful as well. Thanks, Tim |
Hi Erik, the big old ICEpower 1000ASP also had an output impedance of 1000… Perhaps that is one of the reasons why it outperformed the authority of the Boulder 2000 series in authority on Die Muzik…. Not sure of the damping factor of less powerful modules though.
The audible difference between an old ICEpower 1000ASP and an NCore NC1200 is that simple amps based on the old ASP1000 with little design around them did not sound terribly good, no matter how much they were broken in…. ASP 1000 gave the high current, the raw resolution, the compatibility with difficult speakers, but could sound quite harsh unless the designer created a solid input stage to raise input impedance and attenuate common noise….. The native power supply was somewhat weak in regulation…. The better amps used regulated custom SMPS, and at least in the case of M312 and M301 also an integrated power factor corrected rectifier to avoid any grundge contaminating the signal….. So much so that rowland created an external rectifier called PC-1 which could be used with some of his lower end ICEpower amps like M501, M201, and M102.
Here then comes NCore NC1200 with its companion NC1200/700 unregulated supply…. Turns out that a simple implementation of this module inan amp, even without the amp designer doing too much in custom active circuits, usually outperforms any sophisticated class D amps created round the older ICEpower 1000ASP modules. Then, if the designer does apply his more sophisticated input stages, power regulation, power supplies, and rectification to NCore…. Things sore. Having said the above, I have not tried the latest generation of ICEpower 1000ASP, but I have heard that they are much more musical than the older ones.
Guido
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I'm just saying that I am open to the possibility that different Class D amps, like their linear counterparts, may sound different on different speakers. But if this IS true, I won't attribute it to Class D vs. linear. I believe nCore's do have exceptionally low output impedance across the frequency spectrum compared to ICEPower so I'm not surprised. :) It also depends where your speaker is difficult to drive. With my speakers, there's unlikely to be much difference since they are easy to drive. ESL's however have the hardest trouble at the top end. I would not be surprised if the difference between an nCore and ICEpower module was more measurable/audible with them. Other speakers, like say Focal's with double woofers, are hardest to drive in the bass, a place where both nCore and ICEPower excel. Best, E |
Hi Erik, the inability of class D amps to handle difficult loads is one more urban legend.... Most non-trickle down modules that I know have damping factors of 1000 or better, and deliver 30A or better..... NCore NC1200 for one thing drive my difficult to handle Vienna DIe Muzik, with their wild impedance curve, without batting an eye... Even the little Merril Teranis could do it without a sweat, once we raised its gain to 029dB. In olden days, I heard a ROwland M312 (ICEpower 1000ASP) totally trashing the authority and harmonic resolution of a big Boulder 2000 series monoblock pair driving Die Muzik... Not only my opinion either... there were about 15 people in the room. Guido
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Hi @guidocorona The general principles that a higher switching frequency with better transistors yields lower distortion and higher efficiency is not really in question. I question the audibility of anything measurably better than the current state of the art from ICEPower, nCore or Pascal. I question the importance of 0.03% distortion vs. 0.003% vs. 0.00000001%. Having a baking scale that measures in femto-grams does not help you bake a better cookie. If there are audible benefits, I think the answer will be somewhere else. Such as linearity (lack of compression), noise shape or handling difficult to drive speakers (complex impedance curves), etc. I won’t get excited at all right now over an amp with a high switching frequency, or lower distortion. Especially not at high end prices. There may be audible differences between the major Class-D technologies, but harping on things I think were solved a decade ago I don’t think will help me find a "better" sounding amp. Maybe a "different" sounding amp though. Best, E |
@noble100 Tim, I love your quote from the upcoming issue of Acta Philosophica Refutata (Vol XXVIII, Feb 29th, 2017.... I have not yet received this issue *Grins!* Jokes aside, it is my understanding that this conjecture -- it is not a theory in the scientific sense of the word -- asserts that switching frequencies of at least 1Mhz are expected to reduce harmonic distortion to 0.005% or better. It happens that 0.003% has already been achieved for the entire audible frequency band: Mola Mola Kaluga which uses enhanced versions of NCore NC1200 and its matching power supply. ROwland M925 and M825 are also below 0.005% while using stock NC1200 modules. But let us come down to Earth from the audiophrenic stratosphere above.... The reasonably priced $2500 Merrill Teranis, based on the lower cost NC500 NCore module, declares a THD of 0.005%, thus achieving the preported distortion goal, using a trickled-down version of NCore, with is mainstream switching frequency of about 450 Khz. G. |
At $17k a pair? No. No thank you. I’ve heard current linear amps that were about that expensive and I wouldn’t switch to them either. To me the idea that we need super technology to finally fix the Class D problem just wont’ fly. Blame my tin ears if you must, but this was solved a decade ago. Best, E |
"randy-11georgehifi +1 many times over Randy, seems like your one of the few that get it here!" randy and george, I believe I understand george's often stated theory that the current typical class D switching frequency is too low at about 500kHz and results in sonic anomalies within the audible human hearing range of 20 Hz to 20 Khz. This theory further claims that raising the switching frequency to the 3-5 kHz range will cause these sonic anomalies from affecting any frequencies within the audible range of human hearing capacity. My issues surrounding this class D switching frequency theory, that apparently both of you now support, are twofold: 1. Whether to believe 2 people on an audio forum named randy and george, of uncertain class D technical knowledge and credentials,claiming this switching frequency theory is valid but offering no supporting evidence OR whether to believe the actual inventor of class D amplifier technology named Bruno Putzeys who seems to assign no validity to this theory and has stated that "500 kHz is a completely reasonable class D switching frequency". Written down like this, it seems like an especially silly and obvious choice to me concerning whose advice I should rely upon in evaluating this theory. Are you two really suggesting I simply ignore the inventor of Ice and NCore class D power modules and just trust your viewpoint instead? If it was empirically proven that these sonic anomalies exist and are audible to a significant number of humans, I admit I would be curious to determine if it improved the sound of my system once the price was much more affordable As it currently stands, however, I'm not convinced I should care since I've never even heard a hint of any sonic anomalies from any of the class D amps I've used in my system or any I've ever listened to in any system. As Aristotle so famously asked Plato so astutely long ago: "If your class D amp had a switching frequency proven too low and it caused audible sonic anomalies, but you could not hear these anomalies, would they even exist to you?" That hipster Plato then replied to his teacher in the following lesser known and less famous manner: "Mr. Astute, if I cannot hear them pollute then it does not compute and I know the point is thus moot so I properly cease to give a hoot." True story. I'm with Erik and Plato on this one; I've been living with dreamy sounding amps for a while now, too. I don't need my switching frequency increased to have what I consider the best, either. Later, Tim |
You know what I like about my Class D (Primare I32)? It sounds really, really good. I have no idea if it has ICEpower or NCore, or Hypex in it, and I'm really not sure I want to learn enough to know if it matters. Every time I get more educated on the technology of HiFi it causes gear-lust costs me money. I'm much better off listening in blissful ignorance. Seeya, fellas. |
It’s because a simple low order output filter can take the amps full power, but it’s effects reach down into the audio band and still leave some switching noise left overs, hence the need to take it up much higher as Technics did with far higher switching frequencies, so they can be effectively removed, without effecting the audio band. These days when Stereophile tests a Class-d amp, they put on an external output filter, the Audio Precision’s AP0025 filter, which has a -50db rolloff after the audio band so the 1khz square waves look half decent without the switching noise embedded right across it, (good for sales) 10khz square wave still looks a mangled mess though, trouble is this AP filter can only take very low power, would be real nice to leave it in to listen to, but it would blow up in a micro second. http://www.stereophile.com/content/class%C3%A9-sigma-2200i-integrated-amplifier-measurements#31YFAPfYVDGeowzZ.97 And yes steeper filters as you said do have their own set of problems re sound, as ML found out with their No.53 monoblocks. Cheers George |
I always thought the gentle filter slope was b/c steep "brick wall" filtering caused audible distortions... I do agree that the amplifier is the closest component most of us have that is near perfection. Speakers, room tmts, DACs, source material... all are in more need of improvement on a relative basis. |
I'll lay money on it Eric your the one of the first to change to the higher switching speeds when they come available/affordable, hopefully soon, judging by Technics lead in this area of higher switching speeds. I know I will sell my inefficient, hot, heavy, boat anchors just before it happens, before they become worthless, as will today's Class-D amps. Cheers George |
