@georgehifi - How is that any different from digital audio, where DACs get by (very well I might add) with switching frequencies well below a Mhz? And in DACs, there isn’t a practical way to do global feedback since the input is digital, so it’s much more difficult to eliminate filter effects.
Class D
Been thinking of trying a D amp to reduce clutter. Most that I see are not rated at 2 ohms. My PSB Stratus gold's will drop to 3 ohms or lower at some frequencies. So my question is will these types of amps handle this impedance ?
Thanks in advance. Chris
Thanks in advance. Chris
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George, -200 Stop posting tired graphs, of an older technology that no longer represents state of the art. Are you familiar with the saying correlation does not equal causation? You are using the ignorant premise that because one Class-D amplifier has lots of phase shift that all Class-D must. THAT YOU REFUSE TO LEARN what it means to include the filter in the feedback loop shows your dogmatic ignorance. What is really funny is you idolize Soulution, even though the person who designed it is not the person quoted ..... well guess what SUNSHINE, Soulution uses a ton of feedback, just like Atmasphere has said repeatedly. A TON. They do it by having a large gain bandwidth. Really this is 2nd year circuit in University for engineers. Oh right, you don't actually have an engineering education. Silly me. |
How is that any different from digital audio,The amount of power the filter has to contend with in Class-D amps compared to a dac, now your showing how ridiculous your statements are. https://www.stereophile.com/images/1212levin.side.jpg note the size of the 4 x!! output switching frequency filter coils in this $53K ML Class-D they had to use, and that’s a monoblock. They tried to series them all up from what I was told, to get a quicker/shallower roll off, as not to effect the phase down into the audioband like this https://ibb.co/vvwzGV5, but it was a disaster as I believe they reacted with each other at certain frequencies and rang, which was what they were trying to get rid of in the first place "switching frequency noise" Fig.2 Mark Levinson No.53 Reference, small-signal 10kHz squarewave into 8 ohms (no AP testing low-pass filter).But it worked in getting rid of the switching noise in the $53k ML class-d by here is the 10khz!!!!! square wave with NO external AP testing filter used, almost perfect https://www.stereophile.com/images/1212ML53fig02.jpg, no embedded switching noise, "unheard of for a class-D", except for Technics SE-R1 with does it by moving everything (switching frequency and low order low pass filter) up much higher to 1.5mhz. |
How is that any different from digital audio,The amount of power the filter has to contend with in Class-D amps compared to a dac, now your showing how ridiculous your statements are. Seems George does not understand how LC filters work. note the size of the 4 x!! output switching frequency filter coils in this $53K ML Class-D they had to use, and that’s a monoblock. Without talking with the designer I cannot be sure, but looks like they may be toroidal air-cores or a very low permeability magnetic material to fix a perceived issue (that quite possibly does not exist). This caused it to be large. Designers do crazy things all the time. Class-D is a big step up for many amplifier designers used to somewhat cookie cutter designs. There really is not stopping anyone from using a 2 stage LC filter at a high frequency, well other than there is no sonic value to doing so. https://www.stereophile.com/images/1212AM1fig02.jpg That's about 450Khz, which with most speakers will never make it to the driver. Point? |
@georgehifi - I usually try hard not to get personal on these forums, but you’re continued spewing of misinformation is getting on my nerves. A lot of people on this forum count on knowledgeable people to explain how things work. But you just spout ridiculous drivel. And you keep doing it despite a number of experts like atmosphere and audio2design explaining in straightforward terms why your wrong. But instead of trying to understand what they are saying, you keep regurgitating the same old arguments which don’t even apply to what is being talked about. I think you better quit while you’re behind. Who knows how much more ridiculous your counter-arguments will become. |
The amount of power the filter has to contend with in Class-D amps compared to a dac, now your showing how ridiculous your statements are.This statement is wildly incorrect! Although digital and class D amps both employ switching, it is important to understand that one is digital and the other analog. However the primary difference between the two is the the order of ones and zeros has significance with digital as does the word length. With class D it does not (there is no word length for starters....) and it is always switching states at its switching frequency. In a class D amp its the width of the on and off states that has significance, as these widths describe the audio signal. As a result the filters are vastly different. The filter in a digital system is usually operating at a *much* lower frequency than a class D amp. So this isn't just about power!! |
This statement is wildly incorrect! So this isn’t just about power!!It’s more about power, because you can’t see the forest for the trees, with what Mark Levinson tried to do by series up "low order" output filters (so they don’t burn out) and trying to get a steeper roll off as not to introduce phase shift into the audio band in the upper mid/highs, which they achieved, but it had then other problems. https://www.stereophile.com/images/1212ML53fig02.jpg Instead the simpler fix of of doing what Technics SE-R1 did and just raise the switching frequency to 1.5mhz. |
It’s more about power, because you can’t see the forest for the trees, with what Mark Levinson tried to do by series up "low order" output filters (so they don’t burn out) and trying to get a steeper roll off as not to introduce phase shift into the audio band in the upper mid/highs, which they achieved, but it had then other problemsThis comment really says you don't understand what's going on here. ML didn't do what you're describing. Its obvious from the internal photos that the circuit employs what is known as an 'H' bridge output (which tends to be common in higher powered class D amps). Its also common to see two chokes as a result- one for each half of the bridge circuit. Without knowing further details of the circuit its unwise to speculate further, but the fact of the amp being an H bridge is easy to see if you know what to look for. The waveform at the link is a 10KHz squarewave. There is a small amount of overshoot, and what looks like a bit of an oscillation on top of the waveform as it is consistent with each iteration so does not appear to be a measurement error. As square waves go, that's not a bad looking one- most power amps will round the leading edge (if open loop/zero feedback you need 100KHz bandwidth to make that leading edge look right). So I don't see the 'other problems' to which you referred by including that link. I might add though that more modern class D amps do make a better showing of this sort of thing. When you attack a technology based on older examples, it really doesn't help your argument! |
Must be soon, you really have gone into full product protection mode, and there’s no stopping you. Good luck is all I can say, for your new Class-D venture. And Class-D technology has not progressed as much as you want all to here to think (for sales), sure the GaN transistors that I first showed here years ago as a far better alternative for Class-D, you were quite negative about back then, and now you say you use them. How ironic. I first showed the GaN power transistors from EPC (https://epc-co.com/epc) inventors of the Mosfet, to all here many years ago, and yes they have improved things a little, but the only one to use them fully and make a dent in Class-D’s Achilles Heel "switching frequency/switching noise/phase shift" has been Technics with the SE-R1 and hopefully the new SU-R1000 integrated has the same genes. |
Do what I did. Call a tech/sales rep at Sweetwater. Couldn't be nicer and more thorough if he tried. The first purchase was a Crown XLS 1502. Really couldn't be more pleased with that unit. Quiet and tons of headroom; ran a set of Ohm Walsh 5's like nothing. Those have been sold and replaced by a well loved pair of JMLab Mezzo Utopias with a little preamp and a Crown XLS 1002 which to my ears produce nothing less than aurel bliss. Good luck. |
Please don't be stupid. It is stupid to respond to George.....he is a rock....he will never move from his position.....and he has to have the last word.......so it will always go on and on and on. Don't be stupid....he does not want to learn....he just wants to be right. Let it go.....let him go. Just let him post what ever nonsense he wants and pretend it does not exist. You will be much happier, if you do. What we really need is feedback from those that have listened to the latest class D amps versus the latest class A and class A/B amps (within the same price ranges). We need actual listening test impressions.....not all this guess work.....it is just a bunch of noise. The Technics amp that is about to be released has tons of stuff inside that could make it sound great. Technics does not even mention 1.5 meg or phase shift in their literature. This thing could be really fantastic.....but there is no way you can say it is because of 1.5 meg or phase shift. Please read all the info....very revolutionary. It has 4 switching power supplies that switch at 500K....It is not really a standard class D at ALL.....it is fully digital (like the original Tact amp and Lyngdorf). It takes an analog signal and converts it directly to high speed PCM and does all kinds of low jitter manipulations to make the distortion go down. The PCM signal is then changed in software directly to PWM (class D). Please read all the lit. https://www.technics.com/us/products/reference-class/integrated-amplifier-su-r1000.html https://www.technics.com/us/about/press/releases/20200901-su-r1000/index.html https://www.youtube.com/watch?v=b-BJifbtjbI George did start a thread on this new goodie....so when this comes out and people have listened then we will have a REAL idea of how good it is. It looks great....I do hope it sounds great too. |
Build your own GaN based 200w 8ohm stereo power amp For those who have experience and can kit build, here is from the ones that made GaN technology happen for Class-D. A ready made 200w @ 8ohms 300w @4ohms stereo Evaluation board for $1k. Stick it in a nice ready made Chinese chassis add a powersupply and your up and running. I don’t think they used the 1.5mhz switching like Technics did, but it should be as good if not better that anyone else’s that will be much more expensive https://gansystems.com/wp-content/uploads/2020/05/GS-EVB-AUD-xxx1-GS_Technical-Manual_Rev-200526.pdf https://au.mouser.com/new/gan-systems/gan-sys-gs-evb-aud-xx1-gs-audio-evb/ https://au.mouser.com/ProductDetail/GaN-Systems/GS-EVB-AUD-AMP1-GS/?qs=vHuUswq2%252Bsym8eVHEaFTmw%3D... Cheers George |
https://gansystems.com/wp-content/uploads/2020/05/GS-EVB-AUD-xxx1-GS_Technical-Manual_Rev-200526.pdf Instead of just posting a link, you may want to actually read it and understand it. Note the differences between open and closed loop. Note how the closed loop has better performance at low frequencies but the performance degrades quite a bit at high frequencies? This is a consequence of inadequate design, pretty much as atmasphere has repeatedly stated. Thank you for providing yet another excellent example. This eval is tech evaluation platform. It is not intended to push the limits of technology or topology. If someone is looking to buy modules and DIY, they would be better served with ncore or purifi modules with significantly better performance. |
Please don't be stupid. It is stupid to respond to George.....he is a rock....he will never move from his position.....and he has to have the last word.......so it will always go on and on and on.@ricevs I get what you are saying, and regret the diversion that this has often caused. Generally speaking, if there is going to be misinformation on any given thread about class D on this website, the chances are very high that it will be coming from George. Now I could sit back and watch him do that; I have a theory that a rising tide raises all boats. So knowing the truth of the matter should I sit back and do nothing? We've all seen in the past when someone passes misinformation as truth that it is possible that everyone will suffer. OTOH if I do respond, it looks like I have a personal beef with George which I don't - I've never met him. So this has been an on-going dilemma for which I've never felt I've had a good solution. |
atmasphere, ricevs: I don't try to hide that I think a lot of "tweaks" are highly questionable, and as opposed to what many believe, I have had a large group of audiophile friends who over the years have tried them, so I have been exposed first hand to them, and see difference in blind/sighted listening. Some, based purely on the claims, are physically impossible. I know stating that irks someone. Almost never has anyone ever come back with truly empirical evidence to support their position, even if they resort to "I can trust my ears". I do find leaping from "I trust me ears" to "it must be true" distasteful, almost as much as "I like it", therefore "it must be accurate", however, those argument and conversations play out much differently from this. We are not "arguing" over likes, or personal impressions. We are discussing hard, factual engineering topics and concepts. These really are effectively black and white topics, and there is an absolute right or wrong. People who obviously have a deep and accurate understanding of this topic post detailed explanations and why things are the way they are, work the way they are, etc. We don't sugar coat, of exaggerate. In the face of that, someone else, with clearly an incomplete and inaccurate understanding of many of the related topics to Class-D repeatedly posts technically erroneous information. This is not even debatable. It really is black or white, right or wrong. They are wrong. Absolutely provably wrong, and they have been. They don't recant, or consider they may be wrong, they double down and repeatedly post false information labelling it as factually correct, even though they cannot describe it in their own words or justify their position. Last, I find the repeated personal attacks on atmasphere totally uncalled for. It is like he has a personal grudge. |
To others that care about these forums. All we have are manufacturers and their shills, with incessant agenda to get he ball rolling on their latest class-D products, and they use these forums to slyly advertise what they have coming up for sale, and will stop at nothing to counter anything that may effect those future sales. See the immediate angst cause to them with the professionally ready made diy GaN Class-D kit I put up above, which is probably better than anything they could do. One here especially put rubbish on the new GaN transistor technology way back when I showed it to all here, and he said it has no advantage over the Class-D technology used. But now he’s has changed his tune and is actually pro GaN transistors, funny what the mighty $$$$ brings out in people. Like I said they are just here to slyly advertise their goods. You can’t believe them, especially the fusers! At least companies that use GaN like Orchard Audio, AGD ect don’t come here behaving like them. Cheers George |
Here are some interesting developments.... 1. Class D audio (under the Premium Audio name) will soon be releasing their "baby" GaN amp.......stereo, 150 watts a channel into 8 ohms, balanced and unbalanced inputs for a mere $699. 100K input impedance. You will see a tiny bit of info here....wait for the second slider to load to see the pic https://premiumaudioproducts.com/ 2. Orchard Audio is releasing a higher powered version of their GaN amp module. You can buy the module fully loaded or you can just buy the board and buy all the parts and stuff it yourself. This new 250 watt a channel module has higher input impedance (44K balanced) and higher gain then before so makes it more universal. The unloaded boards can be bought for $100. The stuffed boards can be purchased for less than $1000 the pair (till the early bird sale goes away). This would be way better than the eval board put out by the GaN companies.....The Orchard amp measures and sounds very, very good.....800K switching and very very little phase shift. https://orchardaudio.com/shop/ols/products/strk-ltr-mdl/v/STRK-LTR-MDL-SSMBLD The phase response and other measurements of the earlier less powerful module can be seen at the bottom of this page. https://orchardaudio.com/bosc#58053fe9-04a5-4030-9e69-e310ee3f6b5a |
Look at that, no phase shift ... https://img1.wsimg.com/isteam/ip/80cc3d69-5af5-47d4-a047-53c1246a6080/Gain%20and%20Phase%20(8ohm).jp... The low frequence phase-shift is measurement artifact. |
At least companies that use GaN like Orchard Audio, AGD ect don’t come here behaving like them.George's complete lack of self awareness to his own behavior is astonishing. Absolutely one of the worst offenders. None of the others have the product they sell as their avatar. He promotes to sell with every single post. |
Looks very much like the older USA company USA Audio or something even the advertising and MADE IN AMERICA proudly stated, if you look back at my GaN posts, they did say when I emailed them about a year or two go they’d be bringing out an US made Class-D using GaN technology soon, and it will be under $2K. Guess they finally done it. PM: Guess they’re Covid effected, as the sites closed to any ordering. |
You still need to let it sink in sunshine, I showed you what your amp that you push incessantly does to the phase integrity of the upper-mids and highs, up to 70' out of phase!!!!! Oh yes!! wonder why most gripes about Class-D’s sound, is about the upper-mids and highs, never it’s bass. https://ibb.co/vvwzGV5 |
Here is an interesting fact. The IceEdge module has two....yes, two inductors in series on the output. It could be one reason the phase does not measure so well. I removed the last inductor and the last set of caps to ground as part of the last set of mods I did (PS Audio leaves these alone but still the highs are pretty good....please read Michael Fremer"s review of the $6K PS Audio amps where he compared it to the $150K Dartzeel). When I did this it sounded as if I had 2 db more gain. The soundstage came forward....much like my class A amp and the highs were much more extended and airy and the decay went on longer. The depth was now greater but the midrange was more forward. Very cool. Many other mods I did to the module improved the highs as well....and they had nothing to do with bandwidth or phase shift. Everything makes a difference.....It is not just one parameter. |
gFi it’s shocking that you don’t know the difference between your and you’re/you are you’re- you’re ignorant You’re ignorant, I meant to say (your amp) Either, or either, so long as you know. To me the fact is you’re being ignorant to this graph. . You still need to let it sink in sunshine, I showed you what your amp that you push incessantly does to the phase integrity of the upper-mids and highs, up to 70’ out of phase!!!!! |
I did not measure the amount of residual after removing the secondary coil and caps. Since the caps to ground were just 1000 pf....I imagine that the residual looked much the same. IcePower was probably trying to remove ultra high frequency noise as a precaution. So many manufacturers put filters and fuses on things to prevent imaginary problems.....not knowing these fuses and filters actually wreck the sound. Everything you do changes the sound. The output coils that everyone use are ferrite core coils. No one in their right mind would use a ferrite core coil in the midrange and tweeter xover of a serious speaker. Ferrite messes up the sound. So, why do we have ferrite coils on the output of all class D amps? It is because they are smaller, cost less, have less resistance, run cooler and have better contained fields so there would be less rf outputting the amp. It is not because they sound good. If you use a better sounding air core coil the board has to be bigger, the coil costs more, you have to use a large gauge coil to get the resistance down, and you might have to add more shielding in the amp to make it pass rf standards. What is true is that all coils sound different from each other. So, even different ferrite core coils will sound different.....even using the same gauge wire. The type of wire and its coating all affect the sound......just like wire used in an interconnect. The worst being normal copper....OFC is better, cryoing is better, PCOCC is better, etc. Same with the core material and shape and coating and wire directionality and whether you go into the inside or the outside of the coil. Many air core coils I tried in the Purifi module did not sound as good as the stock ferrite core coil. The one I ended up using sounds much better than the stock coil. When I first heard the difference between the stock coil and the one I am using......I said "its like I am sticking my head down the saxophone". I could hear so much more information.....real information....space, separation of instruments, lower noise, etc. We need others to start experimenting with the output coil.....this is more important than what the switching frequency is. There is always more to learn and more beauty to unveil. |
It's often the case that extra filters are added to allow the device to pass FCC requirements and/or to improve stability into arbitrary loads. If you are making modifications for your own use, you can get away with it, but if you are trying to make a commercial product, you will need to make sure the product continues to meet FCC requirements for emissions before offering the product for sale. |
No one in their right mind would use a ferrite core coil in the midrange and tweeter xover of a serious speaker. Ferrite messes up the sound. So, why do we have ferrite coils on the output of all class D amps? It is because they are smaller, cost less, have less resistance, run cooler and have better contained fields so there would be less rf outputting the amp. Less resistance is definitely important leading to high damping. They also have a closed magnetic path which means they are not effected by external steel which could even include component leads ... and they don't turn external steel (which could be anything) into a speaker either. Given the very low distortion and IM, it is hard to argue that the design choice is poor. All depends on the ferrite material and where you operate it on the curve. Lots of well rated audio products have output transformers. Choose your poison. |
You can theorize all you want. What I do is listen. Most EVERYONE who has listened to ferrite core coils in a xover.....knows they suck. I now know they also suck as "full range" coils on the output of a class D amp. You can only know how something "sounds" by listening. If you want to build just for numbers than a ferrite core is fine. I build for sound......the best sound wins. Of course, it is just my opinion. Until others listen to air core coils on the output of a class D amp it is just.....my opinion....based on what I hear. There are lots of opinions where they have used them in speaker xovers.....and the overwhelming opinion is that ferrite sucks. Look at all the pics of the xovers of super high end speakers.....do you see any ferrite core coils used in the mids and highs? Don’t think so. He he.....I am sure someone will find one and post.....just to be right....he he. |
You would be hard pressed to find a ferrite core in a mid/tweeter for even a mid range speaker. Air core inductors are fairly cheap at the frequencies needed. For woofers, there are trade-offs w.r.t. resistance / core impacts. In speakers, the cross-over is in the audio band. In a Class-D amplifier it is not. In a speaker you don't normally have steel nearby. In a Class-D amplifier you may. |
Ferrite messes up the sound. So, why do we have ferrite coils on the output of all class D amps? It is because they are smaller, cost less, have less resistance, run cooler and have better contained fields so there would be less rf outputting the amp. It is not because they sound good. If you use a better sounding air core coil the board has to be bigger, the coil costs more, you have to use a large gauge coil to get the resistance down, and you might have to add more shielding in the amp to make it pass rf standards. You got that right at least!! and it’s why ML in their megabuck class-D flop, use big "air cores" in their No.53 monoblock, and used 4 of them in series to get a far steeper slope to cut the switching frequency noise out, so it doesn’t affect the audio band phase integrity. https://www.stereophile.com/images/styles/600_wide/public/011212ML53-600.jpg |
Because the filter is set at 50K does not mean it does not effect the sound. It's intrinsic sound is still there. No free lunch. Everything makes a difference. But you have to listen to know. Years ago I worked for an audiophile company that made tube stuff. They had a zobel network on the output of one of their amps that had a .1 microfarad cap. . I told them to change their junk mylar cap to a polystyrene but the owner said it was operating at high frequencies out of the audio band so it should not matter. He humored me and tried it. Of course, it sounded much better. There are people that sell external zobel networks and the best sounding ones use the most expensive parts. Again, no free lunch.....everything makes a difference. |
Trouble is the Levinson sounded like crap. Everything makes a difference....again....the truth is in the listening. It does not matter that Levinson used a bunch of air core coils (one thing does not make a whole).......what matters is the sound. They did not get it right. My modded Purifi uses ONE super sounding air core coil. |
Class D is just a cheap form of amplification. Another way to cut cost and corners. I read more than a few interviews from the high-end companies,and they all say "Stay away. The technology is not proven." Especially when the products are from companies who’ve been around for 3 years,or that I’ve never heard in the first place. Class A & Class A/B have been around forever with good reason. |
@zappas -- I’m not sure if you’re still reading this, or if this point has been covered somewhere among the back and forth. The PuriFi modules put out almost 500 watts into 2 ohms. It's easy to find the spec sheet online. I have a pair of Apollon amps made with them, and they drive my Janszen electrostatics better than my more expensive class AB amp did. I am pretty confident they would drive your speakers fine. I don’t know anything about the PS Audio ones. |
Of course, I checked every channel of every amp that I sold and looked at the residual of each channel. I just did not do an exact measurement of the before and after. From what I remember, it was very much the same, about a half a volt or so of pure 500K with no added high frequency noise (but since I did not do an exact measurement then that is what I tell you I did). However, it sounded way better without the extra filter (most class D amps just use one coil and one cap per phase). if I had seen any kind of added noise on the 500K wave or a noticeable increase of value I would of taken note......there was basically no difference (that I remember). The secondary coil is 15 uh and the cap to ground is 1000pf.......so it looks like a 1.3 meg filter......that is not going to make any difference in a 500K sine wave. If you add another 1000 pf for speaker wire than maybe a hair difference. By the way, I first removed the 1000 pf caps to ground on the output and heard no difference. But when I remove the inductor.....OMG When Nuforce started making class D amps I was a dealer. That first amp had all kinds of noise coming out of it. One if the fixes they used was to add a secondary coil right on the speaker output terminal. When I look at the output stage of the latest class D Nuprime amps (Nuforce morphed into Nuprime) then I notice a bunch of coils near the output.....so I believe they are still doing this today. Most everyone just uses one coil and cap. More ferrite coils on the output is not merrier. How many coils (hopefully air coil) are you using on your output? Coils are not good......but you have to have one in a class D amp or you fry your speakers......so make that one the best sounding one in the universe! |
It does not matter that Levinson used a bunch of air core coils (one thing does not make a whole).......what matters is the sound.I did not say that it was the idea of series'd air core coil output filters that ML used to get a steeper roll off as not to give phase shift down into the audio bad that made it sound bad. The fact that a big company like Mark Levinson knew that it is a problem with Class-D, as this phase shift graph from output filters shows (red) https://ibb.co/vvwzGV5 That's why it's seems only fixable by moving the switching frequency and filters way up higher so there's no effect of phase integrity down into the audio band, and the only way to do this is move the switching frequency up much higher to 1.5mhz and the filter as Technics did with the SE-R1 and hopefully with the SU-R1000 also. And you can't fix it but throwing "more global feedback" at it, as that is a sound destroyer in itself. The only way is the > 1.5mhz switching frequency, so the filter can do it's job without introducing phase problems down into the audio band. |