We've already been listening to the amp. FWIW the squarewave response you linked does look pretty bad. Our tube amps can do better than that!
Obviously we're not letting this thing out without it doing what its supposed to do.
The thing is, you can have all sorts of issues when building a switching amplifier. The layout of the boards is critical- if not done right you can get stability problems. The little 'dimples' in the squarewaves you linked say to me that there is a suppressed oscillation in the amp somewhere. The squarewave should have been flat across the top, but its not! That's not a switching frequency thing as it is a stability thing.
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Now the parts we work with are not that expensive, but we found a way to eliminate deadtime. This allow us to switch at much higher frequencies. Naturally your not going to tell us how it’s done, I’m hope for you that you can do it, but also sceptical at the same time, as minds more attuned to solid state Class-D topology than yours have not succeeded, save for Technics who are half the way there. Cheers George |
FWIW the squarewave response you linked does look pretty bad. Our tube amps can do better than that! Of course it can, any linear amp can, not just yours! It’s very good for any Class-D without the need of special external output test filters. https://forum.audiogon.com/posts/1501266 Cheers George |
Naturally your not going to tell us how it’s done, I’m hope for you that
you can do it, but also sceptical at the same time, as minds more
attuned to solid state Class-D topology than yours have not succeeded,
save for Technics who are half the way there. I'll be happy to after the patent is approved. That EE turned out useful after all... |
Just an FYI, and to correct any misconceptions about us. We used to use all the Hypex modules from the NC1200 in the VERITAS Monoblocks, down to NC500 in the Taranis. While we have a superb implementation of these modules, based on direct comparisons done by others to the same modules in other units, we understood there was more to be had. We will shortly be introducing our proprietary designs which takes the level of performance up an order of magnitude, and rivals any of the best of classes available. Using our proprietary ZXOL design that has no feedback loop, we are able to achieve this exceptional performance. We are stepping that up even more with other design and engineering techniques. Look for us at Munich 2018 in ATRIUM 4.2 E226 where we will be showcasing this exceptional sound. Reviewers will be getting their units in February/March. Some have the proof of concept heard it at CAF 2018 and their impressions were in the November Newsletter. Here is a sample of what is to come. https://forum.audiogon.com/discussions/absolute-top-tier-dac-for-standard-res-redbook-cd/post?highli... |
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We will shortly be introducing our proprietary designs which takes the level of performance up an order of magnitude, and rivals any of the best of classes available. Using our proprietary ZXOL design that has no feedback loop, we are able to achieve this exceptional performance."
Hi merrillaudio,
I'm a bit surprised you're going to cease using Hypex NCore 1200 power modules in your amps and use your own proprietary ZXOL design modules, instead. I'm not questioning this decision but I am curious why you decided to go without a feedback loop.
I'm not an engineer or amp designer but I have a strong interest in class D technology. I recall reading an interview with the inventor of Hypex NCore technology, Bruno Putzeys, in which he explained why he believed there was no such thing as too much feedback in the design of his class D circuits.
Are you currently able to state your reasons for deciding to eliminate a feedback loop in your design?
Thanks,
Tim
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Feedback, while suppressing distortion, adds some of its own.
In addition, it is a destabilizing factor in any amplifier design. 'Stable' means that it is resistant to oscillation.
The distortion added by feedback contributes to brightness (a coloration) and hardness (which is unpleasant); both due to the ear's quality of converting all forms of distortion into tonality.
So far we've been running our class D zero feedback as well. Output impedance does not suffer, so driving a load really isn't the problem. Controlling distortion is, but if you are careful with the design that can be controlled too.
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Hi Ralph, Thank you for your informative response. I've been reading for decades that negative feedback in traditional linear amps should be avoided since it (sorry, no pun intended) negatively affects its sonic performance, especially in the upper frequencies. I've taken this as the gospel truth ever since I first learned about the use of feedback in amps. Since I've become interested in class D amps in the last few years and began reading about how it works, however, several articles and white papers I've read have caused me to rethink my view of negative feedback in class D amps. For example, here's a quote on this subject from an interview with Bruno Putzeys, inventor of UcD and Hypex NCore technology: "If you take a simple amplifier which has acceptable distortion (just a second harmonic is what I use as an example) and you start applying feedback, harmonics will appear that were not there originally. Higher-order harmonics, even and odd, turn up out of the blue. So if you apply a little bit of feedback, the second harmonic that you wanted to reduce drops by a little, but out of the blue you get this whole smattering of high harmonics. It is quite understandable that this doesn’t sound good. That observation has been made and published by various people over the years, but the most important conclusion was never drawn: If you keep increasing feedback, if you turn the feedback knob up and up and up, you quickly hit a point where those distortion products all start coming down again and the signal does start getting cleaner. And if you get to very large amounts of feedback, the result is just supersmooth. So that is why I say that it is normal for an experimenter to experience that if you take a good-sounding zero-feedback amplifier and add 6dB of feedback, the result sounds worse. They heard that right. But had they been in a position to add 60dB, well then, suddenly they would have been confronted with a sound that is little short of magical." I've always respected your audio knowledge and found your posts very informative. I have no desire to start an argument with you and I'm fairly sure you've forgotten more about good amp design than I've ever known. I'm just very interested on your thoughts about negative feedback in class D amps. Here's the link to the entire Bruno Putzeys interview I quoted from above: www.soundstageultra.com/index.php/features-menu/general-interest-interviews-menu/455-searching-for-t...Thank you, Tim |
I’ve been reading for decades that negative feedback in traditional linear amps should be avoided since it (sorry, no pun intended) negatively affects its sonic performance, especially in the upper frequencies. I’ve taken this as the gospel truth ever since I first learned about the use of feedback in amps. First you need a bit more clarification on just what "feedback" are you talking about, "global feedback" or Local feedback"? As both are very different. "local" is a good thing if the output stage is designed right with minimum problems. "Global" is also ok if used sparingly and not use to correct big problems. Then there's "feed forward" that I've seen in Rouge M120 monoblocks. Cheers George |
They heard that right. But had they been in a position to add 60dB, well
then, suddenly they would have been confronted with a sound that is
little short of magical." Bruno is spot on with this. The usual rule of thumb is that very low amounts (under 4 db or so) is not harmful, but more than that is a problem; after about 20 db or so things start to settle down. 60db hasn't been practical until the introduction of class D (since gain is developed in an entirely different way); so I have no argument with this; my prior comments should be limited to traditional amps where making the kind of gain is impractical. |
I use the Acoustic Imaginery Atsah monos and also do not experience any high frequency issues or soundstaging issues. The Ncore 1200, imo, is extremely revealing, neutral and transparent and will take on the character of the source equipment, cables and material being played.
As such, careful attention needs to be paid for the Ncores to sing and for its potential to be maximised (just like any high end amp). It has been quite an interesting journey and I have spent considerable efforts matching the appropriate cables with the Ncores and cannot be happier with how they sound at this point. Class D amps are very sensitive to power i.e. power conditioning and power cords and so I will suggest these be properly looked into and matched before any critical evaluation of Class D is made. |
At the risk of making the least contribution to this thread and over generalizing the discussion, my somewhat limited experience with hearing class D amps at various shows and friend's homes has had one thing in common. That quality, almost irrespective of the downstream or upstream gear, was that I always felt I was listening to the instruments as opposed to the music as a whole. Whether its the ultra revealing nature of the technology or the choice of the associated gear, I can't tell but I was consistently blown away by the sound for the first few minutes followed with my brain going into overload with the amount of detail I was hearing and ultimately felt exhausted with the demand. Some may consider this experience the holy grail of audiophilia but for me it felt like I was watching the trees as opposed to enjoying the forest scenery. Perhaps crude analogy but the best I can do. |
Class D amps are very sensitive to power i.e.
Yes they have one of the most dirtiest power supplies made, SMP's That's why you'll see many caring Class-D manufacturers giving them more quieter linear supplies, just to null out one of the problems of Class-D amplification. Cheers George |
"Bruno is spot on with this. The usual rule of thumb is that very low amounts (under 4 db or so) is not harmful, but more than that is a problem; after about 20 db or so things start to settle down. 60db hasn't been practical until the introduction of class D (since gain is developed in an entirely different way); so I have no argument with this; my prior comments should be limited to traditional amps where making the kind of gain is impractical."
Thanks, Ralph. Your statement has cleared this issue up for me.
darknightdk,
Although I use more mid-level class D amps than your Acoustic Imagery Atsah mono-blocks, your described impressions of your class D amps as "being extremely revealing, neutral and transparent and will take on the character of the source equipment, cables and material being played" closely resemble my impressions of my amps. Like you, I've been amazed how clearly audible the performance level of upstream components, cabling, power cords and recordings can be heard and judged as well as how clearly audible the affects of any changes to any of these can be heard and judged. The best description I can think of is the proverbial 'straight wire with gain'.
This level of clarity and detail is not for everyone and any upstream weak links in your system will definitely be exposed. I prefer this honest quality in my system rather than a masking or inaudibility of weak links; weak links can always be upgraded in quality but only if you're aware they exist.
Enjoy,
Tim
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First you need a bit more clarification on just what "feedback" are you talking about, "global feedback" or Local feedback"? As both are very different.
"local" is a good thing if the output stage is designed right with minimum problems. "Global" is also ok if used sparingly and not use to correct big problems."
georgehifi,
According to Bruno Putzeys,
"Local feedback with a bit of global feedback is, actually, identical to full global feedback -- mathematical fact."
I believe he utilizes this approach in his class D designs. He also believes there is no such thing as 'too much feedback' as it pertains to class D amps.
Tim |
"Local feedback with a bit of global feedback is, actually, identical to full global feedback -- mathematical fact."
You can have local without global, this is preferable in linear solid state, if the output stage is well designed you can do without the global and just have local around the input and driving stages, many good hi-end amps do this and it sounds much better for it, Gryphon, ME, Krell ect.
He also believes there is no such thing as 'too much feedback' as it pertains to class D amps
That's his opinion, not by many noted others. And it looks like Ralph's going minimal FB as well. Large amounts of global feedback used in linear amps is used in poor designs, to get good specs, the challenge is to get good specs with only a little local feedback. Cheers George |
Large amounts of global feedback used in linear amps is used in poor
designs, to get good specs, the challenge is to get good specs with only
a little local feedback. George, I'm a bit uncomfortable with this statement- a lot depends on how its interpreted. I'm of the opinion that the amp should have good linearity open loop, then add the feedback once that is achieved. This would make the latter portion of the statement true. But if the amp is to have good specs with only a little feedback, then this statement is likely false. Unless its a very small amount of feedback (under about 4 db) the application of feedback (even in a good design) will be detrimental. This is due to bifurcation of the input signal by the feedback itself (Bruno says that the harmonics 'show up out of the blue' but its easier to understand if you apply Chaos Theory). So the solution for a **good design** is to use a lot of feedback, hopefully on a design that already has good linearity to begin with before the application of feedback. Sorry to go on- I just felt this needed clarification. |
George, I’m a bit uncomfortable with this statement- Maybe I should have said in "most" A little feedback should "only" be used to clean things up a little, not to make design blunders look better on test. And if designed very well, all that needed is "local feedback" In tube amps that have average output transformers global feedback is used to reduce the transformers output impedance to get better damping factor specs, this is a band-aid fix, the output transformer should have it without the need of feedback, and the amp will sound better for it. Global feedback compares output to input and try’s to correct any differences, trouble is that the output is already on it’s way to the speakers. And the more global feedback applied the more unstable an amp can become. If you think about it Ralph, linear solid state amps that are well made but with global feed back and a bit of it, also have the same lifeless sound that many say Class-D has. We have done an experiment ourselves back in the 70's on a very good amp Pass’s A20 Class-A, which we morphed into a 150w Class-A beast with water cooling (a two man lift), which had global feedback and sounded very good, then we changed it and made it local feedback and it sounded superb so much better it wasn’t funny. http://www.firstwatt.com/pdf/art_classa_20.pdf Sorry to go on- I just felt this also needed to be said. Cheers George |
If you think about it Ralph, linear solid state amps that are well made
but with global feed back and a bit of it, also have the same lifeless
sound that many say Class-D has. No argument there, but the kind of feedback Bruno is talking about is a different matter. Nelson Pass wrote a great article about this- you can find it on his DIY site. In it he speculates about 60 db, but points out how impractical it is to add more gain/circuitry to get there! The thing is, in class D making gain isn't a problem. An essential bit of the class D circuit is something called a comparator, which is a lot like an opamp run open loop. If you know your opamp theory, that means you have nearly infinite gain. I'm nutshelling this a bit, but the point is you can make a lot of gain with class D without adding extra circuitry to get there. So 60 db of feedback is very doable. |
Proof will be in the pudding Ralph, 60db of negative feedback makes the hair stand up on my neck.
As everything I have learnt and read from the masters about feedback, say it's in some cases a necessary evil in small amounts, 15-30db and hopefully just local not global, but 60db global!!!! YIKES!!!!
Maybe that the reason for those that hear it in class-D that it's sound is lifeless in character.
Cheers George |
I have been through this thread and a lot of good technical details, most of it I just cannot understand. It has been few months and I am wondering if anyone tried the Class D amps from Nord and the likes?. Who makes a good amp based on Hypex NCore 1200 power on a decent budget?. What are the impressions that might have changed, if any, regarding Class A/B vs Class D with any of the users who posted here?. I am considering Class D amps like ATI AT543NC, Nord, Red Dragon M1000 MKII and Legacy Powerbloc4. |
@geek101,
I highly recommend the ATI AT543NC, the best implementation i’ve seen (so far) of Hypex NC-500 modules along with beefy power supply.
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@lalitk does this mean ATI AT543NC will be a better performer then Legacy Powerbloc4 or similar implementation?. ATI has more power for sure. |
@geek101,
I have not heard the Legacy but I did compare the 543NC with M1000 and Merrill Audio’s THOR....the ATI 543NC amp sound was very dynamic, punchy low end and uncolored sound on both music and movies. |
@lalitk Thank you, I appreciate your insight. M1000 uses ICE so must be similar to Legacy Powerbloc4. Again I am just guessing. |
How old is Ice Power 700ASC module and is it ok to get an amp based on this module when designed well?. |
Summer 2015. What amp are you looking at? |
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@geek101 If you are seriously looking at Class D amps this is one you should seriously look into. I own the stereo version and it is the best Class D amp I have owned (4) including two with Ice Power modules, including the 1200AS, and one NCore NC-500 amp. Nuprime's modules are proprietary and have evolved over the past decade from the highly acclaimed Nuforce amps. They have both SE and XLR inputs. The two units sitting side by side are not quite the width of a full size amp. https://nuprimeaudio.com/product/st-10m/?v=7516fd43adaa |
@jackd point me to measurements if there are any? |
Only been out a couple of months so no reviews or tests only what's on the website for 8 and 4 ohms. When the stereo version was tested by one of the German magazines it came in at 195 wpc instead of 150. I've have tested the stereo version with at least a half dozen speakers in a 24x28x10 room and it had more than enough headroom. Among them the Verity Otello, Nola KO, Odyssey Lorelei, Spatial M3 Turbo and TM and Golden Ear Triton 5. If they are carrying them at AA you can try them out for 30 days. The Mono's are rated at 230 and 320 wpc. |
All Class-D’s today have the same problem. The switching frequency is too low to be filtered out effectively completely with the Class-D’s output filter, without effecting the upper mids and highs. A statement George loves to repeat without practical data to back it up with. He’s the guy who in the 21st century argues airplanes can’t fly because they are heavier than air. Me, I'm loving Class D right now. Best, E |
A statement George loves to repeat without practical data to back it up with. The switching frequency is several 100sKHz at the very least and the output filter does not filter it out entirely. Regardless the filter does not have the effect at audio frequencies that George suggests. The effect of the filter is to remove the switching frequency, which none of them do entirely. What is left is called 'the residual' and will be a sine wave at the switching frequency. It can't be heard, and because its a sine wave does not interfere with radio and the like. But it is energy, and should be unable to damage the tweeter. So it should be at a low level. The inductance of the speaker itself is often enough that the residual is of no consequence unless the switching frequency is stupid low (and there are no class D amps in production like that). |
Isn't the Evolution model supposed to a step above the ST-10? There's a thread about it on AudioCircle, I think. |
@jackd nuprimeaudio stuff looks nice but I think the output from them is not competitive with rest of the market offering at this price. That may not be important for lot of folks I assume. Signal to Noise Ratio (SNR): 91dB @ 10W is this competitive with rest of Class D offering?. |
You all may want to check out Legacy's Powerbloc latest generation amps; I heard them in Atlanta driving Valor and Caliber XD and late this summer at Legacy driving Valor and Whisper XDS. Frankly they opened my eyes to what is possible today with lower cost/higher value/well-designed amplification. I don't know specs but believe Legacy would share anything that they have but they are definitely worth a listen before you spend more than their price point. |
@zephyr24069 I literally have to decide between Legacy Powerbloc4 / ATI AT523NC / Benchmark AHB2 / Coda 15.5. ICE vs Hypex vs Class ABH vs Class AB(high bias class A). Price is all over the place too. So hard to compare.
Reviewers has a good impression of Class D amps till the end but they all add that Class D cannot reproduce Class A magic. It is just so confusing.
What are the pros and cons of having SMPS vs Linear supply like difference between ATI vs Legacy Powerbloc4. I really wish most of amps have the lowest distortion till the first 10 watts. But some have inverted curve for the first few watts and then increase.
At the end I think I just have to spend time and money to compare them at home and pick something. |
Yes...the best advice is to compare them at home in your system; that is the only way to know. I can tell you only about the Powerbloc2 based upon recent hearing. It's amazing and at such a low price I cannot believe what it puts out there in terms of overall musical enjoyment, sound and imaging.
For me it's not Class A as I've always preferred the magic of a great A/B design. My current Esoteric A-02 has a broad power range in Class A before switching but either output range and amp mode provides amazing sound for the money. I may pick up a Powerbloc for comparison and if, not when I also bring a pair of Legacy Valor into this system, I'll need more amps and for that, the Powerbloc is an inviting combination of sonic excellence and price/value! |
