Yeah…
The power supply is arguably the most important part.
(But there are a 100 ways to fail.)
Atma-Sphere Class D Mono blocks
- Thread starter Chorus
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The power supply is arguably the most important part.
(But there are a 100 ways to fail.)
Yes and the Eigentakt Eval board that is cheaply available from Ebay is intender for DIY'ers but they are often found in small-brand finished amps. A few big-brands build under license using better parts, etc - NAD M Series and T+A are the only ones I know of, and their implementation is first class.
Republicoftexas69
Well-Known Member
Yes I have read this but have been less than impressed with the NAD amps I have tried. Gold Note, AGD, Atma-Sphere and Canor all are top shelf GaN and class D, T&A too.
the designer himself has said that he was surprised by the large effect of the input stage.
IMO/IME the class D power supply has to be as robust as the power supply of any high quality amp. I think because the idle current can be so low, many have produced class D amps using competent modules that turned out bad because the power supply was insufficient.
The input buffer is important too and it seems that many in high end don't understand how to design one and perhaps how opamps work. I'm not completely sure of that last bit, but if you have to resort to tubes or some kind of boutique opamp for your input buffer IMO you have an unaddressed fundamental problem somewhere.
I'm not sure I understand you, but Bruno Putzeys is as close to an audio deity as can be expected.
In essence, his amp module offers all the power one would need and, I believe, the lowest distortion numbers on the planet. The DIYer or manufacturer is responsible for the rest. I have had three different variations of his Hypex module and can tell you they are vastly different. The best being his own implementation (the Kaluga) which includes his design of input buffer and power supply. Whatever you put in front of this amp, is what you will hear.
<Off topic, Ralph delete if too far afield.>
An issue with some class D amplifier modules is their (very) low input impedance and requirements for handling charge kickback and such (a number of switched-capacitor ADC and other circuits have similar issues). Buffer selection is critical for those designs. There are also several threads on ASR from a guy who tested a number of different opamps showing fairly widely varying performance. Like many things audio (and otherwise), measured differences can be profound, even though audible differences are often (not always) nil. Just slapping an opamp into a design without thorough analysis and testing can lead to undesirable results. Same goes for opamp "rolling" -- not all opamps are the same, with the same implementation requirements and target applications. The worst case scenario is a random opamp swap that leads to ultrasonic oscillations that destroy tweeters before the user knows what happened. One reason to look for designers that truly understand their designs and the trades involved (I definitely count Ralph among those, and Bruno as well).
An issue with some class D amplifier modules is their (very) low input impedance and requirements for handling charge kickback and such (a number of switched-capacitor ADC and other circuits have similar issues). Buffer selection is critical for those designs. There are also several threads on ASR from a guy who tested a number of different opamps showing fairly widely varying performance. Like many things audio (and otherwise), measured differences can be profound, even though audible differences are often (not always) nil. Just slapping an opamp into a design without thorough analysis and testing can lead to undesirable results. Same goes for opamp "rolling" -- not all opamps are the same, with the same implementation requirements and target applications. The worst case scenario is a random opamp swap that leads to ultrasonic oscillations that destroy tweeters before the user knows what happened. One reason to look for designers that truly understand their designs and the trades involved (I definitely count Ralph among those, and Bruno as well).
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Correct - it’s a pHd and science background.
I am not sure how I can explain it differently than I did in my earlier post to make it clear… but I’ll try:
The term “Designer” - tends to conjure up art and something like making a case body by a 10 year old (or by von Karmen, who was an engineer.)
IMO, he (Bruno) is NOT a designer, as anyone can come waltzing in with a new design and call themselves a designer.
Reminds me of the one about… “What’s the difference between a ski instructor and God?”
Ans: “God doesn’t think he is a ski instructor.”
well, Bruno did design the exterior of the Mola Mola gear. He chose something unique enough that it delayed release of the Mola Mola stuff for quite some time. It is very subtle and needs to be seen close up to appreciate the full extent of why it was difficult to manufacture. Adds nothing to the sound, per se. But why not have the eyes enjoy the scenery too. I'm not sure if Bruno thinks he is a ski instructor either (nor that he thinks he is a deity). He is probably responsible, however, for showing the potential for Class D in the so-called high end audio.
But this is Atma-Sphere's thread... One thing I appreciate about Ralph is his use of science and common sense in his products. Both have led him to a Class D of original design. Took his time too, which I think is noteworthy. But one also needs good ears and a sense of what sounds natural to the human ear. I haven't heard his amps, but the reports are very favorable.
Ok ^that^ is designer work.
I assume you understood the joke then…
I have no idea what Bruno thinks other than the words he has written.
I believe that it was yourself that made the deity comparison… Post #647
And also the work on lower distortion drivers.
And also the psycho-accoustics of the harmonic profile of the distortions.
^Correct^ - but the post #632 asked for a comparison with the purify.
And that is how we got to where we are.
Yes. Especially this. Have learned a lot from Ralph's posts on this topic. And his posts which explain resulting matches between amps and speakers.
^Exactly^ @PYP
Hence the earlier questions about Purify, Benchmark and Topping etc.
They make sense if it is SINAD uber alles, but I don’t subscribe to that vanishingly low distortion camp, as much as having the frequency response harmonics spectrum be free of higher order harmonics.
I am not sure where phase and time domain performance is captured, or if it contained in the two-tone (multi-tone) tests or not.
Are you saying you think that these almost perfect measuring amplifiers have the classical, well studied and documented, phase or time domain errors? Such as TID or TIM?
A class D amplifier, if of the self-oscillating variety, such as our amp or the Purifi, is pretty well immune to these problems. The feedback is also high enough that the phase can be corrected inside the audio band.
No.
I’m not very up to speed on TID and TIM
So I am saying that I do not know whether they have that or not.
They are the same thing, usually expressed as TIM. Its caused by large signal levels (like a transient) causing distortion at the input of a class A or AB solid state amplifier due to an excessive capacitive load on the output of the input stage, essentially shutting down the feedback. Usually the input stage is a differential amplifier pair of transistors. The problem was solved by degenerating gain in that stage. This vastly reduced the distortion caused by the capacitance of the next stage.
IOW, in a nutshell, its a problem that showed up when higher amounts of feedback (applied to one side of that differential pair) was being first used in amplifiers of the 1970s and early 1980s. It took a while to sort out that all you had to do was decrease the gain of the input stage to fix it, and do something about that pesky input capacitance of the stage succeeding it.
Its not a thing when it comes to class D since the topology is completely different.
You can read more about this in an article written by Bruno Putzeys. Start at page 10 if you want to read about TIM. He makes some fabulous comments near the bottom of page 14 regarding how feedback got a bad rap. I can add to that one of the problems that exacerbated this was the feedback used was being applied to the cathode of the input tube, which is non-linear, thus distorting the feedback signal. Of course it won't work!
That's not the fault of feedback. Control theory is well known and works fine in other fields of endeavor. So if you want it to work in hifi, you have to do it right. This is an excellent example of how tradition can cloud our minds; because everyone did it this way for so many decades, it must be the way to do it. Right? Right?? But it isn't.
If you want feedback to work, you have to apply the feedback in such a way that it doesn't get distorted before it does its job.
A simple enough concept but people's minds get clouded by tradition.
So in a tube amp the feedback should be mixed with the audio using a divider network at the grid of the input tube, just like how you would do it with an opamp; IOW treating the amplifier circuit as if its an opamp (which some solid state amps actually are). Not rocket science but you know, tradition...
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