CLASS D MONO AMPS buy ATMASPHERE MUSIC SYSTEMS

When will the specs/measurements be available?

I think that if he wants to compete with the likes of Hypex and Purifi, he needs to publish measurements along the likes of the competition.

@kuribo In most class D designs, the distortion sources in the design are caused by dead time and non-linearities in the encoding scheme. In our design these result in lower ordered harmonics- its not been tailored.
 

There are many sources of distortion in class d amps, not only those you have mentioned, but also in the output filter. Do you use post filter feedback?

Please share some measurements of the frequency response with load, THD+N with power and frequency, FFT's and IM. Also, can you share the switching frequency used? Lots of claims made here (not all by you) so it would be enlightening to see a more complete picture of how this amp performs in actuality, not how it sounds to those who haven’t heard it yet.

Slightly circular I think, because those words define the "market" as being those who like state of the art design, excellent objective performance, as well as a neutral and transparent sound. That is actually quite narrow, by my reading, and so large segment is correct but moot.

My own definition of "market" would be substantially wider, and would include other variables, without necessarily excluding those mentioned. Perhaps a different weighting scheme, for as is conceded, everyone has different tastes.

Perhaps by choice like yourself, or for other reasons.  Irrelevant.

 

 

My comments don't define the market in its entirety- I am simply noting that there is a great number of people in the market who like state of the art design, excellent objective performance, as well as a neutral and transparent sound- in other words, objective and subjective criteria are of importance, not just one or the other. The success of Hypex and Purifi, both commercially and critically, attests to this market dynamic.

I couldn't care less what others think of the sound of this or any other amp. What matters to me is my own opinion, in my room, in my system. The rest is simply noise. I want an amp that outputs a signal as true to the input as possible, only larger. I appreciate good design as verified and vetted by measurements as do others.

People, forget about Hypex, Purifi, et al.
 

Why? They are the current state of the art in class d amplification.

@kuribo From the website -

The Class D amp has the same kind of distortion signature {as tube amps}, but at a much lower level.

This, to me, is reasonably unambiguous. From what I understand of Hypex and Purifi (and others, of course) amplifiers, they make no such claim about harmonics. I suspect measurements may confirm this. I’d bet on it.

No, Hypex and Purifi are more concerned with producing a wire with gain, free from any coloration, tube like or otherwise. Their measurements bear this out as the harmonics, etc., are buried below audibility. If the maker of this amp provides similar measurements, we can make that assessment.

 

 

Here are the facts that Kuribo/ASR miss.

Not a single fact, just more guru babbling not worthy of further consideration or comment.

But Ralph specifically says that his amp does have 2nd and 3rd harmonics at some level..

If I’m interested in buying a car that is grey, I don’t even think to bother the dude who is selling a red car for details about it. That’s just me. I can’t speak for we.

But if I did wish to ask about why the red car is so much better than a dull grey car, I would do so politely and with due respect for the red’s superiority.

"At some level"

What does that mean exactly? Nothing really.

If I’m interested in buying a car that is grey, I don’t even think to bother the dude who is selling a red car for details about it. That’s just me. I can’t speak for we.

Indeed, that is just you. If I am considering a $5000 amp, I would like to know a little more about it than the color. But that is just me, and probably the majority of people.

 

But if I did wish to ask about why the red car is so much better than a dull grey car, I would do so politely and with due respect for the red’s superiority.
 

Superiority? That has not been proven by any measure.

Thanks for the unsolicited advice.

 

@kuribo No. Purifi is last year's news, even if he is now working on a higher powered module, and Hypex... well.  GaN is state of the art--and not the generic stuff being put out by Peachtree and LSA.

Until bettered, ncore and purifi are still the peak of class d design and performance.

GaN is a state of the art device but has yet to be implemented in a class d amp in a way that improves upon what has been already done by ncore and purifi using mosfets. Maybe some day, but not yet.

The frequency response is load invariant within 1/10db from 20-20KHz, with 0 degrees phase shift at 20Hz and less than 1 degree at 20KHz. The invariance due to the output impedance being a few milliOhms, the low phase shift due to the feedback value, which allows the amp to correct for phase shift at the bandwidth extremes.

THD from 20Hz- 20KHz  is < 0.1% at full power (200 W into 4 Ohms) and about 0.005% at 1 watt. We think it might be lower but finding a decent filter to knock out the residual has been tricky during the pandemic. We  found one about a week ago and are interested to see how things differ once its integrated into our test setup. The distortion is lower into 16 Ohms.

The switching frequency is just shy of 500KHz, depending on load. The input is entirely direct-coupled.

The filter I mentioned is an Audio Precision device and is used to knock out the residual to prevent it messing with the distortion analysis. If I got this right its 8th order(!) and puts the residual down about 60dB... This is why we've not posted any more distortion data since the residual throws the readings off.

 

I look forward to plots once you get your filter worked out.

At only 500Khz, what is the advantage of using GaN? None of your specs appear to be anything not already achieved or bettered by amps using good old fashioned mosfets.

Thanks for the info.

I guess Kuribo will have no more to say on this thread

 

no more to say to you anyway.

An Intergrated Class D Amp with Tube Pre-section would be a good idea??

 

Not in my opinion. The benefits of class d done right are neutrality, low power consumption, cool running, etc. which is sort of the antithesis of tubes. Kind of like ordering a diet coke with your two big macs.

Here is the opinion of the Purifi team as discussed in an interview:

Bruno: Well, with the sort of audio performance we’re getting I’d say that we’re asymptotically approaching “perfect”. One could argue that we passed the point of diminishing returns a few years ago already. I’m not saying that a next step won’t have any audible benefits, but in the grander scheme of things, the margin is shrinking.

 

Lars: That’s if you stick to audio performance alone. Otherwise we wouldn’t have bothered going to class D to begin with. You don’t do that for audio quality. You do that to get better efficiency, make the amp smaller and yadda. And then you get a new set of problems to fix, such as what it sounds like. And then there’s reliability, manufacturability and so on. I wouldn’t say that GaN is going to be the answer to those things, and neither is upping the switching frequency.

 

Bruno:  Well for a given efficiency you could probably increase the switching rate, but if I’m going to shell out as much for a pair of FETs as what you’d normally pay for the whole amp, I’d rather benefit from that in terms of higher efficiency. Of course, not everyone is able to make that choice. I’ve spent my career honing control loops, most audio designers haven’t and so have to rely on simpler control loops. In that case, increasing the switching frequency is definitely helpful to reduce distortion.

 

Lars:  We’re as fanatic about audio quality as anyone else, but because we’ve got feedback down to a T now we’re not forced to resort to higher switching frequencies.

 

Bruno:  If we need to be geeky and I guess that the folks who are going to read this interview can handle that -eh Thomas?- lets grab the specs for the FET in our 400W Eigentakt module and its closest GaN equivalent. So that’s the FDP42AN15A0 (OnSemi) on our left and the EPC2033 on our right. Rdson: 36mOhm vs 7mOhm. Clear win for GaN here. 

 

Lars:  It’s also got a higher current rating (24A vs 48A) so if we want to be fair we should be scaling by about 2:1

 

Bruno: Oh erm well, that’s still a minor win for GaN because after scaling it’d come up at 14mOhm. Gate charge is of course magnificently low (30nC vs 6nC after scaling) so driver losses would be low and you can turn them on fast. GaN also has zero Qrr so you can do that if you want. But the main thing that sticks in my throat here is output capacitance. Our good old FDP42, which is from 2002 mind you, has an output capacitance at 100V of 70pF whereas the EPC device puts in a whopping half nanofarad (or 250 puff after scaling). That means your idle losses will go up, or you will have to increase dead time to allow the output inductor to recover the extra stored energy at its leisure. And isn’t it just idle losses that more or less determine real-life power consumption in full? And if power consumption isn’t something to care about, why not just stick with class A…?

 

Lars:  And high dead time combined with high switching frequency sounds even less attractive. That just increases open-loop distortion.

 

Bruno:  In applications like motor controllers and high density SMPS GaN and SiC devices are a breakthrough, mind you. It’s just that audio is this weird application where average power is very low and where dead time actually affects performance.

 

Lars:  And GaN is going to mature so this picture is bound to shift at some point. Just not now.

 

Bruno: True. On the other hand, silicon is doing the same. More recent devices are getting frightfully close to GaN. Sadly they only come in SMD packages that require fairly expensive methods to get the heat out. Like most GaN devices. It looks terribly ancient, but the good old TO220 package is still a neat compromise in terms of performance for the price.

 

Lars:  It’s just a game of tradeoffs. The fact that we’re using normal parts, and the reason why we chose to do so doesn’t make for a sexy story. We all like to believe in a magic bullet but when you’re an engineer you have to make choices based on tangible grounds. So the sexy story we’re trying to push about Eigentakt is that we think it’s a bloody clever design.

In a nutshell, reduced distortion and less heat than MOSFETs

I guess we will have to wait for your distortion plots to determine if your amp measures less than the ncore or purifi amp, which is already far below audibility. As for less heat, that seems like a small advantage, if any, at best, which you have noted. Personally, I don't really see a compelling case for GaN at this juncture.

Switching Speed is the juice

Possibly but this atmosphere class d GaN amp actually has a lower switch frequency than most mosfet class d amps on the market, so I find this comment irrelevant to this discussion. And, other than a Technics GaN amp that came out over a year ago, none of the present GaN based class d amps have a switching frequency materially higher than most mosfet class d amps on the market. So, a claimed major benefit of GaN technology for class d amps, a higher switching frequency, is in fact not even being exploited.

 

 

Class D as good as 2a3 or 300b well made tube amp with horn speakers.Dream on it will be a while yet.If ever.I have heard many class D amps for years don’t come close.

Can you quantify "as good"? What does that mean exactly? Subjective statements such as this are simply unsupportable opinion, not fact.

Some people prefer certain distortion spectra produced by certain amp topologies. That won’t ever change. Some people put steak sauce on Kobe beef. To each his own I suppose.

 

 

Should have been a comma after Class D. Yes it's an opinion however there is something about the speed,stop start and all those subtle variations on that theme,imperfections and long learned  skills that lead to human emotions that Class D is short on. The sound the tone of instruments class D is short on.

More opinion. A great many people would beg to differ. Ultimately, there is no debating opinions. The only thing that can be debated are facts, and on that basis, there can be no denying that class d on an objective basis performs superlatively. Some like it, some don't: there is no "better" subjectively, only different.

 

That’s not true these days consensus is now part of science.

 

A consensus doesn't mean it's rationale nor does it mean it's factual. If it's not based on fact it's just an opinion, regardless.