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Atma-Sphere Class D GaNFET Amplifiers

Martin

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Atma-Sphere showed new class D GaNFET monoblock amplifiers at this weekend's Florida Audio Expo. I did not attend as I did not want to tempt myself into spending more money. I am very happy with my system now and already know which components I will be changing out. I borrowed these images from another poster on another forum.
atma-sphere1.jpg

atma-sphere2.jpg


Preliminary information from the Atma-Spere website: http://www.atma-sphere.com/en/classD.html. I read they are $5,400.00 per pair. I'd love to see them measured.

Martin
 
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dfuller

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JeffGB

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It will be interesting to see how it performs but the specs don't look great. I haven't seen a really great GAN amplifier yet. Some have lower switching frequencies than the PA5, which I thought was supposed to be the main reason for GAN transistors. With great engineering perhaps they will be better.
 

Matias

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Atma-Sphere showed new class D GaNFET monoblock amplifiers at this weekend's Florida Audio Expo. I did not attend as I did not want to tempt myself into spending more money. I am very happy with my system now and already know which components I will be changing out. I borrowed these images from another poster on another forum.
View attachment 188056
View attachment 188057

Preliminary information from the Atma-Spere website: http://www.atma-sphere.com/en/classD.html. I read they are $5,400.00 per pair. I'd love to see them measured.

Martin
5.4k usd for 2 x 200W in 4 ohms with "good 3rd harmonic distortion". When there are already amps that do 2 x 500W in 4 ohms with no audible distortion for 700 usd. Tough sell for ASR, objective-oriented crowd, maybe more to euphonic, subjective-oriented audiophiles?
 
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Bob from Florida

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Specs below from site. Cost comparisons aside, assuming it meets the specs, will you hear .1% distortion at full power?

Output power
100 watts per channel into 8 Ω load
200 watts per channel into 4 Ω load
50 watts per channel into 16 Ω load
Input Impedance
100 KΩ balanced/single-ended
Output Impedance:
~0.010 Ω
Input
2.15 Vrms for full output
RCA and XLR true balanced input
Gain
22dB
Power Bandwidth
1Hz-20KHz
Frequency response
1Hz-20KHz
Distortion
Total Harmonic Distortion (THD) typically 0.1% at full power.
Intermodulation (IM) distortion typically under .04% at full power.
Feedback
35 dB
Power consumption
5 watts at idle (per channel)
Dimensions & Weight
13" deep x 11" wide x 3" high (33 x 28 x 8 cm) per chassis
14 lbs (6.35 kg), per chassis
Warranty
Three year general coverage
 

goryu

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Switching frequency of this amp is only 500KHz, which the seller when questioned on another forum admitted when asked what's the benefit of GaN if you switch at such a low frequency said:

At only 500Khz, what is the advantage of using GaN?

"In a nutshell, reduced distortion and less heat than MOSFETs, not like that's much of a thing. The faster speed of GaNFETs requires less deadtime, which has to be increased at higher switching frequencies (when we first started doing this, I thought the deadtime would be constant regardless of the switching frequency and learned otherwise; either way deadtime becomes a greater distortion influence as you increase the switching frequency)."

State of the art current mosfet class d like Purifi has a higher switching frequency and less distortion without any heat issue. So, one has to wonder, what's the benefit of using GaN if your design doesn't exploit their capabilities/advantages?

The seller has been designing tube amps for 40 years and has been claiming that this new GaN amp has 2nd and 3rd order distortion products which people find preferable. I would say tube people find them preferable and that this is a marketing move to get the tube crowd something more efficient, light weight, and more dependable.
 

MaxBuck

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Specs below from site. Cost comparisons aside, assuming it meets the specs, will you hear .1% distortion at full power?
My bemusement relates to the power vs. cost. Although I doubt this amp is audibly inferior to others, why would anyone want to pay 4 times as much for half the power (comparing to Hypex)?
 

antcollinet

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Its nice to be able to say that we 'cracked the nut' so to speak in making a solid state amp that actually makes tube amps obsolete

Uh oh! :facepalm:


My bemusement relates to the power vs. cost. Although I doubt this amp is audibly inferior to others, why would anyone want to pay 4 times as much for half the power (comparing to Hypex)?

What is the cost - I can't find that anywhere.
 

Bob from Florida

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Well, we have a picture, marketing info from the OEM, price, and specs. It looks like no tests - objective or subjective are available yet.
 

DonH56

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Ralph @atmasphere is a member and will probably chime in at some point. He is a decent guy and good engineer.

Regarding the switching frequency, for audio the plus with GaN is their low device charge storage and how quickly they switch in addition to their low parasitic resistance. Less about the oscillation frequency, more about how fast they switch (slew) between states, with resulting reduced loss and hysteresis ("dead time" as they switch states).

I've been in price shock since revamping my system about ten years ago. Thousands of dollars for things like Bryston amps and other "run of the mill" audiophile equipment. Costs are way up for just good, solid equipment, and the "high end" amps are now in the $20k and up range. The scary thing is that $5.4k for an amp is actually a fair price compared to most of the "mainstream" competition. I'd love to have a set of Benchmark amps, but I'd need at least four to handle my base layer, and at $3k a pop that's a lot of dough. I went with @Buckeye Amps for my overheads (4-ch NC252MP) and have been happy, and will probably look his way again if and when my 12+ year old Emotiva amps give up the ghost.
 

ZolaIII

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I really don't see a point of use of GaN in audio (or pretty much anything else). Next big increase in efficiency for broad use is in FD-SOI (complementary with background biasing). And it doesn't influence quality of engineering.
 

goryu

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Here is the opinion of the Purifi team on GaN 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.
 

Gorgonzola

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I have been in discussions with the owner/designer of Atma-Sphere on another forum. I don't think I misrepresent him when I say he believes that (a) there are audible differences between amplifiers based on their distortion spectra, and also (b) that moderate 2nd/3rd order harmonics are not only agreeable but also mask shortcomings in up- and downstream components and in the recordings themselves. In fact he said as much in the link proved by @Martin

Of course I acknowledge that his view isn't the prevailing one among prominent ASR participants. But he doesn't dwell in the same universe of denial.

Traditionally Atma-Sphere has traditionally produced high-end tube amplifiers so the new GaNFET amp is a departure for the company. The owner acknowledged this on that other forum. It will certainly be interesting if and when comprehensive measurements become available for the new amp, but we should expect that the the results will reflect the designer's philosophy.
 
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SIY

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Of course I acknowledge that his view isn't the prevailing one among prominent ASR participants. But he doesn't dwell in the same universe of denial.

Nor does he dwell in the universe of presenting evidence for these claims.

At least the engineering is excellent.
 

goryu

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There have been numerous studies attempting to correlate distortion spectra with subjective preferences and there has been data presented that shows for some groups 2nd and 3rd harmonic distortion is agreeable to some listeners. This is often mentioned as a reason for the popularity of tube amps with this sort of harmonic distortion spectrum. No coincidence then if a tube amp manufacturer starts selling a class d amp with a similar distortion spectrum in order to please his tube lover customers.

Personally, I prefer an amp that produces distortion below audibility. Producing "agreeable" distortion to appeal to certain listeners or to mask other less agreeable distortion doesn't seem to fit with the purpose of an amplifier: to make a small signal larger, nothing more or less.

This GaN amp, with it's lower power, higher distortion, and lower switching frequency, doesn't improve upon the state of the art class d such as Purifi in any material way, despite a price 3x the Purifi, much less meaningfully exploit the inherent advantages of GaN technology. It might appeal to a certain group of users who like higher distortion of a certain type, who don't need 400 watts, and who might like less heat, more reliability, and a smaller form factor. In other words, the traditional tube loving customers of Atmosphere.
 
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