Atma-Sphere Class D… Amazing

You may have already covered these issues earlier in this thread, but could you please explain a little more about the following two issues with regard to your Class D amps?

1. I noticed that the switching frequency for your amp is 500 kHz while several other GaNFET amps use a higher switching frequency. Did you decide that 500 kHz represented a "sweet spot" for switching frequency in your design? Does the choice of higher rates have unwanted side effects that can adversely affect sound quality?

2. What factors entered into your choice of a toroidal power supply rather than a SMPS? What number and size of capacitors did you use in the power supply and how did you decide on the amount of storage needed?

The allure of a higher switching speed is increased loop gain which allows for more feedback. The downside is that you need to have deadtime and that value is a constant that does not change with switching frequency. Distortion thus increases with the switching frequency, so I guess in a way there is a sweet spot. The other issue is the faster you switch, the crazier the stray inductances become which can result in parasitics at some pretty high frequencies!

We used a toroid simply because a SMPS really should be custom-built for its application. There are a good number of advantages to SMPSs such as voltage regulation and oddly, lower noise (wasn’t the case 30 years ago!). But you have to be careful about current limiting issues which can really be a thing if the amp is subjected to lower impedance loudspeakers and in particular ones with crazy phase angles. So its easier to simply use a toroid.

And Ralph, you have responded to virtually everyone else’s questions and statements including those of the bizarre troll, and yet you won’t respond to mine asking-earnestly- whether your class D amp has true balanced topology and if not, the sonic compromises if any?

Sorry- that was an oversight on my part. If you don’t know, we’ve been pushing balanced operation longer than anyone else in high end audio; our MP-1 was/is the first balanced line preamp ever made for home use. Its not something we backed away from in the class D!

Who is Ralph to declare that his subjective opinion of the sound of his own product is absolute? Ralph will no doubt diplomatically respond that he is not just referencing his own Class D amp. If so, than tell us Ralph which other Class D amps are you declaring to be subjectively better than the best tube amps other than your own?

:) as Capitan Kirk once said ’Who do I have to be?’

Seriously though we think our class D sounds better than our tube amps although we’ve not done serious comparison with our bigger tube amps. We think our tube amps sound better than most other tube amps so its a simple logic statement at that point. But I really wasn’t commenting on our amp in particular; I was commenting on the fact that class D offers a technique (rather than specific amps, although there are class D amps out there that get very nice comments such as the AGD and Orchard) wherein this is possible, since it is very easy to develop the Gain Bandwidth Product that will allow the designer to support an enormous amount of feedback at all audio frequencies. Prior to the recent evolution of class D this really was extremely difficult until the mid 1990s with solid state and impossible with tubes.

That is why we never ran feedback with our OTLs, since keeping distortion vs frequency linear across the audio band is pretty important if you want the amp to not sound harsh. That’s easy in a tube amp if you don’t run feedback! Our OTLs have as few frequency poles as you can get in a tube amp and even with them we ran into issues with their phase margin. IOW, very difficult to prevent oscillation even with a carefully designed feedback loop if running large amounts of feedback. Conventional amounts were no problem but had all the downsides that have given feedback a bad rap in high end audio.

Class D offers a way around that problem. We started with zero feedback prototypes but found out quickly that a zero feedback class D amp has to have a very stable oscillator for the triangle wave, else you get a high noise floor as the oscillator drifts in frequency. With self-oscillating designs this source of noise is eliminated.

How can you then, in good conscience, even offer your tube amps for sale?

Funny thing about that, people still want them and don’t always believe things that I say, as we’ve seen on this thread. You get used to that over time :) But I can see a day when our tube amps become custom order only or gone altogether.

This man has solved the problems leading to 20 years of "terrible missteps" of all that came before him?

No. Class D has been an evolving tech for quite some time. Clearly others have gone before us and it is they that solved the lion’s share of difficulties, Bruno Putzeys in particular. In a way I think we were lucky in that in our design it worked out that the primary distortion sources tended to produce lower ordered harmonics, so although the overall distortion is much lower, the actual distortion signature otherwise would make you think you’re looking at a tube amp.

how can you possibly tell the thousands of us with tube amps and preamps that if we only gave your Class D amp a good audition we would come to the realization that your Class D amp is subjectively superior?

If you look back you’ll see that I answered that question several times on this thread for kuribo. He seemed unable to accept the answer, as best I can make out because he thinks the autonomic senses and taste are the same thing.

One thing that is a bit of a hurdle, now that you bring it up, is the higher output impedance of zero feedback tube amps in particular. This causes some ’warmth’ the class D won’t have because the tube amp will likely have a slight FR error in the bass associated with the impedance rise with most speakers have in this region. The ear interprets that extra bass energy as a bit of warmth and it causes the perception to tilt slightly away from the highs.

Once you compensate for that (on my speakers I used pink noise to set them up with each amp comparison since the driver levels are independently adjustable), then you see what is really afoot.

Ralph, I think you missed your calling. You should have been the US Ambassador to North Korea, China, or Iran. You have side-stepped your bold declaration that tube amps, the entire category bar none, are on their way out. But that is fine. I will not say another word in this thread and I truly wish you the best. I am confident enough in my high-end audio world to not let a different opinion-even yours-bother me any more than it has (which was relatively minor). Perhaps you could be so kind as to look me up three, five, or ten years down the road and tell me when my ARC Ref 150SE and ARC Ref 80 power amps have been rendered value-less. on the market so I can inquire of my accountant if I can declare a depreciation deduction.

@fsonicsmith - I guess time will tell if Ralph's assessment pans out, but I'm essentially with you none of my tube amps are going anywhere unless I purchase some other tube amp, or the powers to be come breaking down the door to mandating its cart-off.

 

 

How much hubris can a man possibly have to make such a pronouncement! This man has solved the problems leading to 20 years of "terrible missteps" of all that came before him?

People have been jumping all over @kuribo, which as @noske described earlier in a puerile fashion, with Troll and Fan Boi descriptions. But this seems like more like what they are describing.

When someone has 40 year in the industry, and brought balanced XRL to home audio, it is different than PS Audio YouTube videos.
 

One can only be so humble and demur, and honesty is not exactly overdoing it in a self promotion way.

I am not sure how Ralph can respond and communicate any better than he has? He certainly does much better than I can do in the sense, but I am also not an expert in the field.

. Who is Ralph to declare that his subjective opinion of the sound of his own product is absolute? Ralph will no doubt diplomatically respond that he is not just referencing his own Class D amp. If so, than tell us Ralph which other Class D amps are you declaring to be subjectively better than the best tube amps other than your own?

He also said that if people like the absolute best numbers and even lower distortion, that Bruno has those in the Purifi Class-D that they sell.

Perhaps you could be so kind as to look me up three, five, or ten years down the road and tell me when my ARC Ref 150SE and ARC Ref 80 power amps have been rendered value-less. on the market so I can inquire of my accountant if I can declare a depreciation deduction.

We can also roll in ARC with Purifi and Atmasphere, but that does not change the fact that they are running a business and have decided that a move to Class-D is a direction that they want to be poised for.

if one asks hard questions, or makes statements that are not appreciated they are referred to as Trolls and Fan Bois, and if they respond civilly then they are referred to as an ambassador.

But that is fine. I will not say another word in this thread and I truly wish you the best.

^great^

@atmasphere  Thanks for the helpful comments in response to my questions about  the choices of switching frequency and power supply for your Class D amps.