Atma-Sphere Class D Mono blocks
- Thread starter Chorus
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@DonH50 got it right.
FWIW, when we came out with our first amps the biggest complaint we got was that the tubes were on the rear of the amp. I've always heard about people liking to play the system in the dark so the room is lit by the power tubes. The simple fact is a lot of people regard the tube glow as a bit of bling.
But I don't care about that. I care that I can listen to the system all day without getting bored or fatigued- that the music simply draws me in. My point was simply that you can love the system for what it does, even if the one aspect of the soothing glow of the power tubes isn't there.
Why?Heartbreaking coming from you, Ralph!
Regarding our OTLs, we ran them without feedback because they sounded better that way. In order to get them to sound right with feedback we would have needed to run a lot of it- about as much as the class D does right now. We couldn't do that because in any amplifier there is a design characteristic called 'phase margin', which, if exceeded, means the amp can go into oscillation. You may recall the Futterman OTL had a reputation for this problem and exceeding the phase margin (via distortion harmonics) was how it occurred.
So instead we did everything we could to linearize the circuit: Class A, triode, one stage of gain, fully differential and balanced and no output transformer. That way without feedback we could still get some pretty good numbers, for example our early MA-1s from the 1980s had a THD at full power of only 3%. Over the years we were able to decrease the distortion, with attendant improvement in detail (since distortion obscures detail/transparency) and a smoother more relaxed presentation on the same account.
From their inception it was obvious that class D amps don't have the same signature of harsh and bright that most solid state amps have. The latter are that way because the 2nd and 3rd harmonics are insufficient in their distortion spectra to mask the higher orders. It might come as a surprise as how profoundly this affects the tonality of an amplifier; all tube amps make more of the higher ordered harmonics that the ear senses as harsh and bright than almost any solid state amp, but because the 2nd and 3rd harmonics are also prominent, they are able to mask the higher orders. SETs are the worst offenders in this regard; its why they sound 'dynamic' compared to other amps but its simply the higher orders on transients that are being perceived by the ear as 'loudness cues'. That is why I tell people that if they really want to hear what an SET does, they need a speaker that is efficient enough that the amp never makes more than about 20-25% of full power, so as to avoid that 'dynamic' problem, which should be coming from the recording rather than the amplifier!
Apparently in a class D you can have very similar distortion spectra as you get in a good tube amplifier. Clearly this isn't true of all class D amps! Otherwise we would not be having this conversation
That is how it worked out in our amp however. But it also worked out that overall, the distortion is lower, so the amp is more transparent, more detailed yet retains the musical mids and highs that IMO are a requirement in any good system.I don't see why anyone would see that as heartbreaking.
Not heartbreaking. Heartwarming without room warming. And not backbreaking either. No worry about where to source tubes. What's not to like?Heartbreaking coming from you, Ralph!
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Was there enough power? I think Ralph told a fellow Sound Lab owner that more power was needed for SLs. Waiting impatiently here for a big brother.
Surely!
How can you be sure others do not? Suspension of disbelief is not physical, it is emotional or intellectual. Some tell us they get it better from mono.
The main problem is not the audio components, but the stereo system. But yes, we use the stereo system variability and flexibility to please our preference. Some people tune their preference for suspension of disbelief, others for other forms of enjoyment, including simple sound quality enjoyment - audiophiles are not obliged to love music.
[text omitted]" Some people tune their preference for suspension of disbelief, others for other forms of enjoyment, including simple sound quality enjoyment - audiophiles are not obliged to love music. ( emphasis supplied)
Microstrip
Would you care to rephrase that counselor?
Microstrip
Would you care to rephrase that counselor?
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No, but I would ask the judge to quote the sentence in full and according to WBF quoting system!
My amps do!!! I have a roaring fire all year long…not just in the winter.I for one would love some tube glow.
Neither my KR's nor my Ayon glow really
Every amp I have ever heard where I was told it sounded “tubelike”…didn’t …
It’s interesting to know that I am seeing some degree of convergence in my neck of the woods amongst people with a lot of live experience and a lot of high end experience.
If I want bling, I can go with the McIntosh or D'agostino meters. Form and function. I must admit a flagship of Atmashere tubes does warm my heart. The meters are not that pretty.
You know what sounds tubelike? Tubes.
Agreed! Each one had its 15 minutes of fame. Upon hearing them I didn't really get what the 'tubelike' thing was about.
After living with any amplifier over time you really get to know what it does. That would have a big effect on how 'tubelike' you might think an amplifier is. I've had the class Ds in my system for a year and a half so far and they still don't sound 'solidstatelike'.
The amps were designed around a vintage idiom. The meters are built to their original 1934 spec by the manufacturer that designed them. We did that sort of thing with the nameplates and pilot lamps as well. The giveaway that they aren't vintage was/is the connectors.
Speak for yourself! I've had my system fool me a few times. Its spooky when it does- especially when its someone singing. I like to think I don't have strangers in my house when I'm at home listening alone...
Sounding “non-solid state like” is not equivalent to sounding tubelike.
Exactly! I hope we can agree that what we really want is something that sounds like music rather than a particular technology.
@Atmasphere : I have a theory hypothesis that the much wider bandwidth of modern class D amplifiers (e.g. self-oscillating) and high feedback applied across a wide bandwidth better suppresses the high-order harmonics compared to conventional designs. Thus they do not have the higher 2nd and 3rd harmonic distortion of conventional tube circuits, but neither do they have the (relatively) higher amplitude high-order harmonics of conventional SS amps. I don't have the data to back that up, however, just a few articles showing the harmonic spectra. Curious what you might think?
You are on to something.
The variable to which you refer is called 'Gain Bandwidth Product'; you need a lot of it to support a lot of feedback. If you don't have enough, distortion will rise with frequency since the feedback is decreasing with frequency. Almost all amplifiers made prior to year 2000 have this problem and it results in harsher sound.
If you've wondered why tube amps with feedback have that 'sheen' on the strings and the like, this is part of why.
In a class D amplifier you can run a lot more feedback than you usually can in a conventional solid state amp. This is because the output devices are so fast (even if MOSFETs) that the GBP is really quite high. The kind of amp we make is of a class called 'self oscillating' . How a self oscillatiing amp works is you apply so much feedback to the amp that the phase margin of the amp is grossly exceeded and the amp goes into oscillation as soon as its turned on. The feedback network is designed so that a certain frequency is favored for oscillation, and this frequency is the switching frequency. Now we have a whole lot of feedback to use, and unlike most tube and solid state amps, the feedback isn't applied to a non-linear node in the circuit that can distort the correction (feedback) signal before it can do its job! Its mixed thru a resistive divder network instead, so the feedback is not only more linear so more able to do its job, but there is also so much of it that its able to clean up a lot of the problems that lessor amounts normally cause (which is why feedback has such a bad reputation).
The thing is though that the output filter prevents the amp from really having actual wide bandwidth. It also introduces phase shift in the upper region of the audio band. But since we are running so much feedback the phase response does get correction. So generally speaking, even though a self-oscillating amp has a very good GBP figure, it really does not have a lot of bandwidth.
The non-linearities caused by the deadtime in the output section tends to result in lower ordered harmonics. The same is true of the non-linearities in the encoding scheme. So this, combined with accurate feedback and a lot of it, results in an amp that really doesn't make a lot of the irritating higher orders.
Professor Don,
I don't' mean to be a smart aleck.
By most accounts the absence of the harmonics you describe would be counterintuitive the notion that they sound tubelike? Or did I sleep through that class?
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