Ralph,
Your comments on this this thread, as on any thread, are extremely informative. I have not had the pleasure of hearing your new affordably-priced Class D monos and maybe they will be playing at the Seattle show later this month so I could hear them then.
You have had a career as a designer and builder of tube gear. You now are selling a Class D amp with the new GaN technology. Don and Lynn of course are solidly tube amplification adherents, make no mistake about that, but you seem to be straddling the line between an affinity for tube gear as well as Class D amplification.
Are you at the point where you feel your Class D amps are equivalent to your best tube amps? I have long anticipated that the day will come where the march of technology might render tube gear obsolete, but in the main at the moment, my experience with Class D amplification is somewhat akin to the unwarranted adoption in the 60s of lousy sounding solid state gear (everybody made a variant of it) over tube gear that took a very long time for the industry to recover from. Tube gear, like vinyl sales, are better than they have been for a long time, but I remain dubious that Class D amps yield the same sonic goodness after extended listen sessions, than the better/best tube amplifiers. But then I have not heard your new Class D monos. Comments?
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@atmasphere
So the cap is not as efficient at the new voltage when new. It takes time for the cap to 'form' to the new voltage. Its important to understand that electrolytic caps have some properties in common with batteries and so are fundamentally different from film caps in this regard. Charging them and polarity are two examples of this similarity. Forming is one way they are unique.
Anyway, when the cap forms up to the new voltage used inside the amp or preamp it will be a more efficient bypass. Its my theory this is what people hear during break-in. I've found it measurable too- the voltage once the caps are formed is every so slightly higher and the supply is less noisy.
Ralph, this is believable and logical.
I recently had a DAC built and delivered to me from Ukraine. The builder (Abbas Esoteric Audio) told me that it will require roughly 200 hours minimum of burn-in time to sound its best. He specifically cited the Blackgate capacitors utilization as the reason. He explained to me that it takes time for these excellent electrolytic capacitors (His opinion) to form.
Sounds right to me based upon my experience with his DAC.
Charles
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A Cornell Dublier engineer once explained to me that the difference between a 150V rated cap and one rated at 175V was the way the cap was formed up and nothing else. Forming is a process where voltage is applied to the capacitor with a target of the rated voltage; something that is done only once in the factory.
But the cap is almost never used at the forming voltage. Usually for best reliability, they are to be run at about 80% of the rated voltage.
So the cap is not as efficient at the new voltage when new. It takes time for the cap to 'form' to the new voltage. Its important to understand that electrolytic caps have some properties in common with batteries and so are fundamentally different from film caps in this regard. Charging them and polarity are two examples of this similarity. Forming is one way they are unique.
Anyway, when the cap forms up to the new voltage used inside the amp or preamp it will be a more efficient bypass. Its my theory this is what people hear during break-in. I've found it measurable too- the voltage once the caps are formed is every so slightly higher and the supply is less noisy.
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My concern for the customer experience might sound big-hearted, but actually it’s purely selfish. Neither Don nor I want ’em coming back. I am 100% retired, Don is thinking about it, and we both want the preamp and power amp to be reliable and good-sounding right out of the box. People tell their friends, etc. etc. So every part going in has to earn its keep in terms of reliability and sonics.
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My concern is reliability and unknown, undocumented processes going on in critical components. This is just bad engineering. Imagine an expensive car where the horsepower and handling changed from day to day, and the manufacturer had no idea why. Cars are 100x more complex than an audio product ... the average car has 35,000 parts, 5,000 of which are moving parts, nearly all of which are critical to performance, reliability, and safety. A single-part failure can make the entire car useless.
What’s the capacitor manufacturer’s excuse? "This is how we’ve always done it" isn’t good enough. "We don’t understand what we are making" is even worse. There’s good engineering, making reliable products that people enjoy, and bad engineering, where mysterious things occur and nobody knows why. Regrettably, this is the situation for much of high-end audio.
For all I know, Don, Thom, and I might end up designing a capacitor conditioner for one of the cap companies. Back when I was working with Gary Pimm, he came up with a gizmo that did that ... pushing through 10 kHz square waves at 1/4 of the cap’s rated breakdown voltage. After twenty minutes of that, it either survived or not. Actually, nearly all survived, and they were "broken-in" for sure after that treatment. And it weeded out the parts that were going to fail anyway.
By contrast, using the cap in a normal circuit, with music stimulus, is barely tickling it. No wonder it takes forever.
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I've lived through many new equipment break-in events over the years. As my experience level increases and the resolving capabilities of my system increases, it has been easier to track changes through the duration of the event. In a moment of judgement, it can be difficult to make statements of progress or regression as we aren't very good at making absolute comparisons, unlike numerical measurements. It's always relative and our powers of perception are better at establishing trends over time than snap judgements. It is possible to fool yourself in a single session. More valid impressions form through multiple sessions.
Here are several notable examples where break-in from new was significant and long in duration.
Antipodes K50 Server. From new, un-listenable for 9.5 days of continuous power up. Utter dreck. By two weeks of on time the performance was quite good. After 1 month, exceptional. After 6 months, fully plateaued. My experience, corroborated by others, and the manufacturer. The reason - power supply capacitor break in.
Daedalus Apollo 11 speakers. Pretty rough on arrival. Grainy HF. Over days the bass would come and go. By 110 hours the sea began to part. The grain and hearing fatigue began to lift. Bass came in. By 150 hours they were quite good. The manufacturer claims 400 hours for full break in. Guess my hearing isn't that good. Mundorf capacitors are the main culprit here.
Taiko Extreme music server. Sounded OK on arrival. After a couple weeks, quite good. After 1 month exceptional. Here's the rub on this one, even after fully broken in. If you shut it down for 15 minutes, unpowered, it takes 4 hours to recover. If you unpower for over 1 day, it takes 4 days to recover. All of a sudden the drapes open and it's a nice sunny day. These experiences are corroborated by the manufacturer too. Cause - power supply capacitors.
The common ingredients in these events are the capacitors. I suspect that these parts are the special sauce that makes this level of performance possible.
I have not heard a power amplifier exhibit this extreme of behavior from new, but that does not mean these parts don't require break in and overall performance will benefit from more run time.
If you are throwing parts in the bin after 30 minutes, I think you are missing out on some opportunities.
I've read plenty of attempts at explaining why parts, particularly capacitors change during break-in (they do plateau, they don't keep changing) but it doesn't matter unless you are a capacitor designer/manufacturer. Results are results. The reasons why don't matter for users.
Engineering is the prostitution of science. Even scientists don't have all the science worked out yet. Not even close.
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I understand that you are referring to the approach you use with judicious application of negative feedback. I was referring to Lynn’s comparison to the “golden age “ PP amplifier which typically used 20db of NFB. Your current class D amplifiers do not fit this description.
@charles1dad
They don't! However, Futterman claimed 60dB of feedback in his OTLs. That was during the 'golden age'... Also Kron-Hite made a transformer coupled tube amplifier (UF-101) that claimed even more feedback! It was built for laboratory use but works great for audio as well. Its specs are astonishingly impressive and having had a set (they were single channel) I can say they sounded quite decent. That was a long time ago but we compared them to an ARC amplifier which got its doors blown off.
If feedback is applied properly it is really beneficial. If its not then it will mess things up with the amounts normally found in tube amps (12-20dB...).
In the last couple of years, I had the VTV Audio EVO 1200 Class D amp with the Purifi module, with the aftermarket ministrations of Ric Schultz, and while the sound was as Ralph describes it,
@whitestix I'm going to contest this; I was not describing those amps at all and haven't heard them. You can tell something is up that isn't right since when you go on the web, you see really variable reports about their 'sound'. I notice that doesn't happen with tubes- everyone agrees that tubes sound smoother and often have more detail and so on. To what degree and what emphasis is the differences between the tube amps. I'm saying I've been playing a class D that you would think is in that category if you heard it. Going back to tubes you don't find that tubes are bringing anything more to the party. I get that seems like a tall statement. Keep in mind that OTLs have ruled the roost in the transparency department of the tube amplifier world and I've been building them since 1977 or so. During that time I've heard many tube amps; I repaired audio for a living as I put myself thru college and afterwards until Atma-Sphere was able to keep me busy full time. So I know what tubes bring and I'm telling you there's at least one class D out there that does the same thing. I suspect there are others.
Sorry I won't be able to participate in this thread for a while- I'll be out of town for 4-5 weeks. Y'all have fun and be well!
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I have had situations with break-in on my own amps, which are very revealing of parts quality, where the sound got better and worse on a two-hour cycle. While there was an overall upward trend, the up and down kept going on, with the cycle timing varying between a half-hour and two hours. At the twenty-hour mark, I finally lost patience and threw the questionable parts in the trash. That experience has made me wary of all parts that require subjective break-in.
My rule now is twenty to thirty minutes, tops. If the part can’t make up its mind in that time, in the trash it goes, no matter how expensive, or what the reviews say. I don’t want unstable parts in my system. Now if the fancy audiophile part requires a half-hour on a burn-in gizmo, fine, but I will regard it with some suspicion.
I think audiophiles and reviewers are too tolerant of this hokum. If it sounds bad for days on end, it is bad. Something is wrong. There is a design or fabrication error.
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A Friend who helped me source my Valve DAC, at one point was into heavily modifying a few CDP Models from the Sony Brand.
It was my introduction to these Modified CDP's being demo'd through Bespoke Built 300b mono's and Horn Loudspeakers, that were the first digital sources to arouse my interest in digital as a source.
I heard these in all their evolving guises and was even able to have extended home loans, which ultimately ended up with my decision to have a Digital Source added to my system.
One Sony Model had the Highest Quality Caps and Resistors used and lots was going on with how the Valve Stages were designed as well.
There was 'creme dela creme' mod' to be carried out that was inclusive of the use of OCC Silver Wire purpose produced Tranx's. When these were incorporated to the design, there was no Run In period that could help, the sonic and attractive impression that was recognised, plummeted from presentation, the overall presentation was perceived as forced and in ones face, quite unattractive and certainly not able to create a settling down and softening of a mood.
When this same individual producing the CDP's had his GM70 Mono's built. I was again being asked to assess them with him. I thought they were sharing noticeable traits in how I recollected the 845's were able to present.
The GM70 owner convinced themselves there were more to be extracted and carried out Mod's on the Amp's. I was again asked to visit and take part in a listening and assessment session, to which I agreed to when the Amp's had a minimum of a 100 hours on them in their new guise. In my view, the Amp's had become lesser, there was from recollection, some of the earlier impression made, now at a place where I was trying to work out where the changes were and why the presentation had lost much of its allure.
As said earlier, when carrying out such demo's with others, there is a time when the opinions will be differing, I held my tongue, and agreed that if the changes made had been satisfying to the end user, then this is the ultimate goal, I politely made it known I had recognised changes had occurred.
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Reviewers and consumers are at a great disadvantage in assessing the sound of a product, because they have never directly auditioned single-parameter changes. For example, a change in operating point (quiescent current) of 20% up or down, or a shift in topology in one part of the circuit. I grade these with a simple metric of:
1) No audible change, or at least nothing at threshold level
2) Different, but neither better or worse, just different
3) Worse (and how quickly is it noticed ... 5 seconds, 5 minutes, or an overall quality of discomfort or dislike)
4) Better (how quickly is this noticed, or is it a change in mood)
There are probably twenty or more points of adjustment in an amplifier or loudspeaker where these changes can be made. Some affect measurements, but most don’t ... they’re purely subjective. Also, conflicts can occur ... a better measurement may result in worse sound. At that point, something has gone wrong, and you need to stop and see where you have gone off-track.
We have to address what can be measured at the current state of the art and what can’t. Here’s just one example: for the the purposes of electronic design, nearly all modern capacitors are perfect. There is nothing to choose between them except voltage capacity and long-term reliability. Distortion is vanishingly small, at or below the threshold of measurement.
But ... in a high-resolution system, they all sound different. They are not neutral sonically. Mylar sounds different from polypropylene which sounds different than Teflon which sounds different from waxed or oiled paper. Metallized film sounds different than solid foil. In a vacuum-tube circuit, there are circuit nodes that actually exaggerate the coloration. Worse, DA, DF, self-inductance, or even price have little or nothing to do with sonics.
Perhaps worst of all, the notorious "burn-in" phenomenon where XYZ parts sounds really bad for the first 5, 10, 20, or 50 hours. With no change in DA, DF, or distortion measurements, and no plausible physical mechanism responsible for this. Anything that slow must be electrochemical, but what is it? Just a lot of hand-waving and supposition from the manufacturer, with no data to back it up. But plainly and clearly audible.
Not only that, some parts have essentially no break-in at all (paper and wax) while others can take 50 hours or more (polypropylene or Teflon). No explanation offered, no measurements, no underlying physical mechanism. Well, it’s not ghosts or psychic energy. It’s physics. But what physics? Nobody’s saying anything.
In loudspeakers and vacuum tubes, break-in is real, measurable, and the reasons are well-documented in papers going back to the Fifties. Caps? Nope. Why does copper wire sound different than silver? Again, no explanation. I accept this, but it is not satisfactory. Something is going on, and it is not self-hypnosis or expectancy effect. Often, the most expensive part sounds the worst, and the cheapo part sounds quite good.
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In relation to what @lynn_olson is sharing about the listening experience being a stimulus and the impression that can form resulting from the stimulus being encountered.
I have on many occasions been an invited party to offer a 'pair of ears', and to offer a assessment of how a New Design is evolving. There are devices experienced that have been built in parallel and a early prototype is kept as such, with a second prototype undergoing changes to see where there is improvements to be discovered. This method is sort of similar to a modern Photo Editing Software Tool where at the Click of a Button, the before image is immediately viewed.
There are also devices that are sole builds and the experiences of receiving demo's a a result of changes being made are in theory a variant of a previous device used. Much of this is reliant on recollection of previous experiences. This as a method is also quite dependent on the demo's not be too fart apart and the other devices in the system being consistent and not being exchanged.
Relating to the first method, it is much easier to identify if the ongoing work, is able to create a improved impression. It is also much easier to suggest trying out a different supporting ancillary as the two Prototypes at hand enable a very useful evaluation of how the exchanges interface with other ancillaries.
Relating to the second method, I find written records of how the demo' was able to impress and sharing through discussion where it has been perceived attractors/repellents are present is a constructive approach. Follow up demo's usually reveal differences are developing, and where there is betterment being perceived.
There will be a time that a divisive situation evolves, as individuals are unique in their preferences for a sonic. The Range of Attraction for Lean/Transparent through to Overbearing/Muddy is what sets all individuals apart. No one can tell an individual where there attractors/repellents are in the scale, they choose these themselves.
When it comes to buying a Device designed/built by the hand of a Trusted EE with Time Served Experience in producing audio devices, it is not just the realised product being bought into, but the designer/builders philosophies for audio reproduction and their IP, the hooks utilised to create the sonic on offer.
It is no secret such IP is classed as a asset, is their not Circuits that when, investigated there are no values to found on components, the printed info is removed to protect the design from being easily plagiarised.
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Such an interesting thread. If I could only hit the Lotto I'd get in line for the coming Spatial amps, pre amp, and a quad of new W.E. 300B's.
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@lynn_olson
This is why the notion of an Absolute Sound is inherently absurd. That’s like saying an Absolute Dream, or Absolute Taste
Hmm, Well if that’s the case how do you determine or judge the sound quality of reproduced or recorded music via electronic audio components?
How did you reach the conclusion that your amplifier sounds “right “?
A reference point is needed to evaluate and judge against. In my opinion the late Harry Pearson was right when he strongly advocated listening to live acoustic instruments and human voice.
What is a more thorough/better assessment of an audio component than a comparison with an authentic instrument (Un-amplified)? Are you exclusively reliant on your test measurements and dismissive of actual listening?
How do you determine your products mimic or come close to the sound of a real cello, saxophone, piano or human vocalist? I’m genuinely curious as to your approach striving for sonic realism (If you believe that it even exists).
Charles
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Snapsec, the unstated point of the Quanta article is that objective reality cannot be experienced directly ... the entire ear/nervous system/brain/mind system processes everything into mental images and impressions.
This is no little man watching a movie theater inside your head. It’s all signal processing, from the neurons in the ear to everything else, continually pattern-matching against memory, expectation, and emotion. Surprisingly, the brain can actually physically alter the hair cells in the cochlea with feedback mechanisms, altering perceptions right at the sensory level.
This is happening all the time ... there is no such thing as passive listening. For that matter, hearing and signal processing are still going on as you sleep, ready to wake up the rest of the fight-or-flight mammalian brain at a moment’s notice. Over the last 30,000 years, the powerful social experiences of speech, story-telling, and music gradually overlaid our mammalian brains, and made our species into the humans we are now.
This is why the notion of an Absolute Sound is inherently absurd. That’s like saying an Absolute Dream, or Absolute Taste. The entire hifi system is an illusion (and emotion) generator, and the quality of the illusion depends a great deal on the set and setting of the listener ... at that moment. Considering how vastly different our individual realities are, it’s amazing we can agree on anything at all.
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Ricevs,
Pardon my incorrect reference to my amp: it was the VTV AMPLIFIER Stereo Purifi Audio 1ET400A Amplifier. The guy that bought it from me was over the moon happy with the sound of the amp.
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Well, I read the Quanta article and I’m not sure if I enjoy my home audio set up or if I’m just imagining I enjoy it… but maybe the reality is that it would be better either way if I had the new amp and preamp??
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Whitestix,
What the heck is a VTV EVO 1200 class D amp with Purifi modules? Never heard of such an animal....he he. You must have your nomenclature confused. What VTV product did you REALLY have? Yes, I mod the VTV amps (Purifi, VTV D300 digital amp and Ncore Nilai).....so am very familiar with all the types and possibilities. Maybe I modded yours......but it was not an EVO 1200.....he he......it don't exist.
Sounds like that 300B amp is killer......me...enjoying the heck out of my modded VTV D300 amp pure digital amp......no DAC, no normal analog stages.....just....very pure sound.
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Show Update: Don, myself, and Spatial team will be at the Seattle show. What you will see and hear will be pre-production prototypes, sonically close to what we plan to manufacture. I can tell you neither Don, nor I, will tolerate any backward steps in sonics. I’ve lived with original Karna amps since 2003, and they remain my personal reference standard. The production amps must match or exceed that standard.
Prices, and names, are still up in the air. I call the preamp the Raven, and the amps Karna Mk II’s, or Blackbird, depending on my mood. Don calls them the Statement 300B’s. Spatial will probably come up with own names for the preamp/amp combo. Don and I are encouraging people to buy the set, but they are flexible enough to interface with industry-standard components.
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At the expense of a small technical quibble, I don’t see Class D as entirely analog. Without the pulse-width modulator, it is a 100~500 kHz AM transmitter that transmits a silent carrier. The pulse-width modulator is what makes the whole thing possible ... the pulse widths are precisely (and I mean very precisely, down to parts per million) 50% positive and 50% negative, if the input is zero.
Deviations from exactly 50/50 alter the pulse widths (to 51%/49% or any other ratio) but the pulses themselves are rail-to-rail, and the output devices are purely switches. It is a modulation system like AM or FM, which are also analog, but it is a modulation system nonetheless. Without the PWM modulator, there is no signal that can get through the amplifier.
Class D has been around commercially since the early Seventies. The trick is extremely fast switching with no overhang, resistance to load reactance, and a (very) low-distortion modulator. An FM transmission chain that achieves less than 0.1% distortion is at the limit of the art, and PWM modulators inevitably have their own set of distortions. PWM is not inherently distortionless, any more than AM or FM. Yes, it can be transmitted, but it would be very sensitive to multipath and group-delay errors ... both would cause distortion. With both FM and PWM, small time errors translate into amplitude distortion after demodulation.
Interestingly, SACD/DSD, at the native 2.8 MHz switching rate, is a type of quantized PWM. Since the pulses of true PWM are variable width, they cannot be recorded on digital media. DSD uses dither encoding and digital feedback (noise shaping) to quantize the PWM pulse train into fixed widths and provide the closest approximation to true PWM on playback.
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@whitestix
A friend has owned the Cube Audio Nenuphars for over 4 years and simply loves them. They’ve taken full range single driver speakers to a very high standard of performance.
Charles
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Charles,
As a 300b amp owner yourself, you know whereof I speak. Expect a report back on this thread in due time when the Cube speakers are run in. Some folks agree that Cube's driver technology is one of the biggest leaps forward in speaker design in a long time. I heard them at Axpona and was compelled to have them in my system.
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@whitestix
Now, with another 100 hours on the amps, I will amplify the comments I made in my OP--- these amps are the most stunning addition to my 50 year quest for more accurate and pleasant sound in my system
I believe you. These amplifiers with your Cube Audio Jazzon is going to be a sublime pairing.
Charles
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Gents,
I have had several Class D amps in my system in the past 10 years, and the earlier versions of them were dry and lifeless after extended listening sessions. In the last couple of years, I had the VTV Audio EVO 1200 Class D amp with the Purifi module, with the aftermarket ministrations of Ric Schultz, and while the sound was as Ralph describes it, there was something missing in the sound after extended listening sessions. It may clearly be due for my inherent biases, I will readily admit that. After listening to the VTV amp for few months, I swapped back into the rack my McCormick DNA .05 which had their Platinum upgrades and after a few minutes of listening to it, I said to myself... "Ah, what was missing with the VTV amp has all been restored." That is what I experienced, plain as day. I later got the stellar Wells Audio Innamorata SS amp, lovely both in its looks and more importantly in its sonic excellence -- easily the best SS amp I have ever had in my system. After a few months of enjoying the Wells amp, I swapped Don's KT88 tube amp back in the rack and it was easy to hear the difference in SQ... back was the liquid sound of tubes with amazing extension on both ends and a soundstage that mesmerized my ears. None of the sluggishness in sound of my old CJ gear, which was appealing to my ears, but far from an accurate sound reproduction, so Don's KT88 amp had all the advantages of a SS amp but had the warmth, richness and liquid sound that I desire which serves to envelope me in the listening experience (which I agree my VTV amp did to a degree initially) but here is the difference: after hours and hours of listening, I loved even more the sound for the KT88 amp, whereas in extended listening sessions, there was a lacuna in the sound with the VTV amp that I clearly sensed and missed.
That said, my new 300b monos are a quantum leap forward in SQ even compared to Don's KT88 amp in all respects and most noticeably this: it sounds as if there is no amp at all... just glorious music enveloping the room, with pure tonal and timbre correctness that astonishes me... and absolutely dead quiet. As good as the Kootenai is, and it is a stunning and powerful 65wpc tube amp, the 300b monos are in a whole different realm.
I have not heard the fairly-price AtmaSphere Class D mono's at any audio show, but as Ralph has come from a tube-centric point of view, I must acknowledge that he might have be on to something with his design, surely he is. There are lots of advantages to using a Class D amp and God bless those that love them.
This erudite conversion with Lynn, Don and others has been a deep dive into tube design philosophy and I personally am hearing the splendor of their creation moment by moment, lucky me, for darn sure. Again, and not to be disputatious on this wonderful thread, for the liquid euphonic and most natural presentation musical reproduction with my new 300b monos, I am still firmly in the tube amplification realm as it recreates music in such a realistic way, so pleasing to my ears. The hell with the heat the 300b monos throw off!
Now, with another 100 hours on the amps, I will amplify the comments I made in my OP--- these amps are the most stunning addition to my 50 year quest for more accurate and pleasant sound in my system.
I am driving my 86db efficient CSS Audio Criton 1TD-X speakers with the 300b amps at the moment and I can play music as loud as I can possibly tolerate it with no sense of distortion or clipping. I have a 8 wpc Willsenton 300b integrated amp which I drove the same speakers with and it got pretty distorted as I rotated the volume knob to the right. I recall that Don said that his mono's sounds "like a 100 wpc amplifier" and he is exactly right.
Boys, you are going to have to pay to play with Don/Lynn's new monos, but it is clear to my ears that if you are looking for an end game in amplification... and have the appropriate synergy with your speakers, then I hope you get a chance to hear them, which I will in the Spatial Audio room at the Pacific Audio Fest this month in Seattle, along with Don's new companion tube preamp.
I have a pair of Cube Audio Jazzon single-driver speakers arriving on Monday which I think will be a stellar match for the 300b monos, but still the the mono's have made my Spatial Audio Triode Masters sound the best they have ever sounded, by far. To be candid, if I had had the new 300b monos, driving my Triode Masters, before I ordered the Cube Audio speakers, I don't think I would have ordered them so as the Triode Masters sound so fantastic. Don Sachs encouraged me to buy them ~6 years ago and now he has as his reference speakers the Spatial X- speakers, clearly an upgrade from my Triode Masters.
I live in Sacramento and would be happy to invite music lovers to come and hear my Don Sachs gear and my Cube Audio speakers. Send me a private message and let's hear them together. Cheers!
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Ralph,
I understand that you are referring to the approach you use with judicious application of negative feedback. I was referring to Lynn’s comparison to the “golden age “ PP amplifier which typically used 20db of NFB. Your current class D amplifiers do not fit this description.
Charles
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Zero NFB seems to uncover a masking effect.
@charles1dad That's not quite correct. It depends on how well the feedback is executed and as I've been pointing out a lot recently, with most amps made in the last 70 years or more that's not happened.
But if its done correctly, amps using it can be amazing- no hint of dryness, nice soundstage; everything you want in an amp.
I've described what's needed often enough, no need to repeat it here.
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That’s why I am agreeing with what Lynn wrote. Zero NFB seems to uncover a masking effect. The subtleties and nuance of virtually everything is revealed as noted.
Charles
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The difference is Class D switches at 100 kHz or higher, with pulse width translating to signal level, while Class A is non-switching and like a preamp, fully analog from start to finish.
@lynn_olson most quality class D amps switch at 500KHz or more. Also to be absolutely clear, class D is 'like a preamp, fully analog from start to finish.' A very different type of circuit, but analog nonetheless.
I do not have the resources to confirm this via test bench measurements as you do. I can only rely upon listening experiences with my own audio system.
@charles1dad Lynn is correct- if you are not running feedback then everything in the amplifier design right down to the component quality, wire and solder makes a difference. When you run lots of feedback you get rejection of things like that- often including sensitivity to line voltage.
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@lynn_olson
Another factor is sensitivity to parts quality. An amp with 20 dB of feedback (which is nearly all Golden Age amps) tends to wash out differences in the sonics of different parts. This is exactly what feedback is meant to do ... 20 dB of feedback is a 10:1 reduction of all sources of coloration. A zero-feedback amp, by contrast, reveals the sonics of every single part, particularly at critical nodes in the circuit. This raises costs compared to the PP KT88 equivalent.
I do not have the resources to confirm this via test bench measurements as you do. I can only rely upon listening experiences with my own audio system. When I placed my 300bSET zero NFB amplifier in my system the first time (2009) the immediate difference/improvement was the sense of naturalness. Very stark and unequivocal. In my system realism and authenticity took a step (Or two) forward.
Charles
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Although a glance at a schematic might lead you to think it is simpler than a classical (Golden Age) PP KT88, the parts are more expensive. Way more expensive, just as 300B’s (as a group) are more expensive than KT88’s (as a group).
Another factor is sensitivity to parts quality. An amp with 20 dB of feedback (which is nearly all Golden Age amps) tends to wash out differences in the sonics of different parts. This is exactly what feedback is meant to do ... 20 dB of feedback is a 10:1 reduction of all sources of coloration. A zero-feedback amp, by contrast, reveals the sonics of every single part, particularly at critical nodes in the circuit. This raises costs compared to the PP KT88 equivalent.
Depending how you feel about the sonics of solid-state and feedback, you can travel a continuum between modern Class D, with sophisticated and complex feedback, to Class AB transistor or MOSFET with 20 to 40 dB of feedback, to Class AB push-pull pentode with 20 dB, to Class A with zero feedback. Each type sounds different and has different distortion spectra.
Comparisons between modern Class D and all-triode Class A are not absurd, despite radically different technologies. Class D and Class A both skip over the many difficulties with Class AB device switching, whether bipolar transistor, MOSFET, or pentode (each device type has different artifacts associated with the AB transition). The difference is Class D switches at 100 kHz or higher, with pulse width translating to signal level, while Class A is non-switching and like a preamp, fully analog from start to finish.
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I just have the first production one running in now in prep for Seattle show. It will be at least $5000 as it is cost and labour intensive and all very high end parts.
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Any indication on target preamp pricing?
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I agree with Atmasphere. Some things cannot be accurately modeled. Put it on a bench, attach a dummy load, light it up, and measure square waves. Tune for nice-looking leading (and trailing) edges. Measure both low-level (below 1 watt) and also just below clipping.
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There is a simple and inexpensive means of dealing with heat due to amplification. Ducts in the ceiling above the amplifier(s) can be added, along with dryer style hose the connects via a squirrel fan to the outside. This can be installed for a few hundred dollars (mostly labor), is quieter and far less power draw than air conditioning.
Do you use load a resistor after the interstage transformer? What kind resistors do you use?
@alexberger If any audio transformer is not loaded it can 'ring' (which is to say it will generate harmonic distortion, which can be quite profound). The correct loading will cause a state of 'critical damping' in the transformer, where when a square wave is put thru the device, it will have little or no 'overshoot'. Since the grid of a tube tends to be very high impedance (other than its capacitance) some form of resistive loading is a good idea to explore!
Since you sound like you are up to something with your own design, I recommend an empirical approach, which might be to drive the transformer with a square wave and have it drive in turn a power tube which is operating normally. A potentiometer and oscilloscope's probe across the output of the transformer would then allow you to vary the potentiometer and observe the result on the square wave. In this manner you can exactly dial in the correct loading value.
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@alexberger
Hi
I am sorry, but I am not giving anything about the design of the amp away. I had ITs custom wound for the project. My amp is PP, but if you need a load resistor with your circuit then I would try two kinds. A good quality wirewound of sufficient rating, and a good old Kiwame 2W or 5W depending on what you need. I usually use wirewounds, and not cheap ones, but Ohmite or Vishay or something else of quality. Which you prefer will depend on the circuit, your ear, and the Hashimoto iron. The resistors are cheap so try both kinds and see what you think.
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Hi @donsachs @lynn_olson ,
I have 300B SET with 6f6 driver in triode mode. I did 2nd harmonic distortion calculation using 3 point method and 6f6 plate characteristic graph. So with RC coupling that I have right now I get more than 2% distortions with voltage swing 140v pick to pick and when I go to interstage transformer coupling I can get around 0.7% distortions with 160v pick to pick. The difference is huge!
I have a couple of question about using transformer. Do you use load a resistor after the interstage transformer? What kind resistors do you use? I'm going to use Hashimoto A-305 transformers. As I understand Hashimoto recommends 100K load resistor for this transformer.
Regards,
Alex.
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Very good article about how the brain distinguishes between reality and imagination. Since audiophiles are endlessly arguing about perception and reality, this is a useful read:
Quanta Magazine
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I use Tubes that also run quite hot, the Amp's these tunes are utilised in are positioned in free space away from other Structures within the room.
I have in the past owned a Portable Air Conditioner Unit, that produced Icy Cold Air, this has been reserved for use when the External Temp's are getting up to the +25 Centigrade to help with sleeping. When using the room the system is set up in during these periods of high Temp's, I have never felt there was a need to run the Portable AC Unit during a listening session.
If increasing Room Temp's are a concern, as a result of a Tube Amp' being used, and a Cooling Device is at hand, cooling the Room in advance of the listening session is certainly going to cool the room and not impact on the Sound being produced.
My cautionary advice to an individual interested in using Tube Devices is no different to the advisories I was given many years past, which is to make sure there is always 'eyes on' the devices in use for the bulk of the time they are Powered On, and have a revisit shortly after being Powered Off. After approx' 30 Years of using Tube Devices, I have not had a concerning experience, only the oddity of a electrical glitch, a spent Valve or a blown fuse.
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@drbarney1
I agree with Lynn in that I won’t work with power supplies over 550-600V. The teflon mil spec wire is all rated at 600-630V so you would have to source 1200V wire for headroom. All normal parts are rated at 630V so you would have to source special caps, resistors, etc... You don’t mess around with 1000V or you will have a fire. Also the transformer set in these mono amps including the custom interstage transformers and choke would eat up most of your budget. I like some Lundahl iron, but I found that their IT started ringing above 15KHz in my circuit, so you would most likely have to get custom iron to do your project as I did. So yes, you could certainly build the project you discuss, but it isn’t simple, there are lots of issues and sourcing of custom parts rated for 1kV and if you use Edcor or Hammond iron you or something else of that ilk you will get medium grade amp, not one that has incredible detail and sounds alive. So if you build that amp with $2000 worth of parts you may be able to do it, but if you spend a lot more you will get a much better amplifier. You will still have a fire risk if you don’t make sure every single part in there that sees high voltage is running at no more that 70-75% of its rating. Easy to do at 500V, but a lot harder at 1000V.
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@dz13
Just outside of Las Cruces.
Wig
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@wig Where do you live? I live in Tucson so I'm guessing Phoenix area?
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Not going anywhere near an 833 or those Eimac transmitter tubes. No thank you. Those things light up a room with a dazzling white light and get serious, room-heater hot. They are designed for transmitter use, with forced-air cooling that ducts to the outside.
And if somebody chooses speakers that are 0.2% efficient, well, what did you expect? Class D or Class AB for you, as well as a dedicated AC power outlet that goes straight to the circuit-breaker box.
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45 is indeed very very nice sounding.
Cost has gone up quite a bit though. $2k will be barely enough these days for a high quality 45SET DIY project, assuming no fancy enclosures and not using big name irons like ISO or Hashimoto.
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Stereophile published an article on the Westinghouse 300B, which, unlike cheap modern 300B triodes, had a triple coated cathode which lasted longer and was the secret to the better sound. If you can tolerate less power the NOS 45 globe tubes were made the same way and many people find them richer sounding than the cheap modern 300B.
Around 2005 there was a Japanese 833A SET amplifier driven by 300B transformer coupled to the grid of the 833A and rumor had it the 833A was run on only 1000 Volts with a positive grid bias to force it to draw more plate current. It sold for $350,000, but the parts and labor could scarcely cost a percent or two to manufacture it. You would not need high sensitivity speakers for it, you can use planar magnetic speakers if you want. Lundahl has probably the best coupling transformer there is for coupling a globe 45 to the 833A grid which can run on zero or ground bias for eliminating a bias supply capacitor from the signal path and this is more than enough power for driving less sensitive speakers. Either a globe 45 or a WE 300B will work for this. Hammond makes a more robust air-gapped output transformer rated at higher DC current than smaller more expensive big-name brands and it is perfect for the 833A.
This is relatively easy to build yourself for less than $2000 retail in parts if you know how to be careful with the 1000 Volt power supplies it needs.
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If a cool room is important, you want Class D (90% efficient or better) and speakers that are more than 1% efficient (a true Theile/Small 92 dB/meter/watt), as well as switching (not linear) supplies for all the other audio components. That’ll make no more heat than a transistor radio.
Class A vacuum tube is the exact opposite. Constant power draw regardless of signal, from silence to clipping, plus heater current of a few watts per tube, and a few watts of excess heat from the linear regulators. Similar to a 1963 all-tube color TV. My Panasonic 58" plasma HDTV consumes 500 watts, a bit more than a pair of Statements.
To put that in perspective, the same as four or five 100-watt conventional light bulbs, or the heat emitted by two people at rest. A light to moderate additional load on the A/C system, less than 1/10 of its capacity. Of course, if your A/C is running more than 50% to 70% of the time (a 50~70% duty cycle), probably not a good time of day to use the oven or turn on vacuum tubes.
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I live in the desert where it reaches over 115 degrees and run my KT88 tube amp nightly and did the same thing when I had my coke bottle 845 and 300b tube integrated amplifier. No issues with heat in my room 😁
Wig
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@donsachs
+1.
Exceedingly absurd and silly.
Charles
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I would think the majority of people who buy class A amps of any sort are quite well aware of how hot they run and are more than happy to deal with it for the sonic benefits. As far as separate AC, that notion is absurd
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Amplifiers using these tubes run very hot.
Very undesirable given the need for separate air conditioning which affects the sound Quality. super inconvenient situation
It's like running a portable heater in the room continuously which is horrifying.
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What are some amps you’ve heard with high feedback that you’ve enjoyed? I’ll have to check them out. I’ve seen the measurements for the Purifi and its distortion is incredibly low, to the point it’s at the limits of what the AP analyzer can measure. It does have raising distortion in the treble but if I had to surmise, it is most likely low order as I find the purifi a touch sweet in the treble. I do run it without an input buffer as my preamp is up to the task of driving the Purifi module directly.
I have yet to hear the new Gan stuff that is specifically designed for audio. I know yourself and AGD specifically designed yours for audio applications unlike many of the other brands. Are you guys going to be at the pacific audio fest? I’d love to come hear your Class D amps and hear how it compares to the 300b statement monos.
@cloudsessions1
Our amp of course, which you have to imagine we’ve compared extensively to our class A triode zero feedback OTLs.
The AGD Audion (although I don’t know how much feedback is employed in this design)
Orchard Audio
Digital Amplifier Company (unfortunately the designer passed away last year)
We won’t be at the Pacific Audio Show- I have a prior booking.
@lynn_olson
Interestingly, Class D amps are free of Class AB transition artifacts, so there’s an entire class of coloration that just isn’t there. The big issue for Class D is nanosecond precision of timing for the pulse-width modulation (Class D is pulse-width-modulation, akin to FM, and not PCM), and insensitivity to reactive loads affecting the PWM modulator.
Yes, crossover distortion artifacts are impossible for any class D using an output filter. Timing issues (which cause an unpleasant hiss) are solved by a self-oscillating topology. This is done by exceeding the phase margin of the amp and the oscillation is used as the switching frequency. This makes for a very high stability amplifier and very large amounts of feedback. Since the feedback is not distorted prior to doing its job, higher ordered harmonic generation is avoided. Essentially the feedback simply reduces the existing distortion (in our circuit this tends to be lower ordered harmonics). Distortion vs frequency winds up being a flat line across the audio band. So it sounds very much like a zero feedback triode amplifier, but more ’focused’ owing to lower distortion, which otherwise obscures detail. You should try it- you make excellent amplifiers and know how they are supposed to sound, so you are in a good position to see how this technology advances the art.
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Pindac has described the stage Don and I are at now: tuning the subjective balance ... there are a couple of nodes in the circuit where parts selection is quite audible, and we’re fine-tuning that.
I wrote an email to Don a couple of days ago that this topology is uniquely susceptible to parts coloration at the critical nodes. You get the same parts sensitivity in non-feedback SET amplifiers, but the much lower distortion of this circuit, compared to SET, exposes parts coloration more vividly. Fortunately, the right parts are available and are not super-exotic.
The circuit is inherently transparent, so there is almost nothing we can do to take that away, nor would we want to. But subjective tonal balance can be adjusted at the critical nodes. Surprisingly, the tuning has no effect on measurements, since topology, operating points, gain structure, tube loading, and bandwidth all remain the same.
Cloud Sessions asks a good question. Why does it sound this way? The best I can give is:
1) The circuit avoids both local and overall loop feedback, so there are no issues with hard clipping (transient overshoots in the FB network), stability margin (running out of gain and/or phase margin at high frequencies), or sensitivity to load reactance (which decreases phase margin and increases settling time after a large transient).
2) There are no differential stages to current-limit when one tube saturates or clips, taking the other tube along with it ... instead, the paired PP-mode tubes are functionally in parallel, helping each other out when the opposite-phase tube saturates or clips. Avoiding series-mode operation has a big effect on subjective dynamics. No SRPP’s, no split-load inverters, no long-tail pairs, no cathode followers.
3) Last but not least, each stage is individually optimized as much as possible for intrinsic linearity over the audio band. This is a matter of optimizing loads and minimizing the effect of Miller capacitance on the preceding stage.
Interestingly, Class D amps are free of Class AB transition artifacts, so there’s an entire class of coloration that just isn’t there. The big issue for Class D is nanosecond precision of timing for the pulse-width modulation (Class D is pulse-width-modulation, akin to FM, and not PCM), and insensitivity to reactive loads affecting the PWM modulator.
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