Today's most innovative amplification technology: tubes or solid state?

[DonH50]

I thought the thread was about innovation, not analog vs. digital?

There have been class D amplifiers for RF implemented with tubes, though I am unaware of any in the audio band.

 

[microstrip]

I thought it was an enlightening presentation and very relevant to this thread since it would fall under the topic of analog innovation. I guess you disagree and think that class D is really not analog?

You guess a lot, but unfortunately many people systematically guess wrong on technical subjects. IMHO Bruno Putzeys was just showing that what is generically known as a class D amplifier is not a pure digital circuit in the sense of digital information or PCM circuits, but has many of the features and problems of analog electronics. So I (and many others) think that class D is digital AND analog. This sentence can be confusing, as most people will not separate it from the crude reality that any digital implementation lives on an analog circuit. But in the case of class D the analog characteristics of the digital electrical signals have a dominate importance. The fact that in some class D implementations the "time" can be analog also can add confusion.

 

[DonH50]

Class D is a mixed-signal design. Typically (not always) analog in and of course analog output after filtering. There is digital processing in between, and the output switches between two discrete levels at varying times with the control circuit determining edge placement and/or pulse width depending upon implementation. What might seem a simple switching stage is actually very challenging to design. There are stability issues throughout the circuit, and class D amplifier outputs (at least all that I have seen) exhibit high sensitivity to the power rails (they need a clean, stable power supply for the outputs).

IME/IMO - Don

 

[mep]

Class D is a mixed-signal design. Typically (not always) analog in and of course analog output after filtering. There is digital processing in between, and the output switches between two discrete levels at varying times with the control circuit determining edge placement and/or pulse width depending upon implementation. What might seem a simple switching stage is actually very challenging to design. There are stability issues throughout the circuit, and class D amplifier outputs (at least all that I have seen) exhibit high sensitivity to the power rails (they need a clean, stable power supply for the outputs).

IME/IMO - Don

If it wasn't for the tantalizing efficiency and cheap cost, I doubt anyone would want to design a Class D amp for the high-end. When you look at how these amps are designed, it's a jungle and not a walk in the park.

 

[dallasjustice]

If it wasn't for the tantalizing efficiency and cheap cost, I doubt anyone would want to design a Class D amp for the high-end. When you look at how these amps are designed, it's a jungle and not a walk in the park.

The best Class D competes on performance against the best Class A and, of course, is much cooler and efficient, IME.

 

[mep]

The best Class D competes on performance against the best Class A and, of course, is much cooler and efficient, IME.

If they truly do sound as good as the best Class A amps, it's a miracle when you understand how the technology works and the gyrations you have to go through in order to make them work. Again, if it wasn't for their super-high efficiency and low cost, I doubt any high-end manufacturer would touch them.

 

[MylesBAstor]

The best Class D competes on performance against the best Class A and, of course, is much cooler and efficient, IME.

What pure Class A vs. what Class D amplifier (s) and under what conditions? Better in what way?

 

[mep]

What pure Class A vs. what Class D amplifier (s) and under what conditions? Better in what way?

Class D runs way cooler than Class A and Class D is way more efficient. Those two points are a given. However, I haven't heard of or read of any head to head comparisons between a Class D amp and a real, no kidding, Class A amp.

 

[Phelonious Ponk]

If it wasn't for the tantalizing efficiency and cheap cost, I doubt anyone would want to design a Class D amp for the high-end. When you look at how these amps are designed, it's a jungle and not a walk in the park.

Can you elaborate on the design challenges you're referring to in language a layman can understand?

Tim

 

[dallasjustice]

Myles, I didn't say "pure Class A"; you did. However, my former Krell 900e amps are heavily biased into class A. I would classify Krell more traditional modern A/B amplifier topology. I have done the comparison between these amps and I know that the best Class D, hypex Ncore 1200, holds up well against one of the best, if not the best, Krell amp ever produced. Before the Krell 900e, I owned a Soulution 710 in the same room/system and felt that the Krell bettered the Soulution. I am NOT saying the Class D amp is BETTER in every way than the Krell. I am saying it competes on the same level as the Krell. It's better in some ways and not better in other ways. However, it's totally on par with what I consider among the best class A/B design.

Just my honest opinion and personal experience listening to the same system in a controlled and familiar environment.

 

[KeithR]

Myles, I didn't say "pure Class A"; you did. However, my former Krell 900e amps are heavily biased into class A. I would classify Krell more traditional modern A/B amplifier topology. I have done the comparison between these amps and I know that the best Class D, hypex Ncore 1200, holds up well against one of the best, if not the best, Krell amp ever produced. Before the Krell 900e, I owned a Soulution 710 in the same room/system and felt that the Krell bettered the Soulution. I am NOT saying the Class D amp is BETTER in every way than the Krell. I am saying it competes on the same level as the Krell. It's better in some ways and not better in other ways. However, it's totally on par with what I consider among the best class A/B design.

Just my honest opinion and personal experience listening to the same system in a controlled and familiar environment.

DJ- can you elaborate on the differences between the two? thanks

 

[dallasjustice]

DJ- can you elaborate on the differences between the two? thanks

Sure. Both amps have unlimited power. That goes without saying. The bass is the biggest difference. So far, I've had both the Acoustic Imagery Atsah Ncore 1200 amps and the Merrill Veritas Ncore 1200 amps. Although I think the Veritas is a little better amp than the Atsah, my comments apply equally to both .

The Ncore 1200 amps have more solid and realistic bass. The mid range is about the same. The hi frequencies sound different. The Class D amps have a more controlled HF whereas the Krell sounds more free and a little more open. But that's not a really good description because it also varies a little depending the type of music. For example, the Class D amps render the HF sound more controlled and natural with complex symphonic music or heavily produced modern rock or electronic music. Considering my music collection, I overall prefer the class D amps to the Krell in every way. But I wouldn't argue with someone else that prefers the Krell.

Michael.

 

[Atmasphere]

Well let's ask this question: what type of innovation would advance the art? Is it new semiconductors? New tubes manufactured? Both? Why are there so few innovations on the tube-manufacturing side? Besides the KT-120 and -150 lately, what other innovations have been made in that respect? And then there are circuits and topologies: are we still innovating, or have all circuits been explored? What about topologies? How are we pushing the art in that respect? And what amplification technology does most (if not all) of the above better, or is the most promising

How about a tube preamp with direct-coupled outputs? That would be an innovation, right?

More to the point if one is looking for Nirvana, the engineering will first have to address aspects of how we perceive sound and actually apply them to the design, something that has been rare in the last 50 years.

I think you are greatly underestimating the cost and complexity of setting up a tube manufacturing facility. It's also not a 'green' business which adds to the cost. Who is making tube manufacturing equipment now? When the Brits got out of tube manufacturing, they sold their equipment to the Chinese and it has taken the Chinese many years to produce tubes that people actually wanted to own. I believe that Richardson Electronics has bought up some of the tube manufacturing gear from American companies as they went out of the tube business. I believe the last American tube company that went out of production was the MPD plant in Owensboro, KY, that made 6550s (formally the GE plant). I believe that Richardson has all of that gear in storage somewhere in Illinois.

Remember that Western Electric tried to put their 300B back into production and they had the advantage of having the original equipment, drawings, specifications, and the doping recipe for the cathodes. It still kicked their ass and during the limited time the new 300Bs were in production, I didn't hear of anyone claiming they were better than the original 300B tubes.

What college is turning out vacuum tube engineers? There are a very limited number who train for the microwave tube industry which is entirely different than the audio tube world. So even though you say it's a well-defined art and process, the original tube companies haven't made their production processes available to anyone to my knowledge and it might as well be a black art. If it was easy to start up an audio tube company, it would have already happened in the U.S. There is a world-wide demand for vacuum tubes for both audio gear and guitar amps, certainly enough to build a business case if one was so inclined to jump in. It's a daunting challenge which would need some very deep pockets. It could take two or more years before you could have acceptable quality tubes that you could sell on the market once you started production.

There is a new tube operation startup in Nevada, which uses computer controlled lazer machining rather than dies to fabricate parts in the tubes. I've only seen their 6L6s so far, but they are fabulous, exceeding RCA's best during their heyday. They don't have a website, but here is some porn from THE Show in Vegas:
http://www.positive-feedback.com/Issue71/theshow14.htm
http://www.theaudiobeat.com/ces2014/ces2014_rch.htm

 

[mep]

Can you elaborate on the design challenges you're referring to in language a layman can understand?

Tim

Tim,
From Wikipedia:

Class D amplifiers work by generating a variable duty cycle square wave of which the low-frequency portion of the spectrum is essentially the wanted output signal, and of which the high-frequency portion serves no purpose other than to make the wave-form binary so it can be amplified by switching the power devices.

A passive low-pass filter removes the unwanted high-frequency components, i.e., smoothes the pulses out and recovers the desired low-frequency signal. To maintain high efficiency, the filter is made with purely reactive components (inductors and capacitors), which store the excess energy until it is needed instead of converting some of it into heat. The switching frequency is typically chosen to be ten or more times the highest frequency of interest in the input signal. This eases the requirements placed on the output filter. In cost sensitive applications the output filter is sometimes omitted. The circuit then relies on the inductance of the loudspeaker to keep the HF component from heating up the voice coil. It will also need to implement a form of three-level (class BD) modulation which reduces HF output, particularly when no signal is present.

The structure of a class D power stage is essentially identical to that of a synchronously rectified buck converter, a type of non-isolated switched-mode power supply (SMPS). Whereas buck converters usually function as voltage regulators, delivering a constant DC voltage into a variable load and can only source current (one-quadrant operation), a class D amplifier delivers a constantly changing voltage into a fixed load, where current and voltage can independently change sign (four-quadrant operation). A switching amplifier must not be confused with linear amplifiers that use an SMPS as their source of DC power. A switching amplifier may use any type of power supply (e.g., a car battery or an internal SMPS), but the defining characteristic is that the amplification process itself operates by switching.

Theoretical power efficiency of class D amplifiers is 100%. That is to say, all of the power supplied to it is delivered to the load, none is turned to heat. This is because an ideal switch in its on state will conduct all the current but has no voltage across it, hence no heat would be dissipated. And when it is off, it will have the full supply voltage standing across it, but no current flows through it. Again, no heat would be dissipated. Real-life power MOSFETs are not ideal switches, but practical efficiencies well over 90% are common. By contrast, linear AB-class amplifiers are always operated with both current flowing through and voltage standing across the power devices. An ideal class B amplifier has a theoretical maximum efficiency of 78%. Class A amplifiers (purely linear, with the devices always "on") have a theoretical maximum efficiency of 50% and some versions have efficiencies below 20%.

Tim-I think this description is fairly easy to follow, but this is a wacky way to generate audio power and you have to go through lots of gyrations in order to clean it from all of the artifacts that are generated due to the process of Class D.

 

[microstrip]

Can you elaborate on the design challenges you're referring to in language a layman can understand?

Tim

Tim,

I tried to introduce them in post #44. Don said them in post #45. What part of the posts did you find too hard to understand?

BTW, I find the Wikipedia article very confusing for laymen - I would not understand it if I did not know what is a class D amplifier.

 

[jap]

How about a tube preamp with direct-coupled outputs? That would be an innovation, right?

http://www.aesthetix.net/images_sidebar/Metis_Munich_PressRelease.pdf

 

[mep]

Ralph-I would love to know more about that company that is making tubes in Nevada. I wonder where they obtained the equipment and the expertise to make tubes and what kind of production capability they have? I wonder how many 6L6 tubes they have sold and how long they have been on the market? I also wonder if anyone has used their 6L6 tubes in an audio amplifier because it's hard to imagine the average guitar player forking over $200 for a single 6L6.

 

[MylesBAstor]

Myles, I didn't say "pure Class A"; you did. However, my former Krell 900e amps are heavily biased into class A. I would classify Krell more traditional modern A/B amplifier topology. I have done the comparison between these amps and I know that the best Class D, hypex Ncore 1200, holds up well against one of the best, if not the best, Krell amp ever produced. Before the Krell 900e, I owned a Soulution 710 in the same room/system and felt that the Krell bettered the Soulution. I am NOT saying the Class D amp is BETTER in every way than the Krell. I am saying it competes on the same level as the Krell. It's better in some ways and not better in other ways. However, it's totally on par with what I consider among the best class A/B design.

Just my honest opinion and personal experience listening to the same system in a controlled and familiar environment.

Nope you didn't. That's why I added the proviso for fairness. "Sliding" Class A and all that are still not Class A.

 

[MylesBAstor]

How about a tube preamp with direct-coupled outputs? That would be an innovation, right?

More to the point if one is looking for Nirvana, the engineering will first have to address aspects of how we perceive sound and actually apply them to the design, something that has been rare in the last 50 years.



There is a new tube operation startup in Nevada, which uses computer controlled lazer machining rather than dies to fabricate parts in the tubes. I've only seen their 6L6s so far, but they are fabulous, exceeding RCA's best during their heyday. They don't have a website, but here is some porn from THE Show in Vegas:
http://www.positive-feedback.com/Issue71/theshow14.htm
http://www.theaudiobeat.com/ces2014/ces2014_rch.htm

I can't get excited til I see something real. Remember that company in the UK that was promising these new ECC83s? That went no where fast. I think they were reviewed by one of the UK mags and that was the last we heard of the company.

 

[mep]

I can't get excited til I see something real. Remember that company in the UK that was promising these new ECC83s? That went no where fast. I think they were reviewed by one of the UK mags and that was the last we heard of the company.

I just went to their website and there is no information about their company.