| Polimorph |
I don't know if someone had this ideea before or if will really work, but is nice to think about it.
I'd like to make some input first. Everyone knows that class D amplifiers are best energy efficient, and have a pretty good response in frequency too and they don't heat much.
On the other give a "nice" saturated, compressed "round" sound.
!!! I wonder what if we combine class D circuit (4ex. LM4651 ) as first stage with power tubes as finals?
Practically we combine the oldest technology with the newest. It will be really nice to have someone who would want to try it! We may have all a big surprise...
ps:interesting compromise, isn't it? |
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| fdegrove |
Hi,
| quote: | | !!! I wonder what if we combine class D circuit (4ex. LM4651 ) as first stage with power tubes as finals? |
Sorry but I fail to see what you'll win by running the input stages in class D?
I mean, those hardly consumer any power except for the valve heaters...
The idea of combining valves at the input and a class D output stage seems more attractive economically speaking.
Cheers, ;) |
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| Jax |
Tubes as switching devices and an output transformer?
That would be a challenge :xeye: :D |
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| TNT |
Start that class D forum NOW !
:D |
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| Polimorph |
Maybe u're right, but I stil don't find any power class D amplifiers, and all of them (I know few) are pretty low in power handeling.
I forgot to mention that class D amplifiers compress sound a little bit, just almost like the tubes and so they have this common feature. I would ask u to tell me if there are tubes capable of switching?
Thanks, we should think about this; I'll just wait for a professional opinion. |
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| fdegrove |
Hi,
Why would anyone want to start a Class D forum????:D
CLASS D
Cheers, ;) |
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| dhaen |
| quote: | Originally posted by Jax
Tubes as switching devices and an output transformer?
That would be a challenge :xeye: :D |
For over 30 years, TV's used this for deflection and high voltage generation. Power? - 20 - 60w. This was generally in resonant mode though. |
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| Polimorph |
| So u say it can be possible to couple the tubes and the class D circuit? |
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| tubetvr |
| quote: | | Tubes as switching devices and an output transformer? |
I think it could be done without transformers quite easily using same tubes that are used in an OTL amp but the benefits would not be the same as in a SS circuit.
Also I fail to see the benefits of building class D amplifiers from a sonic perspective, class D main benefits are small size and high efficiency, there are no benefits from a sonic perspective but in many cases instead sound is suffering due to improper implementation.
Of course there are people arguing that class D amplifiers sound so much better than anything else but that is the same exaggurated sales talk that was used to sell the first transistor amplifiers, "tubes are obsolete! buy our new modern transistor amplifier" We all know what happened, when most of the transistor hype had calmed down some people who where not afraid to say what they really thought said "Hey, my old tube amp sound better than this modern stuff that shoul have been so more advanced" and people started to be interested in tube amps again.
I predict that the same thing will happen with class D, in many applications they will be dominant as non-switching SS technology is today but in those cases where the ultimate in sound production is important there will be hard battle between tubes, non-switching SS and class D.
I also predict that there always be people that fall for all the hype and sales talk for any new tecdhnology and fool themselves into believing that everything new and modern is superior, that is OK , it would be very difficult to introduce new technology without these kind of people driving the market.
Regards Hans |
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| Sch3mat1c |
Bah. Tubes are only useful for quality class A or AB sound and the occasional kW class C radio using them purdy 3-500Zs or such. :D But since you want a design challenge...
The later sweep tubes certainly are good at switching, that being their designed purpose after all. With a saturation voltage as low as 30V while passing 500mA one gets the same performance as a transistor whose Vsat might be around 1.5V and 10A. Ran from +300V, the tube gets a max. of 300-30 = 270V across a load, drawing .5A, putting 135W into the load and only 15W in the plate. Said transistor, from +15V, would get 15-1.5 = 13.5V at 10A = 135W into the load and 1.5*10 = 15W collector dissipation. Unfortunately the heater dissipation is equal to plate dissipation here, ruining total efficiency, and let's not even touch peak screen current.
But you run into the problem of coupling the high voltage signal to the speakers. 1/2A isn't any good to an 8 ohm speaker. You can't just transform it because the supposed advantage of class D PWM is small size -- the carrier will easily transmit through a HF transformer but the audio will be lost as operating current because the transformer ignores anything so slow. To do it this way you'd have to use a regular OPT for impedance matching and do the carrier filtering before it. Although you could count it as part of the speaker's weight, that's not fair. ;)
Tim |
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| Polimorph |
My knowlege base says that the main problem with class D is that they distort much more (especially @ HF) than other classes of amps. Now this defective effect it's because of the speed of switching. But the switching is done by the final active parts in such amplifier. When I say class D I refer basiclly to the comparator (4 ex. LM4652) and with this comparator who gives actually the benefical effects of this class type and I think few of the negative ones, replacing the MOSFETs with the tubes as final stage will only sound better than some MOSFETs, because tubes are more self controlled than transistors, especially @ high frequencyes where the problems can appear. All that I want now to findout is a serial no for some tubes who have comparable switching speeds with traditional silicon devices.
Any other opinions? |
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| Polimorph |
| So the circuit drives the sitching tubes who now can operate more efficiently than in pure tube amps. And there we have it. If I'm assured that tubes can lower the distortion level (or keep distorting but in their own way - the good one "the ordered harmonics"), the results will be more than great! |
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| Jax |
The transformer can be as small as in a typical PC supply. You only need to transform the carrier that is pulse width modulated by the audio.
Compare with the PC supply, you create a carrier by chopping 300V DC and pulse width modulate it with the DC level you want at the output.
DC is slow, very slow :D
I know it's silly to design a class D with tubes but I see it as a revolt against technology changes that are not always for the better.
Hans is right but the difference now compared to the 60's is that we now know that older technologies will survive. We declared the death of the tubes in the late 60's. We are not going to declare the death of linear semiconductors this time.
My prediction, boomboxes and mainstream audio like HT systems will have class D in a near future. |
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| Eli Duttman |
| quote: | | My prediction, boomboxes and mainstream audio like HT systems will have class D in a near future. |
I fear Jax is correct. The "big time" electronics manufacturers are interested in profit only, not good sound. Get ready for another set of "big lie" advertising campaigns. :( |
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| Sch3mat1c |
| quote: | Originally posted by Jax
The transformer can be as small as in a typical PC supply. You only need to transform the carrier that is pulse width modulated by the audio. |
Please check out the effect PWM has on an "AC" signal then get back to me on this statement.
| quote: | Compare with the PC supply, you create a carrier by chopping 300V DC and pulse width modulate it with the DC level you want at the output.
DC is slow, very slow :D |
It is also demodulated with a rectifier and due to the capacitors and load, any attempt at coupling audio through the system would be incredibly inefficient.
AC and DC are different beasts. They cross over at some points but this isn't one of them.
| quote: | | My prediction, boomboxes and mainstream audio like HT systems will have class D in a near future. |
No doubts here. There are already kits with little 8 pin chips that give 10W output, IIRC.
Tim |
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| Jax |
| quote: | Originally posted by Sch3mat1c
Please check out the effect PWM has on an "AC" signal then get back to me on this statement. |
A constant amplitude square wave with varying duty cycle. We are chopping a DC source here.
| quote: | It is also demodulated with a rectifier and due to the capacitors and load, any attempt at coupling audio through the system would be incredibly inefficient.
AC and DC are different beasts. They cross over at some points but this isn't one of them. |
Yes, the easiest way to demodulate the PWM is a diode. Choose a low pass filter after the diode with a suitable time constant and you will see the audio. You will have to remove the DC component of course.
Efficient? Not really but that was not my point.
You could also just feed the PWM directly to the speakers and use the mechanical mass as filter. :xeye: Not recommended though.
My point was not to come up with an efficient class D amplifier with tubes, just that it is possible and with a large dose of humour. ;) |
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| tubetvr |
| quote: | | If I'm assured that tubes can lower the distortion level (or keep distorting but in their own way - the good one "the ordered harmonics"), the results will be more than great! |
Yes, I think that it would be possible to build a class D amp using tube that in some ways is better than when using SS, (as an example tubes have no reverse recovery charge problem so reverse recovery is more or less instant and not really dependant on the driving circuit as in a bipolar SS cirtcuit, compare schottky devices).
but WHY? why do anyone want to build a class D amp if the goal is sonic pleasure? it is much easier to build a tube or even SS amp that sounds good than trying to build a class D amp giving the same sound quality, there is nothing in a class D amp that make it sound better than an analogue amp but there are a lot of problems with not ideal switches and filtering problems in a class D amp that affect the sound in a negative way so why build one if not needed in the first place?
Regards Hans |
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| Circlotron |
| quote: | Originally posted by Jax
My point was not to come up with an efficient class D amplifier with tubes, just that it is possible and with a large dose of humour. ;) |
That's half the point of DIY!! It's like sitting by an open fire is not the best way to keep warm but it can be enjoyable. It's an end in itself. A class D tube amp is definitely not a me-too, cookie-cutter, plastic, commodity, seen-one-seen-them-all piece of stuff.
I say do it! :cool: |
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| Polimorph |
quote: "why do anyone want to build a class D amp if the goal is sonic pleasure? it is much easier to build a tube or even SS amp that sounds good than trying to build a class D amp giving the same sound quality[...]"
Because if this way (class d+tubes) if it can sound at least at same quality, we can obtain some important economical benefits. Anyway all the world is trying now to make things as small and low energy as it can.
In other order of ideea, i found some switching tubes that could do the job. They're called "Trochotron" VS10G. The bad part is that they're used in nuclear bombs too :hot:, so I think there could be a dificulty in buyng one of those. Maybe one of you heard about this kind of tubes, but here's a link 4 the others: http://www.tubecollector.org/vs10g.htm .
4 Profi: "can this work?" |
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| Polimorph |
You're all so against class D....
I just wanna say one thing now. Class D is very efficient but low quality. The lower quality it's caused by switching. The final stage in class D a.k.a. MOSFETs are the switcing devices. M I correct? (pls correct me if not). Just if we replace MOSFETs with conventional high speed switching tubes could we have a hope that they'll operate better than transistors?
Overall the amplifier remains class D, because of the analog modulating and comparator system and because of switching in the final stage. |
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| tubetvr |
| quote: | | Because if this way (class d+tubes) if it can sound at least at same quality, we can obtain some important economical benefits. Anyway all the world is trying now to make things as small and low energy as it can. |
That argument , (economical and high efficiency) is just not valid for most people interested in high quality sound reproduction, personally I don't care if my amp is inefficient, for the moment I am using an OTL amp that draw ~400W in idle and give 2 x 25W.
If it would be so, (I hope not!) that availability of electric energy would be limited in the future I probably would prefer to listen a shorter time each day to my inefficient but good sounding amp than to have to listen all day to something very efficient but not so good sounding.
Regards Hans |
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| Sch3mat1c |
| quote: | Originally posted by Polimorph
You're all so against class D....
I just wanna say one thing now. Class D is very efficient but low quality. The lower quality it's caused by switching. |
No, the switching is quite obviously filtered out. I would say errors in the comparators. For instance when you compare the audio to a triangle wave, any nonlinearity in the triange wave will cause the switching point to move, causing distortions.
Tim |
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| Polimorph |
| Distortion is given by the switching, not the comparator. Any professional opinion on this? |
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| Polimorph |
| You don't care but most ppl will do. |
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| tubetvr |
| quote: | | You don't care but most ppl will do. |
I am quite sure that most people on this forum are willing to spend some energy and money if its needed in order to experience good sound.
However please read once more what I wrote:
"I probably would prefer to listen a shorter time each day to my inefficient but good sounding amp than to have to listen all day to something very efficient but not so good sounding."
That is I rather listen 1 hour per day using an inefficient but good sounding amplifier than have to listen to something less good sounding the whole day.
BTW, if you are concerned about minimising energy consumption it is better to concentrate on improving speakers as they are normally extremely inefficient, I am using horns which is the most
efficient type of speaker existing with easily 10 times more efficiency than most other types, therefore I can live with a relatively less powerful amp thereby minimising total power consumption.
Regards Hans |
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| Polimorph |
If u use tubes, the worst ideea is to use worst quallity output system witch is horn loaded speakers.
Best for u will be tubes and compression. |
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| fdegrove |
Hi,
| quote: | | If u use tubes, the worst ideea is to use worst quallity output system witch is horn loaded speakers. |
And class Dump amps are best, right?:mad:
If I only had heard a single one that sounded half decent....
Cheers,;) |
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| tubetvr |
| quote: | | If u use tubes, the worst ideea is to use worst quallity output system witch is horn loaded speakers. |
I am sure that you have listen to many horn speakers as you can say this so strongly. Horn speakers are not for everyone but there are many people enjoying low power tube amps with horns, have you listened to any good such combination?
| quote: | | Best for u will be tubes and compression. |
I think you have to explain what you mean by this.
Regards Hans |
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| Polimorph |
And I'm talking here just with you guys, maybe my wors travel more than this. I hope my ideeas wiil get far far away (Shrek2) than just a site. Anyway if u don't like this ideea (v. thread) you should post anyway 'cause all that can do a critical eye is improve. ("what doesn't kill you it makes you tougher").
Thank you all again.
ps:maybe my tone is a little bit rough, don't take it like this, I just want to make my point. |
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| serengetiplains |
| quote: | Originally posted by tubetvr
That argument , (economical and high efficiency) is just not valid for most people interested in high quality sound reproduction ... |
"Most" people? Care to give us the actual numbers, Hans?
Some day in the future, vacuum tubes, sigh, will be surpassed, even in PP mode (gasp). Spears were surpassed, horse-drawn buggies were surpassed, slide rulers were surpassed, the Edsel was surpassed before it existed, Plaid pants were (mostly) surpassed, George Michael was surpassed, the Volkswagen Rabbit was surpassed. E=MC2 will be surpassed. Turntables will be surpassed. My beloved teflon capacitors will be surpassed. My best ideas are already decisively surpassed. The future is something better than we already got. Who's to say the shape of it, Class D or other? |
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| Polimorph |
quote: "And class Dump amps are best, right?"
No and I already had my point. This thread is meant to improve or to give us a light over class D. Using tubes instead of transistors could be better. |
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| Polimorph |
| Indeed we shouldn't applause a thing that is new at one point. But a bigger mistake than that is to block it from the begining. |
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| Polimorph |
| Who wants to give a hand? My main question was what tubes have high switching speed? |
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| fdegrove |
Hi,
| quote: | | Some day in the future, vacuum tubes, sigh, will be surpassed, even in PP mode (gasp). |
With all due respect but I've heard that said about a number of things and yes, most of it has been replaced by something "better".
Question is better for what, for whom?
Fact remains that for some things there will still be tubes and there's alot more of them around than most people realise...
No, not just for audio. It would be totally naieve to think that the tube industry would survive on the production of audio tubes (how many are there, real audio tubes that is?) alone.
Still, the tube has been notoriously hard to beat in audio for a number of reasons.
The most important one is they just sound better than anything else to a vast number of ears, no matter how advanced technically other devices may seem.
No, we don't want another cheap "tubes versus transistor" flame fest...Or do we?:hot:
Just unwinding my old cylinder grammophone here...
Cheers, ;) |
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| serengetiplains |
| quote: | Originally posted by Polimorph
Indeed we shouldn't applause a thing that is new at one point. But a bigger mistake than that is to block it from the begining. |
The to-be history of innovating something better than ... turntables (currently the best we have, in my experience) might involve: lousy souding cd players as a flawed first start, better but still not state of the art SACD players, fancy shmancy Microsoft medialess HD encoding, ETC and ETC until ... *presto* ... something better than turntables. But not to mistake, turntables will be surpassed, and who am I to separate necessary from unnecessary on the path to getting to that point ("CD was a useless diversion," "why bother with SACD it's not state of the art" etc)?
Guys, put away your defensiveness toward innovation. People who express ideas perhaps not yet tested provide a valuable service. |
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| Polimorph |
| With all the respect, I don't want to give the ideea of replacing tubes, I want you folks that tubes can give us another good reason to keep them alive. Now comes the challenge. Can we? If you're so radical you only cut your own tree branch. I'm tube fan too, hey! |
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| serengetiplains |
| quote: | Originally posted by fdegrove
Still, the tube has been notoriously hard to beat in audio for a number of reasons.
The most important one is they just sound better than anything else to a vast number of ears, no matter how advanced technically other devices may seem. |
No question about it in my experience, so my ears included, and of course tubes are not dead yet, they perhaps will not die in our lifetime. In the spirit of my previous post, class D amps might be (might not be, who's to say is the issue) one necessary step on the path to bettering the best of what we now have---call that tubes, for argument's sake.
Regards! |
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| Polimorph |
| I like you... in a good way. :D Relax I'm younger that you anyway :D. |
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| fdegrove |
Hi,
Where on earth have I heard that one before?
| quote: | | Guys, put away your defensiveness toward innovation. |
Sure let's make a better tube amp....can't be too easy after all those years, can it?:D
| quote: | | People who express ideas perhaps not yet tested provide a valuable service. |
As long as they don't come shooting at us with their own preconceived ideas, I don't mind.
It seems to me a little premature to already declare class D as the way to go, won't you agree?
Those Hunfortunate Henough to be the proud Howners of a pair of very Heffecient Hornloudspeakers are now Hadvised to switch to class H.
Class H will be defined as class D with Horrendous amounts of gridcurrent modulated at 27.9 MHz...:clown:
Cheers, ;) |
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| tubetvr |
| quote: | | "Most" people? Care to give us the actual numbers, Hans? |
Maybe it is just my experience but I have never met anyone willing to spend subtantial efforts in getting good sound that have been saying that efficiency of a power amplifier is of any great importance, on the contrary I see more interest in inefficient class A amplifiers with high output power now then before.
For boomboxes I can agree that class D with its current limitations is a good choice for economical and efficiency reasons.
As I wrote earlier, it is anyway probably more whortwhile spending efforts in improving speaker efficiency making it possible to use lower power amplifiers than to make the amplifier more efficient, but also in this area modern speakers are if anything less efficient then before.
| quote: | | Guys, put away your defensiveness toward innovation. People who express ideas perhaps not yet tested provide a valuable service. |
I dont think I am defensive against new technology but I am carefully investigating if the new technology has something better to offer, if I am critical it is probably something that I learned from my work, I also usually don't fall for sales talk be it technical or otherwise.
BTW it is good to read about all more or less crasy ideas in this forum, many ideas are not new but has been earlier considered to be unrealistic, that is the same with innovations in other parts of industry, take car technology where very old ideas suddenly gets new life beacuse it is easier to implement them today.
If I should design a class D amp I would probably try to use something efficient as a switch and therefore give up the idea using tubes, I am sure that class D amps will continue to be improved and maybe one day all amplifiers are built using this tecnology, who knows?
Regards Hans |
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| smoking-amp |
If someone wants to combine tubes and switching, its already been done and on the market too (although not using class D), the David Berning switching impedance converter. Reviewed in Glass Audio Vol. 12, No. 1, 2000 page 22-30 and the following issue also. The Berning design eliminates the HV xfmr. and the output xfmr., making for a lightweight amplifier.
For DIY implimentation, I would suggest modifying the Berning scheme to use two 90 degree overlapping phases (diode commutated), instead of one, and slowing the square wave transition times to prevent generation of EMI (like Linear Technology Inc. does in its ultra-quiet PWM switcher designs). (requires the two phases in order to do this in the Berning design.)
Don |
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| phase_accurate |
A friend of mine is a tube-o-phile. He once mentioned that class-d has been done with tubes (maybe just for modualtor stages in AM transmitters). I will ask him for more info.
Those who want to try: don't forget a fast antiparallel rectifier tube, for each switcing tube, that deals with the output filter's freewheeling current. ;)
I by myself I wouldn't even bother to try a tube class-d amp.
Regards
Charles |
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| stalin |
i am building a class d tube amp, and was thinking about using cold-cathode switching tubes for the output stage. i know they can switch up to 100k, which is almost 5x faster than i need, but am not sure about output power. has anyone worked with cold-cathode switching tubes before? any thoughts or suggestions?
thanks. |
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| Polimorph |
| Man... "Let's make things better" was or is the PHILIPS's motto. "...it can be better" isn't a motto is just saying... Anyway when Polimorph will be a strong registred concept I'll let u kno' what motto I'll chose. |
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| koldby |
Hi all
Just my 2 cents:
A supposedly sonic advantage wiyh Class D is there is NO crossover distortion. Only class A can claim this as well.
Tubes in D:
One of the main factors of distortion in D is the nessesary deadtime you have to introduce to avoid shootthru in the MOSFet's ... If shootthru happens, the MOSFet's are history! So you have to operate with a certain safty margin.
Tubes on the other hand will be more tolerate to shootthru, so you can operate with almost no deadtime.
Perhaps there are other benefits, but these are enough for me to play with the thought..
2 x 2 PL509/6kg6 would probably do the trick..
koldby |
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