Does SS power amp have advantage over tubes? - diyAudio
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Old 28th October 2014, 01:54 AM   #1
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Default Does SS power amp have advantage over tubes?

I am new in audiophile, so excuse me if I offend anyone here. I am not trying to stir up trouble. I always though tube gives even harmonics that is more pleasing to the ears. BUT, I read quite a few posts here. Sounds like the main thing about sound quality is low distortion. Both here and SS forum here are saying the same thing, the lower the distortion, the better the transparency and bigger the sound stage. So I just look at the two approaches and here is my opinions:

1) By the nature of tubes that you only have equivalent of NPN or NMOSFET, it is already a clean disadvantage to SS design that they have complementary devices like PNP or PMOSFET. Lots of advantage to be have for cancelling distortion using complementary devices cannot be done with tubes.

2) Then tube circuit has to have OPT, one more source of distortion and reduce open loop gain because it is stepping down. Lower loop gain implies more distortion.

3) Then it is so much easier to get higher gain for SS stage. Gain of the tube is limited, triode has internal plate resistance that limit the gain. In feedback circuit, the higher the loop gain( not open loop gain), the lower the distortion. You can't get enough gain with 3 tube stages particularly the OT is going to reduce the voltage to lower the output impedance. Again, lower loop gain implies higher distortion.

4) The output impedance of SS circuit with emitter follower or source follower is going to much lower than any tube amp output either through OPT or even no OPT. The speaker load is going to affect the amp. This with the fact the tube amp has lower loop gain, You can't get the output impedance low enough!!!

4) Also, most tube circuit is much higher impedance and bigger in size, this make layout much more critical and much harder to avoid crosstalk. In guitar amp, at least you only deal with 5KHz. Here you deal with 20KHz and the amp needs to be able to go much higher frequency response. Layout and wire length is going to that much more critical. I am reading the Audio power amp book by Bob Cordell, he is talking about the amps are design to have 500KHz BW. This is going to be a whole lot tougher for tube amp to run good at that frequency.

If tube distortion is not helping the sound of the tube power amp, I just don't see how tube circuit can be better than SS amp in respect of distortion performance.

Please correct me if I am wrong in any of the points.

Thanks

Last edited by Alan0354; 28th October 2014 at 02:04 AM.
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Old 28th October 2014, 02:11 AM   #2
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The right kind and amount of Harmonic distortion adds a "warmth" or "musicality" to the signal which some find preferable, so low distortion is not necessary for a good 3 dimensional playback system, also speakers and room have a lot to do with the outcome. Tubes can be very linear and can produce very low distortion, it's the inefficiency (heater current), size, and cost that solid state wins at, and this is why the tube has been somewhat defeated. Also layout and design is less important in SS gear, tubes are naturally high impedance devices.

Tube amps do not have to have an output transformer, check out some OTL designs.

Last edited by famousmockingbird; 28th October 2014 at 02:13 AM.
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Old 28th October 2014, 02:21 AM   #3
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There's distortion and there's distortion. If you have the opportunity, listen to a Harman/Kardon Citation II that's in good repair. That's the sound SS has been striving towards and hasn't quite got.

A quality SS power amp can be the better choice with certain speakers. Big Thiels come to mind, as they exhibit hideous impedance dips down to 1 Ω. You can't get the gargantuan damping factor needed from tubed circuitry.

Proper mating of speakers and amps is crucial to obtaining good performance. A super efficient horn speaker will not sound good in combination with "sand", as the combination is badly over damped.

System synergy IS the name of the game and it can be obtained in several ways.
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Old 28th October 2014, 02:26 AM   #4
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SS amps have advantages over Tube amps and Tube amps have advantages over SS amps..

It's hard to find a SS amp that stays enjoyable over the long term..
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Old 28th October 2014, 02:31 AM   #5
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See, this is not a lot of people here said. I very specifically asked and was told low distortion is everything. That's why I am confused. I always agree that there is distortion and there is distortion. You guys don't need to convince me on that. I am just repeat what quite a few people told me here.

I know for fact that tube guitar sounds more organic and warmer than SS, there is no comparison. But I was told here that it's exactly opposite in audiophile. People here using all sort of tricks to lower distortion. I have been reading Audio Power Amp by Bob Cordell, he did everything in the first few chapter to lower distortion. So which is it?

I can accept low distortion is everything, I can accept that tube gives the distortion characteristics that is pleasing to the ears. But I cannot accept both at the same time, that low distortion is everything but tube amps sounds better!!!!

Last edited by Alan0354; 28th October 2014 at 02:35 AM.
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Old 28th October 2014, 02:36 AM   #6
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It's a preference chosen by the listener, if it sounds good then it sounds good Especially over extended periods of listening where fatigue can set in.

If fidelity (as in Hi-Fi) is the goal then lower distortion is desired, studios probably strive for high fidelity for they are in the business of sound engineering and any coloration to the recordings from playback equipment is a no no
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Old 28th October 2014, 02:38 AM   #7
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You have very big arguments against tube amps......but I will tel You. SE tube amp has very limited passive elements, about 10-20, but SS - hundreds! Every passive element decrease Quality of sound and is not wellcome to the structure.
And the tube sound is more clean, fresh, detail......Most important is that "the parts" cross vacuum from cathode to plate!
/my moto is HiEnd is back proportional to the number of composite parts/.
About OTs - my latest project - OTL-OCL 6AS7 Gen Electric is without OTs, that is for a level higher SS amps for $$$$.
I'd like to advice You, to compare every expensive SS amp with OTL Atma-sphere or big projects SE GU81, 300B WE, 2A3 RCA with Hi Quality speakers and You will sense the difference. /IMO, Electrical parameters are not very important, against the sense of pleasant sound/.
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Projects: OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,... PPs 6005 Gen. Electric, EL34 Mullard, 6L6....
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Old 28th October 2014, 02:38 AM   #8
Keit is offline Keit  Australia
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Alan, you have it roughly right.

Your Point (4) is weak though. While it is true that a circuit occupying a larger volume will offer more problems with crosstalk, as any designer of switch mode power supplies usually gets to learn the hard way, in practice its isn't hard to get acceptable performance in tube amps with good construction practices.

Crosstalk between channels is not much of an issue in itself as almost all audio sources have not a lot of isolation in recording. However in class AB push-pull circuits, stray coupling from power rails back into input circuits is a pernicious source of distortion. Solid state amps for economic reasons are almost always class B, and suffer from this problem a lot more than tube amps, because in a class B circuit the current drawn by the output stage inherently contains a lot of harmonics.


In practice, you can't really tell beteen the best of tube amps and the best of solid state amps. There's too much focus on harmonic distortion in amateur audio circles. It was never so much of a focus in professional electronics.

It's actually easy to get very wide power frequency response in tube amps. The wide bandwdith in audio amps is itself totally inaudibile, but it is one way to avoid transient intermodulation distortion. This is where the driver, itself driven by neg feedback, tries to force the slower output stage to do something it can't. Fast power transistors cost big bucks, so in solid state amps we have to use other more subtle ways to eliminate TID.

In the 1950's, GEC released designs of several tube amplifers using KT66's or KT77's in ultralinear push pull, and push pull drivers. These amps had sub- 0.1% total harmoic distortion. Today, we can do 100 times better than that in solid state, and we can even do quite a bit better with tube amps, transformers and all!

But.... Noted RCA research engineer Harry Olson in the 1940's did some carefully designed experiments with audiences. He found that few people can detect distorton less than 1%. Somwhat later, similar work was done by Philips in Holland. They came to the same conclusion, and it was the origin of a 1960's era European consumer protection specification for "Hi-Fi". To legallly qualify as Hi-Fi, an amplifier had to have harmonic distortion less than 1%.

These results need to be treated with considerable caution, as audio sources are so much cleaner now, and people have got used to distortion levels much lower than was available form records in the 1940's and 1950's. But it is still definitely the case that competently engineered amplifiers, whether tube or solid state, will deliver distortion performance well below what you can hear.

Note that I said competently engineered! If the design is no good, that's a diferent story. It IS easier to get a solid state design wrong.

I have significant experience in the radio broadcast industry. When AM broadcastig was king, the better radio stations spent a LOT of money on studios - really good studio acoustics, very good practices for looking after records, limits on the number of times a record could be played, etc. But your typical AM transmitter was plate modulated by a Class-B high power audio amp, usually without any negative feedback at all! A few had NFB. Harmonic distortion, measured end to end from programme input to transmitter detected output was seldom better than 1% - some brands were worse!

When FM came in, distortion was only slightly better. The early generation of FM exciters with servo-stabilised reactance-modulated oscillators were doing well if the distortion was less than about 0.7%.


Note that even order distortion is just not very noticeable. The ear generates plenty on its own! Some people even find even order distortion pleasant! If you enjoy a Class A tube amp with nor feedback, that's what you will get. If you like it, that fine! Enjoy - its a free country.

Last edited by Keit; 28th October 2014 at 02:53 AM.
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Old 28th October 2014, 02:46 AM   #9
Vasquo is offline Vasquo  United States
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Quote:
Originally Posted by Alan0354 View Post
I can accept low distortion is everything, I can accept that tube gives the distortion characteristics that is pleasing to the ears. But I cannot accept both at the same time, that low distortion is everything but tube amps sounds better!!!!
Do all tube amps sound better? Do all SS amps sound bad?

It also depends on the application. Will you find tube amps doing sound reinforcement duty in a church, concert hall or auditorium? Or will you find SS amps there?

And lastly, it's sometimes funny when people/manufacturers strive for 0.0017% distortion in their amps, so it can connect to speakers that have 0.2 to 14% distortion in itself (more so at higher SPL). -- it's like all the work done on lowering distortion on the amp, gets thrown out the window anyway when connected to a speaker.
Loudspeaker Distortion At Low Frequencies Article By R. A. Greiner (Wisconsin)

In the end, don't worry about what other people think. Pick what sounds good to your ears.
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Old 28th October 2014, 02:56 AM   #10
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Thanks guys, I'm with you that the right distortion can sound better. AND distortion of speaker and recording dominate everything. I just want to put it out because as I said, there are quite a few that insist on lower distortion is everything and for the life of me cannot imagine you can make a lower distortion tube amp than SS amp if everything is done right ( important that everything is done right, you can have mess up design in either side).

I made a mistake in my OP that I have two 4). I did a lot of pcb layout for RF and signal integrity design. Yes, it is possible to layout the tube circuit just as good, BUT it is going to be much harder. That's a fact. You have high impedance circuit that swing a lot higher voltage with longer leads ( bigger components), it's is going to be a whole hell of a lot harder to layout. Believe me, in my years of EE and manager of EE, good layout people is very very hard to find, even an engineer is not necessary a good layout person. I am one of those odd balls that love doing layout because I love to deal with signal integrity. I even layout boards for engineers that worked for me. Layout is easy to talk and very hard to do, for tube circuit, layout is a very big percentage of the design.

I hope the people that believe low distortion is everything can come join in. I want to hear your side.

Last edited by Alan0354; 28th October 2014 at 03:07 AM.
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