Who said tube amps sound better?
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Tube amps tend to produce less unpleaseant-sounding higher-order odd harmonics than solid state and potentially more even lower-order harmonics which are pleasing to the ear.Piano overtones are stretched over harmonics and beat with them. On overly warm gear piano sounds like out of tune. I believe that we got so used to home gear that produce some distortions, that perfect reproduction of life event, that you enjoyed, at home sounds wrong - sterile, analytical etc. Distortions make sound more dynamic and often we want them for this reason. I suspect that it is because of compression. We try to get back dynamics of the real performance. Either way - there is no right or wrong, just a matter of taste. I'm in the accurate camp, choosing accurate timbre over false dynamics. |
The question posed is a red herring. "Tube amplifiers sound better because of the euphonic distortions they add to the music." Where the Hell did you read or hear that?! Bill Johnson always said he used whatever technology was available to make the best sounding electronics he could. He didn’t introduce his tube amps and pre-amp in 1970 (the first of the "modern" era) to offer audiophiles euphonically-distorted sound. He did it because at that time tubes provided him with the means to make products that reproduced music possessing the least distorted sound he could. But all electronics add their own sound to the signal as it passes through them. Is tube distortion more euphonic than solid state distortion? Ralph Karsten (Atma-Sphere) postulates that solid state amps tend to produce high-order "odd" (the 3rd, 5th, 7th, 9th, etc.) harmonic distortion, tubes low-order "even" (2nd, 4th, 6th, 8th, etc.) harmonic distortion. Since even-order distortion is more consonant to music than is odd-order (it is related, harmonically), it is less offensive to the brain. An amp producing even 1% hmd can sound "better" than an amp producing only 1/10%, IF the former’s hm distortion is low-order even, the latter’s high-order odd. Roger Modjeski was of the opinion that inter-modulation distortion is a far more serious problem than is harmonic. The large amounts of negative feedback used in many solid state amps (to lower static hd, to lower the amp’s output impedance/raise it’s damping factor, and sometimes to make the circuit more stable) is a well known cause of inter-modulation distortion. Tube amps tend to use less nf., though the original Futterman OTL amps used huge amounts of it. Why Futterman did that---and why his amps still sounded great---was explained by Modjeski in his late, lamented Forum on AudioCircle. Though that Forum is dormant, Modjeski’s writings are still available for viewing on the AudioCircle site. |
"...That was one way out wacky theory kijanki..." No it's not. Distortion, at a certain volume level, is an clue to loudness, if you can get that clue at less than extreme levels your brain thinks you are at the limit and really rocking. In the home environment, that's a good thing. If you have a huge room to fill and need to really crank it up, early distortion may be detrimental. I listen at low volumes, so tube amps give me that live music experience that I seek. YMMV. |
Tube amplifiers sound better because of the euphonic distortions they add to the music.Distortion is in all forms of amplification. Of course we want it to be as low as possible but the ear poses some real challenges. It uses the higher ordered harmonics (5th and above) to sense sound pressure, and to do that it has to be keenly sensitive to them! The ear is more sensitive to the higher ordered harmonics than almost anything else. For this reason, a THD of 0.01% can be very audible if that’s mostly higher orders. The ear assigns tonality to all forms of distortion! The higher orders get ’harsh and bright’. We’ve all been hearing this in most solid state amps made in the last 70 years. Its why tubes are still around!! The lower orders (2nd, 3rd and 4th) are nearly inaudible and mostly contribute to ’bloom’ and ’warmth’ using audiophile terms. The ear has a masking principle where louder sounds mask the presence of quieter sounds; if the lower orders are in sufficient quantity, they will mask the presence of the higher orders. When this happens, the amp will sound smooth and because the lower orders are mostly inaudible it will appear to be relatively neutral. If the amp has such a distortion signature this will be the case whether tube or solid state. But for technical reasons (its very hard to build a zero feedback solid state amp), until recently this has mostly been describing tube amplifiers. The problem has been up until fairly recently that the the devices (whether tube or semiconductor) didn’t exist to allow the amplifier design to have a sufficient amount of feedback (on an engineering basis, the devices didn’t exist to allow for sufficient gain bandwidth product). You have several hurdles to cross; first when adding a lot of feedback you can’t exceed the phase margin of the amp otherwise it becomes unstable and can oscillate. Phase margin is an engineering way of saying that there’s a certain high frequency above which the negative feedback applied is no longer negative due to phase shift in the circuit. The second problem is you have to have an enormous amount of gain- and with gain you get phase shift- because you really need north of 35dB of feedback in order to allow the amplifier to clean up the distortion caused by the application of feedback itself (which tends to be almost entirely higher ordered harmonics, caused by the process of bifurcation occurring at the point where the feedback is combined with the input signal). These higher ordered harmonics are of course audible which is why feedback has gotten a bad rap in high end audio over the last 40 years. So you have to blow off 35 db of gain with feedback and still have a good 25dB of gain left over- so this means that at a minimum any amplifier that uses feedback properly will have a total gain (called ’loop gain’) of at least 60dB! Most amps made have far less than that which is why solid state has garnered a reputation for harsh and bright. Between 12 and 20dB is the area where feedback generates the most distortion: its on a bell curve. Yes, it does suppress distortion but my point here is that its makes some of its own too. Because this is such a tall order, most amps simply didn’t do it. To deal with this problem, the industry (sweeping this under the carpet) only tests harmonic distortion of amplifiers at 100 Hz. At this frequency almost any solid state amp has enough feedback which is why they can play bass so well. But if you measure the same amp at 1KHz or 10KHz you’ll find the distortion is much higher- and of course that is why the amp sounds bright and harsh (its not a frequency response error). This increase of distortion with frequency is a sign that the amp lacks Gain Bandwidth Product. GBP is to feedback what gas is to car. When you use it up by increasing frequency, at some point there’s no more feedback. At any rate distortion is increased! Tubes avoid this for the most part by having a greater amount of the lower ordered harmonics. So they lack the harshness and brightness not because they are lower distortion but **because the higher orders are masked**. There are a number of solutions. One way to get tubes to be much lower distortion is to design the circuit to be fully differential and balanced from input to output. In this way, even orders are cancelled not just at the output but throughout the circuit. This results in a 3rd harmonic as the primary distortion and since the 3rd is quite close to the fundamental is treated by the ear the same as the 2nd. But it can easily be at a level 1/10th that of an amp that does not employ this technique, and succeeding harmonics will fall off at a faster rate according to a cubic progression because distortion isn’t compounded from stage to stage. For this reason such an amp is said to have a ’cubic non-linearity’ and is considerably more neutral and transparent than amps that express the 2nd order as dominant (a ’quadratic non-linearity’), yet just as smooth. This is true whether the circuit is tube or solid state. Feedback can be avoided altogether, thus avoiding the brightness that occurs with its application. SETs are an example of this as well as our OTLs (which are fully balanced and differential) and there are solid state examples as well, such as the Ayre. Another solution is to simply have enough gain and bandwidth using newer semiconductors so enough feedback can be applied so that the amp has consistent distortion at 1KHz and 10KHz as it does at 100Hz, and won’t oscillate with +35dB of feedback. This is a bit of a trick but it is doable and there are a few solid state amps of traditional design that do this- the Benchmark and Soulution come to mind. Finally, class D amps can be built that have so much feedback that their phase margin is grossly exceeded and they go into oscillation as soon as they are turned on. The oscillation is then used as the switching frequency. This type of class D amp is known as ’self oscillating’ and can have very low distortion. Because of non-linearities in the encoding scheme and also due to dead time, lower ordered harmonics might be generated. If this is the case, such an amp will sound every bit as smooth and transparent as the best tube amps (due to masking) but with greater neutrality and transparency due to vastly lower distortion overall (in case its not clear, distortion masks detail). |
op i believe the recording and mastering processes ’bleach out’ the sound to some degree ... there are losses at each step... therefore the sympathetic distortions in reproduction ’rebuild’ or ’restore’ some of the warmth, body, and dimensionality of the music (even most ’analog’ recordings are digitized, and even analog handling has losses) like every time you store or handle or freeze food, you lose some of the texture and original ’realness’ of the food... thus ’seasoning’ often make it nice again... different, but nicer than if you didn’t... |
And there you have it: Ralph (atmasphere) just gave you a thumbnail version of the master-class in amplifier design he could teach@bdp24 you are mistaken, this is not a thumbnail (I know you are not criticizing him, quite the opposite, but I have to say something), I have been following close Ralph’s post and I had the chance to share 1 hour with him with no one else around at RMAF, and another hour at the Florida show, having time with Ralph believe me you should be paying him for it, he was wearing flip flops and honestly I understood 60% percent of what he was saying back then years ago (sorry Ralph if you got the impression I could understand it all) This post of him I will save it and it is golden, I think with the years he is becoming less cryptic and more on the teacher side but what he is saying right there is bible code. I know, I know, many will say he doesn’t know what he is talking about, he has a lot of haters, but he is giving you right there in that post the details you need to understand distortions. After all his amps do not distort :) |
@atmasphere Thanks for that lengthy description. I emailed that one to myself for future reference. You never know when Audiogon will delete this thread. I have 4 types of gear and they sound different but smooth. Your post may explain what I am hearing. - KRELL K-300i (Class AB very smooth and powerful) - Benchmark HPA4 + AHB2 (extremely clear and smooth) - D-Sonic M3a 800s (Class D smooth and powerful) - CODA 07x preamp (SET smooth) |
@atmasphere Thank you for the clear and detailed response. You provided me a level of education in audio that I never thought would be obtained on a forum. |
what I am trying to understand is if the original recording is with euphonic distortions that are deemed as positive then don't we want the most transparent system to hear the original and How does tube euphonic distortions add a stage to the sound?I wouldn't worry about the original recording! Some are great and some are terrible. The way distortions occur and how some are added in the studio causes things to work out differently. When you are playing back you simply want the most transparent you can get but without the playback editorializing on the content. By this I mean the playback apparatus has to be well-behaved. I've seen some systems sound great with a great recording and then freak out when a poor recording is played. But get that same poor recording on a properly set up system and while it won't sound great, at least the playback won't exacerbate problems. That is one reason I eschew brightness and harshness in the playback as it will make bad recordings worse. It sucks when a favorite artist has a lousy recording; it sucks worse when your system can't be graceful about it. With regards to sound stage, it appears that a prominent 2nd or 3rd harmonic somehow helps the ear winnow out detail in the recording. I do not know why this is the case so I'm going on a lot of anecdote (and familiarity with recordings I've made on location and in the studio), but I did encounter one paper where the experiment was to add a 2nd harmonic to the playback and improved soundstage was the result. I think more research is needed. At any rate in my own work it appears that the *amount* of distortion isn't the point- but what is important is that even if the distortion is super low, most of it should be the lower orders. |
A very interesting thread about distortion. It's really a subject that is hard to understand as there are so many aspects also related to our hearing and perception of sound. To me it seems like if we in a playback amplifier add some low order harmonic distortion with a distribution similar to our aural harmonic distortion, this may be an interesting way forward. In a paper from Cheever, 1989 there is an interesting discussion about aural distortion and high order distortion. Both Cheever, Pass and several others agree on that to much negative feedback create high order harmonics that we are very sensitive to. Cheever also discuss aural masking and the effect by adding such distortion to the playback system. But does this masking effect also apply to to some extent to intermodulation distortion? I have not a clue. Is it so that we should focus on how much an amplifier deviates from our hearing aural harmonics? I had the opportunity to borrow a Benchmark AHB2 for a weekend. To listen to it and to measure its performance using my audio measurement system. From a pure "standard" measurement point of view its really hard to beat its performance. Super low distortion for example. But to me it was not playing musical. Transparent and with high resolution of course. Not engaging but very neutral. This amplifier is a technical masterpiece. Using forward error correction that from a measurement point of view more or less eliminate distortion. At least to very, very low levels. By the way, error correction, is to my knowledge a superior method to manage different kind of distortions compared to for example global negative feedback. But that's another story. To me, there is more going on than masking effects by adding a falling level of low order harmonics. Maybe its about the improved dynamics? Here is my idea... Instruments may be more clearly defined in all of its natural harmonic spectra by adding well defined low order harmonics. We get the masking effect and we also "enhance" the natural sound of voice and instruments if we add some harmonics that are inline with our hearing harmonics. We are very sensitive to unnatural and high order harmonic distortion and this would just make use of the way our hearing and perception of sound works. As long as we stay close to the aural harmonics we just get a more musical presentation. Without changing the timbre (I think). I think this might have a good effect on the holographic image as well. Hope these ideas may bring something to the subject. |
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A very interesting topic. I recently read a paper from Cheever (1989) that's quite interesting. Our aural distortion seem to play a role here. Both from a masking perspective, but also from a musicality and holographic soundstage perspective. I got the opportunity to borrow a Benchmark AHB2 over a weekend some weeks ago. For listening and measurements. I have an audio measurement system that I use for development so it would be interesting to measure some on the very high performance AHB2 amp. And indeed, it has a very very low distortion. Its a real masterpiece in that sense. And by using forward error correction instead of traditional negative feedback they have reached some incredibly good numbers regarding "traditional" amplifier measurements. That's one part of the coin. The other task was to listen to it. And to me it was not musical or engaging to listen to. But of course transparent, good dynamics and with high resolution. Papers I have read, own experiments with harmonic distortion and discussions have got me into an idea around distortion. If we add low order harmonics inline with our hearing harmonics we get a masking effect but we also, for us as humans, a natural way to increase harmonics from instruments and voices. Without affecting timbre (I think). This could maybe also explain improved holographic imaging. A least to how I think. |
A very interesting topic. I recently read a paper from Cheever (1989) that's quite interesting. Our aural distortion seem to play a role here. Both from a masking perspective, but also from a musicality and holographic soundstage perspective. I got the opportunity to borrow a Benchmark AHB2 over a weekend some weeks ago. For listening and measurements. I have an audio measurement system that I use for development so it would be interesting to measure some on the very high performance AHB2 amp. And indeed, it has a very very low distortion. Its a real masterpiece in that sense. And by using forward error correction instead of traditional negative feedback they have reached some incredibly good numbers regarding "traditional" amplifier measurements. That's one part of the coin. The other task was to listen to it. And to me it was not musical or engaging to listen to. But of course transparent, good dynamics and with high resolution. Papers I have read, own experiments with harmonic distortion and discussions have got me into an idea around distortion. If we add low order harmonics inline with our hearing harmonics we get a masking effect but we also, for us as humans, a natural way to increase harmonics from instruments and voices. Without affecting timbre (I think). This could maybe also explain improved holographic imaging. A least to how I think. |
I don't agree, it's impedance that is important for tube amps. From what I've experienced, tube amps don't like low impedance. Yes newer speakers typically have lower impedance than older ones, but tubes play well with 8 ohms or more. Are there speakers after 1965 that have 8 ohm or higher impedance, yes. |
Interesting. A few years ago I made a prototype mosfet amp with adjustable output impedance (or damping factor if you will). By using adjustable current feedback. Damping factor of 20 was preferred with my speakers. I tested with DF 30 down to negative output impedance. Just to see how the sound was affected by this. But it comes down to what the speaker was design together with. I also did a spice simulation model of my speakers to be able to simulate the behaviour with respect to source impedance. Used this for some simulations of a current amplifier together with the speaker simulation model. However, my experiments using the MOSFET (class A voltage gain and push-pull output stage and some global negative feedback) did not show a strong correlation with tube sound. There where some to changes in the base as the base driver gets a bit more freedom. But this was not a scientific analysis, and it was only tested on my setup. I could not increase the DF over 30 in the design. |
Both Cheever, Pass and several others agree on that to much negative feedback create high order harmonics that we are very sensitive to. Cheever also discuss aural masking and the effect by adding such distortion to the playback system. But does this masking effect also apply to to some extent to intermodulation distortion?Intermodulations do not get masked. I agree with Cheever and Pass on this- but only to a certain extent. If the feedback is creating higher ordered harmonics there simply isn't enough of it. That is why I say you need in excess of 35dB. With that amount the amp will have the ability to clean up the distortion created by the feedback itself. |
Thanks atmasphere for clarification about IM. I agree with you that either very much feedback to clean up high order distortions or less than perhaps 10dB or so. There are different types of feedback and I’m referring to traditional "loop" feedback. Degeneration is a bit different. But I think error correction is much better if that is possible in the design. What is your opinion about that? |
Tubes do add bloom
Tube amplifiers sound different than solid state but are much more particular with speakers than solid state so if you want the tube amp experience to be as good or better than solid state you need a pre 1965 speaker to play on it. Repo OMG really? Maybe the ones you owned or heard but not always true. |
Some months ago I listened on wonderful tube amp sound from Engstrom Arne (Swedish highend) as maybe one of my most memorable listening experiences with tube amps. The new Marten Parker speakers where used. But I still think you are right. Tube amps in general should work much better with speakers at my age... or older as speaker impedance can be very low these days. |
+1 bigkids I have heard at least three different model speakers on a Duelund cap upgraded PrimaLuna DiaLogue Premium HP (which incidentally was much higher resolving than stock), and they all sounded pretty remarkable to me. These were all new only a few years ago. There are some newer US made valve amplifiers I'd like to audition, when I'm ready to sell a limb or win lotto. @atmasphere - thanks for the write up, very informative. Particularly the later developments with class D amps. I have owned just one class D and I've heard a few in my time, just nothing that was really really good sounding. I'm not trying to pick a fight, I'm just saying that I haven't been introduced to a class D that sounded as good as many of the solid state A, AB and valve amplifiers I have been able to listen to over an extended period of time. I am open to discovery, and I am eager to discover things have gotten better with class D. Some of the best class D under $10k and under $5k that you have heard please? (I'm not likely to be in the market for a $25k amplifier, unless something drastically changes in my finances) |
