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In Reply to: RE: 3B SST... posted by morricab on April 04, 2014 at 05:19:18
Listen to 12 antique tubes in one mono block ? I am not crazy I have excellent central heating.
Edits: 04/04/14Follow Ups:
Antique does not equal obsolete. That simple really. Besides, KR Audio, Ayon and Emission Labs have all designed new tubes in the last 15 years.
TRIODES versus BIPOLARS from a friend of mine
It all depends on how one interprets "facts" for example a pretty standard bipolar stage with a current mirror load and a constant current source at relatively low cost will produces vanishingly small levels of distortion, whilst producing much of the required gain in an amplifier.. The sort of values in distortion terms are typically 0.00001% at I kHz and 0.0006% at 50kHz this sort of circuitry with a CCS, the VAS stage will and can produce a total distortion of better than 0.0015% in what is called a blameless amplifier at full power of 50 watts and 30+ kHz. Quote Douglas Self , there is no valve amplifier out there that can get anywhere near these values and for a very good reason. The triode suffers one distortion which is rarely measured or noted , that of an early effect , which basically is this, that when the grid goes positive the anode current increases and in doing so reduces voltage on the anode due to the voltage drop across the anode load , this drop will cause the signal during + half cycles to have a significantly different amplitude to the - half cycles , effect of this is that if you take a high Mu triode used to get the gain required and introduce current negative feedback by not decoupling the cathode resistor the lowest distortion you wil get is about 0.2% or worse. CCS's have been tried with Triodes but the early effect still remains.
You may already know that the second grid was introduced to make the valve less dependant on this effect but because of the screen grid alone caused a kink in the curves , they introduced the suppressor grid to even it out again, the new valve the pentode has unremarkable distortion characteristics... in summary it is unfair to try to make comparisons with such devices because they are so totally different in the way in which they can be used , one other factor that must be considered is that a thermionic valve will be swinging across its transfer characteristics significantly higher voltages than a transistor, effectively stretching its distortion range because you are using more of its curve area , a transistor is concerned with just a few volts and so a much smaller area is being used.
There is no doubt at all many valve designers have today pushed the limits of circuit design to produce some overall sweet sounding amps which many people prefer , Tim de Paravicini for instance who also has OTL designs and has used mosfet O/Ps to simplify the heat & current requirements , but in any event many people are not after distortionless amplification , rather they want a sound that does not fatigue after long term listening and in which the very nature of valves presenting even order harmonics is perhaps better suited to those requirements which will also be commensurate with the speakers thay are using, meaning that many speakers have a very bright presentation and usually reflexed so that a tight bass from the valve amp will largely go unnoticed anyway and the easier top will be more acceptable to those modern speaker designs which I frankly find irritating on any amplifier.
regards etc. Humble
Edits: 04/05/14
"It all depends on how one interprets "facts" for example a pretty standard bipolar stage with a current mirror load and a constant current source at relatively low cost will produces vanishingly small levels of distortion, whilst producing much of the required gain in an amplifier.. The sort of values in distortion terms are typically 0.00001% at I kHz and 0.0006% at 50kHz this sort of circuitry with a CCS, the VAS stage will and can produce a total distortion of better than 0.0015% in what is called a blameless amplifier at full power of 50 watts and 30+ kHz. Quote Douglas Self , there is no valve amplifier out there that can get anywhere near these values and for a very good reason"
First: Show me ONE amplifier out there with numbers that good other than Halcro, which if you ever heard them you would know why the numbers don't mean anything when massive feedback is used.
Second: Those numbers are not achieveable without negative feedback... a lot of negative feedback. It is also a fact that negative feedback does not cure the ills of a Class AB amp's residual crossover distortion.
Third: When are you going to learn that it has become clear after the last 50 years of "blameless" amplification that psychoacoutically transparent and Oscilloscope transparent are NOT the same thing.
Quote from Geddes paper I:
"To be useful the metric must be consistent and reliable the same number must mean the same thing in every context and there must be a close correlation between the metric and the response that it is intended to scale."
"This is precisely where the signal-based distortion metrics fail. In our next paper we will show that .01% THD of one type of nonlinear system can be perceived as unacceptable while 10% THD in another
example is perceived as inaudible. Even one of these simple examples is sufficient to invalidate THD as a viable metric for discussion of the perception of distortion. Furthermore, 1% THD is not at all the
same as 1% IM, but we will show that neither correlates with subjective perception. While some of the signal-based metrics may be better than others, it is our opinion they all fall short of what we are seeking."
"If we take these facts and join them up with our Perception Principles then we can make the following statements, which are, perhaps, not exact, but they are, none the less, more valid than not.
The masking effect of the human ear will tend to make higher order nonlinearities more audible than lower order ones.
Nonlinear by-products that increase with level can be completely masked if the order of the nonlinearity is low.
Nonlinearities that occur at low signal levels will be more audible than those that occur at higher signal levels.
Again these may seem intuitively obvious."
"If the amplifier has crossover distortion then this type of nonlinearity violates both of our principles it is both very high order and it increases (as a proportion of the linear terms) with decreasing signal level. Based on our hypothesis, one would expect that this type of distortion would be highly objectionable and it is."
Quote from Geddes Paper II:
"Of primary interest in the present study was the correlation between the mean subjective ratings and the various metrics. Table 5 provides the Pearson product-moment correlation coefficients between the
mean ratings across subjects of the twenty-one stimuli, and each of the three metrics. A negative weak relationship was observed with the THD (r = -0.42, p=0.06) and the IMD (r=-0.35, p=0.13) metrics. These results suggested negligible predictive values when utilizing THD and IMD metric in this context."
"These results supported the skepticism that THD and IMD metrics were poor predictor of subjective perception of sound quality ratings."
http://www.gedlee.com/downloads/Distortion_AES_I.pdf
http://www.gedlee.com/downloads/Distortion_AES_II.pdf
Based on their studies, they found that there was a slightly NEGATIVE correlation with THD and IMD and sound quality!!!
That is because of how modern amps make distortion and that the negative feedback trick doesn't make it much more listenable.
CHeever also made the same observations and he said that THD once upon a time was a pretty good indicator of quality when amps were all SET and none used negative feedback. Once they went to PP, AB and lots of feedback then THD and IMD no longer correlate with sound quality.
You can take your numbers all you want, I listen to music not numbers and I can tell you that the WORST sounding amps I have ever heard were all the best measuring ones. Your engineer friend and also Doug Self are just delusional and brainwashed by 50 years of engineering "best practice" that had nothing to do with sound quality.
OK Have it your way to say 10% THD is inaudible ? However I would agree that at the end of the day it is all about how it sounds and I would not waste my time again listening to any valve or Class D amplifier. I have auditioned the Devialet Class AD at Home gets highest SQ rating from Paul Miller HFN & RR best Class D to date but I still prefer my old Class AB amplifier, had the Devialet been better I would have bought it despite only being interested in the power amp section.
Edits: 04/07/14
I don't say that 10% is inaudible but 1 or 2% of mostly 2nd harmonic is almost certainly inaudible. How can you say that for you it is only about the sound when you are wantonly ignoring the psychoacoustics of sound and catergorically dismissing whole technologies...one of which clearly more closely matches psychoacoustic ideals of what kind of distortion an amp should make...seeing as it is impossible to have a zero distortion amp. I don't offhand dismiss any technology based on my "feelings" of the technology (your comments about tubes being antique for example), I base it on my current understanding of psychoacoustics and the types of distortions made by each technology. This along with lots of listening tells my Class AB ANYTHING (transistor, tube or hybrid) isn't the way to sonic nirvana. Class D is also not the solution because of the noise and distortion pattern it generates. The signature is obvious even if somewhat more subdued with the Devialet.
As I said, I haven't used a pure tube amp for several years. I find that the current SOTA without spending a king's ransom comes from hybrids running Class A or a VERY simple transistor design like the First Watt SIT amps. For pure tubes, either you need OTL or VERY expensive output iron and then you get there.
There was a review of the KR Audio Kronzilla monos in a German magazine many years ago (that version is now about 2 generations behind). The measurements showed about 3% THD at around the rated power (droping like a stone with lower power I might add) but nearly all of it (over 2%) was 2nd harmonic some 3rd, a bit of 4th a tiny 5th and not much else above -120db.
It follows Cheever's Aural harmonics nearly perfectly and as a result SOUNDS nearly perfect. I had a generation newer at home as a reviewer and it made other highly regarded amps (like the ASR Emitter II Exclusive) sound broken by comparison...it was not subtle. Another German magazine had the older version monos as their highest rated amp for 10 years!!! (2002-2012) and it is still in the top 3. It was FAR ahead of the competition and still among the very best. It is a hybrid. My current NAT is also a hybrid.
Speaking of the Devilet, I too had it at home and it did not compare favorably against the amp I had at the time, The Einstein "The Absolute Tune", which was one of my least favorite amps that I have owned in the last 10 years (still it is quite good just not compared to what I owned before it and not what I own now). The Einstein was notably more musical and just as resolving. The Devialet failed to move me to think higher of Class D. I have also heard the Devialet 110 in a friend's home...he now has an all Audio Note system with the Devialet long gone.
What is your current Class AB amp that you find so realistic sounding? The ONLY one I have heard that truly competes at the highest level is the now defunct Edge NL series amps. They were GOOD. BAT VK amps are pretty good too but a bit darkish sounding to me that reduces their realism. BATs tube amps are better.
Amps I have heard from Accuphase, Soulution (current darling), MBL, Krell and others have failed to move me at all (either AB or A offerings). Who in your mind is making the best amps out there?
Morricab: Triodes versus Bipolar from Humble
You may be interested to learn young man that between Disbeliever and myself there amounts to over 100 years of listening to both valve & transistor amplifiers , we do not essentially disagree with you about sound quality and can concur that many amplifiers that measured well were largely overrated. However you appear to be widening the goalposts, originally stating that triodes had less distortion than bipolar transistors being a blanket statement without any circuit references, so I had to challenge you. You then go on to rubbish any form of feedback as if it were the bane of any design concept in the audio domain.So firstly allow me to clarify a few points, it is true that taken as as an individual device transistors do have more intrinsic distortion than say a high mu triode but the point I have re-iterated is that a solitary transistor is rarely used in isolation as a straight amplifying device in a high quality amplifier, so the point about distortion becomes irrelevant , simply put, a circuit topography is used because the way in which transistors work allows it to be used to cancel out the very distortion that nonlinearities produce, but in such a way that it essentially still remains within the domain of a single device, meaning no phase anomalies an increase in speed thus widening the bandwidth and significant reduction in all distortions, yes it is essentially within the realms of current negative feedback, but the electrical reaction within the topography is without detriment , it,s now a symbiotic unity. The simplest of which is the longtailed differential pair to the more complex Current mirror load and constant current source, the same CCS is often used to feed the next stage the VAS to improve its linearity.
Now it is also true that with this type of topography very high intrinsic gains are achieved and further distortion from the output devices and drivers are also reduced by negative feedback, however many articles have been written about the proper use of feedback and all those other artifacts of SID, TID etc. which includes nested feedback to reduce phase anomalies , but you can not rule out the fact that many very good amplifiers have been designed with both high & low amounts of feedback, and some like Onkyo with no Global feedback which still produce relatively low amounts of distortion because the circuits are an amalgam of topographies used to reduce the additive stage distortion and if I remember correctly the Onkyo produced around 0.02% that Company believing as you do that an amp with limited distortion sounded better but in fact did,nt.
Referring to Geddes and Lee have you considered what happens when when say an audio amplifier of the transistor variety uses differing devices throughout the amplifying stages , for instance a J.Fet front end with it,s slope character followed by a standard B.polar VAS stage then followed by by say Mosfets, here you have three different slopes all adding their own particular distortions , feed all these back into the early stage and you have a disparity of control which results in both odd and even harmonics but more importantly some of the harmonic intervals are not amplitude consistant meaning some harmonics in the higher reaches have a larger than those proceeding, perhaps this is one reason why feedback can have rather unpleasant sounds with some designs , but is not generally known as a casual link,.. but in the end preferences will always be the deciding factor, however for proof of the proverbial pudding just take a well respected modern amplifier of each variety , in the case of the transitor version remove the input filter if it has one , then feed it with a square wave set at the same level as a valve version , then monitor the output into a dummy load , I think you will be very suprised at the result, because all the other factors of the amps will come into play which include the reaction by capacitors in the signal path and the interelectrode capacitance of the triodes CGK+(A+1)CAG, this then becomes a measure of accuracy not necessarily distortion, because it is measuring the filtering effect of both types of amplifier .
I have already conceded that there are many amplifiers of the valve variety out there which sound very sweet, so essentially we are not in any conflict whatever, I simply believe that a properly designed Transistor amplifier will give very satisfactory and pleasing results and can be blameless, I have had many debates with well regarded audio engineers , consultants and other speaker designers. Everyone has a preference for their particular beliefs and experiences , but they would all tell you that sound quality is of paramount importance but more often than not are convinced that their way is the only way forward and so sometimes get caught up in a negative feedback loop. ha ha.
Humble
Edits: 04/09/14 04/09/14 04/09/14 04/09/14
No need for the condescension. Maybe you guys have learned something during all your years of "experience" but based Disbelievers amps of choice I am inclined not to think so. Experience is not a substitute for talent.
As for the linearity of devices there is no debate, triodes are more linear than bipolar transistors by a long way. So are FETs for that matter...at least running Class A. Adding more non-linear devices in a circuit doesn't make the circuit more linear, it makes it less so. This is only logical and it can also be shown easily if you build any kind of circuit with them and don't wrap it up in negative feedback...fact is that if you go with multiple stages you MUST use some negative feedback and often it won't be stable without it. At least with a FET or SIT you can take one, run it Class A and it will be stable, sound very good and measure ok to a few watts. With a tube amp you need probably at least two stages but the whole thing will run without feedback and still measure ok and sound really good as long as you used good parts.
Making an amp with multiple stages (this is also true for FETS or tubes) only makes it less linear and then NECESSITATING the use of local and/or global feedback just to control the way too high gain and stability issues.
"essentially within the realms of current negative feedback" Heard amps with this topography like Accuphase and well YAWN, they didn't sound very good despite the glowing press...They sound gray and dead.
"believing as you do that an amp with limited distortion sounded better" Their problem is the same as others, the use of the wrong design gives a poor sound not the absolute amount of distortion. The design dictates what the form of that distortion will be and it is that pattern that is important. Find the design parameters that deliver the right pattern and you get good sound...stray into ultra low distortion techniques and you pay in sound quality. It is not as you think that it is because the distortion is low it is because of what was done to the signal to get it low that is the problem.
"Referring to Geddes and Lee have you considered what happens when when say an audio amplifier of the transistor variety uses differing devices throughout the amplifying stages , for instance a J.Fet front end with it,s slope character followed by a standard B.polar VAS stage then followed by by say Mosfets, here you have three different slopes all adding their own particular distortions , feed all these back into the early stage and you have a disparity of control which results in both odd and even harmonics but more importantly some of the harmonic intervals are not amplitude consistant meaning some harmonics in the higher reaches have a larger than those proceeding, perhaps this is one reason why feedback can have rather unpleasant sounds with some designs"
Once you have multiple stages and complex topologies in each stage AND feed all that back to the input I don't think it matters anymore what the elements are. Especially if one of the stages is Class B. Like I said, a tube push/pull amp in Class AB that is not triode and uses negative feedback will suffer many of the same problems because a non-triode tube is also highly non-linear, feedback exacerbates the problem AND it is likely to have transformer saturation issues unless the output iron is very good. I don't cut them any more slack than most transistor designs.
I have found that one thing that works very well is a hybrid design with two stages only, running Class A or very high bias AB (so like Class A 10 or more watts). With a FET output this can be run without any feedback and will sound very good with low absolute and low order distortion primarily. Make this single ended and it will sound even better but the amp will have to be physically huge.
Of course the pure tube variant and reverse hybrids (like KR Audio) can also sound phenomenal.
"I simply believe that a properly designed Transistor amplifier will give very satisfactory and pleasing results and can be blameless,"
And I would simply argue that no such animal exists or has ever existed, nor will exist until a truly linear amplification device is invented. Until that device is invented then I will stay with the psychoacoustically correct path for sound reproduction.
I also don't really care too much what engineers think on these matters...they are usually designing by what they learned is proper circuit design and to price points for the market. The majority of them are not scientists and don't know how to make the proper observations about what their products are doing. I am a scientist, which makes me a professional observer, which means i hear things in their products that they don't or wish not to hear. I may or may not know how to design various cool and tricky circuits but I know how to tell when one is doing the right thing and one is not. THen I bother to find out what was used and how it was implemented and wait to see other similar examples and how they sound. One can build a mental library of what sounds consistently good and what doesn't and start to draw conclusions about various "innovations" in circuits. I have done so and came up with some guidelines for a good sounding amp. I would share them with you but I doubt you would take them seriously. I have posted them before so feel free to search under my name and you might find my ideas.
"in the case of the transitor version remove the input filter if it has one , then feed it with a square wave set at the same level as a valve version , then monitor the output into a dummy load , I think you will be very suprised at the result"
Why on earth would you remove the input filter? That's silly. All systems have finite bandwidth and dynamic range and I think that one of the biggest failures of home audio gear is NOT limiting the input to what the device can swallow. Many audio people think the world stops at 20Kc. and removing input filters just punishes those that know better.
But... I am very much in favor of evaluating systems by using square waves, I'm just not in favor of modifying them first.
Rick
From HUMBLE
Input filters were originally used amongst other things to prevent the main amplifier from suffering SID especially , when the pre-amp was much faster. Bearing in mind that many earlier amplifiers had relatively slow Bi-polar output devices which meant that as the frequencies increased less feedback was available and distortion crept up sometimes significantly, modern out put devices like Sankens and some Toshiba audio devices are extremely fast with an FT up to 40mhz making the amplifier much faster and thereby keeping the distortion lower at much higher frequencies. BY removing the input filter and some amplifiers don,t have them ,enables you to see what the amplifier is capable of without the inhibiting effect of that filter which often comes into effect depending on the designers criterion of frequencies as low as 150kHz, taking the filter out of the Hafler 200 series enables a beautiful square wave to be reproduced above 10kHz, with the filter in the square wave was much more rounded as you would expect.. There is a strong correlation between the speed of transistors and point of roll-off in the treble particularly prevalent with slow output devices a factor that feedback does not totally compensate for, of course Mosfets enable a much faster performance and often noted for a detailed treble especially with supertweeters. When the JL Linsley-Hood 75 watt amplifier was first produced it had 2 t 3 mhz FT O/P devices, later these were substituted with BDY56 10 MHZ devices and immediately the distortion dropped by almost a decade and that amplifier had 78 db of NFB, it also sounded faster and easier on the ear.
Humble
Good Post!
I have no problem with injecting test signals after an input filter, or any place else for that matter to evaluate a system's response. I also believe that using square-waves and a scope are far more likely to get you to the root cause of audible problems than peering in the frequency domain with a spectrum analyzer, especially an FFT one that doesn't go very far out-of-band.
All "properly designed" systems need to make a reasonable attempt to not accept signals that they can't handle. I think the best case is to have enough bandwidth margin to allow a simple RC LPF as the dominant pole and still be high enough to not mange the treble.
Regards, Rick
I have no idea who is making the best amps out there. My own 18 year old close coupled design ( similar to Hafler )Class AB stereo amplifier Prime Design A100 has the following specification:
Transistors two 17 amp. 40 mHz per side. High grade 500 Va toroidal transformer, 80,000 mfd capacitance, damping factor at 40Hz in excess of 200, THD 0.005% has had a few upgrades and still sounds excellent.
.005% THD, at which frequency? I bet at higher frequencies it is significantly worse (above say 1Khz)...that would be typical for a high feedback design (the only way to get THD that low).
However, it is irrelevant because as I have said and the research shows there is even a slightly NEGATIVE correlation between THD/IMD and sound quality...That is what Geddes found and Cheever as well and many others before them...at least since the dawn of PP circuits and negative feedback.
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