There are of course many legitimate reasons why someone might not be able to hear the difference between two amplifiers or between anything else, like say cables. Unfortunately most of those reasons are not very complimentary.
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What Ralph said https://benchmarkmedia.com/blogs/application_notes/power-amplifiers-the-importance-of-the-first-watt This explains why my amps are designed as Class A to 2/3 power. The switching distortion at high output is insignificant compared to everything else. However at very low levels switching distortion is audible (at least on test signals) - so it is preferable to be in Class A at low levels (of less than 1/10 of a watt) The article confirms to me that only carefully designed listening tests at very low levels will lead to audible differences between well designed high quality power amplifiers. Alternatively, stressful loads or extreme power requirements would audibly differentiate the amplifier with better performance. |
Damping factor of the Macs is said to be 12.@dentdog with that much feedback, none at all. OTOH, the fact that the amp runs feedback means it will *sound* a little brighter on top due to added trace amounts of higher ordered harmonic distortion. The emphasis is added on account of on the bench no change in frequency response would be seen. |
Notwithstanding my personally-held belief that high end stuff sounds better to me, I am willing to concede that some of the claimed superiority I (we) claim to hear in amplifiers or perhaps cables as well is due to the fact that the products we are attempting to A/B are not level matched to within a very tight tolerance. There are just too many people that seem to fail these comparison tests when the products are level matched to ignore the statistic totally. I think. |
nordicnorm @geoffkait Hmmm. Interesting. Perhaps there isn’t as much difference between violins? What do I know? I’m only a trumpet player. ;^) >>>>>>I actually think it doesn’t necessarily mean that at all. I think there may very well be significant differences between/among good violins that trained musicians cannot distinguish, or cannot distinguish in a test, in particular a controlled blind test. Some people don’t test well. 😀 My evidence: exhibit no. 1 is that some of the worst sounding audio systems I ever heard were those of musicians. Now, all you musicians out there, please don't send me a bunch of angry emails, I'm sure some of you can hear OK. 😀 nordicnorm That doesn’t mean that musicians are unable to tell the difference between other instruments (as in my Oscar Peterson example). >>>>>Actually, I suspect it might mean that musicians may not be able to tell differences between other instruments. It’s the process or perhaps the test subjects themselves that’s flawed somehow. Can trained musicians tell the difference between cables? Power cords? Fuses? Can you? |
@Nordicnorm Not sure what you're referring to when you say they were not live instruments. Here's a link to a discussion of the two Stradavarius tests. http://www.thestrad.com/blind-tested-soloists-unable-to-tell-stradivarius-violins-from-modern-instru... |
@geoffkait Yes, I did read the article. I don't understand your question though? Nowhere in it are they talking about differentiating between "live" instruments? Which was the basis of my post as I was responding to your statement: " Why couldn’t they pass the test? The same reason why a panel of experts cannot tell the difference between a Stradavarius and any other well made reasonably good sounding violin." I then provided a real life example disproving this statement. |
The complexity of the scenario is go great, that all you can do is try it and see if it works for you. It's not quite random, but it is so complex that these scenarios really are individual in nature. The paring can be measured and listened to but fully fleshed out ahead of time and then take that and compare it to how your personal discernment and learned aural function relates? Not so much. Generalizations like horseshoes and hand grenades (close is enough to get some sort of job done), is just about all that is predictable. |
Good thread. I appreciate this type of discussion because it provokes good technical insight as to speaker reaction due to various impedance variables and damping factors. I have ZU Definition IV speakers driven by Macintosh MC60 amps. The impedance curve on the Defs are lowest at 50Hz to around 225Hz, being around 6 Ohms at the lowest, with a prolonged rise through the mids and treble. Damping factor of the Macs is said to be 12. What, if any, difference in frequency response of my speakers should I hear due to the varying impedance curve? And just to throw something else out there, I recently purchased a quad of NOS TungSol 6550s that completely changed the bass characteristics of the speakers. The bass is softer but eminently more tuneful, with considerably more detail and nuance. |
In fact I would love it if I could make the output impedance of our amps lower. The problem I have with solid state is that many semiconductors have a non-linear aspect about them that causes them to have higher ordered harmonics (at low levels, but as I pointed out earlier, the ear is very sensitive to that sort of thing) and hard clipping. The only devices that I have found that don’t are the static induction transistors made by Sony. IMO They had a chance to really set the audio world forward, but in true Sony fashion (which is to come up with an innovation and then shoot themselves in the foot) failed to make a full complement of driver and voltage amplifier devices to go with their rather amazing output devices. Then when you add in high levels of feedback (there are various forms of feedback and I’m speaking in general terms), you end up with micro changes in transient values of the harmonic structure, all smeared out of time and out of level, shape, expression, and so on. This is sometimes...the new detail found in some recordings. People mistake this false data as real and write the given amplifier up as being revealing. Yet one good listen to the given amp by an aware person who has heard differently (and possibly understands what is going on), will drive said person from the given room with hands clamped on ears. The brain and aural learning, generally moves forward. It is the cognitive speed and lack of aural projection (parallel aural paths in forms of known neural discernment and learning)..which makes the difference in this question and answer pairing (in it’s evolution). Ie, the brain has a masking and pre-load issue that it uses to keep aural experiences from taking too long to discern -it pastes in learned data on new and current aural experiences. Learning to defeat that mechanism takes time and awareness. Or, for the intrepid audio explorer -"what has been heard, cannot be unheard". Complex crossovers with low impedance considerations..exacerbate said issues, and make the given high feedback amplifier even more illiterate with fine transient function - and increase false harmonic structure. Which drives those who hear it, even faster.... from the given room. This falseness is, more importantly -- covering up real detail and real harmonics. Using feedback in audio is tricky, at best. This is cognitive function like learning and intelligence. It takes time to learn to discern these things, aurally. Some people ’get it’ sooner, some people ----never do. |
@geoffkait wrote: " Is A Stradivarius Violin Easier To Hear? Science Says Nope" Maybe not to the average listener, but to a trained, professional violinist? Yes, absolutely! Many years ago I worked at the Banff Centre, which is where professional artists, musicians, & conductors go to hone their skills. Over the years, the Banff Centre has built up a sizeable collection of Steinway grand pianos (mainly through bequeathments). At last count (~2016), they had approx. 115 Steinways. Every Steinway had a name. Musicians and conductors would be in residency at the Centre for anywhere from 3 weeks to 4 months. Some would specifically request their favourite Steinway by name. In 2004 I asked one of the piano techs (who have a contract with the Smithsonian in Washington to repair their Steinways) if someone could actually hear the difference between the pianos. The tech told me that he did a blind sound test with Oscar Peterson in 1974. Oscar, who was the director of the new Jazz Program that summer, was being very picking in selecting a piano for the summer, so the tech arranged to have 20 pianos brought together onstage for Oscar to test. The tech blindfolded Oscar and then played each piano for him. Oscar was able to correctly identify all 20 pianos by name, blind-folded. |
Not in that sentence, surely! I don't think I jumped the gun; the statement is a common myth and I showed why in my post. You don't need a lot of current to 'control' a speaker, what you need is an output impedance that is sufficiently low, and you don't need 'current' to get that.Ralph you jumped the gun mate, read again, I never tied output impedance and current output together in the same sentence.Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.This is a common myth. Also to add, an amplifier "with low output impedance", but with not much "current ability" like otl's, have no chance driving a pair of Wilson Alexia's and like, which drop to an EPDR of .9ohm around 100hz (the power region) without serious problems. As an OTL manufacturer I might be recognized as having a bias, but here is the simple truth of the matter: The output section of an OTL has to do the same sorts of things that a solid state amp might do- and that is drive a speaker. It has to be able to make current to do that. Our amps don't have a particularly low output impedance owing to little or no feedback, but if they did, driving this particular speaker really isn't that hard. All of the Wilsons have been fairly easy loads for tube amps in general despite their impedance! We've had very good results with the Sophias, which are a similar load. I've heard that combo many times. I've not heard the Alexias yet. FWIW, the sales manager of Wilson had our amps for some years until an outside organization tried to take over Atma-Sphere about 13 years ago. At that point he sold them to be out of the possible politics. To give you an example of how much current is available in one of our amps, while tampering :) with a set of MA-1s many years ago I noticed that if the output section was deprived of bias, all by itself (IOW not including the filament circuit) it could blow a 15Amp fuse without damage to the power tubes! Certainly, with that sort of current, the power tubes would overheat fairly quickly, but for short (no pun intended) periods of time they can survive much larger amounts of current than one would expect. Our driver section has the ability to drive the output tube grids to about 15Volts positive with respect to the cathodes (which means there can be quite a lot of grid current; this is 15V more than the output section would have on the girds if deprived of bias!) and the output section can be linear in this region. IOW we operate the amplifier class A2. IOW, we have the current, but not the low output impedance. Weird, huh? The fact that the amp does not act as a voltage source is simply because to do so requires about 20 db of feedback. We've certainly built amps that way but never got them to sound as good. Proper application of feedback is a lot trickier than most engineers think! You can't just apply it according to the formulas and expect it to work, because the formulas don't cover everything. This article (be sure to read part 2 as well) does a good job of covering the problems and also proper application, which as far as I can tell is not executed by about 95% of **all** amps employing feedback: http://www.normankoren.com/Audio/FeedbackFidelity.html If the principles laid out in this article were applied in audio today, it would advance the art. So far, its been simpler for us to achieve our design goals by being pragmatic and recognizing that our amps won't drive all loads. But if we can get the amp and speaker to work together, the combination has the ability to cross the line between music and hifi. Roger said that though the OTL/QUAD combination was indeed considered by many to be a good synergistic match, he considered it to be the opposite---an OTL being the absolute worst amp design for use with that speaker.Roger and I don't agree on that one- we have a lot of customers with Quads. I've heard his RM9 (an excellent amplifier BTW) against our amps on ESL63s a lot as a friend used (may he rest in peace) to have them. |
I was told by out 80+ year old Sydney Quad speaker restorer Otto Major http://www.stereo.net.au/forums/uploads/monthly_12_2014/post-106213-0-29462600-1419899180.jpg who was good friends with Peter Walker, that yes original Quad 57’s were voiced with early Quad prototype tube amps and also maybe Williamson’s?, with not much current ability or wattage and high’ish output impedance’s (low damping factor) From what Otto told me the Quad 63’s was eventually released for sale in 1981 and were voiced around transistor amp/s of the time, and that the Quad 303 and later 405 amp was developed around it, much lower output impedance’s and higher damping factor and current drive than the tube amps were for the 57’s, I think they may have been Williamson’s. http://www.oestex.com/tubes/WW12-1943-BPT.jpg Cheers George |
It has long been considered common wisdom that OTL amps are great with the original QUAD ESL. When I had just gotten my first pair of the speaker, I asked Roger Modjeski at an instore seminar for his view on amps well-suited for the QUAD. He had worked on many Futterman amps, and in the 1980's designed his own OTL, which he ended up selling to Counterpoint. He also worked on the direct-drive tube amp used in the Beveridge ESL, fixing some problems he found in the amp when he went to work for Bev. Roger said that though the OTL/QUAD combination was indeed considered by many to be a good synergistic match, he considered it to be the opposite---an OTL being the absolute worst amp design for use with that speaker. The reasons included the matter of the impedance swings in the speaker, of course. Roger has designed and currently offers an ESL with a direct-drive (no speaker transformer) tube amp, which I am dying to hear. |
I was going to write some quibbles, but instead I will just point you to this article from Roger Sanders. While the amp he talks about has long been superseded, the problems about ESL's and phase angles and currents remains true. http://www.enjoythemusic.com/magazine/manufacture/0702/ Best, E |
Ralph you jumped the gun mate, read again, I never tied output impedance and current output together in the same sentence.Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.This is a common myth. Cheers George |
Wow, what a great post from Ralph/atmasphere. As always!+1. Also, while it doesn’t directly affect anything that was said in Ralph’s excellent post, to be precise I would just add that Ohm’s Law and the stated definition of power apply to resistive loads. And to the extent that a speaker’s impedance is partially capacitive or partially inductive at various frequencies the amount of current corresponding to a given power consumption by the speaker will differ somewhat from what Ohm’s Law would predict for a resistive load having the same impedance magnitude (i.e., the same number of ohms). In particular, impedance phase angles that are highly capacitive at some frequencies can increase current requirements to a significant degree, at those frequencies. But not by nearly as much as some manufacturer literature and some reviews might lead us to believe. Best regards, -- Al |
Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.This is a common myth. An amplifier can have a very low output impedance without having much 'current'. I put the word 'current' in quotes because Ohm's Law says without exception that the current flowing in the load is going to be directly related to the power being dissipated by the load, and that current will be the same regardless of the output impedance of the amp. Example: 2 amps, one solid state with an output impedance of 0.1 ohm, and the other with an output impedance of 4 ohms are both making 50 watts into an 8 ohm speaker. How much current is present? The Power formula is a derivation of Ohm's Law, and is current multiplied by voltage (1 watt = 1 Amp x 1 Volt). If you are dealing with an impedance, in this case 8 ohms, the derivation is Power = Amps(squared) x Resistance. So: 50 watts = 8Ohms x Amps squared. Solving for Amperage we get 2.5 Amps. Note that at no point does the output impedance of the amplifier figure into this- its not like an amp with a lower output impedance will somehow cause more current to flow. IOW the current is determined by the resistance of the load and how much power is being made. Now there is the issue of the amp 'controlling' the speaker. The speaker cone moves in relationship to the energy applied to its voice coil and returns to rest when that power is taken away. What we are concerned about here is the issue of overshoot; that is to say any motion that is not having to do with the signal applied. This is where the concept of damping comes in. If the speaker is in motion and further is motion that is entirely overshoot then what happens is it will make a voltage, since there is a voice coil moving in relation to a magnetic field (this is known as 'back EMF'). That voltage has to be absorbed, and that is done by the output impedance of the amplifier, which acts as a short to that voltage. From this you can see that the amount of current available in the amp really does not play a role in this damping effect. The output impedance however plays a huge role! So what we can conclude is that a low current amplifier that can make the power needed will do the job as long as its output impedance is low enough to provide proper damping of the load. FWIW, no speaker is known to need more than about 20:1 for optimal damping, and each speaker in a box (or not) has an optimal damping. For this reason back in the old days there were a number of amplifiers that had a variable damping control, which was a feedback control balancing current feedback and voltage feedback to allow the amp to have an adjustable output impedance over a wide range such that it could work with any speaker. In the last 4 decades though there has been a race to get more and more damping factor out of amplifiers, but the effect has been to cause most loudspeakers to be over-damped. We've all heard 'tight' bass that has thump but not much in the way of definition. Its a thing that a lot of audiophiles like but its not natural- 'tight' bass does not seem to exist in real life. When the speaker is overdamped, the cone cannot make its full excursion before the waveform starts going the other way. So bass notes in particular get truncated- the body of the bass is less prominent although the thump is there. By limiting the damping factor to no more than 20 or 30 to one this effect can be reduced or eliminated with most modern loudspeakers. |
Yes speakers manufactured back in the the old days that were "voiced" by manufacturers using tube amps with little to zero or very low damping factor amps should be used with the same with the same amps to get the frequency right as the manufacturer wanted you to hear. But I know of no speakers for the last four to five decades that are voiced using low damping factor amps, maybe some horns or single driver Lowthers or similar. For those that don’t know what amplifier output impedance or damping factor is Low damping factor is high output impedance EG: more than .5ohm High damping factor is low output impedance EG: Less than .5ohm EG: for an amp to have a damping factor of 8 into a theoretical flat 8ohm speaker, the amp would have an output impedance of 1ohm, If it had a damping factor of 16 the output impedance would be .5ohm If it had a damping factor of 20 " " " " " " " .4ohm If it had a damping factor of 100 " " " " " " " .08ohm and so on. Cheers George |
@georgehifi , that's correct! As I pointed out in the article, any time you mix equipment from the two technologies, the result is likely to have a tonal aberration. The example you give is a good one, although 'fry your ears' is likely not what would happen on account of the higher impedance would result in low distortion from the amplifier. It just would not make the bass energy since designer is expecting 3 db more power output out of the amp in the bass region. Another example is solid state driving an ESL- with the reduced impedance at high frequencies and the tendency for the load impedance to vary about 10:1 (IOW, if 10ohms at 50Hz, could be about 1 ohm at 20KHz) over its range, the result will also be too bright with not enough bass. The reason is that the impedance curve of the speaker is based on a capacitor and not a driver in a box, so the impedance curve is not also an efficiency curve. This is quite unlike a driver in a box, where the resonance of the driver is represented by a peak in the impedance curve (IOW the impedance and efficiency curves are the same thing). This is why the equipment matching conversation is still very much with us 5 decades on! Its also why of two amps on the bench that might measure perfectly flat to 100KHz, one might sound bright while the other does not. Its worth pointing out that if the designer of the speaker is expecting the amp to have a higher output impedance that the crossover will be designed differently as well. The fact that the source impedance of the amp can affect how the crossover works means that drivers might be operating outside of the area for which the designer intended! This is one of the reasons that horns got the reputation for being 'honky'. |
Ampilfers need to have a low output impedance preferably far less than < 1ohm, otherwise they start to act like a tone control instead of being flat. If an amplifier with high output impedance (>1ohm) were to drive these speakers there would be very little bass!! All you would get is upper-mids and highs that would fry your ears. http://www.stereophile.com/images/1213Walexfig01.jpg Cheers George |
What Al said, plus You know, it is a real shame that you take this tack, because I actually think you have a lot of fans, and built good products, but I've gotten really tired of you constantly hammering the superiority of high output impedance amps as a feature based on false and misleading (that's your own phrase) statements you repeat over and over again. What is it that you're saying here? That I build good products, but - ? they aren't real or something? I'm sensing a contradiction here. IMO you've been misreading what I've been writing. I have qualms about **feedback**, not output impedance, as long as the low output impedance does not come with added higher ordered harmonics. And I can back my qualms up easily enough without going into the weeds. If you are not familiar with Norman Crowhurst, he is a well-known authority in the field of amplifier design. His books are likely a bit rare but the important ones are a free download from Pete Millet's site: http://www.tubebooks.org/technical_books_online.htm In fact I would love it if I could make the output impedance of our amps lower. The problem I have with solid state is that many semiconductors have a non-linear aspect about them that causes them to have higher ordered harmonics (at low levels, but as I pointed out earlier, the ear is very sensitive to that sort of thing) and hard clipping. The only devices that I have found that don't are the static induction transistors made by Sony. IMO They had a chance to really set the audio world forward, but in true Sony fashion (which is to come up with an innovation and then shoot themselves in the foot) failed to make a full complement of driver and voltage amplifier devices to go with their rather amazing output devices. With such technology we could have had low distortion, zero feedback and low output impedance all at the same time! For the most part, what I'm really hammering on is the simple fact that you can't seem to get low distortion **and** low output impedance at the same time. Now I do this in the face of the fact that many solid state amps **appear** to have very low distortion, but what research in the last 40 years has shown is that the ear has distortion on a curve of sorts; the lower ordered harmonics being unimportant to the ear and the higher ordered harmonics are really really important. I freely acknowledge that this flies in the face of the test and measurement regime, which I feel is outdated by research of the last 40-50 years. Can you describe the sound of an amplifier by looking at its spec sheet? Most audiophiles can't; so why is there a spec sheet? The fact is most spec sheets are there to make the product look good on paper and have nothing to do with how the ear hears. That's a pretty good example of the Emperor's New Clothes... Now if one is to say that the specs are the final arbiter, great, no worries. Have at it. But I feel that the ear, not the specs, is why we buy audio equipment and that equipment will sound better if the gear follows the rules of human hearing. Did you mention what your speaker brand is? I missed that bit. |
Hi Al, There are flat impedance speakers out there, which is often accomplished with additional impedance normalizing circuits in the crossover. Certainly a niche. In these cases it is rightfully argued that the output impedance of amplifiers will have negligible effect on the frequency response. If this was Atma’s argument I would leave it alone. His repeated disinformation that the high output impedance is BETTER because it has constant power output regardless of impedance is nonsense. In no measurable case is it ever better. The measurements by SoundState and Stereophile are consistent. With "normal" speakers high impedance causes significant deviation from ideal. Of course, buy what you like. Best, E |
Erik_Squires 5-15-2017I’ll have to disagree with you on this, Erik. The ideal amplifier is a voltage source if the speaker it is used with is designed to sound its best when driven by a voltage source. As Ralph indicated, many speakers are not designed that way. While some others (such as the Daedalus Ulysses I use) don’t particularly care about amplifier output impedance or voltage source behavior, as their own impedance is very flat. And of course many people get great results with tube amplifiers such as SETs that have output impedances similar to the output impedances of Ralph’s designs (e.g., 2 to 4 ohms or so for most models). Also, as Ralph indicated the output impedances of his designs are not nearly high enough for them to be considered to be current sources. Finally, as I said earlier in the thread, "the bottom line with respect to the tube-friendliness or lack thereof of the ESL57 is perhaps indicated by the fact that it was designed before solid state amps existed." Although admittedly my understanding is that many of the tube amps of that era did incorporate significant amounts of feedback, which in the case of those amplifiers brought them somewhat closer to behaving as voltage sources than many high quality modern tube designs. Best regards, -- Al |
@atmasphere I am saying your entire argument is bunk, because the ideal audio amplifier is a voltage source, not a current source. In essence you are also arguing for amplifiers of TINY damping factor being ideal. Not supported by anyone but you. In fact, the amplifier I quoted, has a damping factor of around 0.8. That's about 400x worse than even a mediocre solid state amps. Complementing the amplifier design, speakers are measured by the output vs. frequency based on constant input voltage. For your theory to be at all accurate, speakers would have to have flat power efficiency (input vs. output) and ....they don't! The power efficiency of almost all multi-way speakers varies tremendously based on frequency. The LAST thing on earth you want is a constant current amplifier, unless you want your output to look like your impedance curve. If you are right, then man, 10 Ohms is too low. You should make amps with 30 or 50 ohms at the output, you would get even more ideal current sources! << hahahahah >> You know, it is a real shame that you take this tack, because I actually think you have a lot of fans, and built good products, but I've gotten really tired of you constantly hammering the superiority of high output impedance amps as a feature based on false and misleading (that's your own phrase) statements you repeat over and over again. Best, E |
If this had any basis in reality, at all, speaker testing would be based on power vs. frequency. It isn’t. It is input voltage vs. frequency. Hmm. So you’re saying that a solid state amp can make as much power into a 30 ohm load as it can an 8 ohm load? And that with an ESL, the impedance curve is also a graph of its efficiency? I think we both know that neither is the case. SoundStage Magazine online has a review for the Atma-Sphere MA-1 Mk II.2 mono-blocks: The conclusion here is false; starting with ’with an excellent...’. The reason is that the MA-1 is a zero feedback device and is not a ’typical’ tube amp! If it had enough feedback (about 20db), it would behave as a voltage source and the test as shown would have measured flat. Also, this does not debunk the idea that a solid state amp will have troubles driving higher impedances. IOW, this is typical behavior of a **zero feedback** tube amp and not that of one employing feedback. So one has to ask why we would make an amplifier that has no feedback with resulting (apparent) FR errors, and the answer is that feedback adds higher ordered harmonic content that is easily detected by the human ear. We get low distortion without feedback (assuming that the test equipment does not ground one of the speaker terminals which can result in a bogus test) so then we are simply looking to find a speaker with which the amp will have flat response. Dr. Herbert Melcher, a neuro-scientist, has shown that the brain has a variety of tipping points. One of them appears to be that the ear/brain system will favor distortions interpreted as tonality over actual FR errors. So our approach is that if we can minimize the tonalities generated by the amp due to distortions, it can often appear to be more neutral than amps that measure much flatter on a given speaker on the bench.
We don’t try to give this impression! Erik (@erik_squires what is the brand of speaker you make?) is correct otherwise; most speakers are Voltage Paradigm devices. But not **all**; some are based on the prior Power Paradigm, as are zero feedback tube amplifiers (see link at the end of this post). If you’ve ever seen an older speaker with midrange and tweeter level controls, the reason they are there is not to adjust the speaker to the room but instead to match to the voltage response of the amplifier. These controls are not seen on Voltage Paradigm loudspeakers. Long ago we discovered that our amps sounded much better without feedback (smoother, more detailed, wider and deeper soundstage). It took a while to find out why! In the meantime though, we have always been very careful to ascertain which speakers would be a good match. This is important (at least to us), because this is the dividing line between what makes for a good hifi as opposed to what sounds like real music. That we are still around 40 years later suggests that there are good number of speakers that work with our amps. This is not to say that a Voltage Paradigm speaker can’t sound like real music; it is saying that if that speaker won’t have flat response without an amplifier employing a lot of feedback, then that speaker will never sound like real music on account of the amp. The **reason** is that loop negative feedback ignores a fundamental law of human hearing which is how we detect sound pressure. Rather than detecting the volume of a fundamental tone, our brains sort out sound pressure by detecting the strength of higher ordered harmonics associated with that sound (which are increased if feedback is employed, although in ’trace’ amounts, but our ears are literally tuned to detect those traces). If the harmonics are louder than they should be, then the fundamental(s) will be interpreted to be louder too. That would not be such a bad thing but the extra harmonics are also interpreted as brightness and hardness by the ear /brain system and that is why they impart the sound of a hifi instead of real music. BTW, this is easy to prove using simple test equipment. So we abandoned feedback and as a result the Voltage Paradigm as it has that fundamental flaw (although otherwise works great) and went back to the Power Paradigm (which was what was around prior). We’re not the only ones; SETs, horns, ESLs and a number of other speakers (which are admittedly limited to high end audio) are also built around Power Paradigm principles; we’re not the first or only ones that have sorted out that loop feedback isn’t perfect (see the writings of Norman Crowhurst; these problems have been known for over 50 years). The Soundstage test assumes that all amps are based on the Voltage Paradigm and the simple fact is they are not. If your amp’s impedance is high enough, it will become an ideal "current source" where the output current has nothing to do with the load, and therefore the voltage at the speaker will vary wildly with the speker’s impedance. Atma-sphere has a unique perspective on this issue, and seems to constantly be suggesting a current source is ideal. He stands very much alone in this area.This statement is mostly false. Why: We don’t hold this viewpoint, and Also a current source amp will have an output that in fact varies according to the load, but in an inverse way. Nelson Pass has built some amps based on this principle, but he never made any such amp for production, and I’m not aware of anyone who has. Current Source amps IOW never developed any sort of following. Put another way, if the impedance of the amp is low, it is likely to act as a voltage source. If the output impedance is medium (a few ohms, like SETs and our amps) then the amp will act as a Power source (constant power into all impedances rather than constant voltage). If the output impedance of the amp is very high, multiples of the speaker impedance, then it will be a current source. That being said, the question of sound quality and amp/speaker matching is purely subjective, and you should listen for yourself. I’m pretty sure my favorite tube amps of all time, the CJ Premiere 8s were quite high in output impedance, but I’m not going to try to sell new physics to convince anyone to buy them.Listening of course is what this is all about :) The cj has a fairly low output impedance owing to the loop feedback employed and behaves as a voltage source. It has a classic tube sound as you might encounter with any excellent hifi. For more on the Voltage and Power Paradigms see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php |
Theory is too difficult to do in these forums, especially without graphs, but let’s talk some real world effects. SoundStage Magazine online has a review for the Atma-Sphere MA-1 Mk II.2 mono-blocks: http://www.soundstage.com/revequip/atmasphere_ma1ii2.htm with an excellent set of measurements which to illustrate what the output impedance problem is with typical tube amps and how much it is. The very first graph shows how the amp interacts with the complicated impedance of real world speakers. See the green line? That is what the electrical output looks like when driving a simulated speaker load. The frequency response can vary around +-3 dB (a bad thing) when driving an NHT: http://www.soundstage.com/measurements/atmasphere_ma1_mkii2/ I think this is quite typical behavior for tube amps. Most solid state speakers would be quite flat, debunking the idea that solid state amps have a harder time, ever. Despite the impression Atma tries to give, almost all speakers are designed as voltage-dependent devices. I know, I make them. :) That is, the prime quality we seek is to have a smooth and controlled frequency response for a given input VOLTAGE, not power. The power is going to vary up and down based on the crossover, drivers and even cabinet. We like to assume the amps driving our speakers is what is called an "ideal voltage source." where current (and power) output will vary based on the speaker, but the output voltage is purely a function of the input signal. This gets harder to do with high output impedance amps, or low impedance speakers. If your amp’s impedance is high enough, it will become an ideal "current source" where the output current has nothing to do with the load, and therefore the voltage at the speaker will vary wildly with the speker’s impedance. Atma-sphere has a unique perspective on this issue, and seems to constantly be suggesting a current source is ideal. He stands very much alone in this area. That being said, the question of sound quality and amp/speaker matching is purely subjective, and you should listen for yourself. I'm pretty sure my favorite tube amps of all time, the CJ Premiere 8s were quite high in output impedance, but I'm not going to try to sell new physics to convince anyone to buy them. Best, E |
I suspect that what Shadorne calls ’difficult’ (and for that matter the author at the link Erik provided) is the simple fact that solid state amps (even ones known for driving difficult loads) can’t make as much power into the relatively high impedance that the Quad presents at low frequencies. oh sure. Uh huh. If this had any basis in reality, at all, speaker testing would be based on power vs. frequency. It isn't. It is input voltage vs. frequency. Best, E |
yage With respect to the talk on old and new violins, I’m surprised no one has mentioned these two studies: Is A Stradivarius Violin Easier To Hear? Science Says Nope Double-Blind Violin Test: Can You Pick The Strad? >>>>Actually, your humble scribe mentioned those inconclusive "scientific" tests by trained professionals with Stradivarius vs X brand 4 days ago on this very thread. Hel-loo! |
With respect to the talk on old and new violins, I'm surprised no one has mentioned these two studies: Is A Stradivarius Violin Easier To Hear? Science Says Nope Double-Blind Violin Test: Can You Pick The Strad? |
I cannot totally Agree, I have been running pure class A Pass Labs And most certainly better then the majority of Class An amps Even my brothers Pass 250.8 is far superior yhen most evrn st low volumes We compared a bunch of Audiophile friends gear over 6 months. The average AB amp could not compete in resolution . One big reason is the very High bias in class A for almost the first 20 watts Which is a lot with a 90db dpeaker.. The Valvet mono blocks are around 100 wpc Into 4 ohms pure class A and incredibly detailed at Low volume . Vitus, is another HIGH POWER great sounding amp even met low late night Low level, as well as Gryphon Diablo ?this and the Vitus,integrated are the 2 best Integrated amps I have ever heard at all levels and passed the acid test . I owned a Aufio store until 06 in Europe the new models are even Better. If you are willing to spend these are exceptions to the rule. |
Old news - Peter Aczel was saying this in the 80's. Not worth talking about IMO. I've owned $25k amp/preamp combos and liked them and I've also used a $200 Onkyo reciever while an amp was being repaired and I liked that too. Personally, I think the more expensive high-end stuff sounded better and that's what I choose to own and listen to and I couldn't give two shites about what someone else thinks. And respectfully, either should you . |
The Quads have issues. First of all they need to be on stands, I had the Arcici stands. Secondly, they need to have their metal grills removed. The grills suffocate the speakers. The Mylar dust covers should also be removed. If you’re nervous about dust in the room get an air purifier or two. Finally, the Quads benefit from better power cords. All of these actions result in tremendous dynamics and bass performance. |
They need about 15 Watts of the best amplificationThe above quote is taken from the link Erik provided. I've serviced the 15-watt tube amps that Quad made to go with the '57s; in a nutshell driving a 'difficult load' is something they can't/don't do. But they drive the Quads just fine. When 15 watts is all that's needed, its not a hard load and no mistake :) As Erik points out, the impedance curve is very typical of an ESL. I suspect that what Shadorne calls 'difficult' (and for that matter the author at the link Erik provided) is the simple fact that solid state amps (even ones known for driving difficult loads) can't make as much power into the relatively high impedance that the Quad presents at low frequencies. So you might need a 60-watt solid state amp to make the sound pressure on the Quad that a 15-watt tube amp can. But it will still play it, and if one puts one's hand on the heatsinks of said solid state amp, it will be found that the heatsinks won't get all that warm, despite hours of operation (unless the amp is class A)! IOW, the solid state amp isn't working that hard. Why? Its not a difficult load; the amp is never asked to make anywhere near the power of which its capable. The 'difficulty' might be that the Quad will easily reveal the shortcomings of any amp which is asked to play it; so to get the best out of this speaker, you need a good amp. But that amp does not need a lot of current capability, which is traditionally associated with driving 'difficult' loads. We have lots of customers with Quads and they usually use our smaller amps. Folks, 'small OTL' and 'the ability to drive difficult loads' are two concepts not normally found together :) The simple fact is, this speaker can be driven by a variety of amps (including SETs) that are not known for being able to drive 'difficult' loads. I would not use an SET in this case simply because I don't know of 15-watt SETs that can make the bandwidth that the Quads can, but if you have one, it will work fine. This is an excellent example of how not all amps are the solution for all speakers! |
And as I mentioned, some speakers are deliberately hard to drive in the bass, or use smaller-dual woofers which put a strain on amplifiers. When I look at the impedance curves and read about reviewers talking about how "discerning" this speaker is, how easily it could tell the difference between a Boulder XYZ amp and their Onkyo receiver, well, duh. It was made that way.Yes, I am very much in agreement, Erik. As I and some others (including Shadorne) have said in other threads here, the musical resolution of a component or system, and its ability to resolve differences between components, cables, or tweaks, are two different things. And generally speaking the correlation between the two, while certainly not zero, will be a loose one. My perception has been that many audiophiles fail to recognize that point, as evidenced by how quick some are to allege lack of resolution (referring to musical resolution) as being the reason others may not hear differences when performing comparisons between various hardware. Regards, -- Al |
So this brings me full circle. I've seen speakers that are hard to drive at the top end, at the bottom and all across the spectrum. The ESL speakers come by their low impedance and difficulties as do the full-range planar-magnetics (Apogee) via legitimate reasons. That is, the speaker technology itself poses challenges which the designers accept in exchange for other benefits. ESL's are essentially giant capacitors, no way to get around that. The sacrifice is made to submit the amplifiers to brutal loads in exchange for having a large single driver driven across it's surface (how well ESL's actually do this is arguable, but not for here). I think that with the worst of these panels, a lot of OK amps are going to perform quite a bit differently, which with "nice" speakers could perform nearly identically. And as I mentioned, some speakers are deliberately hard to drive in the bass, or use smaller-dual woofers which put a strain on amplifiers. When I look at the impedance curves and read about reviewers talking about how "discerning" this speaker is, how easily it could tell the difference between a Boulder XYZ amp and their Onkyo receiver, well, duh. It was made that way. But this discernment does not make either the amplifier or the speaker more musical. It's just more demanding. Best, E |
