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#1
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
Some time ago the now defunct stereo review had an interesting article
on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve |
#2
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
Steve writes:
Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? I can't answer your question, but in my opinion, output impedance is one of the most important distinguishing features. The lower the amp's output impedance is over frequency, the better, although this (as anything) can be taken to extremes. Unfortunately, I don't believe many manufacturers publish their output impedance, especially over frequency. -- % Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven. %% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and %%% 919-577-9882 % Verdi's always creepin' from her room." %%%% % "Rockaria", *A New World Record*, ELO http://www.digitalsignallabs.com |
#3
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
Steve wrote:
Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Amplifiers do not all sound the same. Some may. Some do not. They certainly do not measure the same. The THD or IM specs do *not* tell the story. Those who are still doubters, may review Dr. Earl Geddes research on this subject. It provides the necessary scientific and engineering basis for the above assertion. There are a few other 'confounding" factors to account for when an individual is trying to decide these things: - there may be masking effects from other parts of the system (for example a perfectly blameless amp could not be discriminated from one that was not blameless, if there was sufficient "objectionable" harmonic signature produced by another element in the system). - the listener may or may not have physical deficits that prevent such a discrimination. - the listener may never have heard a system without many of the typical "objectionable" artifacts (no basis for comparison). - there may be other factors, including subsonic sound and ultrasonic sounds in the environment, excessive reverberation, etc. that interfere. As far as "A/B" or "ABX" tests, they are usually valid for the specific test condition, as made. Suitability of those tests for generalized application, if they lack controls for at minimum the above factors, and some others (such as basic THD, IM, polar response, room reverberence, noise floor, etc...) makes the ones that I have seen published so far - that is a preponderance of those I am aware of - not meaningful. Others will disagree, I am sure. The key to assembling a system that one enjoys listening to depends on one's thresholds for certain types of "irritants" (and avoiding them), a bit of luck, serendipity, and in some cases knowledge of matters technical and acoustic. Money, per se, does not play the major role in this respect, since there is lots of excellent used gear, and the possibility of DIY... :_) _-_-bear |
#4
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
In article ,
Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Steve, This is two of the topics most likely to generate a lot of heat--amps sounding different and blind a-b tests. Before it gets too wild let me put my two cents (Australian) in. Of course different amplifiers sound different. Since they are made differently, with different components, and they measure differently, how could it be otherwise? Whether the differences are significant is a matter of personal decision. You make your decision and plonk down your money. Some will argue that well-made amps that measure the same will sound the same. This is necessarily true--it is a tautology--assuming that we measure everything that can be heard. Blind a-b testing is the gold standard of testing for difference. It does however have to be done well and usually isn't. Some of the subtle differences in music reproduction are very difficult to pick, and often require extensive experience or training to distinguish. As well, some differences show up after long trials (days, weeks, or months!) and testing of this longitude are as rare as hen's teeth. Our auditory memory is very short, and often very inaccurate, and that is an argument NOT for short duration tests, but for using something that is longer lasting and more reliable, namely the emotional response to the music. I know from my own experience swapping interconnect cables that while I couldn't pick which cable was in my system at any one listening session, over months I came to prefer one set--based on my desire to put on another record and listen more, or turn the music off and do something else. These preferences were a surprise to me and I performed enough swaps to make certain. If you can, audition each amplifier on your list for long enough to know whether you enjoy the way it produces music. After all, you will be using it to produce music, not listen to sound. Greg |
#5
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
On Dec 24, 11:32 am, Steve wrote:
Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve The reprint is a nice summary of the eternal battle between magic and engineering. Inexpensive but well-engineered amplifiers have performance specifications that are very similar to (or perhaps even better than) than very expensive audiophile amplifiers and under double blind testing will be essentially indistinguishable. The really weak link in sound reproduction is with respect to loudspeakers. Money is best spent on good speakers rather than exotic amplifiers. Similar disputes also continue with D/A converters, cables, preamplifiers, etc. in which measurements indicate little or no improvement with high-priced hardware. |
#6
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
Steve wrote:
Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. Maybe you should talk to more people. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). If levels are matched on all channels, and the system isn't being driven to distortion, your result is not unusual. Has any more work been done on this subject, esp. blind a/b tests? http://www.provide.net/~djcarlst/abx_pwr.htm see also E . Brad Meyer Stereo Review 1991 Are your speakers turning your amplifier into a tone control? http://www.soundandvisionmag.com/fea...interface.html ___ -S "As human beings, we understand the world through simile, analogy, metaphor, narrative and, sometimes, claymation." - B. Mason |
#7
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
Greg Wormald wrote:
Of course different amplifiers sound different. Since they are made differently, with different components, and they measure differently, how could it be otherwise? Whether the differences are significant is a matter of personal decision. You make your decision and plonk down your money. THe logical fallacy here is that 'measuring different', or using 'different components' must lead to audible difference. It doesn't. Some will argue that well-made amps that measure the same will sound the same. This is necessarily true--it is a tautology--assuming that we measure everything that can be heard. Blind a-b testing is the gold standard of testing for difference. It does however have to be done well and usually isn't. Some of the subtle differences in music reproduction are very difficult to pick, and often require extensive experience or training to distinguish. As well, some differences show up after long trials (days, weeks, or months!) and testing of this longitude are as rare as hen's teeth. So, where are the careful blind test results done by 'amps sound different' believers? WHo is doing the assuming here? Let us take the case of John Atkinson, editor of Stereophile. By his own account , his Damascene conversion to 'subjectivistm' came after he chose the 'lesser' of two amps, after he failed to hear a difference between them in a DBT. After a few weeks of living with it he was dissatisfied, and upon swapping in the other amp, found it sounded much better. His conclusion was the blind testing misled him, while living with the gear -- a 'long trial -- revealed the truth. But he didn't bother to do what wold be obvious to a scientist -- re-take the blind test *after* the 'acclimation period'. Surely the effect of long expsire doesn't 'go away' under blind conditions, right? Btw, Tom Noisaine has done 'long term' trials, and the results were negative when levels were matched and amps were driven below their limits. Our auditory memory is very short, and often very inaccurate, and that is an argument NOT for short duration tests, but for using something that is longer lasting and more reliable, namely the emotional response to the music. You have managed to actually reverse the implication of short aural memory. It points to using short sound samples during a trial, to gain best dscrimination of difference. However, if acclimation is thought to be necessary for best discrimination, I ask again -- where are the blind test results from people who make such claims? I know from my own experience swapping interconnect cables that while I couldn't pick which cable was in my system at any one listening session, over months I came to prefer one set--based on my desire to put on another record and listen more, or turn the music off and do something else. These preferences were a surprise to me and I performed enough swaps to make certain. And then you did a blind test, after you were sure you could hear the diference...right? THe fact is, your typical audiophile or high-end magainze reviewer is SURE they hear a difference, often without any long-term trial. So, are they folling themselves, or likely to be right? If you can, audition each amplifier on your list for long enough to know whether you enjoy the way it produces music. After all, you will be using it to produce music, not listen to sound. And again, it's as easy to 'fool' yourself -- perhpas easier, given possible emotional investment -- after a long trial, as short one, *if* the comparison is sighted. ___ -S "As human beings, we understand the world through simile, analogy, metaphor, narrative and, sometimes, claymation." - B. Mason |
#8
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
bear wrote:
Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Amplifiers do not all sound the same. Some may. Some do not. They certainly do not measure the same. The THD or IM specs do *not* tell the story. Those who are still doubters, may review Dr. Earl Geddes research on this subject. It provides the necessary scientific and engineering basis for the above assertion. Hopefully it provides the blind test results to demonstrate audible difference. There are a few other 'confounding" factors to account for when an individual is trying to decide these things: - there may be masking effects from other parts of the system (for example a perfectly blameless amp could not be discriminated from one that was not blameless, if there was sufficient "objectionable" harmonic signature produced by another element in the system). - the listener may or may not have physical deficits that prevent such a discrimination. - the listener may never have heard a system without many of the typical "objectionable" artifacts (no basis for comparison). - there may be other factors, including subsonic sound and ultrasonic sounds in the environment, excessive reverberation, etc. that interfere. or, the two amps really do not sound different, when used within their limits. As far as "A/B" or "ABX" tests, they are usually valid for the specific test condition, as made. Suitability of those tests for generalized application, if they lack controls for at minimum the above factors, and some others (such as basic THD, IM, polar response, room reverberence, noise floor, etc...) makes the ones that I have seen published so far - that is a preponderance of those I am aware of - not meaningful. Double Blind tests have been and continue to be used by Harman for generalized application in loudspeaker development. And amplifier (and cable, btw -- mentioned because you sell 'high end' cable that you claim sounds better than plain cable) difference tests have been done where the listener who claimd to hear difference between *his* gear and others, was tested with his gear, against other gear. And failed the test. Others will disagree, I am sure. The key to assembling a system that one enjoys listening to depends on one's thresholds for certain types of "irritants" (and avoiding them), a bit of luck, serendipity, and in some cases knowledge of matters technical and acoustic. Money, per se, does not play the major role in this respect, since there is lots of excellent used gear, and the possibility of DIY... :_) Have you ever ABX'd differences in amps, and if so, under what conditions, and what scores did yuou obtain? ___ -S "As human beings, we understand the world through simile, analogy, metaphor, narrative and, sometimes, claymation." - B. Mason |
#9
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
From Earl Geddes' online book chapters, concerning objective measures and
blind tests http://www.gedlee.com/downloads/Chapter4.pdf "If one accepts the fact that subjective evaluations are less reliable than we would like, then it should be obvious how objective measurements would play a crucial role in audio. Whatever one might say about measurements, for the most part they are stable and yield the same results over and over. something that subjective assessments have trouble doing. I used to believe that objective measurements alone were all that one needed, and I still believe that objective measurements can tell us most of what we need to know about a system or component. I believe that I could predict the judgement of a panel of blind listeners with an accuracy of about 90-95% correct from objective data alone. I know one company that claims a 99.9% accuracy in correlation between objective data and panel judgements. Objective data should always be the place where one starts when looking for system components. That is, if one knows how to interpret the measurements that are available or the data that they are shown. I find that most people shy away from objective data simply because they don.t really understand it. As far as believing that objective data is all that we need, at the moment, that probably isn.t the case. There are things that we are learning day-to-day that have a strong bearing on the correlation between measurements and subjective preference. But that.s also not to say that we can.t ever get to the point where objective data alone is sufficient. In fact this point may be closer than you think. What I do find ridiculous is the position of many that because measurements don.t tell us the complete story that they are of no use at all, that listening alone is the only way to truth - that 'Measurements can.t tell us what we hear'.. I personally love that one." In other words, Geddes finds the mainstream 'audiophile' view of evaluation, where 'sighted listening trumps all' , to be *ridiculous*. Me too. ___ -S "As human beings, we understand the world through simile, analogy, metaphor, narrative and, sometimes, claymation." - B. Mason |
#10
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
On Tue, 25 Dec 2007 08:39:58 -0800, Randy Yates wrote
(in article ): Steve writes: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? I can't answer your question, but in my opinion, output impedance is one of the most important distinguishing features. The lower the amp's output impedance is over frequency, the better, although this (as anything) can be taken to extremes. Unfortunately, I don't believe many manufacturers publish their output impedance, especially over frequency. Output impedance is one of many criteria. Mostly, it affects damping factor for the loudspeakers. The way I understand it is If a dynamic speaker is looking down it's cable into the output stage of an amplifier and sees, what is in essence, a dead short, the cone will stop instantly when the signal stops, because of the back EMF being generated by the shorted voice coil in the speaker's magnetic field (try this experiment: Get a raw driver and flex the cone by hand at the dust cap. Then connect the terminals of the speaker together with a jumper and flex the cone again. Notice how much more difficult the cone is to move this time. That's the phenomenon behind regenerative dampening) But even this is an oversimplification. In reality, most speaker voice coils are looking into an inductor in the crossover and the resistance of the speaker cable before it sees the output stage, so its anybody's guess how much a low output impedance actually affects the overall result. Frankly, I think that the sound of an amplifier is more a result of the complex load presented by the speaker system that it's driving than the speaker's sound is influenced by the amplifier. |
#11
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
On Tue, 25 Dec 2007 08:44:45 -0800, bear wrote
(in article ) : Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Amplifiers do not all sound the same. Some may. Some do not. They certainly do not measure the same. That is true. The THD or IM specs do *not* tell the story. That is correct. Up to a certain point, both seem to be relatively unimportant. Research has shown that humans aren't very sensitive to the harmonic and IM distortion produced by amplifying devices. Back in the "golden era" of tube hi-fi, manufacturers would outdo themselves trying to get the most zeros between the decimal point and the numbers. This made them bias their tubes far into the linear portion of the tube's transfer curve. This lowered distortion all right, but it made the tubes run very hot and self-destruct with alarming rapidity. After it was found in double-blind tests that levels up to over 1% in amplifiers were undetectable by humans, manufacturers started backing off on output bias. over the last thirty years or so, we have seen the life of output tubes increase dramatically from a mere few hours to many thousands of hours over a number of years. Of course, the tradeoff is that harmonic and IM levels have gone from 0.001% to 0.1% or even higher. Nobody notices. |
#12
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Do all amplifiers sound the same?
On Tue, 25 Dec 2007 08:47:44 -0800, Greg Wormald wrote
(in article ) : In article , Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Steve, This is two of the topics most likely to generate a lot of heat--amps sounding different and blind a-b tests. Before it gets too wild let me put my two cents (Australian) in. Of course different amplifiers sound different. Since they are made differently, with different components, and they measure differently, how could it be otherwise? Whether the differences are significant is a matter of personal decision. You make your decision and plonk down your money. Some will argue that well-made amps that measure the same will sound the same. This is necessarily true--it is a tautology--assuming that we measure everything that can be heard. Isn't that the "rub" as Shakespeare would say? Blind a-b testing is the gold standard of testing for difference. It does however have to be done well and usually isn't. Some of the subtle differences in music reproduction are very difficult to pick, and often require extensive experience or training to distinguish. As well, some differences show up after long trials (days, weeks, or months!) and testing of this longitude are as rare as hen's teeth. Our auditory memory is very short, and often very inaccurate, and that is an argument NOT for short duration tests, but for using something that is longer lasting and more reliable, namely the emotional response to the music. Exactly. People talk about "calibrating their ears" by listening to as much live music as possible. Human auditory memory is so short, that it has been found that just a couple of hours after a concert, the listener has already reverted to his personal "taste" in sound, I.E. what type of bass he likes, how much presence in the midrange, what kind of highs ring his bell, etc. It has also been suggested that the female of the species has a far better auditory memory than the male.... |
#13
Posted to rec.audio.high-end
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Do all amplifiers sound the same?
On Tue, 25 Dec 2007 08:48:47 -0800, jwvm wrote
(in article ) : On Dec 24, 11:32 am, Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve The reprint is a nice summary of the eternal battle between magic and engineering. Inexpensive but well-engineered amplifiers have performance specifications that are very similar to (or perhaps even better than) than very expensive audiophile amplifiers and under double blind testing will be essentially indistinguishable. The really weak link in sound reproduction is with respect to loudspeakers. Money is best spent on good speakers rather than exotic amplifiers. Agreed. Many component manufacturers are, I believe, aware that there is little difference above a certain engineering level and seek to distinguish their brand (and justify its price) by using every "expensive" looking cosmetics. Thick, brushed aluminum front panels, chromed transformer end-bells, fancy receptacles and jacks, etc. Similar disputes also continue with D/A converters, cables, preamplifiers, etc. in which measurements indicate little or no improvement with high-priced hardware. Now it's not true that everything sound alike and an outboard D/A converter might very well sound better than the D/A that comes in a stand-alone CD player because the D/A in the player is fraught with design compromises that the outboard D/A may not be. |
#14
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Do all amplifiers sound the same?
"Greg Wormald" wrote in message
om Of course different amplifiers sound different. Since they are made differently, with different components, and they measure differently, how could it be otherwise? Two amplifiers can be different, but sound the same, if their deficiencies are smaller than that which can be reliably heard. This happens all the time. Whether the differences are significant is a matter of personal decision. Not if the differences are too small to be audible. You have no choice - they have no audible signficance to you. Some will argue that well-made amps that measure the same will sound the same. The myth here is that two amps could measure the same. Even each channel of a stereo amplifier will measure differently, given sufficiently accurate measuring gear. This is necessarily true--it is a tautology--assuming that we measure everything that can be heard. Reality is that we can readily measure things that we have not a chance of hearing. There have been no reliably observable exceptions for decades. Blind a-b testing is the gold standard of testing for difference. It does however have to be done well and usually isn't. Compare that to sighted evaluation with is never done well, because there is no way to do it well. Some of the subtle differences in music reproduction are very difficult to pick, and often require extensive experience or training to distinguish. Interesting that people don't seem to need any extensive training or experience to hear differences in sighted evaluations. As well, some differences show up after long trials (days, weeks, or months!) and testing of this longitude are as rare as hen's teeth. The point is that people obsess over the problems with blind tests, and the inherently flawed results of sighted evaluations with nary a concern. Our auditory memory is very short, and often very inaccurate, and that is an argument NOT for short duration tests, ????????????????? but for using something that is longer lasting and more reliable, namely the emotional response to the music. That's an unproven assertion. I know from my own experience swapping interconnect cables that while I couldn't pick which cable was in my system at any one listening session, over months I came to prefer one set--based on my desire to put on another record and listen more, or turn the music off and do something else. These preferences were a surprise to me and I performed enough swaps to make certain. Yet another unproven assertion. If you can, audition each amplifier on your list for long enough to know whether you enjoy the way it produces music. After all, you will be using it to produce music, not listen to sound. If one is not listening to sound, what is one listening to? |
#15
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Do all amplifiers sound the same?
On Dec 26, 12:01 pm, Sonnova wrote:
snip Similar disputes also continue with D/A converters, cables, preamplifiers, etc. in which measurements indicate little or no improvement with high-priced hardware. Now it's not true that everything sound alike and an outboard D/A converter might very well sound better than the D/A that comes in a stand-alone CD player because the D/A in the player is fraught with design compromises that the outboard D/A may not be. Are you saying that D/A converters that provide essentially the same measurements will still sound different and can be differentiated in double-blind tests? |
#16
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Do all amplifiers sound the same?
On Dec 25, 11:47 am, Greg Wormald wrote:
Our auditory memory is very short, and often very inaccurate, and that is an argument NOT for short duration tests, but for using something that is longer lasting and more reliable, namely the emotional response to the music. Sorry, but this is complete nonsense. Before the data passes into long-term memory, it MUST pass through short-term memory. If you assertion is that short-term auditory memory is defective in some way, than long-term memory cannot be better. And, in fact, contrary to the fantasies and wishes of any number of audiophiles, this property of auditory memory is supported by quite a bit of actual research. |
#17
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Do all amplifiers sound the same?
Sonnova writes:
On Tue, 25 Dec 2007 08:39:58 -0800, Randy Yates wrote (in article ): Steve writes: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? I can't answer your question, but in my opinion, output impedance is one of the most important distinguishing features. The lower the amp's output impedance is over frequency, the better, although this (as anything) can be taken to extremes. Unfortunately, I don't believe many manufacturers publish their output impedance, especially over frequency. Output impedance is one of many criteria. That's why I said it's one of the most important distinguishing features and not "it's the only distinguishing feature." Mostly, it affects damping factor for the loudspeakers. I think damping factor was an attempt at simplifying output impedance, so this is a little circular. The way I understand it is If a dynamic speaker is looking down it's cable into the output stage of an amplifier and sees, what is in essence, a dead short, the cone will stop instantly when the signal stops, because of the back EMF being generated by the shorted voice coil in the speaker's magnetic field I have heard of this effect and admit I do not fully understand the dynamics between back-EMF and output impedance. However, it seems that such effects are secondary. What seems even more important is that the correct output voltage is applied to the speaker. A zero output impedance makes an amplifier an ideal voltage source, i.e., the correct output voltage will be maintained up to the limits of the current-sourcing ability of the amplifier. -- % Randy Yates % "She tells me that she likes me very much, %% Fuquay-Varina, NC % but when I try to touch, she makes it %%% 919-577-9882 % all too clear." %%%% % 'Yours Truly, 2095', *Time*, ELO http://www.digitalsignallabs.com |
#18
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Do all amplifiers sound the same?
On Dec 26, 11:58 am, Sonnova wrote:
On Tue, 25 Dec 2007 08:44:45 -0800, bear wrote (in article ) : Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Amplifiers do not all sound the same. Some may. Some do not. They certainly do not measure the same. That is true. The THD or IM specs do *not* tell the story. That is correct. Up to a certain point, both seem to be relatively unimportant. Research has shown that humans aren't very sensitive to the harmonic and IM distortion produced by amplifying devices. Back in the "golden era" of tube hi-fi, manufacturers would outdo themselves trying to get the most zeros between the decimal point and the numbers. This made them bias their tubes far into the linear portion of the tube's transfer curve. This lowered distortion all right, but it made the tubes run very hot and self-destruct with alarming rapidity. After it was found in double-blind tests that levels up to over 1% in amplifiers were undetectable by humans, manufacturers started backing off on output bias. over the last thirty years or so, we have seen the life of output tubes increase dramatically from a mere few hours to many thousands of hours over a number of years. Of course, the tradeoff is that harmonic and IM levels have gone from 0.001% to 0.1% or even higher. Nobody notices. Part of the reason could be coming from the other end: the source has gotten much cleaner. Before it was vinyl and cassette recordings with distortion levels magnitudes higher than with digital lossless files we play today. On a slightly different note, I found one way to easily distinguish a lossy audio file from its lossless counterpart: distortion. The Lossless file will play much louder and cleaner than the lossy file on the same system. CD |
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Do all amplifiers sound the same?
Steve wrote:
Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Some amplifiers sound different, some don't, depending on what they are connected to. Don't get hung up about others opinions and blind tests, there is no definitive answer. Select a few well regarded units to audition and make up your own mind. With those speakers, the differences between amps will be subtle compared to a speaker upgrade. I used to own Epos ES11, worked well with Audiolab 8000A, but I can't recommend NAIM. -- S i g n a l @ l i n e o n e . n e t |
#20
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Do all amplifiers sound the same?
"Steve" wrote in message
om... Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? What was your recent "audition"? These things have to be done carefully, with the exact same system (I assume it was) but also well volume matched (use a test tone and multimeter to check the voltage output from the amp.) Also, you'll want to use material that you're very familiar with. Ultimately the overall resolving power of the entire system (the system includes the room acoustics) will determine if you can tell a difference (as well as if there is any discernible difference between the amps, of course.) Sometime of course you can tell a slight difference, but is one really better than the other, or just slightly different? Is the difference worth paying for? I was able to tell the difference between an Adcom 545 and 555 (voltage matched of course) every time. Both were operating well below max capacity. That was enough to convince me there are differences between amps (I don't even think the company intended there to be any difference here.) |
#21
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Do all amplifiers sound the same?
"Arny Krueger" wrote in message
... Some will argue that well-made amps that measure the same will sound the same. The myth here is that two amps could measure the same. Even each channel of a stereo amplifier will measure differently, given sufficiently accurate measuring gear. I don't believe the measuring tests are really that accurate. If you doubt this, consider: voice recognition is extremely difficult for even the most sophsticated equipment, yet trivially easy for even children. The same is true for image recognition. Measurements might be good enough for the cell phone generation, but that ain't sayin' much. Theoretically, if it can't be measured it can't be heard. But just because it can be measured doesn't mean it is being measured. |
#22
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Do all amplifiers sound the same?
wrote in message
... On Dec 25, 11:47 am, Greg Wormald wrote: Our auditory memory is very short, and often very inaccurate, and that is an argument NOT for short duration tests, but for using something that is longer lasting and more reliable, namely the emotional response to the music. Sorry, but this is complete nonsense. Before the data passes into long-term memory, it MUST pass through short-term memory. If you assertion is that short-term auditory memory is defective in some way, than long-term memory cannot be better. Well, short term memory is defective in some way. These things are very simple and have been known forever. For example, drive to work and when you get there you can't remember anything about your trip. The point is not that long term memory is "better", the point is that we take a lot of things for granted when saying that a short term test (of anything really) is going to be reliable. Lots of people get buyer's remorse, or after a time start appreciating new aspects of a product. Another simple example: look at a picture but just don't see what's there. Then one day you realize it's a picture of Jesus. It could take a minute it could take a year. But once you see it, you can't not see it. This isn't rocket science, or voodoo, or snake oil marketing. These are well known phenomenon. Having said that, when an advertiser claims "dramatic, obvious, jaw dropping, my-non-audiophile-wife-could-tell-immediately-from-across-the-street differences, and you are straining to hear any difference at all, be it long or short term, then something is obviously not as claimed. |
#23
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Do all amplifiers sound the same?
"Steven Sullivan" wrote in message
... . I used to believe that objective measurements alone were all that one needed, and I still believe that objective measurements can tell us most of what we need to know about a system or component. Well, try looking objectively at a chess board at the beginning of a game and determine who will win - black or white. Objective computers measurements can't figure out that one either. There is a lot in this world that isn't known or understood, trust me. |
#24
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Do all amplifiers sound the same?
On Dec 26, 11:57 am, Sonnova wrote:
Output impedance is one of many criteria. Mostly, it affects damping factor for the loudspeakers. Mostly, it does not at all. The way I understand it is If a dynamic speaker is looking down it's cable into the output stage of an amplifier and sees, what is in essence, a dead short, the cone will stop instantly when the signal stops, because of the back EMF being generated by the shorted voice coil in the speaker's magnetic field (try this experiment: Get a raw driver and flex the cone by hand at the dust cap. Then connect the terminals of the speaker together with a jumper and flex the cone again. Notice how much more difficult the cone is to move this time. Unless you're moving the cone VERY fast, you're not going to see any difference. Now, try the experiment REALISTICALLY: Try doing it and trying to sense the difference between a 0.4 ohm resistor across the terminals vs a 0.1 ohm resistor across the terminals. That's the phenomenon behind regenerative dampening) There is no "regenerative damping." It's just damping. But even this is an oversimplification. Yes, it is an oversimplification to the point of being wrong. In reality, most speaker voice coils are looking into an inductor in the crossover and the resistance of the speaker cable before it sees the output stage, And, in oversimplifying, you neglected the fact that the single LARGEST resistance is ALWAYS there, and that's the DC resistance of the voice coil. The inductor might add a fraction of an ohm, same with the leads, but the DC resistance of a typical niminal 8 ohm driver is in the realm of 6-7.5 ohms, and THAT resistance completely dominates all others, including the amplifier's output resistance, and it is the voice coil resistance that essentially determines the damping of the system. so its anybody's guess how much a low output impedance actually affects the overall result. Actually, it's not guesswork at all. The series resistance the voice coil dominates, and unless the other series resistances are pathologically large and the so-called damping factor is larger than 10-20, the amplifier's output resistance will have NO appreciable effect on the damping of the system. Frankly, I think that the sound of an amplifier is more a result of the complex load presented by the speaker system that it's driving than the speaker's sound is influenced by the amplifier. That may be the case, but, again, it's something that can be determined. If we have an amplifier whose damping factor is "low" by contemporary standards, say, 20 at 8 ohms, and we connect it to a speaker whose impedance varies from 6 to 30 ohms. The result is that the voltage at the speaker terminals varies by 0.44 db between the minimum and maximum impedance. Now, get yourself an amplifier with an alledged damping factor of, oh. 200. The resulting error is now on the order of 0.05 dB. Do you think that you can hear the difference resulting from a smooth change in broadband frequency response of about 0.4 dB in a room with dynamically changing music? |
#25
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Do all amplifiers sound the same?
On Thu, 27 Dec 2007 08:47:53 -0800, codifus wrote
(in article ): On Dec 26, 11:58 am, Sonnova wrote: On Tue, 25 Dec 2007 08:44:45 -0800, bear wrote (in article ) : Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? Steve Amplifiers do not all sound the same. Some may. Some do not. They certainly do not measure the same. That is true. The THD or IM specs do *not* tell the story. That is correct. Up to a certain point, both seem to be relatively unimportant. Research has shown that humans aren't very sensitive to the harmonic and IM distortion produced by amplifying devices. Back in the "golden era" of tube hi-fi, manufacturers would outdo themselves trying to get the most zeros between the decimal point and the numbers. This made them bias their tubes far into the linear portion of the tube's transfer curve. This lowered distortion all right, but it made the tubes run very hot and self-destruct with alarming rapidity. After it was found in double-blind tests that levels up to over 1% in amplifiers were undetectable by humans, manufacturers started backing off on output bias. over the last thirty years or so, we have seen the life of output tubes increase dramatically from a mere few hours to many thousands of hours over a number of years. Of course, the tradeoff is that harmonic and IM levels have gone from 0.001% to 0.1% or even higher. Nobody notices. Part of the reason could be coming from the other end: the source has gotten much cleaner. Before it was vinyl and cassette recordings with distortion levels magnitudes higher than with digital lossless files we play today. That could be true, but "source" distortions tend to sound very different from amplifier distortion. For instance, I would never mistake an over modulated audio tape for amplifier distortion. They do not sound the same. On a slightly different note, I found one way to easily distinguish a lossy audio file from its lossless counterpart: distortion. The Lossless file will play much louder and cleaner than the lossy file on the same system. That is very true. A friend recently gave me an 340k MP3 of the end title cut for the movie soundtrack "The Mummy Returns". When I got it home, I was disappointed at how distorted it sounded. I then borrowed the CD from him and did my own "rip" using Apple Lossless. The end result was as clean as the CD. I still maintain that compression artifacts are clearly audible and very nasty sounding, but others keep telling me that it's my imagination. These same people also tell me that all amplifiers sound the same and that redbook CD is perfect and indistinguishable from SACD or 96 KHz/24-bit DVD-A. One thing is sure, though. Either I'm deluding myself or they can't hear and I'm betting on the latter. :- |
#26
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Do all amplifiers sound the same?
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#27
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Do all amplifiers sound the same?
On Thu, 27 Dec 2007 08:34:49 -0800, jwvm wrote
(in article ): On Dec 26, 12:01 pm, Sonnova wrote: snip Similar disputes also continue with D/A converters, cables, preamplifiers, etc. in which measurements indicate little or no improvement with high-priced hardware. Now it's not true that everything sound alike and an outboard D/A converter might very well sound better than the D/A that comes in a stand-alone CD player because the D/A in the player is fraught with design compromises that the outboard D/A may not be. Are you saying that D/A converters that provide essentially the same measurements will still sound different and can be differentiated in double-blind tests? I don't see anything in my quoted post above about the D/A converters in question measuring the same, but my stand-alone converter definitely sounds better than the one in my pro Otari DAT recorder or the one in my TASCAM CDR-7000P CD burner/player. |
#28
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Do all amplifiers sound the same?
jeffc wrote:
: "Arny Krueger" wrote in message : ... : : Some will argue that well-made amps that measure the same : will sound the same. : : The myth here is that two amps could measure the same. Even each channel : of : a stereo amplifier will measure differently, given sufficiently accurate : measuring gear. : I don't believe the measuring tests are really that accurate. If you doubt : this, consider: voice recognition is extremely difficult for even the most : sophsticated equipment, yet trivially easy for even children. Very bad analogy. Voice recognition requires hearing the same person speaking on two occasions, and matching them -- i.e. it's Uncle Jimmy on the phone, the same guy that called on Thanksgiving. The equipment he's calling on (if you're hearing a phone call -- the other factors obtain if he's right in front of you), how much mucous he has in his vocal tract, how loud he's speaking, and a lot of other factors make his voice objectively different on each speaking occasion. These differences can be measured. The problem of this sort of recognition is thus: taking two *acoustically different* signals and somehow extracting the components that are unique identifiers of the source system. In audio equipmnt land, this would be like doing the following: taking an amplifier, and on two different occasions hooking it up to very different components (speakers, wires, rooms), fiddling with the volume, and maybe changing the voltage running through it, maybe corroding some of the connectors, turn one speaker so it's facing the wall, and put th other one in the kitchen, and so on, and still being able to identify the specific amp out of all the amps you've ever heard. A more correct parallel in voice recognition to the equipment issue in this thread would be: take two copies of one recording of Uncle Jimmy's voice, measure them, and make sure they're identical on all measures. Then label one file JIMMY1, the other JIMMY2. Play them. Do they sound different to you? And can you tell them apart when you're not looking at the file name on the computer screen? -- Andy Barss |
#30
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Do all amplifiers sound the same?
writes:
Actually, it's not guesswork at all. The series resistance the voice coil dominates, and unless the other series resistances are pathologically large and the so-called damping factor is larger than 10-20, the amplifier's output resistance will have NO appreciable effect on the damping of the system. You're speaking in static, DC terms. What about dynamically? For example, when the voice-coil is traveling and the back-emf is opposing the amplifier's output voltage? Yes, there is still the DC resistance of the coil in series, but the amplifier is working harder than under DC conditions. -- % Randy Yates % "I met someone who looks alot like you, %% Fuquay-Varina, NC % she does the things you do, %%% 919-577-9882 % but she is an IBM." %%%% % 'Yours Truly, 2095', *Time*, ELO http://www.digitalsignallabs.com |
#31
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Do all amplifiers sound the same?
Steve wrote:
Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf interesting ref, although 3.76MB is a bit much fwiw, the tubes vs solid state "squabble" went well beyond the '60's and in fact likely continues to this day in my own not too distant past, tubes still sounded better; bleeding problem is their lack of practicality, not to mention that they now cost so much more than in the 60's After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? believe nothing that you read trust your ears i can add that imho solid state has come a very very long way forward in the last 20/25 years. bill |
#32
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Do all amplifiers sound the same?
jeffc wrote:
"Steven Sullivan" wrote in message ... . I used to believe that objective measurements alone were all that one needed, and I still believe that objective measurements can tell us most of what we need to know about a system or component. Well, try looking objectively at a chess board at the beginning of a game and determine who will win - black or white. Objective computers measurements can't figure out that one either. That's an absurd argument. We're not talking about predicting the future. There is a lot in this world that isn't known or understood, trust me. Why should I trust you? There are lots of things that are known. One of them is that our senses are easily fooled. That's why blind tests are valuable. ___ -S "As human beings, we understand the world through simile, analogy, metaphor, narrative and, sometimes, claymation." - B. Mason |
#33
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Do all amplifiers sound the same?
Sonnova wrote:
On Thu, 27 Dec 2007 08:47:53 -0800, codifus wrote On a slightly different note, I found one way to easily distinguish a lossy audio file from its lossless counterpart: distortion. The Lossless file will play much louder and cleaner than the lossy file on the same system. That is very true. It's very not true. A friend recently gave me an 340k MP3 of the end title cut for the movie soundtrack "The Mummy Returns". When I got it home, I was disappointed at how distorted it sounded. I then borrowed the CD from him and did my own "rip" using Apple Lossless. The end result was as clean as the CD. Then there was something wrong with your friend's mp3. I still maintain that compression artifacts are clearly audible and very nasty sounding, but others keep telling me that it's my imagination. You've never presented good evidence to the contrary. As in, performance on an ABX test, with a good mp3 vs. source. ___ -S "As human beings, we understand the world through simile, analogy, metaphor, narrative and, sometimes, claymation." - B. Mason |
#34
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Do all amplifiers sound the same?
On Dec 29, 11:40 am, Randy Yates wrote:
writes: Actually, it's not guesswork at all. The series resistance the voice coil dominates, and unless the other series resistances are pathologically large and the so-called damping factor is larger than 10-20, the amplifier's output resistance will have NO appreciable effect on the damping of the system. You're speaking in static, DC terms. What about dynamically? For example, when the voice-coil is traveling and the back-emf is opposing the amplifier's output voltage? Yes, there is still the DC resistance of the coil in series, but the amplifier is working harder than under DC conditions. Think Mr. Thevenin. That resistance is ALWAYS there, under ALL conditions. There is absolutely NOTHING special about the "back-EMF" that makes the situation in any way unique. A mechanically resonant system with electrical coupling behaves electrically exactly the same way a straightforward parallel RLC resonant tank circuit with a series resistance behaves. The onl;y time the "back-EMF" exactly opposes the amplfier's voltage is when the two are exactly in phase, and that occurs at the fundamental mechanical resonant frequency. At that point, the electrical impedance is at its highest and dominated by the series combination of the DC resistance and the reflected mechanical and (to a very small degree) acoustical losses. And by "DC resistance" of the voice coil, I do not mean that it's only valid at DC, rather that this resistance, for the purpose of discussion, has no appreciable frequency dependence. In other words measure its value at DC and at, say, 100 Hz and you will find no significant difference. |
#35
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Do all amplifiers sound the same?
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#36
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Do all amplifiers sound the same?
On Fri, 28 Dec 2007 08:45:57 -0800, jeffc wrote
(in article ): "Arny Krueger" wrote in message ... Some will argue that well-made amps that measure the same will sound the same. The myth here is that two amps could measure the same. Even each channel of a stereo amplifier will measure differently, given sufficiently accurate measuring gear. I don't believe the measuring tests are really that accurate. If you doubt this, consider: voice recognition is extremely difficult for even the most sophsticated equipment, yet trivially easy for even children. The same is true for image recognition. Measurements might be good enough for the cell phone generation, but that ain't sayin' much. Theoretically, if it can't be measured it can't be heard. But just because it can be measured doesn't mean it is being measured. And since even if everything we hear could be preceisly quantified and weighted according to the requirements of human perception, that still doesn't mean that the ordinary audiophile would have access to the equipment with which to make those measurements for himself. We have two instruments we can use when choosing audio equipment and we carry them with us everywhere we go. Use 'em! |
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Do all amplifiers sound the same?
On Sat, 29 Dec 2007 08:40:53 -0800, willbill wrote
(in article ): Steve wrote: Some time ago the now defunct stereo review had an interesting article on blind a/b tests between different amplifiers - I saw a reprint here; http://bruce.coppola.name/audio/Amp_Sound.pdf interesting ref, although 3.76MB is a bit much fwiw, the tubes vs solid state "squabble" went well beyond the '60's and in fact likely continues to this day Likely? Based upon the twin facts that there are more companies building tubed audio components today than at probably any other time since the transistor came on the scene in the middle 1960's and that recognized tube brands like Audio Research, VTL, VAC, etc (even Dynaco), have much higher resale value than SS gear of similar initial costs (with some exceptions), I'd say that this particular "squabble" was very much still with us! in my own not too distant past, tubes still sounded better; bleeding problem is their lack of practicality, not to mention that they now cost so much more than in the 60's I have a pair of VTL 140 tube monoblocs that I'm going to be buried with (along with my Alfa Romeo GTV-6). That's the only way I'll give 'em up is to be dead. Also I find my tube gear to be very practical. I bought out an old ham operator of his stash of NOS JAN WWII vinatge 807s (each amp uses six of them) for pennies each. They're better than newly manufactured 807s. Anyway, I think I've replaced ONE tube in the last 10 years. I'd say that's pretty practical! Modern tube components (my VTLs were manufactured in the early 1990's), unlike their 1950's and 1960's antecedents, are not biased so heavily, so the tubes last a really long time. After a hiatus of many years I am now putting together a system and every one I talk to tells me there is a difference between amplifier sounds. I am sceptical and in a recent audition could not tell a Creek EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd source). Has any more work been done on this subject, esp. blind a/b tests? believe nothing that you read Oh. I think you can trust a math textbook :- trust your ears Oh, yes. After all, they're the only "test instruments" that most of us posses. They do require a bit of training, however. i can add that imho solid state has come a very very long way forward in the last 20/25 years. That too is true. I still prefer tubes for music though. SS amps mostly sound too clinical for my tastes, although they are probably more accurate. In an ideal world, where recordings were perfect, perhaps the clinically accurate solid state amps will sound "better" than the euphonically colored tube equipment, but I don't see that happening anytime soon. I listen to music for pleasure and tubes give me more. There is not, nor does there need to be. any other justification than that. bill |
#38
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Do all amplifiers sound the same?
What was your recent "audition"? *These things have to be done carefully,
with the exact same system (I assume it was) but also well volume matched (use a test tone and multimeter to check the voltage output from the amp.) Also, you'll want to use material that you're very familiar with. Ultimately the overall resolving power of the entire system (the system includes the room acoustics) will determine if you can tell a difference (as well as if there is any discernible difference between the amps, of course.) Sometime of course you can tell a slight difference, but is one really better than the other, or just slightly different? *Is the difference worth paying for? I was able to tell the difference between an Adcom 545 and 555 (voltage matched of course) every time. *Both were operating well below max capacity. That was enough to convince me there are differences between amps (I don't even think the company intended there to be any difference here.) This was at a dealers and I had no way to objectively set the volume to equal. So I set the volume by ear changed the volume each time up or down according to whim. Not very scientific but similar to what one would do at home. |
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#40
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Do all amplifiers sound the same?
On Dec 30, 11:55 am, Sonnova wrote:
On Fri, 28 Dec 2007 08:59:42 -0800, wrote (in article ): On Dec 26, 11:57 am, Sonnova wrote: Output impedance is one of many criteria. Mostly, it affects damping factor for the loudspeakers. Mostly, it does not at all. The way I understand it is If a dynamic speaker is looking down it's cable into the output stage of an amplifier and sees, what is in essence, a dead short, the cone will stop instantly when the signal stops, because of the back EMF being generated by the shorted voice coil in the speaker's magnetic field (try this experiment: Get a raw driver and flex the cone by hand at the dust cap. Then connect the terminals of the speaker together with a jumper and flex the cone again. Notice how much more difficult the cone is to move this time. Unless you're moving the cone VERY fast, you're not going to see any difference. Now, try the experiment REALISTICALLY: Try doing it and trying to sense the difference between a 0.4 ohm resistor across the terminals vs a 0.1 ohm resistor across the terminals. Well, of course. That's what I was saying about "real world results" Well, here you harp about "real world results" after someone objects to your experiment which has nothing to do with "real world result." But while one cannot tell the difference between an output impedance of 0.1 and 0.4 ohms. one can certainly tell the difference (in the bass) between an amp with an output impedance of less than an ohm and one with an impedance of output transformer! And with the exception of some degenerative, patholoigcally bad designed tube amplifiers, the typical tube amplifier with it's output transformer exhibits effective output resistances of an ohm or less. That's the phenomenon behind regenerative dampening) There is no "regenerative damping." It's just damping. The damping occurs because of the regenerative back EMF. There is no "regenerative." You are either misusuing the term or misunderstanding the concept. But even this is an oversimplification. Yes, it is an oversimplification to the point of being wrong. No, it's not wrong. It just isn't as great an effect as the classic demonstration would have one believe. No, your oversimplification is ORDERS OF MAGNITUDE off the mark, enough that your suggested demonstration, which you implicitly admit is far from "real world," simply does not reflect the real world AT ALL. In reality, most speaker voice coils are looking into an inductor in the crossover and the resistance of the speaker cable before it sees the output stage, And, in oversimplifying, you neglected the fact that the single LARGEST resistance is ALWAYS there, and that's the DC resistance of the voice coil. The inductor might add a fraction of an ohm, same with the leads, but the DC resistance of a typical niminal 8 ohm driver is in the realm of 6-7.5 ohms, and THAT resistance completely dominates all others, including the amplifier's output resistance, and it is the voice coil resistance that essentially determines the damping of the system. I would have thought that was a given. No, in your discussion, it most assuredly WAS NOT a given. If it was, you would have realized and hopefully discussed the fact that the other resistances you cite are simply insignificant by comparison. so its anybody's guess how much a low output impedance actually affects the overall result. I agree. I was merely explaining the "shorted turn phenomenon". And you neglected to then point out that almost every amplifier on the planet provides that "shorted turn," given that it is NOT a significant source of loop resistance. Actually, it's not guesswork at all. Not if you know all the factors, no. Then it becomes a simple matter of the combination of the various DC resistances, and the various inductive and capacitive reactances involved The inductive and capacitive reactances have no effect on damping resonance. The series resistance the voice coil dominates, and unless the other series resistances are pathologically large and the so-called damping factor is larger than 10-20, the amplifier's output resistance will have NO appreciable effect on the damping of the system. Modern Solid state amps can have damping factors of greater than 200. Try it again, a damping factor of 20 or so is sufficient to control all resonances in a speaker. 200 will NOT damp ten times better than 20, in fact, in most cases, the difference is nearly unmeasurable. Frankly, I think that the sound of an amplifier is more a result of the complex load presented by the speaker system that it's driving than the speaker's sound is influenced by the amplifier. That may be the case, but, again, it's something that can be determined. If we have an amplifier whose damping factor is "low" by contemporary standards, say, 20 at 8 ohms, and we connect it to a speaker whose impedance varies from 6 to 30 ohms. The result is that the voltage at the speaker terminals varies by 0.44 db between the minimum and maximum impedance. Now, get yourself an amplifier with an alledged damping factor of, oh. 200. The resulting error is now on the order of 0.05 dB. Do you think that you can hear the difference resulting from a smooth change in broadband frequency response of about 0.4 dB in a room with dynamically changing music? I'm not arguing about broadband frequency response, I'm talking about the amp's ability to damp (or stop) a large, high mass magnetic bass driver abruptly when the signal stops. And that was PRECISELY what I was talking about earlier. Your dismissive comments that the DC resistance "was a given," your inclusion of inductive and capacitive reactances and your claim that it is all"guesswork," clearly indicates you're not grasping the true nature of "damping" in it's formal electromechanical sense. And that very mature is central to the operation of loudspeakers. The damping of the entire system is determined PRIMARILY by the DC resistance of the voice coil. The output resistance of the amplifier has, at most a MINOR effect. In fact, if you look at the reciprocal of the damping factor, THAT number gives a good indication of how much of the electrical damping is provided by the amplifier. So take an amplifier with a damping factor of 10: only 1/10 of the total electrical damping of the system is controlled by the amplifier, 90% is controlled by the DC resistance of the speaker. How about a damping factor of 100? Well, 1% of the damping is provided by the amplifier, 99% is by that DC resistance of the voice coil In other words, the higher the damping factor, the LESS the amplifier contributes to the damping of the speaker. This is why the "damping factor" is such a useless specification. It was born PURELY out of marketing. And all this discussion ignored the fact that the mechanical losses in the system provide more damping than even the worst amplifier. Given that in most high-quality electrodynamic woofers, the mechanical losses are on the order of 1/5 to 1/2 the electrical damping due to the voice coil, it further diminishes the contribution of the amplifier output resistance. Take a typical speaker with a Qt of 2 and a Qe of 0.7, and now we find that the amplifier with a damping factor of 10 contributes only 5% or so of the total damping. At your leasure, try the following: www.cartchunk.org/audiotopics You can also google for my ame and "damping factor." To reiterate: It is the voice coil DC resistance and NOT the amplifier output resistance that determines the damping of the VAST majority of amplifier and speaker combinations "Experiments" such as trying to see the difference between an open circuit and a short circuit in terms of "observing" damping are wholely unrealistic and flawed because they represent comparisons that wuill NEVER occur in the "real world." And all of this is quite well understood and not subject to any guesswork at all, assuming the appropriate compcepts and models are being used. If not, then any guess is as bad as any other. |
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