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Do different amps make a difference?

Discussion in 'Hi-Fi Stereo Speakers' started by kc5819w, Mar 16, 2017.

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  1. kc5819w

    kc5819w
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    I've come across a number of people commenting on amp tonalities. I have attached a link below here which is a blind test of different amps and even CD players and interconnects.

    System A features a cheap amp, a cheap DVD player, and cheap interconnects of RCA type.

    System B features top end equipment

    The speakers and speaker wire remain constant.

    The room was acoustically treated.

    Out of 38 human testers who were all trained ears and used to extensively listening to high end equipment, the outcome of the "best sounding system" comes below.

    The result X is no preference/unable to hear differences



    Indeed, more listeners chose the cheap amp setup as best to the expensive one.

    Matrix HiFi --> Blind testing high end full equipments
     
    Last edited: Jan 6, 2018
  2. PiperCub

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    This is quite a ridiculous study and here is my post from the other thread, but glad you made it the subject of a new thread;


    "People with decent audiophile kit will, I think, recognise what I am about to say, I'm sure; This test is the one I already commented on in my post before (where I mentioned the 'red sheet test'). These are my observations to this very unscientific 'survey' ;

    1) It says 'a good number of them participated'. It also refers to newcomers participating in the tests - in para 1, so there is some contradiction in the later paragraph you state. Exactly how many were newcomers and experienced people. Also what types of kit did the experienced people own. This is pertinent because;

    2) If someone is inexperienced in hi fi, you don't know what to listen out to distinguish whether the sound is dynamic, how it's detailed if so, how edges of notes are defined, how speed is important, besides many such considerations. I may go into a hi fi shop owning no system and think an expensive system is nothing special to my iPod dock, but it's just without experience that I don't know what to look out for. This isn't an elitist or snobbish approach it's just real world to experiences. Much of our views is based on what we know. Just like playing a musical instrument there is a certain level of knowing whether an instrument sounds right, which isn't objective but if you hear a dynamic on/off drum beat and a not so dynamic one, which is better to the uninitiated. You tend to learn this as your hi fi improves or you listen more and more to set ups. So the testers may not be on an equal playing field in that regard.

    3) Listening to a system in an environment which is not one you are used to can give widely different results as to the performance of kit. That's why reviewers in magazines have to use a standard set up and with good acoustics and maybe room acoustical treatments (although treating walls seems stupid to me at home, you just need to be used to the environment if it's a reasonably good one for hi fi). Now I'm not necessarily saying the environment was bad in this test, but if it's different, it can affect perceptions. So if I took my whole system to a dealer and set it up, it would probably sound a lot different. That will affect my perceptions as to its quality. I've already explained before I could not pick out my mono x200 amps in a dealer test using same make and model speaker I had there too, against cheaper x powers the dealer had which I owned at home, keeping all the rest of the kit the same except cables. Get the x200s home and it was a totally different story. They were awesome.

    Now these testers may not know the kit but that's hardly the point to the effect acoustics can have on a system.

    So the point is they may have been audiophiles with such kit, but could this unfamiliarity of environment affect their judgements.

    4) Is the variance of 14 picking the cheaper system against 10 the expensive one, statistically significant and what significance level would you give it. Is a test of 24 people scientific and conclusive to a statistically significant view. This is hardly scientific and the sample size is not big enough for me.

    5) Are the people sitting in the same position, the chairs are set behind the other listeners. This has to to be a standard in a test, to eliminate all variables. At the Bristol show a guy couldn't discern two cables. Where was he? Sitting in the back fifth row! They should use at least a sofa immediately between the two speakers with seats equidistant left and right, and testing two people at a time.

    6) What are the people's hearing like. Is it good and have they been asked if they have hearing issues or not. Eustacian tube dysfunction etc. This hasn't been revealed by this 'study'. It's not scientific. A scientific test would look at hearing and set people in the same hearing quality brackets in tests and compare results. Having bad hearing doesn't preclude you from taking part but I suspect the results will show similar levels of significance to finding which is the best, between groups of people with the same standard of hearing.

    7) The kit being tested as cheap and expensive, is it, in consideration of the amp and speakers, considered to be poorly performing or good performing at the price or not. Now I doubt this would be an issue because such systems with prices so wide apart are very unlikely to have similar performance. So of the many other variables, it is the least likely one to be an issue.

    8) are they talking to each other. Are they being affected by bias of others saying , yes that one sounds a lot better. Particularly if 'John Hi-Fi' is there strutting his stuff around and is an authority. What about the testers doing the same and commenting.

    9) what part did volume play in any bias ie one being louder than the other, because with two amps they won't get the volume the same. They mentioned testing this but how did they get the sound pressure level the same by adjusting the volume knob. Was it exactly the same spl. Was is by the db Reading on the amp, or was the multi-tone used between each of the tracks.

    10) they had no scientific means of giving a view of either a or b in double blind, from each track, to compare similarities and differences in the results and do this more scientifically. They just gave one view each at the end, which is even more suggestive of bias of others affecting their judgements. In a science survey they would not have been allowed to talk to each other, so as not to affect this bias. Results would be kept confidential in the test conditions. This was a group friendly meet where conversation was the purpose of attending. How long did the whole thing go on to affect familiarity.

    They could have played something with drums, maybe billy jean by Mj and asked each tester which they thought was better. Then do the same with Mozart etc and same for maybe 10 different tracks. Did a pattern emerge as to the type of music enabling the more expensive system to be picked out or not. This is what science tries to work out,tests within itself.

    They also had no means of indicating if all the music they heard represents tracks they know, so did one person listen to 2 CDs they knew against someone else, 7 CDs. How many CDs did they listen to , to consider good results. Were the CDs the same between different set ups.

    11) what were the intervals between swapping the cables over. Why not use a means of doing this quickly eg speaker junction boxes to avoid possible continuity errors on unfamiliar systems.

    12) the study has no hypothesis (what are they seeking to test) and the controls are poor. A control seeks to remove all other variables. They don't analyse and just go straight to conclusions. There isn't any significance testing at all, no graphs. Nothing. A science survey does the test with controls and compares in non control circumstances, and seeks to explain the differences.

    This goes to show this is not a scientific test and it never will be and saying this study is scientific and to be believed insults the minds of those who have the inquisitiveness and astuteness to realise how many variables come into these amateur studies to make them unreliable. They would have done well to realise it, rather than as a confident group professing 'the results speak for itself'. Hardly.

    This is largely why these types of tests have no credibility and the scientific community has no interest for reasons it's not an important debate affecting people's health etc, and to do them as amateurs with credibility is extremely difficult. That's why even if I tried to do one, I doubt the results would be reliable as a great deal of effort would need to go into it, probably beyond the will of collective desires to find out."
     
  3. kc5819w

    kc5819w
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    Thanks for the detailed reply, I'm not saying anyone is right or wrong, I wanted to get some thoughts on the matter. It does seem there are problems with this test and I agree the conclusion they have is quite wild.
     
  4. PiperCub

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    Yes, not that I was saying you had taken a stance but the widely ranging views on this type of debate as well as those regarding cables (which I won't elaborate on as going off topic) is that the tests which people say support a view are wildly unscientific and lacking any credibility. This amateur internet test is just one of many I'm afraid. But worryingly, easily led people believe it.
     
  5. andy1249

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    Almost all amps, be they stereo or multichannel receivers , sound different.
    Often deliberately so.
    There are far too many different design factors for this not to be the case.
    Put any two different amp designs on the bench, and they will measure differently.

    In theory, " If " an amp follows general design guidelines and outputs across the audible frequency range without clipping and with minimal distortion then they should be indistinguishable.
    A purist would say this is what should be done.
    However it seems that very few are doing this.

    Most these days are deliberately enhancing / altering some or all of the frequency spectrum for some purpose or other, whether that be hiding the effects of lossy file playback, getting that (insert manufacturer name here) signature sound or, and I have specific culprits in mind here, ignoring output quality in favour of adding " features".

    This is nothing like the cable issue, where fraudsters claim "magic" copper.
    Amps have wildly different designs , component, and feature counts , they can and do perform and measure differently.

    ABX tests are not scientific.
    They fail on two major points as to the validity of the data.

    1. Repeatability, good data is repeatable , ABX tests are rarely repeated and even when they are no two data points are the same.
    2. Reproduceability. Any experiment must be reproduceable by anyone else wishing to carry it out. As these tests involve a large human factor as well as a great many other variables ,that is not possible.

    ABX tests can be useful as a personal exercise , or to settle an argument to the personal satisfaction of a like minded group, beyond that though, they are pretty much irrelevant as far as rigorous scientific methodology goes.

    If you want science involved in any of these discussions its down to measurements.
    Nothing that can be heard is immeasurable.

    In that respect , high priced or "special" copper wires are doomed.
    Measurable and audible dfferences are there until you hit the minimum cross sectional area, after that, nothing , no matter what the seller says.

    With amps , its extremely rare to find any with the same output frequency response these days. It " should" be the case, but it isnt the case.
     
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  6. PiperCub

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    Maybe you'd except on theoretical explanations that cables can't make a difference, but I think my post above gives serious credibility to the matter that, it seems, there are no definitive conclusive scientific abx double blind tests with cables and this applies to any amp debate on the subject too. So I don't think you could claim that one on the cable debate, until such time as there is a proper study or studies on abx.

    A list of sites and threads were posted by 'triple x G' on cable blind tests, of which this 'red sheet' test was one, some threads had broken links, most it seems could be critiqued in the way I have. But with the amp question, as there are so many design variables, I totally agree they are going to sound different. But nobody knows how much distortion, at least I don't think they do, starts to effect sound quality. 10% and above is banded about as doing so, but less than 0.05% is frequently quoted in amp specs, but my question is who is to know how any comparisons of figures between two amps having below this 0.05 figure would effect the chain, and sound quality, with really good speakers. Eg 0.01 versus 0.045. Some manufacturers suggest you check harmonic distortion and signal to noise rario figures in considering purchasing decisions, as well as listening of course, and that seems to me a very sensible thing to do.

    I agree with you that double blind tests would need to be repeatable to be reliable. So you'd have one person doing a study in a slightly different way to another, drawing disparities and similarities. This is what science studies in biology do for example. The more that confirm the original or set view, the more it's accepted. They can be repeated in the study to make sure reliable as a starting point for that study and science studies often do this, sometimes as the first thing they do. That can it can't discredit the previous. But your assertion that abx is not scientific and it suits personal justification is unfounded since an abx test doesn't seek to be science, it seeks to prove a hypothesis and analyse and explain and then conclude. Also if it's statistically significant it needs to be explained and a test which seeks to ask the question can people discern differences in abx testing, and why so, is no less valid than what can and can't be measured. Most of theories are based on data which seeks to explain a position, and until a better one comes along, especially has been historically the case in evoloutionary biology and genetics which I've studied.

    I think the point made by another poster that machines can't discern differences in dynamics, detail etc, is a very strong and good one indeed, and why you'd never win your argument on a measurement level. Wires aren't doomed because people buy them
     
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  7. andy1249

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    ABX tests will never be accepted as data for the reasons posted.
    They never will be.

    They can however , remove personal Bias from the equation and justify (or not ) an expensive purchase.
    They are useful enough in that respect.
    It is quite amazing how perceived audible differences disappear when you dont know which item is which.

    I believe you are planning one.
    Interested in the results.

    I,m in semiconductor design , specifically HDMI at the moment, and have over the years seen many many pieces of equipment and accessories on the bench.
    My views on cables come from a very practical position.
    Suffice to say , copper is used in semiconductors today, its properties are literally known down to the quantum level.
    Copper interconnects are deposited on almost every microchip these days with machines that can do it one atomic layer at a time.

    I dont think high priced cables are a fraud, I know it for a fact.
    For me , its not theory, its very real practice.

    Amps of course are not the same argument at all.
    It can be proven that no one has special copper.

    It can be proven that everyone has different amps.
     
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  8. Wall Of Sound

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    each amplifier I have ever owned has had a different sound signature

    1997-2013 : Arcam Alpha 7 - Relaxed, laid back presentation
    2013-2015 : Cambridge Audio 851A - clear and clean, lovely amp but for me missed the fun factor
    2015-2016 : Roksan Caspian M2 - didn't get on with it, too much bass influence.
    Current : Naim Supernait 2 - If you love rock then it's a fantastic rhythmic amp


    There is no brand bias here, other than what I wanted at the time of purchase.

    Given my past it's safe to say the next amp will be something better and not the same house name as before.
     
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  9. PiperCub

    PiperCub
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    But your position as regards abx doesn't come at the right way for me,with the greatest of respect. You say Abx tests remove personal bias, another way of saying for justifying discerning a difference, but then you say audible difference dissapears when you don't know which cable is which. This is, as I perceive it in the aforementioned way and the way you've explained, a contradictory statement.

    You can't say abx are not scientific because they are rarely repeated, and there are not enough tests. That's a quantitative function of the number of tests and studies, not the tests themselves as a basis for a scientific argument and attempting to explain. Your second point about reproducibility I'm half with you in a context. The reason and context being that there isn't the inclination, as I mentioned and for reasons I stated, but this doesn't mean that because there are lots of variables in an abx test, that you can't discern differences and conclude why cable a is picked out against cable b. If the inclination was there and it was as an important question around science and health for example, these studies would be very much reproduced through a process of studies to get to the issue. Human factors can be removed but have to be explained in a study. That's what a control in a scientific study attempts to do. It tries to remove all other variables to keep the study results reliable.

    So if you accept for a moment that a cable could be discerned as being different in a number of abx tests to another, with similar cable qualities but different cable design, and that you could then attempt to explain the reasons for those differences, as science attempts to do, then you are not quite there to say cables are a fraud. You've reached a conclusion before you've attempted to explain any such positive case in abx testing and data for discerning between similar cables with same conductors but different designs. Particularly if you accept the abx tests are not often enough and are not reproduced, and as you say, which I think is correct ie not common enough to be subject to any scrutiny.

    You base an explanation on technical knowledge I feel without attempting to know what abx data may or may not show, then explain that with your knowledge and others, assuming it were in favour of picking out a over b. This is the crux of the issue really and is the question which is ignored. The leap of faith is these amateur tests show abx tests cannot pick out cables, but they are it seems very unreliable, and as you concede, they are rarely repeated. And even if repeated, it's repeating poor tests unscientifically for concerns I raised in my previous post.

    Your question about price is quite a different one which has no basis for scientific study, as assuming the abx test did reveal differences, it's very much up to the person how much they spend. A difference is all it attempts to reveal. We all have different judgements of worth which is dependent upon lots of things including income and nothing to do with material science.
     
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  10. andy1249

    andy1249
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    Its not my position.
    Its ABX vs requirements for what constitutes rigorous science.

    In any rigorous methodology , the same method always produces the same results.
    For example every method there is to measure the speed of light produces the same result.
    I use meters and scopes to measure inductance, capacitance and resistance of any piece of copper, I always get the same result no matter how many times I make the measurement.
    That is repeatability.


    This can never be said of ABX.
    So far Ive never seen an ABX test that verifies a cable difference where the cross sectional area meets the minimum requirement.
    But regardless, even though the result is negative, the actual figures are still widely varying statistical values.
    In other words there is no repeatability in terms of figures, which is why the results are never taken as hard data and never will be.
    From a science perspective this will always be nothing more than statistical curiosity.
    Thats just the way it is. There is nothing contradictory about it.

    When I say ABX removes Bias I mean expectation Bias, which of course it does.
    There is no expectation Bias when you cant see the subject under test.
    It is of value to those involved in the test only.

    ABX is not scientific and will never generate any further studies into the properties of cable or anything else.
    You would need hard data for that.
    That means repeatable measurements as outlined above.

    The properties of copper have been largely understood since the late 19th century.

    I work in an ndustry where copper is made into a gas and grown to the required lengths of interconnect on semiconductor substrates with extremely precise values of impedance.

    The idea that there is something new to be learned about it and that cable manufacturers are the Pioneers of this new science is ridiculous.

    Regarding price, this is mentioned only because it is without doubt the reason this " debate" exists.
    These ridiculous products only exist to sell what is a cheap commodity, i.e. Copper , at ridiculously inflated prices.
    Justifying a higher price with dishonesty, no matter how modest this increase in price may be , is fraud in every country in the world.
     
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  11. PiperCub

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    I don't think one is attempting to set abx testing against rigorous science, abx is a conduit to attempt to explain if picking out cables is significant or not.

    You are conflating it with absolutes because this isn't an absolute test and question we are seeking to answer in using abx in the first place. Science doesn't have to be absolute too.

    You want to know as much as I do, can people pick out similar cables (of same conductors but different design) in proper scientific tests with variables controlled. Of say 1000 hi fi enthusiasts, 500 may say cables matter, the other 500 they don't. It's an interesting question.

    You are i think conflating an argument now about repeatability of abx with an absolute measurable test, going off the question.

    I agree an abx test hasn't done that test re cross sectional area, but as you've already conceded there aren't any. So that's a circular argument.

    There are no statistics in these unreliable amateur tests, as far as I can see.

    They can be repeated if you use the same principles of test and analyse results, which we dealt with.

    I think you've missed the point that what the study serves to test is abx significance and what are the reasons, if the results are statistically significant that then they can't be ignored.

    If you are removing confirmation or expectation bias in an abx test as a means of choosing an item for sale, that means you are discerning it from another, that means in other words there is a difference, which is what I said. So your argument in para 2 of your post at 4:45 is not explained by para 2 of your reponse. I'm not sure what you are trying to say.

    Abx doesn't generate studies into the properties of cables it seeks to ask the question is there a statistical difference, as a basis for explanation. Then tests try and explain that. We've covered that. Hard statistical data is a basis for explaining something. You don't necessarily need to have empirical electical evidence to explain a cable makes a difference or not, which this debate stems from. Though I think it is ideal. So you could attempt to get the results, get them in a positive light and then test them, with evidence and if no evidence you could still say cables are picked out in a statistically significant way and the best explanation is x or y, if no other evidence can back that up. That's how evolutionary theory developed, it was not proven beyond doubt. What you are doing is not even knowing what you should test before you've got there or not. Clearly you don't need to test further against a statistically insignificant result.

    I agree price does inflame it but I think the arguments against are caught in the rut of it being a con through some form of conspiracy type therory ignoring market economics, the viability of such firms existing to a small market, if they didn't charge a lot on some higher range cables. Also the issue that price v performance is often a misnomer and not a rule, which is latched onto by detractors cables make a difference. The same would be true with the amp debate.
     
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  12. andy1249

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    You mean that if you remove Bias during and ABX test, and you " successfully pick out the difference" then there is a difference to you.
    This is what I mean by the test being useful, its useful on a personal level.

    If you succeed , please post the results, as far as I know , nobody has done that to date.
    I am of course referring to the test being planned with others on here, independantly verified and presented.

    By the way, even though ABX is not hard science , the AES ( Audio Engineering Society ), have mountains of statistical data on ABX cable tests , all negative and totally in agreement with the hard empirical data... both agree, once the cross sectional area is correct for the setup, no one can tell the difference between cables...its not real, it is a fraud.
     
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  13. PiperCub

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    Yes but what I was confused with is when you then said perceived audio differences disappear when you didn't know which is which.

    I think you said before that you don't think cables utilising same thickness conductors and utilising metals of a similar type should not sound different, with different designs like shielding and dialtetrics etc. Also that different metals like silver and thickness can change frequency response and fair comparison. If I'm wrong please correct me on that. But in this regard your obersevatios about perceiving bias are presumably on non comparable cables, in the aforementioned respect.

    If I cant borrow switches that don't degrade sound, don't damage my kit, im not sure about taking this further as don't fancy plugging cables in and out and damaging stuff as I said. But subject to this being ok, I could buy the switches if they are cheap too.

    Tests can be with people on here and others.

    But this debate was about amps so sorry if I have gone a little off topic but the original debate was about blind testing, so I guess this can equally apply.
     
  14. Abacus

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    Humans have evolved over time, with changes coming when things changed in the environment, and because of this, humans are fatally flawed in every department, hence to use them to prove a fact is pointless, however, they can think outside the box, and design tests to bypass the human’s inadequacies to get an accurate result.

    Because of the above, subjective observations without rigorous controls are meaningless, and cannot be trusted. (Just because you believe you can hear a difference, doesn’t mean that one exists)

    Question? In a stereo system, if you can hear a sound coming from between the speakers, is there an actual sound there? Or is your brain playing tricks on you, causing you to believe that there is a sound there, even if there isn’t?

    How you answer the above question, will say a lot about what you believe to be true, so think carefully about your answer, as it will apply to every subjective test you do.

    Have fun

    Bill
     
  15. PiperCub

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    No that can't be true I don't think as we would never have developed an understanding of gravity or evolution and the list goes on. Designing tests to bypass inadequacies are picked up by scrutiny and in science, by sicientific scrutiny and rubbishing. So what doesn't hold up gets dismissed and ignored.

    I think you are saying if you can't explain something it's not rigourous. I don't agree as you can give a best possible reasons to significant results from the abx test, asssuming they were positive in my line of argument, even if you cannot catergorically give a reason for these. A best guess is as good. They wouldn't be subjective too, as the results of the abx tests would be objective.

    The trick on us is what the abx tests try and eradicate (or not)

    Cheers Simon
     
  16. andy1249

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    You have a knack for spin I,ll give you that!

    Obviously , in that sentence about perceived difference, I meant cables where you already think you've " heard" a difference, but now the object is to blind test to see if you can still tell the difference.
    In all cases so far reported, these previously heard differences are gone under a blind test, meaning that they were never real, just a result of expectation Bias.

    In plain words.
    The main contributor to the circuit is the resistance of the copper itself.
    All other effects are so minuscule they can be ignored.

    Silver makes no appreciable difference.
    Shielding makes no appreciable difference.
    Dielectric makes no appreciable difference.
     
    Last edited: Mar 16, 2017
  17. lindsayt

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    So what's the THD+N of my power amplifiers at one tenth of a microwatt?

    I can hear a sine wave at one tenth of a microwatt through my speakers. I have not come across anyone that can meaningfully measure THD+N at such low power levels.


    And what measurement of amplifiers gives a reliable indication of the lack of focus / clarity / low level detail resolution? This is something that I can hear with certain amplifiers. Not come across any meaningful measurements of this.
     
  18. Abacus

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    Assuming the amp is not driven outside its operating limitations, then the sound of the amp can be determined by the frequency response, Distortion & Noise it produces. (This is how Hi-Fi manufactures create their house (Coloured) sound, whereas pro amps aim to be a straight wire with gain, thus neither adding or taking anything away)

    Hope this helps

    Bill
     
  19. Paul7777x

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    I'd guess that most don't boogie to one ten millionth of a Watt of sine wave.

    But it's a easygoing world so knock yourself out :facepalm:
     
  20. lindsayt

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    Yeah, but THD+N is ALWAYS measured by feeding the amplifier a sine wave - as that's the only signal with which measuring equipment can produce a THD+N figure.

    I listen to music at a wide range of volumes. I'd expect everyone reading this to do the same.

    At lower volumes, the low level detail / tail end of the decay of the notes in the music will be at power levels of about one tenth of a microwatt in my system. I have never seen any reliable THD+N measurements at such low power levels.

    The most commonly given THD+N figures from amplifier manufacturers is at power levels just below clipping. For my 300 watt solid state amps, my speakers would break if fed therm that much power! If I fed my speakers 150 watts I'd be getting about 125 dbs at 1 meter! I never listen at such deafening volumes.

    THD+N at one tenth of a micro-watt would be much more relevant to me than THD+N at 150 watts.

    @Abacus, frequency response and the distortion and noise measurements that I've seen; none of those tell me whether the amplifier will make a recording of a grand piano sound like a grand piano or like a bunch of electronic components trying to reproduce the sound of a grand piano.
     
  21. andy1249

    andy1249
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    Because this is worst case scenario.
    At any lower volume THD + N will be less.
    For any distortion measurement you are comparing the input signal to the output signal.
    The aim is to reproduce the input signal exactly as is.
    Measuring input signal vs output signal at such low volumes would give a misleadingly favourable result.
     
    Last edited: Mar 17, 2017
  22. lindsayt

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    andy1249, as a percentage, THD+N in solid state amplifiers rises dramatically as the volume and therefore power levels are reduced. Check out the measurements page on any of the online Stereophile amplifier reviews.

    The situation is exactly the opposite of what you say. Measuring THD+N at power levels just below clipping (and therefore very high volumes) gives misleadingly favourable results.
     
  23. Abacus

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    Hi Lindsayt

    The frequency response should be as flat as possible and the distortion & noise as low as possible, (This is what pro amps aim for) to get an accurate representation of the sound being input, the farther away from this, then the less accurate the sound produced will be, it’s as simple as that. (A good quality amp should not create any sound of its own, if it does, (Particularly if it has been designed that way) then it is adding colouration, and should be avoided at all costs)

    Hope this clears up your confusion

    BTW: the speakers used in the original post are pro studio based, so sound accuracy is more prominent then a lot of H-Fi speakers, this combined with the A500 power amp (Which is designed for professional use (Straight wire with gain) is probably why the differences are small. (Although relatively cheap (And not a looker) the A500 is the equivalent of Hi-Fi amps of between 3 – 5 times its price)

    Bill
     
  24. lindsayt

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    Abacus, to take one memorable example, the Bel Canto Evo2 amplifier has a flat frequency response and vanishingly low levels of THD+N at the headline just-below-clipping power levels.

    It was relatively poor at recreating the sound of a grand piano.


    We could play the semantics game by saying that the Bel Canto amp was producing more distortion than the 300b SET amp it was compared against. It's just that the type of distortion from the Bel Canto amp has not been measured by any laboratory equipment yet. IE that if we did the right measurements we would find distortion from the Bel Canto that was not there in the Coincident SET. However, those measuements have never been done and probably never will.

    So where does this leave us when it comes to buying and keeping decisions? Should we rely on the woefully inadequate measurements that are available or should we rely on listening to the equipment and making our own minds up?
     
    Last edited: Mar 17, 2017
  25. Abacus

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    The biggest variation of the sound from a system is the room itself, (It dwarfs everything else) with the second being how the amp interreacts with the speakers, (Therefore active speakers tend to give a more accurate sound, as the amp and speaker drivers can be optimised for each other) so unless the measurements are done in the room that the system is in, it is not possible to determine the final sound via measurement alone. (Hence you must always try before you buy)

    While there are many variables in amps, providing the designer follows the principle of straight wire with gain, (As most pro amps do) then providing it is not overdriven, it minimises the effect it has on the sound.

    Hope this helps

    Bill
     
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  26. andy1249

    andy1249
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    Total Distortion is made up of many distortion types.
    Two main components are clipping type distortion ( main concern) which increases with level, and crossover distortion ( lesser concern ) which decreases with level.

    Clipping distortion being the major contributor and least desirable (Most destructive), measurements are made for worst case scenario of this type.
     
    Last edited: Mar 17, 2017
  27. lindsayt

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    andy1249, yes indeed there are many types of distortion that amplifiers can produce. In posts #21 to #23 we were talking about total harmonic distortion and noise (distortion). Here's the Stereophile THD+N vs power graph for the Boulder 2150 amplifier.

    [​IMG]

    A side effect of clipping is that this graph goes up nearly vertically at the onset of clipping.
    This graph cuts off at 100 milliwatts. IE a long way away from the one tenth of a micro-watt that I will be listening at late at night. The X axis of the graph would need to be about two and a half times bigger in order to extend it down to one tenth of a microwatt! You can also see that THD+N as a percentage increases dramatically as the volume is decreased from 500 watts to 100 milliwatts.
     
  28. lindsayt

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    Would you rate how the amp interacts with the speakers as being of more importance to the variation of sound in systems than the selection of the speaker drivers and the cabinet design?


    And even if you do all measurements in room are you aware of any set of measurements that have ever been made on amplifiers that co-relates to how well that amplifier will recreate, for example, the sound of a grand piano? Amplifier frequency response and THD+N measurements do not come remotely close to doing that - in my experience.
     
  29. PiperCub

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    So in laymans terms does this mean thd and signal to noise ratio matter even at small figures and that what you are saying is that with even very small differences under less than 0.05% on thd, it could matter in terms of sound quality and recreating realism as with piano. Therefore it's something to look out for if an amp is 0.01 or 0.05 in reword to thd.

    That's how I've always understood it, that thd measurements do make a difference even though small. Am I Right?
     
  30. andy1249

    andy1249
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    All amps have some distortion plus noise.
    Clearly, as the measurement is a ratio of noise in output signal vs noise in input signal, the lower the level of signal the more the inherent noise in the amp is an issue.

    Indeed it is possible to measure any amp with a spectrum analyser right down to the level where ratio becomes 1 ( THD +N = 100% ) and signal is indistinguishable from the amps baseline noise level.
    Every amp has this level.
    This level " Should" be vanishingly small.

    The standard measurement is mainly concerned with clipping distortion, the assumption being that low level noise should be negligible at usable levels.

    This is not always the case.
    Indeed Many amps / receivers available at present have significant noise and crossover distortion at lower levels.
    One of the many reasons it can be proven that not all amps are the same.
     
    Last edited: Mar 17, 2017

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