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Thread: Amplifiers - how big, how small? The truth.

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    Default Amplifiers - how big, how small? The truth.

    We constantly receive emails from anxious customers asking which amplifier they should use with their Harbeth speakers. Will XYZ amp to too powerful? Will ABC amp not be powerful enough?

    Of all the questions here, this amplifier issue seems to be the one that causes the most (needless) concern. Amplifier power capacity is a simple technical matter perverted by downright falsehoods, mumbo jumbo, irresponsible gossip and no concept of what an amplifier actually does. I've tried to allay these fears in various postings that I've made here over the years (clearly without success) so here for the final time is my opinion in one posting. Note that I have not made any comment about the claimed sonic benefits of amplifiers - that is another matter which I will leave entirely alone for you to decide for yourselves. But it's unlikely that there is a perfect correlation between amplifier power and sound quality. So let's just look at amplifier power rating.

    Typical questions that you ask us almost daily and our answers ....


    You ask: "Can I use a really powerful amplifier with my speakers? For example, can I use a 250W amplifier with my Compact 7s?"

    My answer: It doesn't matter if the amplifier is rated at 50W or 250W or even 2500W. What matters is how you use the available power.

    You ask
    : "Really? Surely the big amplifier has 'too much power ' for the speakers?"

    My answer
    : No. It is irrelevant how big the amplifier is. The amplifier could be 1,000,000W (one maga watt).

    You ask
    : "But surely that is too much power for the speaker?"

    My answer
    : Yes, that is a huge amount of power but ... who is in command of the power? You or the amplifier?

    You ask: "Surely the amplifier forces power into the speaker so that if the amplifier is too big (too many watts) it will destroy the speakers?"

    My answer: Who is in command of that power? The amplifier doesn't have a brain. It is dumb. It is your servant. It does what you command it to do.

    You ask: "What do you mean I am in command?"

    My answer: Is your hand on the volume control? If so, YOU are in command of the amplifier. YOU and you alone decide how much loudness, how much volume and how much power will be made available to the speaker according to YOUR setting of the volume control.

    You ask
    : "So the volume control is like a bath tap, and if the tap is only open a little, only a small stream of power will flow. If the tap is fully open, a torrent of power will flow. Right?"

    My answer: Absolutely correct. YOU decide upon the power level you wish to deliver to your speakers. The amplifier doesn't sneak power past the volume control into the speakers! The volume control is the power-control gate and YOU control the gate! The water from the reservoir does not gush into your bath flooding your house - it is controlled by the tap.

    You ask: "So the amplifier does not push or force the power onto the speakers, the speaker is permitted by me to draw power according to the setting of the volume control? So actually it does not matter how big the amplifier is, what matters is how I command the power by adjusting the volume tap."

    My answer
    : Absolutely correct! You are the boss! You are in command. If you have a big amplifier act responsibly. Do not play too loud!

    You ask: "Doesn't the volume control on the power amp protect the speakers? Surely turning the volume down will will prevent excessive power reaching the speakers?"

    My answer: No. The volume control is right at the front of the power amp circuitry, which is running at full potential all the time. Read here.

    Conclusion: There is a danger that excessively powerful amplifiers will damage loudspeakers.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default Amplifiers - how small?

    The other question we are frequently asked is about the minimum recommended power for an amplifier. This question is a little more complex that the 'too big?' question as I'll try and explain here. When I say smaller amplifier or bigger amplifier I don't mean the size of the case, I mean only the power output rating of the amp. The case size is irrelevant: the circuitry may only occupy a small part of the inside. You cannot judge the power rating of an amplifier by the size of the case! Marketing people are smart enough to disguise small amplifier circuits in big cases! You have to check the specification. It will say something like "Power rating .... 75W into 8 ohms continuously per channel".


    You ask: "If I look inside a small amplifier or a big amplifier what difference would I expect to see?"

    My answer: The circuit may be exactly the same. But the bigger amplifier has more of a reservoir of power compared with the small amplifier.

    You ask: "What do you mean that the bigger amplifier has 'more of a reservoir of power'?

    My answer: I mean that the bigger amplifier has a bigger transformer and bigger PSU capacitors so that it can draw more power from the mains and store that inside the circuit ready to deliver to the speakers according to how you adjust the volume control.

    You ask: "So if the speakers are not connected, or if the volume control is at zero, no power is being drawn from the reservoir so that It doesn't matter if the reservoir is small or large. Right?

    My answer: Correct. The only (technical) advantage of a big amplifier is when you are playing loud. At low volumes, there are no (technical) advantages to having a big power amplifier. If you are not actually drawing from the power reservoir then it doesn't matter how big the reservoir actually is. It's like the reservoir from which you draw water for your home. If you don't turn on your water taps then it's irrelevant how much water there is in the reservoir - it could even by completely dry.

    You ask: "How much power is needed to play music at home?"

    My answer: It depends upon how you set the volume control, the type of music, and how loud you like to listen, and how good your hearing is.

    You ask: "OK, but typically, how much power is needed to play at a moderate listening level?"

    My answer: Surprisingly little. To make a medium-loud sound on classical music (or jazz) you only need about 5W -10W or so.

    You ask: "Really? Only about 10W? But why would I need an amplifier of more power than 10W then?"

    My answer: Because a 10W will give you no reserve power because it has no power reservoir within the case from which you can draw immediate power to handle loud peaks. It will have small capacitors to store the power and/or a small transformer and/or it will waste much power as useless heat. So the available power reserve for the speakers will be very small.

    You ask
    : "So it's a good idea to have some reserve capacity available on demand for those sudden peaks in the music, or where I chose to briefly play an exciting musical piece louder than normal?"

    My answer: Yes it it always a good idea to have some reserve power. But how much? If 10W will fill a room with sound, then 50W or 100W should give plenty or reserve power. Anything more than about 100W is just a luxury - a power reserve that you will never dare command from the amplifier.

    You ask: "Never dare? What do you mean?

    My answer: I meant that even though you have a massive reserve available in a big amp, commanded by your operation of the volume control, you have to ask yourself can the speaker handle so much power?

    You ask: "But I am always careful and responsible when adjusting the volume. I have neighbours and they will not tolerate too much volume from my hi-fi system. So I will never strain the speakers."

    My answer: That's good. No matter how big the amplifier, if you are careful then you won't strain the speakers.

    You ask: We're talking here about how little power I need. You said 10W is typically all that's necessary to make a reasonably loud sound. Is there any advantage to using a small amplifier? Maybe I should buy a small amp? Or a big one? I can't decide.

    My answer: As I've said, let's pick a minimum power rating of (say) 25W. It could be 15W or 30W, something in that range would provide some reserve for louder than normal use. At the other end, perhaps about 150W represents all the power you would ever sensibly need before you risk damaging your hearing and if you are careless with setting the volume, your speakers too.

    You ask: "So if I pick an amplifier in the 20W - 150W range I should be able to make great music at home?"

    My answer: Yes; the lower powered amplifier will fill the room with sound but will not have much reserve power. The 150W amplifier will have a lot of reserve which you must command carefully. You must respect the fact that the speakers can't handle 150W continuously.

    To be continued ...
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default Measuring amplifiers and interpreting the numbers

    Last week I was carefully measuring a selection of amplifiers to give us an objective performance base line. The results were rather interesting.

    First, even expensive amplifiers with a good pedigree and long warranty produce distortion. All amps do. The nature of that distortion varies somewhat from specimen to specimen. Surprisingly (to me) the individual distortion components down on the noise floor are granular in nature; that means those distortions are at many frequencies that are not immediately obvious to me as harmonically related to the test signal* and spread right across the audio band, not just the more familiar and easily identifiable second, third .... distortions of the input test signal.They may be there as well.

    What has come to light though is - and this is just my initial comment, I may be wrong - that amp manufacturers seem to shelter behind a presentation of the distortion (and noise) components on paper. First, amplifier distortion (plus noise) seems to be quoted when the amp is at or near full power. As the background hiss (noise) is fairly constant (it seems) that this noise can then be quoted as a percentage of the full power, which on paper, makes it seem lower than it perhaps is to the ear with little or no signal passing through the amp and speakers.

    Second: Maybe my maths is wrong, but let's take an typical high quality amplifier manufacturer's specification for distortion and noise - say, "0.05%". Looks extremely impressive doesn't it as it is such a small number. Now, as I understand it, 0.05% equates to five parts of distortion in ten thousand parts of signal or the distortion is 1/2000th of the total output. Again, impressively small number. But let's convert that to a log number and express the distortion in decibels as we do generally with audio things. I calculate that 0.05% distortion as -66dB relative to the full output. Now, that's not so impressive a number (on paper).

    Please check my maths.

    P.S. I subsequently found this on-line tool for number conversion which you may find useful.

    * With a little personal experience with amp design in the previous HHB and Monitor 40Active modules, I suspect that these very low level distortions near the noise floor are related to circulating (earth) currents in the PCB's, wire looms and power supply. Extremely small differences in any of these will definitely change the distortion spectral display; whether or not they are audible I doubt at such a low contribution level to the overall signal.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default Small amplifiers, power reserve

    More on small amplifiers and power reserve here
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default Too much power?

    THE FOLLOWING POSTS HAVE BEEN COPIED FROM A CLOSED THREAD, HERE. Discussion continues here.



    Quote Originally Posted by Jerome W View Post
    An other possible explanation was given to me by the founder of Mulidine, the french speaker company. In certain rooms, with certain speakers, high power amplifiers sound less good because they just make the speakers overloading the room.
    There is a Room - amplifier - speaker "trioling" and not just a room - speaker coupling.
    Is it at all possible that an amp gives more power than a speaker requires? Is it at all possible that an amp overloads anything at normal listening levels?
    Harbeth M30

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    Unhappy 'Small amps strangle sound' - discuss

    Quote Originally Posted by Tompj View Post
    Is it at all possible that an amp gives more power than a speaker requires? Is it at all possible that an amp overloads anything at normal listening levels?
    Gentlemen, please, I implore you. Would you kindly listen to me?

    I, and others, have stated time after time after time the reality about amplifiers, specifically relating to how much power you need to generate an approximately life-like dynamic experience at home with the correct relationship between the loudest points in the music - the white lights - and the quietest, darkest moments and all the tone colours in between. It's all here to read. All of it. In immense detail, with examples, presented in a way that the average disinterested teenager could grasp. So why is it not read? It beats me. It truly does.

    One or two posts have resurrected the 'small amps sound wonderful' and 'I can hear a night and day difference between amps', so here is our position, again. Truthfully. Factually. Provably. Go check it out yourself or go into the electrical dept. of your local university and talk it through with them. They'll tell you the same thing.

    OK, from the top:

    1. The dynamic range between loud and quiet in live music is huge. It cannot be accurately reproduced at home. Why? Common sense tells you that two 5" or 8" drivers or two 12" plus two 8" drivers simply cannot, ever, under any circumstances, generate the acoustic power or loudness of an orchestra with 80-100 instruments. That sound power cannot be realised at home and if it could, it would shatter your windows and damage your building structure, let alone have you in trouble with the police and damage your ears.

    2. What we can generate in our listening room is a scale-model sound of the orchestra, accepting that we cannot generate (and must not generate) 120dB orchestral climaxes at home.

    3. We must accept that in lieu of peaks of, say, 120dB, our peaks must be much lower, perhaps 100dB or even less

    4. We must also accept that WE (I keep hammering this point home; it's vital), WE, with our hand on the volume control, decide how loud WE want the peaks to be. The amp doesn't decide this for us. Nor does the music, directly, WE set the loudness maxima, or we think we do. But that assumes that the amplifier has enough volts available - i.e. is a powerful amplifier - that as we turn up the volume control, the sound loudness truly increases, not just on the easy, middling loudness parts of the music, but the fast, power demanding peaks. We'll look at that shortly with an example.

    5. When we set that peak loudness, the speakers respond to the voltage that appears across their terminals ...

    6. And according to their electrical impedance, they SUCK current from the amp. Lots and lots and lots of it. Amps and amps because loudspeakers are virtually a short circuit to the amp. They have a very low impedance and amps HATE low impedance because it's the equivalent of weighing-down a lorry struggling to climb a hill.

    7. If the speakers don't get the current to support your voltage (loudness) setting, as commanded by your operation of the volume control, they are sonically strangled. The music waveform (the voltage) needs a certain current to make the speaker cones move, and if the current is limited inside the amp, then they cannot faithfully follow the outline of the music waveform as encoded on the disc. Power compression is the result

    8. P L E A S E could contributors not use this forum to restate the miracle they have discovered that they are are (uniquely) able to clearly hear significant differences between amplifiers. OF COURSE YOU DO! You shouldn't be proud to admit that! You will hear differences. I will hear differences. The finest musician on the planet will hear differences. The Archbishop of Canterbury will hear differences. We'll all hear differences. You should expect to hear differences! There is something wrong with your hearing if you don't hear differences! These differences are there! They are real!

    BUT ... what you are almost certainly hearing is not the latent difference in the amplifier circuitry, but the difference of a change in loudness. Until you take the trouble to measure two amplifiers with test equipment (cost around $200) and carefully turn the volume controls until amp A is at EXACTLY the same loudness as amp B, your ears/brain is confusing the change in loudness with a change in quality. Or to put it another way, if someone takes that position, they are making a fool of themselves, as with more rigor in the testing methodology (where levels are matched) they may not be able to tell the amps apart at all. And that is so very, very, easy to prove. This aspect of human hearing has been accepted for decades and is well researched.

    And the next bit to utter nonsense to dispel is that there is some magical correlation between amplifier power rating and sonic quality, so that a puny little amp will have superior sonics to a big amp. Rubbish. Utter twaddle. Completely untrue. Marketing BS. The one thing that a small amp guarantees is that the voltage available at its output will be small, so the sound will be quieter, the peaks will be less loud and the amp will be running hard, and depending upon the music, may be in more or less continuous soft clipping. The fact that you can't hear soft clipping is again nothing to be proud about; it's another lamentable limitation of the human ear.

    You need power if you are serious about creating anything approaching the sound of real life at home with normally efficient speakers. You need volts at the speaker terminals. You need watts. There is no substitute for power. Power makes things move, and speaker cones with their 1% efficiency of electrical to acoustic power conversion are like the steam trains of yore: they need lots and lots of coal to feed their voracious appetite.

    So no, it is not possible for the amp to run-away with itself and ram power into the speaker whether it wants it or not: YOU set the volume and the speaker just takes what current it needs. Not an atom more.

    Do we 'get it'? I despair.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default

    I have been made aware of this some time back indeed sir by yourself, and I know you are right. My questions therefore where merely rhetorical.
    Harbeth M30

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    Default

    Here is an example from a wonderful CD I picked up in charity shop today. A great example of how you need massive power reserves if you want to create something approximating to the concert hall experience at home. I do. For me that's what makes high fidelity sound worth having. You may not. You are perfectly at liberty to enjoy a concert at home as background music whilst reading a book. Sometimes I too like that. But just as with having a sports car, roof down on a sunny day, there is no substitute for the thrill of sheer power. That's how I feel about music where the score - and recording - utilities a wide range of tone colour. And for the correct dysnamics you need power. Lots of it. Why would you want to spend-out good money on Harbeth speakers if you didn't have a passion for live sound? You'd be wasting your money.

    Who in their right mind would take out the V12 6 ltr. power plant from a Jaguar sports car and replace it with a 1500cc engine? Madness surely.

    Loading the player ...
    Clip 1: the CD source

    Here is the same wide-dynamic recording with reduced dynamic range in the loud passages (from about 1 minutes in). Both tracks are identical until that point, because the small amp would have no difficulty delivering power until the music becomes loud. This synthesises a small amp incapable of delivering the correct amount of power as demanded by a given (user) volume setting. You are hearing power compression, aka soft clipping.

    Loading the player ...
    Clip 2: power compressed

    Source: Chandos - The film music of Ralph Vaughan Williams CHAN 10007 (highly recommended)
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default

    Alan, don't despair. I believe it was a French philosopher who said, in effect: Everything that needs to be said, has been said. But no-one was listening, so it must be said again.
    Ned

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    Default

    Quote Originally Posted by Ned Mast View Post
    Alan, don't despair. I believe it was a French philosopher who said, in effect: Everything that needs to be said, has been said. But no-one was listening, so it must be said again. Ned
    Huuuumph.

    OK, we can take it one step further ... just so that you're absolutely clear what power compression sounds like (an essential prerequisite for being able to talk meaningfully about amplifiers at all) I've spliced the two above clips together and flipped from one to the other. I have not adjusted the volume controls at all throughout. I have only applied some signal limiting when the signal exceeds a certain loudness level simulating what happens when a small amplifier runs out of power; below that loudness level there is no signal adjustment and both a small and large amp deliver to the speakers whatever power the recording demands for a fixed volume setting.

    You will note that the two "amplifiers" sound (and obviously measure) the same when the music is just idling along, but at about the 1min 40 toggle from the 'powerful amp' to the 'small amp' you can clearly hear what power compression sounds like. In fact, up to 1 min 40, there are eight preceding flips from A to B (see image); I doubt you'd hear any of them, because the music was not especially demanding, and the 'small amp' had enough power to drive the speakers as the score requires.

    You probably didn't hear the effect of power compression coming in on Clip 2, above did you, but again, when we juxtapose audio events in an A-B, side by side presentation, then we really can make sensible comparisons. This power compression manifests itself when the smaller amp just cannot produce the volume (loudness) that the music demands for a given user setting of the front panel or remote volume control, and from that point in the music onwards, the difference in musical dynamics between these two 'amps' is very evident. This demo is necessarily dramatic to illustrate the point.

    Doubtless, some listeners will prefer the easier-on-the-ears compressed sound as in Clip 2 above, but as we will hear when they are flipped without delay, that is not what was recorded and is not how it should sound and is the sort of effect you will definitely get when listening to dynamic music at higher volumes with small amplifiers. There is no justification whatever - none, zero - for selecting a low powered amplifier unless you have good reason to compress the dynamics in your replay music. It really is that simple.

    Loading the player ...
    Clip 3: flip from source (first and last) to power compressed
    Attached Images Attached Images
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default I love tubes for their shortcomings

    Alan,

    I am very sorry to make you so upset. I will take the time to read everything very carefully. I will stop posting here because it seems to me that the language barrier is too strong anyway.

    Just a few points to clarify : I have no problem in thinking that I am not hearing a musical work as it was intended to be heard by the maker because no one on earth as you said can reproduce real life music on a Hifi system. As Verdier said " I love tubes for their shortcomings". I love tubes for the same reason, and low power amplifiers too.
    I am not going to argue with you on electricity and acoustics : I am an orthodontist ! :D So obviously you are right and I am wrong. My ears just happen to love the way I am wrong ! :lmao:

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    Default The importance of dynamics

    Quote Originally Posted by Jerome W View Post
    ...Just a few points to clarify : I have no problem in thinking that I am not hearing a musical work as it was intended to be heard by the maker because no one on earth as you said can reproduce real life music on a Hifi system. As Verdier said " I love tubes for their shortcomings". I love tubes for the same reason, and low power amplifiers too.
    You are not upsetting me. My concern is only that as this forum is read internationally as a source of solid, pragmatic advice, care has to be taken to disseminate advice, advice that is at odds with basic physics. A small amplifier running out of steam is just another form of distortion, and an avoidable one at that, and high fidelity is, or was intended to be, about eliminating distortion. Surely?

    Power compression or soft clipping or whatever you want to call it, is a fact of life with power amplifiers, and a serious issue with 'small' amplifiers. What defines a 'small' power amplifier is not its case size, nor price tag, nor use of particular exotic components - it's none of those things. What defines a 'small' amplifier is how much energy there is available in its power supply storage capacitors when it is turned on and ready to work. Small amplifier = small energy reserve. Big amplifier = big power reserve, and yes, a big reserve inevitably means a physically bigger case to hold the physically bigger capacitor bank.

    The analogy is exactly the same with the motor car. The same model available with an entry-level 1ltr. engine or a 3ltr one. Around town there is little practical difference in power drawn from the engine unless you stamp your foot down on the throttle, the equivalent of cranking-up the volume control. But out on the open road, would anyone, anywhere, actually prefer the performance of the 1ltr. engine revving to a scream, inevitably limited acceleration, reduced reliability, when they could make use of the easy power potential available at our command from the bigger engine? I find the preference for 1ltr. over 3ltrs. incomprehensible. Power reserves always gives a more satisfactory experience on the road, and at home with the audio system. Do not underestimate how much power is required to get speaker cones moving remembering that about 99% of the available power at our command is wasted as heat and produces no sound at all.

    The dramatic sonic example I have given demonstrates that whilst we cannot, and should not, attempt to reproduce the maximum loudness of a full orchestra playing at full power at home, what high fidelity sound aims at is preserving the shades of tonality in the music, with the overall peak scaled down for domestic listening. In other words, to preserve and reproduce the dynamics of the music even if not the full peak loudness. If that were possible with an all-in-one system with a 5W amplifier then there wouldn't be a high fidelity industry.

    Great composers, great orchestras and great recording engineers strive to make music interesting by the use of tone colour, sometimes loud, sometimes soft; sometimes building to a climax interweaving the different sections of the orchestra to make the musical journey exciting and fulfilling. If we deliberately compress the dynamics through the selection of underpowered equipment at home, we might as well have picked a second rate orchestra, in a second rate hall, with a junior conductor who was uncertain how to extract the dynamics from the musical resources he has available - the whole performance just boring.

    One explanation of all of this is that too few home hifi enthusiasts actually go and listen to live orchestras. Before spending a cent more on hifi upgrades, including loudspeakers, invest in a few evenings at the concert hall and remind yourself what the objective of high fidelity sound is intended to be! One thing you will surely marvel at is the dynamics of an orchestra under a good conductor: it is borderline terrifying at times.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default Amplifier headroom

    A useful link on amplifier headroom, and why it makes sense to buy as much amplifier power as possible.
    http://www.glasswolf.net/papers/headroom.html
    Much the same arguments, but usefully set out.

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