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Thread: Amplifier selection for your Harbeths (general, not specific Harbeth models)

  1. #361
    Vlado Guest

    Default Re: Amplifier selection for your Harbeths (general, not specific Harbeth models)

    Hi All,

    try to check (if stated in technical specification) what is the maximum peak current of the amplifier. This is the key!
    (by keithwwk mentioned Electrocompaniet AW120 DMB has a peak current of 100 A )

  2. #362
    tricka Guest

    Default Re: Amplifier selection for your Harbeths (general, not specific Harbeth models)

    Thanks all for your replies.

    Ha ha - Alan my car is a Honda Jazz (Fit) so I fit in the puny end of spectrum! I just let everyone pass me on the motorway - besides here you are limited to 60mph (100km/hr) which is strictly enforced. As an analogy I am limited in my listening levels (everyday driving) to mid 80's tops (50mph) and usually (mostly) mid 70's (30 mph). 90% Classical. 10% everything else.

    Interestingly living in a busy city I suspect ambient noise also has a lot to do with it. The other evening it was softly raining which keep the noise right down (that is shut the fruit bats up) and the micro detail was so much clearer at low volume.

    Righto - it sounds like I might have to change the speaker to the SHL5 rather than change my amp. Or just stop whinging and enjoy what I have.

    As an aside I was listening to a album last night (Renegade Soundwaves) which I had not played in a while: I heard all sorts of things on it that prior to the Harbeth's I had not. It was a totally different presentation compared to my last 15 inch Coaxial monsters (as one would expect) - which were the perfect rock speaker as described by Alan. But pretty average at everything else.

    Cheers
    Andrew

  3. #363
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    Default 100A amplifier output potential or how to set fire to your speakers!

    Quote Originally Posted by Vlado View Post
    ...maximum peak current of the amplifier ....has a peak current of 100 A )
    Whoa! Wait a moment! Stop now! This is crazy! Mayber or maybe not a certain amplifier has huge peak current capability. Do you know how much damage 100A can do? 100A is a seriously huge amount of destructive power. It could easily kill you and cause your organs to fry. It has no place in hi-fi. Or maybe it does have. Perhaps it's the extra thrill we're all seeking? I invite you to decide after carefully studying these facts ....

    First, let me show you what 100A can do .... take a look here at this arc welder used to weld steel together. See the welder's control dial is graduated up to 150A? 150A! That's what you need to weld steel. Now look at the destructive power of 100-150A and how you need a proper ventilation system. So remember folks - open the door before playing your hi-fi if you are driving 100 amps into your speakers! Essential - have the fire department on standby.

    Now look here look at what just a puny 1.8A can do. Frightening. This is exactly what I have been saying about needless amounts of power. You can't actually use it. The speaker just can't handle it. So why have it with all its destructive potential waiting to catch you unawares?

    OK - now the Christmas quiz. How many amperes does it take to utterly destroy a loudspeaker? Supplementary question - how many microseconds would the speaker last?

    Tip: before answering, check out this video. Answer maybe here .... count the seconds. Frying tonight? - probably only about 5-10 amps.

    Now, let's get back to the real world! Speakers can take hardly any power at all. The working heart of a speaker is the voice coil shown here upside down, the woofer cone/coil removed from its chassis. This shows what happens when too much power is applied. First the smoke, then the smouldering, then the fire?


    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  4. #364
    Vlado Guest

    Default Re: 100A amplifier output potential or how to set fire to your speakers!

    Quote Originally Posted by A.S. View Post
    Whoa! Wait a moment! Stop now! This is crazy! Mayber or maybe not a certain amplifier has huge peak current capability. Do you know how much damage 100A can do? 100A is a seriously huge amount of destructive power. It could easily kill you and cause your organs to fry. It has no place in hi-fi. Or maybe it does have. Perhaps it's the extra thrill we're all seeking? I invite you to decide after carefully studying these facts ....
    Hi Alan,
    the 100 A peak of that amp is measured indeed in microseconds and in 0,5 Ohm ( the manufacturer guarantee the stability of that amp in 0,5 Ohm load). The high or very high peak current of an amplifier is important only at the moment where the impedance and phase curves are at their largest divergence. At that moment the amplifier should not limit the current consumption of the speaker. ie the speaker is drawing the current from the amp and not the amp is pushing the current into the speaker.

    BTW: the specification of that amp is 120 W/ 8 - 200W/ 4

  5. #365
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    Default Re: 100A amplifier output potential or how to set fire to your speakers!

    Quote Originally Posted by Vlado View Post
    ...the 100 A peak of that amp is measured indeed in microseconds ...
    Even more weird! Music does not contain *any* frequencies that are as brief as microseconds. The real power and energy in music is built from frequencies that last about a thousand times longer than that i.e. milliseconds not microseconds. So, as I read it, the astonishing capabilities of the amplifier make it eminently suitable for generating a welding spark at radio frequencies (microseconds) and have no relevance whatever to the reproduction of music audio.

    Am I missing something?

    Now, here's an interesting thing. In this User Group we often say that Harbeths are designed and optimised for listening at a moderate listening level. We've recently put a number on that loudness of around (roughly) 85 or 86dB at the listening chair, say 2m from the speakers. Now, coincidentally, a typical Harbeth has a sensitivity of also about 86dB "for 1W at 1m" or something like that. So, if you are listening at our moderate level, 1m from the speaker, how much power would you need from your amplifier? Answer - 1 watt. Yes, that's right. Just one meagre puny little watt!

    Now, to be fair, most people don't listen at 1m from the speaker they listen at about 2m away. That extra distance from 1 to 2m reduces the loudness at the listening chair by 6dB (spl dB). So they need to turn up the amp to bring the level back to 85dB at listening spot. They will need to double the amplifier output and double it again (+3dB, +3dB power dB). So they start with 1W, they double it to 2W and then again to 4W. Let's add a bit for comfort and call it 10W. So what that means is that, with negligible power reserve and on low-dynamic music, it should be possible to produce the moderate sort of sound level we approve of with a small amplifier. Forget all about hundreds of watts. Completely disregard huge ampere specification. Ignore crazy peak output ratings. They are all totally unnecessary when driving a Harbeth at home. And never forget, regardless of how much power you pump into the speaker and how big the amp is, the speaker's power handling capacity is very small as I showed on the videos in my previous post. Too much power and it will burn out and/or catch fire.

    I'm pulling my (remaining) hair out wondering what I have to say or do to wean folk off the idea that you need brutal, monstrous killer amplifiers to make adequately loud music at home?!

    Look here: very good explanation.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  6. #366
    tricka Guest

    Default Re: Amplifier selection for your Harbeths (general, not specific Harbeth models)

    Thanks Alan
    I have got the message and will happily stay with what I have got!
    60wpc is indeed ample.
    Cheers
    Andrew

  7. #367
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    Default Re: Amplifier selection for your Harbeths (general, not specific Harbeth models)

    Good man! Could you hold a hot 60W light bulb in your hand? No. So don't expect the poor voice coil to be able to handle that power too!
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  8. #368
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    Default IMPORTANT! Amplifier and speaker power and efficiency.

    We've frequently touched upon the subject of amplifier power rating, speaker power rating and speaker efficiency.

    For example here and here and here and here.

    The misconceptions and myopic view of this particular subject really does worry me. It leaves the potential that you will damage your speakers (or amplifier) and waste time and money on spare parts. It's because consumers consider only one side twin sided problem. The user is looking only from his side, the consumption side, considering only how much power he wants to ram into the poor loudspeaker. But from my perspective as a designer, I'm acutely aware that what is far more important is the production side: what power the speaker can actually handle and what it can reliably deliver as clean sound, year after year.

    There are constant anxiety about 'how much power is needed to drive speaker ABC'' and there are those who believe that huge, macho amplifiers are essential to hi-fi reproduction at home. Conversely, there are others who claim that only small amplifiers have detail and resolution. I'll leave you to mull over all those sonic arguments for and against big/little amplifiers. I'm going to show you the reality of the the situation from the perspective of the poor little loudspeaker. It's clear to me that huge macho amplifiers are not only unnecessary but a hazard in waiting. So, to start at the beginning - attached is a photo of a steam train and a conventional 8" woofer. As you can see, the train is puffing its heart out pulling the coaches up a long incline.

    Question: What have the steam train and woofer in common?

    Answer: They are both power converters. The steam engine converts the energy locked within the coal into heat, and then into steam and finally through pistons into motion. The woofer takes a current from the amplifier which cause the voice coil to move, and as the coil is attached to a cone, causes motion of the cone which produces a variation in local atmospheric pressure which we call sound.


    Question:
    Can the efficiency of the steam engine and woofer be measured? I mean, can we calculate how much of the energy going into the them (from the coal, from the amplifier) arrives at the wheels as motion, or as sound pressure from the woofer?

    Answer: Yes we can. We can measure the number of watts of energy in and out. For example, we know that a kg of coal has a certain calorific value (we can convert calories to watts) and our domestic electricity meter measures the wattage being drawn by the amplifier from the national grid.


    Question: What happens to the energy that doesn't reach the wheels as motion or as sound pressure generated by the woofer?

    Answer:
    It's wasted as heat. Heat is useless. It doesn't move the train any further or faster. Heat doesn't make the woofer any louder. Once energy is wasted as heat, it's lost forever. Although we've paid good money for that energy we've thrown it away. We've nothing to show for it apart from a rise in temperature. That's a really lousy bargain.

    Question: Have a guess at the % efficiency of a typical steam engine or woofer. In other words, guess how much of the power input is wasted as useless heat.


    Ready for a nasty surprise........ ?

    >
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    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  9. #369
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    Default Re: 100A amplifier output potential or how to set fire to your speakers!

    10 watts, Alan? So my 12 watts are fine? Right? At 2 metres...

    David

    PS I love steam trains, but their efficiency is appaling. About 8%? Don't know how loudspeakers match up...

  10. #370
    tricka Guest

    Default Re: Amplifier selection for your Harbeths (general, not specific Harbeth models)

    Ok...I just dug out my 2-3 wpc SEP:


    hooked it up, mucked around with my Dac/Pre output and let me say at normal listening levels on simple music it is sounding pretty darn good.

    So if I only have 2wpc going and it's working well I guess that means all I need.

  11. #371
    jasontan Guest

    Default Re: Amplifier selection process and service backup ...

    Quote Originally Posted by Teuton View Post
    True, I have not heard of people pairing the two. Though I doubt it would prove to be a bad match.
    Hello everybody,

    Belated response to this post, just came across it. My first post!

    Just for the record, I tried a Bryston 4B ST with a pair of P3 and P3ES back around 1996 (I think with Quicksilver and Gryphon preamps) for a month or so. The sound in my 20x12 ft living room (speakers on the long wall, open to the rest of the house at one end) was very well balanced and all of a piece; good to very good overall, with no apparent faults. The combination sounded, well, bomb-proof, such was the integrity of the reproduced sound.

    I still have the same pair of P3ES, and would run the 250 watt Bryston but for owning an Audio Note Kit 1, 8-9 watts, single-ended triode, in a smaller room, approx 15x10ft.

    Won't bore you with a description of the sound, suffice to say it works too. How about that for the P3's versatility.

    jason

  12. #372
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    Default Re: IMPORTANT! Amplifier and speaker power and efficiency.

    Quote Originally Posted by A.S. View Post
    Question: Have a guess at the % efficiency of a typical steam engine or woofer. In other words, guess how much of the power input is wasted as useless heat.
    D.S. has commented (different thread) that "PS I love steam trains, but their efficiency is appaling. About 8%? Don't know how loudspeakers match up... "

    Sadly, you're way off target. The answer to my question above is that 99% of the energy input to the steam train (from the coal) and the drive unit (from the amplifier) is wasted as useless heat. Only 1% of the coal's energy reaches the wheels as useful motion and less than 1% of the amplifiers energy to the loudspeaker is converted to sound. Typically, a boxed loudspeaker has an efficiency of about 0.5%. Truly shocking isn't it.

    So my point is this .... it's madness to believe that you can force lots of power into a speaker because 99% of the power you apply just cooks the voice coil. And because so little of the power input becomes sound, the user turns up the volume (more power input to the speaker) which speeds-up the cooking process. In addition, under heavy-drive conditions as the copper wire of the voice coil heats up, its resistance increases, so it draws less power from the amp, so there is less sound generated. So the user turns the volume up even more and the coil further heats-up. This is typical of what happens at a party, when the parents are out and the kids are home alone with the hi-fi. This cycle continues until the coil is destroyed by overheating. And remember - the heat is an unwanted by-product due to the appallingly low efficiency.

    Also have a look at what happens to the voice coil when this process runs-away .... a destroyed woofer returned from the BBC due to an amplifier fault. This speaker was connected to a very powerful amplifier which failed when the engineer was away from the studio on his tea break. When he returned, it was too late to save the speaker. Had he been using a smaller amplifier with less power (less damage potential) of a more appropriate power match to the speaker he may have had enough time to disconnect the amp (or switch it off) and could have saved the speaker. Or the smaller amp with a smaller fuse may have tripped. The bigger amp, with obviously a bigger fuse didn't trip for several minutes.

    Huge, powerful amplifiers are no more reliable than small ones. But when they fail, their destructive potential is far greater. So, beware of using a power amp that is needlessly larger than the power you actually need for everyday hi-fi listening at home. Forget hundreds of watts and huge current potential - all that does is puts you into the meltdown danger zone which is not covered by Warranty.

    >
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    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  13. #373
    Hu Guest

    Default Plinius amplifier specification ...

    Dear Alan,

    How much about my Plinius SA102, is it huge and powerful amp?

  14. #374
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    Default Huge amplifiers, huge car engines = danger

    I don't know. What does the Instruction book say?

    I'm sorry to bang on about this subject, but I've been stating my opinions about amplifiers, power, vice coil practical limitations for some years. Clearly during that time lots and lots of hugely powerful amplifiers have been sold to presumably happy users so my influnce over consumption behaviour, even as a speaker designer, is obviously zero. The last person to take any advice from is of course the chap who does the job, day in, day out. Now, as you may by now be aware, the tell-tale signs of amplifier overload of the speaker drive unit are obvious. As is the burning smell. We can video the dissection of any defective drive units (according to our IS09001 procedures) and we cannot provide any Warranty support for overloaded drivers - they need to be replaced outside Warranty.

    New drive units are expensive but they are not profitable business for us because they divert time from production of complete systems. So we do not want you, our users, to damage your speakers because unlike many other brands, we do not position or want our spare parts business to be a profit earner (profit centre). This is a very important business strategy point.

    Huge amplifiers increase the damage potential as huge car engines perhaps increase the chance of a crash and a very expensive repair.

    Don't be nervous. Again, as I've said here before in explicit detail, it is you, the user that has to power to command the amplifier. You switch it on. You set the volume level. You have to be responsible for your actions. As I said, using a big amp is like driving a big fast powerful sports car. The reason insurance companies penalise young drivers is because they know from their records, that power in the hands of a young enthusiastic driver is a fatal combination. But the same engine power controlled by a middle aged man is quite safe - unless the brakes fail. It's the same with amplifier.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  15. #375
    Hu Guest

    Default Power and class A or AB?

    This, Alan, is what my Plinius SA102 instruction book say:

    Power:
    125 watts continuous per channel into 8 Ohms
    2 channel stereo mode
    400 watts continuous into 8 Ohms
    Balanced mono mode

    Does that mean my SA102 has 125 W at both A or A/B mode? Thanks!

  16. #376
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    Default Power and Class A or AB heating (cost of electricity)

    I think what you mean is actually this ....

    Power:
    (a) 125 watts continuous per channel into 8 Ohms, 2 channel stereo mode
    (b) 400 watts continuous into 8 Ohms, Balanced mono mode

    Well you can ignore (b) because you are using the amp as a stereo amplifier. But it's impossible to factually answer your question "Does that mean ...125 W at both A or A/B mode" without knowing a lot about the design and maybe talking to the designer. But I think we can make some general deductions ....

    1. Class A amplifiers are running at 100% power all the time even with no music playing.They are wasteful of electric power and they contribute to global warming. Almost all of this power they draw from the mains supply is wasted as heat. If the amp was working at 125W in class A mode, the case would be as hot as a 125W light bulb. Is it? Be careful not to touch the bulb or the amp case if hot. I think that all tube amps are of this class A type?

    2. Class AB means that most of the time the amp is working in class B mode, which has high efficiency (perhaps 70%?) and only on the very quietest notes in the music is it working as class A. This is a good overall balance of energy and efficiency. The case only heats up (slowly) according to how loud you play the music because the 30% inefficiency is converted to wasteful, global warming heat.

    My guess then is that you amp's case is not normally hot, just mildly warm. This implies then that it is a class AB or class B design. Agree?

    P.S. Thought about financial cost of running a power amp. Turn off all electrical equipment in you apartment and read your electricity meter. Write down the meter reading. Borrow a class A amp, hook it up and play it for six hours. Read the meter again, subtract initial meter reading. Calculate how many kW/h of power you have used (and will be charged for). Change over to class AB or B amplifier. Play same music at same loudness for six hours. Re-read the meter. Calculate how much power you have now used. It will be much less. I guesstimate that the running cost of a class A amp in power consumed is about USD3-10 per month. You may or may not think that is much money. In the winter time it's a good idea to have a class A amplifier which is simultaneously a room heater!
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  17. #377
    Hu Guest

    Default Re: Power and Class A or AB heating (cost of electricity)

    Thank you very much for your time, Alan! My Plinius SA102 could work as A/B or class A amp. You can not even imagine how hot that could be at A mode, like burning, so nearly all the time I use its A/B mode, as you said, mildly warm. I don't have to read your electricity meter, I know exactly how much I have to pay when I have more equipments. But all of them are for my Harbethes.

  18. #378
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    Default Re: Amplifier selection for your Harbeths (general, not specific Harbeth models)

    I think the issue is not just about power but the findamental issue is the potential of power. The Harbeths are an easy load to drive and can be paired with many types of amplifiers, from SETs to bigger powered amplifiers. As mentioned in my previous posts, I have tried my SHL5s with 8 watt SETs to 180 watt A/B amplifiers. While the 300B SET can drive the Harbeths within moderate listening levels and with easy musical scores (vocals, jazz quartets), you will need much more power to be able to resolve complex orchestral pieces, allowing the speakers to identify and distinguish individual instruments/singers. Using Alan's car analogy, its fine to drive a low powered cc car for most of the time but occasionally you will need extra power to safely overtake a car. This is where the potential of a bigger powered engined car has the advantage over the Honda Jazz!

    This is where indivifiaul listening experience becomes important: if you always or mostly listen to vocals and small groups of musicians (quartets, for example), you will be very happy with the 300B SET or a smaller powered amplifier. But, if you are listening to the 1812 Overture, you will need more power to segregate the various instruments. Otherwise it sounds like congealed noise!

    As always, this is just my o.o2 cents' worth!

    Best Regards
    Dennis

  19. #379
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    Default Lorries, aerodynamics and loudspeakers

    Quote Originally Posted by denjo View Post
    ... the fundamental issue is the potential of power. The Harbeths are an easy load to drive and can be paired with many types of amplifiers,...But, if you are listening to the 1812 Overture, you will need more power...
    Correct. But remember that the more power pushed into the speaker, the greater the heating effect on the voice coil and hence the greater the power that is lost (wasted) as heat. So you need to apply even more power to cover the losses which invokes even greater heat loss ... which you try to overcome with even more power ... which invokes even more heat losses. This game spirals out of control quite quickly and the result is voice coil burnout.

    Powering a woofer is rather like driving a big, square lorry with poor aerodynamics. At low speeds although power is wasted forcing the lorry through the air, relative to the power wasted in tyre friction and all the other inefficiencies it's in proportion and not an issue. But imagine that you fitted a huge jet engine to the lorry and fired it up and accelerate to 100mph. Now the terrible aerodynamics are really exposed - the lorry has the aerodynamics of a small house i.e. incredibly bad. So, to get from 100mph to 110mph you may need to apply a three times increase in input power because the wind resistance is so strong (i.e. the losses are so great) and to get from 110mph to 120mph you need to multiply the power ten times. And from 120mph to 130mph you need to increase the power fifty times by fitting another jet engine. You can't keep on increasing the power like this even if you have it available. The weakest part of the system will catastrophically fail. Perhaps the gearbox will explode or the types burst or the cab rip away from the body. A point is reached when all of the input power is wasted as frictional heat and none of it actually results in motion of the lorry or the drive unit. The lorry just cannot go any faster.

    That's my point concerning loudspeakers: they are fragile, inefficient devices with the aerodynamics of a brick. They have a small but predictable power envelope between just enough power in for them to be comfortably loud and so much power in that they burn out. We really must break away from thinking only from the perspective of the power input but consider mainly the acoustic output situation (plus all that heat). That's what really matters. Having the power available is one thing, but being able to turn it safely into sound is a totally different game.

    It's about fifty years now since the first passenger carrying jet airliners appeared. The top speed (about 550-600mph) has not increased, so journey times are about the same even though engines are much bigger and much more efficient. Why? Because of wind resistance (= frictional losses). The amount of power needed to achieve even a small increase in speed is huge and almost all wasted as frictional heat along the aircraft skin. So, in place of cheap aluminium aircraft skins, the jet makers would have to use expensive and exotic heat resistant metals as they do on space rockets. So, just as with drive units, there is a point beyond which the power input is totally wasted as useless heat. This is a very typical situation right across engineering - the need to balance power in to a system with realistic expectation of useful (non-heat) power output.

    Note: Concorde was fast but the energy efficiency was miserably low. Its skin was at boiling temperature due to wasteful frictional heat and the fuel consumption was horrendous to punch even its aerodynamic shape through the air. It could have travelled even faster - the engines were powerful enough - but the top speed was strictly limited to minimise the wear and tear on the airframe. Just a little faster and the boiling-hot external panels would have disintegrated due to heat. The absolute maximum permitted temperature on the nose was 127 degrees C (water boils at 100C) and this temperature defined the maximum speed (faster speed = more friction = more heat) not the engine power available. Here.

    This is exactly the same situation with a loudspeaker. What limits the useful maximum output (the 'speed' of the speaker) is not the amplifier driving power available (the 'engine') but the heat that builds-up in the voice coil (the temperature of the nose).
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default What about fuses?

    This has been an excellent discussion. It seems to me to raise the question of whether loudspeakers shouldn't be fused to prevent overload that could result from high settings of the volume control. This could happen either by oversight or because the person operating the system does not appreciate the limitations. Decades ago it was quite usual to install fuses in series with speakers.
    Last edited by templetune; 25-12-2008 at 10:32 PM. Reason: changed title

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