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  1. #1
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    Question What makes a good Power Amplifier?

    Wattage?
    Class?
    Ohms?
    Resistors?
    Capacitors?
    Type?
    Power transformer?

    Bill

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    Forum Regular Peter_Klim's Avatar
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    what's important to you?

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    A good power amplifier always starts out with a good power supply. One that can easily supply all of the current and voltage necessary to deliver the rated power to the load, one that is fast and quickly recovers from momentary overloads, one that is stable and relatively immune to changes in line voltage including noise, and one that comes as close as possible to the ideal of a battery. No matter what type of amplifier you like or use, it cannot be better than its power supply. That is the heart and soul of every one of them.

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    I'd say what makes a good power amp is one that works when the switch is in the ON position.

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    That only makes one that functions, not necessarily one that performs well.

  6. #6
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    Quote Originally Posted by BillB
    Wattage?
    Class?
    Ohms?
    Resistors?
    Capacitors?
    Type?
    Power transformer?

    Bill
    The answer to this depends on how you define "good". To me, a good power amp delivers lots of amps for not much money (<$500) money. I have a heavy amp, but I would prefer a small light one if it could perform similarly.

    Obviously, we want distortion to be below audible levels into various impedances (or at least into my speakers' impedance) and at all frequencies in the audible band (20Hz-20KHz).

    Good binding posts for speaker wire would be nice.

    Who cares what kind of capacitors they use? I'd like my amp to last a long time, so I want some build quality. Such quality might get me to cough up more money, but it depends on how MUCH more money. For the price of some expensive amps, I could buy a new reasonably priced one every few years and still save money.

    One must always justify why it wouldn't be better to buy the cheaper amp and spend the extra money on better speakers.

  7. #7
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    Talking listen..listen.....and then decide

    I would like to add something to what skeptic said.
    1.Whatever he mentioned is the ideal for a power amp. But you need to know the fact that you will be looking at the spec sheet to check this out. But from my experience, you should listen and find if the spec sheet is lying. This is the case with most mass brand amp manufacturerers. I can tell you lots of stories of how the customer has been taken for a ride.Under ideal conditions (this condition exists only in utopia), all amps with the same specs should behave the same and show similar tonal characteristics. But nothing is further from the truth.LISTEN, LISTEN... and decided on what you like.
    2.You need to mate the right amp with your speakers. A bright sounding mega watt power amp with a pair of klipcsh(horn loaded high sensitivity speakers) will give you ear fatigue. The same amp will work well with low sensitivity,laid back sound speakers (example - dynaudio).
    3.One good way to avoid bad amps is to avoid most of the neon bulb brands. Have fun.

  8. #8
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    Quote Originally Posted by BillB
    Wattage?
    Class?
    Ohms?
    Resistors?
    Capacitors?
    Type?
    Power transformer?

    Bill
    You asking the wrong questions...Just listen to some amps that you think are the one. Then make your choice of amps....believe your ears...thats the most important thing in our hobby.

    Greetz MF

  9. #9
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    BillB

    Unless you are using Magnepan speakers, I would not worry about this very much beyond the "good power supply design" comments by Skeptic combined with adequate power at reasonably low distortion levels... which are easily found in many, many amplifiers today.

    I have found that cone speakers and electrostatic speakers sound the same when used with ANY reasonable choice of amplifier. The only exceptions to my ear are Magnepan speakers whose sound can be greatly altered by your choice of amp. But even tube amps for use with Magnepans should be selected with care. I never cared for Audio Research amps with Tympani- the resulting sound was agressive and not at all natural for my ears.

    Of course, if you do not religeously attend live recitals, you will never develop the "ear" that will allow you to obtain a realistic sound, and this will make your amp quest completely moot.

  10. #10
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Mash
    Unless you are using Magnepan speakers, I would not worry about this very much beyond the "good power supply design" comments by Skeptic combined with adequate power at reasonably low distortion levels... which are easily found in many, many amplifiers today.
    Do tell me why you think this is so. They are nearly a purely resistive load.

    Quote Originally Posted by Mash
    I have found that cone speakers and electrostatic speakers sound the same when used with ANY reasonable choice of amplifier.
    On which cone speakers and which electrostats is your opinion based?

    rw

  11. #11
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    Electrostatic speakers have coupling transformers which consist of a pair of coupled wire coils. A coil of wire is an inductance, and an inductance is the equivalent of a mass in a spring-mass system, i.e. electrical inertia. The voice coil in a cone driver is likewise an inductance, and again an inductance is the equivalent of a mass in a spring-mass system, i.e. electrical inertia. Basic physics. This is why the people who conduct DBT on amplifiers always claim that all amps sound the same when those amps are used within their limitations for power and load handling capabilities....because invariably amp DBT were conducted with cone speakers. Try a DBT using Tympani or other Magnepan speakers and the conclusions will be different.

    Remember that filters and cross-over networks are composed of inductors and capacitors.

    True, Magnepan speakers are simple resistances, particularly when directly tri-amped, because their voice-wires are arranged into straight lines up and down the proprietary membrane drivers, i.e. there are no wire voice-coils to add inductance and so there is no inductance created. Furthermore, those proprietary Magnepan membrane drivers are designed (tuned, if you will- refer to a good book on frequencies & mode shapes; I can recommend one if you want to learn the subject) for specific response ranges rendering extensive LC cross-over filters unecessary. Cone speakers present a very different set of physics and so powerful LC cross-over circuits must be used to control and blend their output ranges.

    You do not have to investigate every duck on earth to cofirm that ducks quack.

  12. #12
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Mash
    You do not have to investigate every duck on earth to cofirm that ducks quack.
    No, but there is quite a variance among ducks.

    So the presence or lack of inductance is a primary source for audible differences among amplifiers. Is that the sole determining factor?

    rw
    Last edited by E-Stat; 08-22-2004 at 08:23 AM.

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    When you get beyond amplifier distortion products versus available output power versus needed power, load sensitivity, and so forth, the inducive and capacitive qualities of a type of loudspeaker will limit what you can hear from that speaker type. Some loudspeakers of a given type will be better than other loudspeakers of that given type, but observe that even the very best and most expensive auto on the market today makes a lousy boat. Note again that electrical filters are composed of LC elements.......

    One can build cone drivers combining heavy ceramic magnets with a high magnetic density with a large voice coil intended to drive a well-stiffened, and therefor relatively more heavy, cone but at the same time voice-coil inductance has been increased. Not to mention that the speaker cone basket must be stiffened to keep the heavier magnet from vibrating at an audible frequency. The heavier magnet and basket structure means the speaker enclosure mounting board must be stiffer and thicker, and therefore heavier, to again keep the heavier cone driver assembly from vibrating at an audible frequency. This is a loosing battle in every sense of the word.

    Remember that natural frequency equations can be complicated but they are all a variant of
    natural frequency = (a constant) x Square Root (System Stiffness / Mass )

    So if you double the stiffness without adding any mass, you raise frequency by 41%. Wow!!

    But then you will have to double that stiffness without changing mass by using UnObtanium that has a Young's Modulus of 30,000,000,000,000 psi and a density of 5 nano-pounds per cubic yard.

    One can consider some real-world structural metals:
    Steel: Young's Modulus = 30,000,000 psi and density = 0.3 pounds/cu in.
    Titanium: Young's Modulus = 16,000,000 psi and density = 0.16 pounds/cu in.
    Aluminum: Young's Modulus = 10,000,000 psi and density = 0.1 pounds/cu in.

    Notice anything??

  14. #14
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Mash
    When you get beyond amplifier distortion products versus available output power...
    Have we?


    Quote Originally Posted by Mash
    One can consider some real-world structural metals:
    Steel: Young's Modulus = 30,000,000 psi and density = 0.3 pounds/cu in.
    Titanium: Young's Modulus = 16,000,000 psi and density = 0.16 pounds/cu in.
    Aluminum: Young's Modulus = 10,000,000 psi and density = 0.1 pounds/cu in.

    Notice anything??
    Why don't you tell us.

    rw

  15. #15
    Big science. Hallelujah. noddin0ff's Avatar
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    Ok, I've learned that all ducks quack and that a good car still won't float. Is it a witch? Burn it?

    I'm not following. To paraphrase my impressions. Mash, I think your argument is that Amp output doesn't vary much from unit to unit, model to model, operating with in the specified range. And that what you hear is speaker dependent. I'm not sure i followed the speaker physics lesson except to note that surely what you hear must also depend as much on acoustical design and material in the speaker as on magnets and inductance. I don't think physics is the whole answer.

    I have no idea what the real world structural metal example is supposed to indicate. I don't plan on using my speakers as a floatation device, just listening to them. It sounds like you describe that the speaker/amp pair set up an electrical oscillation at a frequency that may or may not be supported by the material components of the speaker. But, since most big, great speakers out there obviously aren't audibly humming (or people would not be buying them), I don't see where this point is going?

    I could use an synopsis in english...

    noddin0ff

  16. #16
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    Quote Originally Posted by noddin0ff

    I don't think physics is the whole answer.

    I could use an synopsis in english...

    noddin0ff
    The advice of "just listen" can't hurt, but understand that you would have to listen on the same speakers in the same acoustic space (ideally, your listening room). You also have to level match or you will likely prefer the amp that is playing louder.

    As nobody (I have every heard about in over 20 years) has been able to show that they hear a difference, good luck. The bottom line is that you have to have some really abnormal (weird impedance) speakers, such as some electrostatics, for most amps to have a problem.

    If physics (electronics and acoustics) isn't the whole answer, what is? The only logical response is psychology, which indicates that people will think they hear differences based on their expectations. This is a long established principle that is completely ignored by subjectivists as it iindicates that their keen perceptions are illusions.

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    The data on the three (most popular) structural metals was provided to allow you to notice that for all three metals the result of [Yonngs Modulus / Density] is the same. The structure's mass is volume x density, and the structure's stiffness is a direct function of Young's Modulus. Hence simply changing materials will not necessarily get you a change in natural frequency. Note that enclosure vibratory response can often be perceived as a reduction in clarity rather than being heard as "buzzing".

    Every amp DBT I have ever read about used cone speakers for listening, and every time the conclusions, as I recall, were that the amps were DBT indistinguishable one from another. I believe the inductive electrical characteristic of the coned speakers used blurred the discinctions among the amps while the essentially resistive electrical characteristics of Magnepans would allow the discinctions among the amps to be audible. Its a consideration for those wishing to hold another amp DBT.

    Almost all electrostatic speakers in existance have coupling transformers, and amps also used to have coupling transformers but coupling transformers were eliminated from amps for improved sonic performance. One exception I remember is a high-voltage electrostatic speaker featured in The Audio Amateur c1975 which was direct-connected to a dedicated high-voltage tube amp. As I recall the high-impedance membrane was charged to 3000 volts. This speaker was described as being a killer in every sense of the word.

  18. #18
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by RobotCzar
    As nobody (I have every heard about in over 20 years) has been able to show that they hear a difference, good luck.
    Tests are entirely valid for that which they test. For what they don't test, they stand mute.

    Quote Originally Posted by RobotCzar
    The bottom line is that you have to have some really abnormal (weird impedance) speakers, such as some electrostatics, for most amps to have a problem.
    You presume that audible differences only occur upon distress. Differences in amplifier design, implementation and construction have zero effect whatsoever, right?

    Quote Originally Posted by RobotCzar
    If physics (electronics and acoustics) isn't the whole answer, what is?
    You will only know that to be the case for when the testing encompasses all that which is available. I agree that there is little difference between a Buick and an Oldsmobile.

    rw

  19. #19
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    Quote Originally Posted by Mash
    Every amp DBT I have ever read about used cone speakers for listening, and every time the conclusions, as I recall, were that the amps were DBT indistinguishable one from another.
    Do share with us the specific amplifiers included in the tests to which you refer. Please don't resort to the circular reasoning fallacy that such does not make any difference.

    Quote Originally Posted by Mash
    One exception I remember is a high-voltage electrostatic speaker featured in The Audio Amateur c1975 which was direct-connected to a dedicated high-voltage tube amp. As I recall the high-impedance membrane was charged to 3000 volts. This speaker was described as being a killer in every sense of the word.
    You really do need to catch up on history a bit. The Acoustat X design, released in 1976 also ran high voltage tube amps directly to the plates of electrostatic panels at slightly over 3kV. Later, they replaced the tube amps with bi-formers increasing the drive voltage to around 5 kV. The current Sound Labs electrostats run the bias higher still. I seem to have lost your point with your dissertation about a product for which I have used for more than a quarter century.

    rw

  20. #20
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    Other amp characteristics.

    Quote Originally Posted by RobotCzar
    The answer to this depends on how you define "good". To me, a good power amp delivers lots of amps for not much money (<$500) money. I have a heavy amp, but I would prefer a small light one if it could perform similarly.

    Obviously, we want distortion to be below audible levels into various impedances (or at least into my speakers' impedance) and at all frequencies in the audible band (20Hz-20KHz).

    Good binding posts for speaker wire would be nice.

    Who cares what kind of capacitors they use? I'd like my amp to last a long time, so I want some build quality. Such quality might get me to cough up more money, but it depends on how MUCH more money. For the price of some expensive amps, I could buy a new reasonably priced one every few years and still save money.

    One must always justify why it wouldn't be better to buy the cheaper amp and spend the extra money on better speakers.
    In "How to Be a Sophisticated Audiophile and Resist Trendy Stupidities," in The Audio Critic, vol. 25, Winter 1998-99, p. 17, Peter Aczel gave the reasons why he thinks there is no reason why good mid-priced solid state preamps and amps should sound different from well designed higher priced stuff:

    "The midpriced equipment also has high input impedance, low output impedance, flat frequency response, low distortion and low noise--and that is what we can hear. There is no such thing as an effect without a cause, and there's nothing to cause the high-end equipment to sound better."

    Of course, The Audio Critic put amplifiers through a set of tests including dynamic power output down to 2 ohms into reactive loads. Some speakers are difficult to drive, and that can be significant under some circumstances.

    Yeah, good binding posts are a definite plus--also on the speakers at the other end of the cables!
    "Opposition brings concord. Out of discord comes the fairest harmony."
    ------Heraclitus of Ephesis (fl. 504-500 BC), trans. Wheelwright.

  21. #21
    Big science. Hallelujah. noddin0ff's Avatar
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    Quote Originally Posted by RobotCzar

    If physics (electronics and acoustics) isn't the whole answer, what is? The only logical response is psychology, which indicates that people will think they hear differences based on their expectations. This is a long established principle that is completely ignored by subjectivists as it iindicates that their keen perceptions are illusions.
    I guess I should have parsed my questions better. I would agree that physics probably describes very well how an amp performs. Signal in, signal out. Mash goes on about the 'physics' of speakers with mass, inductance, stiffness, density,coils, Young's modulus etc. Confusing. However, what he seems to be describing is the physics of energy transfer and of resonance. Which can be accurately measured but do not have a bearing on accoustics and the quality of sound, only the energy imparted to the air. I would parse 'acoustics' separately from 'physics' because there's no way his equations and a super computer could calculate the acoustics, and they certainly aren't amp dependant.

    Certainly psychology has a role. And I am a great believer in physics. (I know pounds is not unit of mass, e.g.). But some things can be measured. Sometimes its difficult for the aspiring audio nut to learn how far numbers are meaning full. And at what point they are bullsh't. And, where in the field of audio equipement diminishing returns begins.

    So, my question and confusion lies in which parts describe actually pertain to the amp and which to the speaker. I think judging the physical performance of an amp by the perceived sound of a speaker is not quite right, but I suppose if the speaker type is actually altering the physical performance of an amp, that would be interesting, and I'd like to try to understand what he's talking about. A lot of the jargon sounded like a description of speaker physics which doesn't strike me as so critical for amp performance.

    Am I off?

    noddin0ff

  22. #22
    Forum Regular Peter_Klim's Avatar
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    Quote Originally Posted by Mash
    The data on the three (most popular) structural metals was provided to allow you to notice that for all three metals the result of [Yonngs Modulus / Density] is the same. The structure's mass is volume x density, and the structure's stiffness is a direct function of Young's Modulus. Hence simply changing materials will not necessarily get you a change in natural frequency. Note that enclosure vibratory response can often be perceived as a reduction in clarity rather than being heard as "buzzing".

    Every amp DBT I have ever read about used cone speakers for listening, and every time the conclusions, as I recall, were that the amps were DBT indistinguishable one from another. I believe the inductive electrical characteristic of the coned speakers used blurred the discinctions among the amps while the essentially resistive electrical characteristics of Magnepans would allow the discinctions among the amps to be audible. Its a consideration for those wishing to hold another amp DBT.

    Almost all electrostatic speakers in existance have coupling transformers, and amps also used to have coupling transformers but coupling transformers were eliminated from amps for improved sonic performance. One exception I remember is a high-voltage electrostatic speaker featured in The Audio Amateur c1975 which was direct-connected to a dedicated high-voltage tube amp. As I recall the high-impedance membrane was charged to 3000 volts. This speaker was described as being a killer in every sense of the word.

    Imagine this... a world where all amps sound the same...

    We have now entered...the Twighlight Zone...

  23. #23
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Peter_Klim
    Imagine this... a world where all amps sound the same...

    We have now entered...the Twighlight Zone...
    Hey, let's all stay with the good spirit here.

    rw

  24. #24
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    Gee, E-Stat, it is good to learn that
    the Acoustat X design, released in 1976 also ran high voltage tube amps directly to the plates of electrostatic panels at slightly over 3kV.
    Later, they replaced the tube amps with bi-formers increasing the drive voltage to around 5 kV.
    The current Sound Labs electrostats run the bias higher still.

    Did these people buy the rights from the dude who had published the direct-coupled high-voltage electrostat concept in Audio Amateur ? Or did they simply rip him off? Do you know ? Did you research to learn if these speaker companies held valid patents to the concept? You can't get a valid patent on what someone else invents and publishes......

    Jim Winey got his first patent in 1972 and that patent caught my eye. I built a small test panel and found the idea worked quite well even if my demo unit had very low output.

    Peter Kim: There are two issues:
    1. Do all amps sound the same?
    2. Will the speakers you use allow you really perceive any differences between amps that may actually exist?
    The DBT tests I read said "all amps sound the same". My little test said "They don't" But my test was for my benefit: what to use on Tympani. The "answer" I got is why I have Futtermans.

    Noddinoff: Stereophile measures cabinet vibrations and publishes 3-D output charts in their speaker tests on the correct premise that cabinet vibrations includingthose in the cone mounting board that occur in response to the audio being played blurs clarity.
    Ever hear the horn of an approaching train at a RR crossing and notice the pitch of the horn drop as the locomotive passes you? That is the (Doppler) effect of a moving source. Or do you race to cross the RR tracks before the train can reach the crossing?

  25. #25
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Mash
    Did these people buy the rights from the dude who had published the direct-coupled high-voltage electrostat concept in Audio Amateur ? Or did they simply rip him off? Do you know ? Did you research to learn if these speaker companies held valid patents to the concept? You can't get a valid patent on what someone else invents and publishes......
    Is this it?

    1975 Audio Amateur estat

    This hybrid TL woofer / electrostatic design was by Roger Sanders (later of Innersound Labs). James Strickland of Acoustat originally began work in 1962 on his full range electrostat following Arthur Janszen's 1953 sheathed conductor design to extend a technology previously limited to tweeters. Acoustat was founded in 1972 and the first model X was in production by 1976. Did he copy Sander's design? Don't think so. It takes quite a while from prototype creation to production. Sanders didn't start producing his own electrostatic speaker until decades later. Strickland was granted patent 4,324,950 submitted 6/25/79 for his direct drive tube amplfier design. Harold Beveridge also hold a slightly earlier patent on another tube amp design. Ironically, both Sanders and Strickland moved on to better transformer designs.


    Quote Originally Posted by Mash
    The DBT tests I read said "all amps sound the same". My little test said "They don't" But my test was for my benefit: what to use on Tympani. The "answer" I got is why I have Futtermans.
    Very interesting.

    rw

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