Class ABCD ?

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  • 06-28-2005, 06:21 AM
    noddin0ff
    Class ABCD ?
    I've been wondering what these designations mean for a while now. Can anyone tell me simply what the different amplifier classes (ABCD) refer to? And why should an Audiophile care?
  • 06-28-2005, 06:36 AM
    kexodusc
  • 06-28-2005, 06:40 AM
    Resident Loser
    Actually...
    Quote:

    Originally Posted by noddin0ff
    I've been wondering what these designations mean for a while now. Can anyone tell me simply what the different amplifier classes (ABCD) refer to? And why should an Audiophile care?

    ...an audiophile should KNOW...anywho...try this:

    http://www.moodym.com/audio/ampclass.html

    ...whether it's technically 100% or not, I'm not sure...basically it looks OK

    jimHJJ(...less typing for me...)
  • 06-28-2005, 07:34 AM
    noddin0ff
    Quote:

    Originally Posted by Resident Loser
    ...an audiophile should KNOW

    Which is why I consider myself an 'enthusiast'
  • 06-28-2005, 08:13 AM
    Resident Loser
    I used to consider myself...
    Quote:

    Originally Posted by noddin0ff
    Which is why I consider myself an 'enthusiast'

    ...an audiophile...now I know better...most of 'em are snot-nosed, ego-centric snobs...as in my earlier comment.

    jimHJJ(...as an ex-everything, I consider myself a hobbyist...)
  • 07-01-2005, 02:05 PM
    sam9
    ABCD etc
    In addition to what you see in the Wikipedia here are come comments that may (I hope) more directly address you issue.

    A: The output device(s) are "on" all the time, even when no input signal is applied. All versions generate a lot of heat and have poor efficiency. Some better/worse than others. Some configurations actually run cooler the louder they are playing beause some of the energy is diverted from heat to the sound. Big advantage is NO crossover distortion (see B). Since crossover distortion is usually the dominant form of distortion Class A is potentially the lowest distortion type of amp available. Note potentially -- soome have been built and sold where the distortion performance of the rest of the amp more than offsets the advantage. Big dissadvantages: heavy, hot, expensive and limited too about 100W unless extreme and exotic design choices are taken.

    B: The output devices are barely on when no signal is present. When a signal is present one device amplifies the posative half of the signal while onther handles the negative part. Each are alternatively off for half of each cycle. Big disadvantage is that it is impossible to perfectly match up the two halves -- there is a brief period where both are "on" and even if the problem is overcome there is at least a very slight discontinuity between the voltages as they switch from one device to the other. Thus you have crossover distortion. This was a really big problem 30 years ago. Amplifiers have evolved enough so that the problem has been greatly reduced. Still the best Class B amps have higher distortion than the best Class A. Big advantage is they are more efficient, run cooler, need smaller heasinks, resulting in smaller lighter overal size.

    AB: Appearently a good idea- have an amp run in Class A at le volumes but switch to Class B for higher volumes and peaks. However, some who have looked closer say that switching between the two modes creates more distortion than either A or B. A present there doesn't seem to be an easy (or any?) way to overcome this.

    (You may hear a smartie say that since the switch over in Class B is never perfect, there is always an A region, hence Class B doesn't exist only variations of AB. Technically this is probably true but useful only as a debating point to impress listeners.)

    C: Not used in audio, just in RF.

    D: A technique that chops the signals in to pulses which are used to drive output devices. Very, very effient requiring a very small power supply comparred to the above. Distortion and noise levels are generally above "audiophile" standards but progress is being made. They are getting better all the time.

    G & H: Techniqies by which the power supply switched to higher voltages (and watts) only when needed. Advantage is a much lighter cooler running amplifier. Very common in pro gear. Earliest example for consumer gear was the Carver M-400 Cube. A continuously variable version is used by Sunfire. Like Class D, all the switching add to distortion but there have been big improvements and more should be expected.
  • 07-01-2005, 06:30 PM
    GMichael
    Great answer!
    Quote:

    Originally Posted by sam9
    In addition to what you see in the Wikipedia here are come comments that may (I hope) more directly address you issue.

    A: The output device(s) are "on" all the time, even when no input signal is applied. All versions generate a lot of heat and have poor efficiency. Some better/worse than others. Some configurations actually run cooler the louder they are playing beause some of the energy is diverted from heat to the sound. Big advantage is NO crossover distortion (see B). Since crossover distortion is usually the dominant form of distortion Class A is potentially the lowest distortion type of amp available. Note potentially -- soome have been built and sold where the distortion performance of the rest of the amp more than offsets the advantage. Big dissadvantages: heavy, hot, expensive and limited too about 100W unless extreme and exotic design choices are taken.

    B: The output devices are barely on when no signal is present. When a signal is present one device amplifies the posative half of the signal while onther handles the negative part. Each are alternatively off for half of each cycle. Big disadvantage is that it is impossible to perfectly match up the two halves -- there is a brief period where both are "on" and even if the problem is overcome there is at least a very slight discontinuity between the voltages as they switch from one device to the other. Thus you have crossover distortion. This was a really big problem 30 years ago. Amplifiers have evolved enough so that the problem has been greatly reduced. Still the best Class B amps have higher distortion than the best Class A. Big advantage is they are more efficient, run cooler, need smaller heasinks, resulting in smaller lighter overal size.

    AB: Appearently a good idea- have an amp run in Class A at le volumes but switch to Class B for higher volumes and peaks. However, some who have looked closer say that switching between the two modes creates more distortion than either A or B. A present there doesn't seem to be an easy (or any?) way to overcome this.

    (You may hear a smartie say that since the switch over in Class B is never perfect, there is always an A region, hence Class B doesn't exist only variations of AB. Technically this is probably true but useful only as a debating point to impress listeners.)

    C: Not used in audio, just in RF.

    D: A technique that chops the signals in to pulses which are used to drive output devices. Very, very effient requiring a very small power supply comparred to the above. Distortion and noise levels are generally above "audiophile" standards but progress is being made. They are getting better all the time.

    G & H: Techniqies by which the power supply switched to higher voltages (and watts) only when needed. Advantage is a much lighter cooler running amplifier. Very common in pro gear. Earliest example for consumer gear was the Carver M-400 Cube. A continuously variable version is used by Sunfire. Like Class D, all the switching add to distortion but there have been big improvements and more should be expected.


    Very usefull information for us audio-wannabe-philes. So when I see an amp that says .03 THD at max volume & .01 at most normal settings, I probably shouldn't even care if it A B or A/B? Just as long as the distortion is low it's cool?
  • 07-01-2005, 07:06 PM
    E-Stat
    Quote:

    Originally Posted by GMichael
    Very usefull information for us audio-wannabe-philes. So when I see an amp that says .03 THD at max volume & .01 at most normal settings, I probably shouldn't even care if it A B or A/B? Just as long as the distortion is low it's cool?

    THD measurements really do not equate to perceived performance. Newer designs by diverse companies such as Pass Labs and Crown both sport higher distortion specs than their respective predecessors of twenty years before. I owned an AR integrated amp once which sounded great at high levels but lost its resolution at lower, more normal listening levels.

    I look for amps that are remain biased class A for the first five percent or so of output which is where you spend most of your listening.

    rw
  • 07-02-2005, 06:50 AM
    kexodusc
    E-stat's right...THD is a pretty insufficient stat by itself to pay much attention too...and if memory serves THD is the best kind of distortion you can get because it sort of hides in the sound...I've heard some old tube amps that probably have 1 or 2% THD that still sound pretty good, better than ultra-low THD a/v receivers.
  • 07-02-2005, 07:05 AM
    sam9
    Quote:

    Originally Posted by GMichael
    Very usefull information for us audio-wannabe-philes. So when I see an amp that says .03 THD at max volume & .01 at most normal settings, I probably shouldn't even care if it A B or A/B? Just as long as the distortion is low it's cool?

    It would be nice if this were true but there are thing that conspire against it. First it is hard to tell if the two figures were obtained under equal (or even similar conditions). Even if that condition were met it would probably be at the "standard" 1kHz which is where nearly every solid state amplifier has lowest distortion. A few manufacturers, publish distortion vs. frequency charts which would be more helpful if only they all did it. A spectral analysis showing what the distortion components are made up of would also be informative if everyone did it. Fortunately nearly all modern solid state amplifiers perform very well in this regard when played within their capabilities.

    To the extent there are audible differences, there is a school of thought that it occurs when the peak signals are just slightly clipping or just below clipping. Distortion rises dramatically at this point and some amp seem to deal with it more gracefully. Although designers are aware of this there doesn't seem to be any standard way to test and charaterize it. The problem becomes moot if you have enough power to avoid this, or choose speaker with higher sensativity.

    More important in my mind is reliability, freedom from grounding problems (humm, buzz), freedom prom picking up random RFI or other external noise, freedom from turn on thumps , buzzing transformers and other quirks. Ability to handle a wide range of more or less normal loudspeader impedances. (There are a few bizarre loudspeaker out there that are difficult for nearly all amps. I wouldn't hold it against and amp that had difficulty in this regard.) Mundane considerations such as good binding posts, i.e., insulated, accepts standard sizse spades, banana and spaced to reduce chance of stray wire strands shorting the speaker cables. ----Failure in any of these areas will do more to ruin your listening experience that stightly higher distortion. An amp that produces no sound can be said to have 100% distortion.

    BTW- I have a prejudice against amps with advertising copy that describes them as "musical", "emotional", "etherial" and so on. In my opinion this is just a smoke screen to cover up the fact that the unit has nothing special going for except a high price. Soundwise it's probably quite competant, but so is most of the competition.
  • 07-02-2005, 08:36 AM
    GMichael
    No short cuts huh?
    So there are no shortcuts for an enthusiast like myself to pick out an audiophile quality amp. We must research, ask questions, get adivice, listen and then listen some more. OK, it's a tough job, but I'm up to it.

    The amp I am looking into now is the Parasound HCA-1500A. It's 2 channel Continuous power output: Stereo, 205 Watts RMS x 2 (20 Hz - 20 kHz) @ 8 ohms, both channels driven; 315 Watts RMS x 2 (20 Hz - 20 kHz) @ 4 ohms, both channels driven; Mono, 630 Watts RMS (20 Hz - 20 kHz) @ 8 ohms
    Current capacity: 60 A peak per channel
    FR: 5 Hz -100 kHz, +0/-3 dB at 1 watt
    THD: <0.03% at full power; <0.01% typical levels
    S/N Ratio: >110 dB, input shorted, IHF A-weighted
    IM Distortion: <0.03%
    TIM: Unmeasureable
    Slew rate: >130 V/u second
    Dynamic headroom: >1.5 dB
    Interchannel crosstalk: >80 dB at 1 kHz, >60 dB at 20 kHz
    Input impedance: 33 kW
    Input sensitivity: 1 V for 28.28 V; THX Reference Level; 1.2 V for full output
    Damping Factor: >800 at 20 Hz
    Dimensions: 19" wide, 5.25" high, and 16" deep (.875" high with feet)
    Weight: 40 lbs.
    Manufacturer's limited warranty: 10 years parts, 5 years labor.

    I don't see anything about A, B or A/B.

    I see it has an MSRP of $1000.
    I can get one new at $750.

    Lookinig to drive two maggies (MG 1.6) so my Yammie can drive the surrounds etc.



    Thanks
  • 07-02-2005, 10:25 AM
    RGA
    basically in my years of listening while I have owned som reasonably nice amplifiers of the A/B variety -- Class A has for whatever the techno-babble sounded much much better if in Single Ended fashion. The Sugden A21a has been sold since 1968 and is the longest running amplifier in production despite its no frills 25 watts pure class A Single Ended operation and average technical numbers. It continuously sells it is kept by owners and it consistently wins bline listening auditions against it's brand new technologically "advanced" (so-called) competitors. http://www.hifichoice.co.uk/review_read.asp?ID=1933

    This from a rather opinionated maker of maybe the world's leading Class A single ended tube amp maker:


    "all transistor amplifiers sound poor for the simple reason that transistors are inferior amplifying devices. The word 'semiconductor' really means what it says and it says it all, 'half'-conductor, sonically this could be translated to mean half the signal! Which is really what it sounds like. Pure and simple, transistors are highly un-linear and need a lot of correction (feedback of some sort) to have a bandwidth wide enough to be able to reproduce any music signals, they are not natural voltage amplifiers.

    Likewise both the pentode or tetrode requires corrective feedback to lower the load sensitivity and improve bandwidth, they are less un-linear than transistors being high impedance devices that require matching from an output transformer. Thus they sound better when used well, especially when used single-ended or in pseudo triode mode by connecting the grids together. Pentodes and tetrodes are more efficient (give higher static power) and much cheaper than triodes, this price advantage is paid for in poorer linearity and therefore overall open loop power bandwidth and load stability, nature always gives with one hand and takes with the other!

    Directly heated triodes on the other hand are highly linear amplifying devices, the directly heated triode is the original voltage amplifier, the first, only and still the best, it responds well to better circuits, components and materials, but they are less efficient and more expensive than pentodes and tetrodes. Thus they require efficient speakers, with power output being at a premium price."

    You don't have to agree --- in my experience so far listening to the top Krell, Bryston, Classe, YBA and Levinson amps even some that run in class A -- outside of the Sugden due to it's very sensible price point there isn't a SS amp that to me serves the music in a positive manner.
  • 07-02-2005, 04:02 PM
    Florian
    So far all my equipment is class-A but my Pathos is AB and sounds just as good to my ears. Dont look at specs too much, but listen :p ! You can ask Audiophiles with big pocket books since they usually bought the equipment and heard it.... lol
  • 07-02-2005, 05:30 PM
    theaudiohobby
    Opinionated and wrong
    Quote:

    Originally Posted by RGA
    This from a rather opinionated maker of maybe the world's leading Class A single ended tube amp maker:...

    Good marketing spill but like most other ad-copy's it is factually wrong, not the least because the much vaunted triodes use negative feedback to linearize their output just like any other amplifying device be it tetrodes, pentodes or transistors.

    Inherent feedback in triodes
  • 07-02-2005, 06:22 PM
    RGA
    that article has been discussed and refuted on other forums - it is not the same as negative feedback and you SHOULD know that.
  • 07-03-2005, 02:25 PM
    theaudiohobby
    Could you post a link
    Quote:

    Originally Posted by RGA
    that article has been discussed and refuted on other forums - it is not the same as negative feedback and you SHOULD know that.

    Could you post a link to any of these threads, some may disagree with the contents, but refuting the contents, highly unlikely.
  • 07-03-2005, 10:06 PM
    RGA
    Before I do I want to ask you if you are saying that there is no such thing as a no-feedback amplifier?
  • 07-04-2005, 02:07 AM
    theaudiohobby
    Ho..hum.. I take it that there is no thread that refutes that article then. :)
  • 07-04-2005, 02:08 PM
    RGA
    No feedback means no global feedback which was the word I was trying to locate. It is the industry standard meaning of no feedback. Sorry TAH but I don;t save every thread on my hard drive for years just int he off chance get morons arguing semantic points of real engineers which it is clearly obvious you are not by the totally incompetant ways you read the Elac graph and it's frequency response.

    " the article actually says that its possible to consider a triode as a pentode with feedback. Its just a mathematical construct. Doesn't mean anything one way or the other."

    http://www.audioasylum.com/forums/se...ges/39794.html
  • 07-05-2005, 01:13 AM
    theaudiohobby
    Global feedback can be avoided in other amplifying devices
    Quote:

    Originally Posted by RGA
    No feedback means no global feedback which was the word I was trying to locate. It is the industry standard meaning of no feedback. Sorry TAH but I don;t save every thread on my hard drive for years just int he off chance get morons arguing semantic points of real engineers which it is clearly obvious you are not by the totally incompetant ways you read the Elac graph and it's frequency response.

    " the article actually says that its possible to consider a triode as a pentode with feedback. Its just a mathematical construct. Doesn't mean anything one way or the other."

    http://www.audioasylum.com/forums/se...ges/39794.html

    :p :p :p , Big Laugh! I see that you were so embarrassed on the ELAC thread, confronted with three curves, you managed to pick the wrong one :p :p and in case you missed it, the adjusted curves are also mathematical constructs, duh :p :p. I hope you realise that other amplifying devices can be designed to avoid global feedback, however they still require some form of feedback to maintain linearity and in the case of the triode it is inherent to the device, so whichever you cut it, your original post or more correctly ad-copy ;) amounts to erroneous marketing froth.
  • 07-05-2005, 04:09 PM
    RGA
    Triodes have degeneration, not feedback. They ain;t the same --- sorry but you have no clue. :D :D :p :D :p :D

    No I read all the graphs on the the Elac correctly -- it is their measurements -- which is suspect as it is and even then they look bad -- all reports from listeners I know and the credible reviews think it's pretty unlistenable. Given the other speakers you like I'm hardly surprised. :rolleyes:
  • 07-06-2005, 12:17 AM
    theaudiohobby
    Another popped bubble.
    Quote:

    Originally Posted by RGA
    Triodes have degeneration, not feedback. They ain;t the same --- sorry but you have no clue. :D :D :p :D :p :D

    Ho Hum :rolleyes: :rolleyes: ...from the same thread

    Quote:

    Originally Posted by RGA
    theaudiohobby presented me with this 1953 article and says that sets all have feedback and there is no such thing as a no-feedback amp

    Quote:

    Originally Posted by Horneman
    There is I believe indeed no..no feedback amp..that is no news..but there is such a thing a local feedback and global loop feedback

    .

    Quote:

    Originally Posted by Russ57
    I offer no real rebuttal other than to say that those that understand tube circuits consider this info old, self-evident news. If someone wishes to model a triode as a pentode with "built-in" feedback that is their business and it may work for their needs within that model's limitations. Many such models are used. Some may model a pair of triodes in cascode as a pentode for example.

    Quote:

    Originally Posted by Thorsten
    The triode has certain inherent features. Among them is that if the anode voltage is lowered the anode current lowers, because there is less tension between cathode and anode and thus less electrons are attracted by the anode from the cathode.

    Now we may call this a feedback mechanism or not.

    Now for the clincher..

    Quote:

    Originally Posted by Stockman
    The method is of particular interest for control circuits and output stages utilizing low-ยต triodes, since the back action from the anode on the emission-controlling field at the cathode is then appreciable. Fundamentally, this electric field action is a form of negative feedback

    correlated to the transistor behaviour

    Quote:

    Originally Posted by wiki
    Simple transistor amplifiers use emitter degeneration to achieve negative feedback, which gives a relatively predictable gain compared to the gain of the transistor itself, which varies widely.

    Degeneration is fundamentally used to achieve negative feedback in analog circuits, it is as simple as that. If it looks like a duck and quacks like a duck, it is a duck. Another popped bubble. :D

    PS: You might as well give up now....Neither your english degree nor PQ marketing blurbs have equipped you for a technical discussion. Maybe I should post your blunders for the world to see that you do not know how to read FR graphs. Worse than that, you proceeded to do some character assasination in your referenced SET thread, shame on you :( .
  • 07-06-2005, 12:47 PM
    Pat D
    Quote:

    Originally Posted by sam9
    AB: Appearently a good idea- have an amp run in Class A at le volumes but switch to Class B for higher volumes and peaks. However, some who have looked closer say that switching between the two modes creates more distortion than either A or B. A present there doesn't seem to be an easy (or any?) way to overcome this.

    Perhaps you should tell this to Bryston!

    I think most amplifiers nowadays are Class AB.

    Some have raised the question of distortion. While it is true that low distortion measurements tell us nothing about the sound, the comparison of tubes and solid state on this basis is often useless, as distortion is usually below audibility.

    The biggest difference in sound between solid state amps and tube amps lies in the output impedance. For most solid state amps, the output impedance is quite low, usually below 0.1 ohm and such amps have almost as flat a frequency response into the varying impedance load of most loudspeakers as they do into a resistor. For most tube amps, the output impedance is several ohms, and these do not maintain a flat frequency response into the varying impedance of most speaker loads. Check the frequency response measurements of tube amplifiers into the NHT simulated speaker loads on the Stereophile or Soundstage sites and you can see what I mean. Here is a comparatively mild example:

    http://www.soundstagemagazine.com/me...ts/arc%5Fvs55/
  • 07-06-2005, 01:03 PM
    RGA
    Quote:

    Originally Posted by theaudiohobby
    .Neither your english degree nor PQ marketing blurbs have equipped you for a technical discussion. Maybe I should post your blunders for the world to see that you do not know how to read FR graphs. Worse than that, you proceeded to do some character assasination in your referenced SET thread, shame on you :( .

    Too chicken to go on the AA thread yourself and battle with the engineers.

    Sorry I can read graphs with the economics and math courses I have taken. you have little character to attack.
  • 07-06-2005, 01:42 PM
    theaudiohobby
    Quote:

    Originally Posted by RGA
    Too chicken to go on the AA thread yourself and battle with the engineers..

    Why battle anyone :confused:, shouting on an internet board does not make anybody right, The dissenting 'engineers' should publish a rebuttal to the Stockman paper, it's been over 50 years and the 'engineers' with a dissenting opinion have yet to publish a rebuttal, why? Because Stockman is correct.

    Quote:

    Sorry I can read graphs with the economics and math courses I have taken. you have little character to attack.
    You evidently forget how to read graphs correctly then, :rolleyes: and you said this

    Quote:

    ...the audiohobby poster wants to argue about negative feedback because he often argues with peter Qvortrup of Audio note -- so rather than be a man and talk to them directly he posts on internet forums with info that doesn;t quite address the specific discussions. He's artful at the strawman and avoiding arguing of specific issues.
    and this

    Quote:

    I directed him to this thread already...he has chosen instead to argue that Elac speakers are the most accurate available. So I simply will let it go.
    Liar :( :( .