Class ABCD ?

[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?

[kexodusc]

http://en.wikipedia.org/wiki/Class_A...lifier_Classes

[Resident Loser]

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...)

[noddin0ff]

...an audiophile should KNOW

Which is why I consider myself an 'enthusiast'

[Resident Loser]

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...)

[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 ! You can ask Audiophiles with big pocket books since they usually bought the equipment and heard it.... lol

[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.

[GMichael]

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?

[E-Stat]

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

[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.

[sam9]

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.

[GMichael]

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

[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.

[Pat D]

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/

[theaudiohobby]

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....

I think the real key to the difference is thermal noise, as Ken Ishiwata said a while back (not an exact paraphrase) , "It is their noise that makes them suitable for audiophile applications, if you design well, this noise will give a 3D atmoshphere that transistors can never have"

[GMichael]

I think the real key to the difference is thermal noise, as Ken Ishiwata said a while back (not an exact paraphrase) , "It is their noise that makes them suitable for audiophile applications, if you design well, this noise will give a 3D atmoshphere that transistors can never have"

Is there a way to find out what the thermal noise is for a given model?

[RGA]

the audiohobby only posts to me to make an argument that I never made -- you want to be corrected on your article go to the AA thread and argue against the rebuttle there. There is zero in that article that mentions anything directly against what AN posted and there is zero rebuttle from you in mathematics to the pnts raised in the AA thread. Take it there because it is off topic here.

You merely go after everyone on every forum you visit. You never make any real technical arguments with any sort of real evidence just post links which almost but doesn;t directly make a case against what is being discussed. Sort of luike an ex=poster here named Mrtycrft who would post a DBT of amplifier s inn 1980 when the topic is about cables. there is no conclusive evidnce in that aticle as AA posters have already said -- you choose deliberately to avoid those poster's comments and try and weasal out of it here.

I will hear your tilted up cold unengaguing treble that the reviewers mention next year. LOL even you had to get new speakers I see -- But the 705 is useless and so your ear says it all to me.

[theaudiohobby]

Is there a way to find out what the thermal noise is for a given model?

For a given model, Yes but not easily, the thermal noise generated by the tubes utilised can be calculated and an extrapolation can made for a given model provided the amplifier's operating conditions are known.