You don't seem to understand how class A works. What your saying doesn't describe class A at all .
Class A versus A/B
- Thread starter opusarlo
- Start date
You don't seem to understand how class A works. What your saying doesn't describe class A at all .
infullview
Super Member
Doesn't make sense to me either. Is this person sying that the sine wave is not symmetrical?
Got me... It sounds like he's confusing class A with class B.
For those unaware, class AB amps are just a pair of class B amps run in opposing compliment to each other. A push-pull class A amp is 2 single ended class A amps run in complimentary opposition to each other. The benefit to class A is the nonlinearity of each half of the amp cancel each other out. To do that with class AB you need to carefully match the opposing parts.
Sine waves are, many sound waves are not. This relates to acoustic polar asymmetry and what makes natural sounds identifiable.
Amplification should be polar symmetrical on sine waves to be correct on all possible input content.
I should stay away, since this stuff tends to become mysticized anyway, for reasons which I can't fathom. But I can't help myself.
I feel there is some descriptive sense to this, but it isn't literally correct for most audio amps, and it doesn't at all address the fundamental difference between B and AB, which is that the former has devices in conduction for 180 degrees of phase, and the latter has devices in conduction for more than 180 degrees (but less than 360). (Where "phase" is used in the context of a sine wave, even though music isn't sine waves.) The output devices of most solid state push-pull amps are in conduction for slightly more than 180 degrees, because they run a small amount of idle current. (There are some audio amps where the output devices are class B - perhaps even better described as class C - because they run no idle current. But in these amps the drivers will be running class AB and there will be a relatively low-impedance path between the drivers and the amp's output point.)
I'm afraid I don't see any way to interpret this as correct. The benefit to class A is that the devices operate in a more linear region because they are always in conduction. The cancellation mentioned works for complementary push-pull stages of either class A or class AB. (Edit: I now believe I'm wrong about the italicized part. Still think that cancellation is not the most important benefit of push-pull class A, though.)
As has been commented above, there seems to be conflation between class and topology. They are really pretty independent concepts.
Sorry to get all hard-core but, well, this is pretty hard-core stuff. There is no mystery to it at all, and damn little "wiggle room".
Descending from high horse, and yet still riding into the sunset,
chazix
I feel there is some descriptive sense to this, but it isn't literally correct for most audio amps, and it doesn't at all address the fundamental difference between B and AB, which is that the former has devices in conduction for 180 degrees of phase, and the latter has devices in conduction for more than 180 degrees (but less than 360). (Where "phase" is used in the context of a sine wave, even though music isn't sine waves.) The output devices of most solid state push-pull amps are in conduction for slightly more than 180 degrees, because they run a small amount of idle current. (There are some audio amps where the output devices are class B - perhaps even better described as class C - because they run no idle current. But in these amps the drivers will be running class AB and there will be a relatively low-impedance path between the drivers and the amp's output point.)
I'm afraid I don't see any way to interpret this as correct. The benefit to class A is that the devices operate in a more linear region because they are always in conduction. The cancellation mentioned works for complementary push-pull stages of either class A or class AB. (Edit: I now believe I'm wrong about the italicized part. Still think that cancellation is not the most important benefit of push-pull class A, though.)
As has been commented above, there seems to be conflation between class and topology. They are really pretty independent concepts.
Sorry to get all hard-core but, well, this is pretty hard-core stuff. There is no mystery to it at all, and damn little "wiggle room".
Descending from high horse, and yet still riding into the sunset,
chazix
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No, the complimentary operation does NOT cancel any nonlinearity in a class AB amp because one half of the gain stage is off for 179 degrees of the wave form. The primary reason push-pull class A amps exhibit less distortion is due to cancelation effects between two active devices conducting at the same time. Them operating in a more linear region tends to produce lower distortion at low and moderate power levels.
No offense, but you don't seem real clear on the operation of amplifier classes either. Class AB amps are, by definition, two class B amps operating in compliment of each other with a small bias. That's what the B stands for.
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mashaffer
Super Member
Perhaps he is confusing Class A with Single Ended. [Shrug]
Possible, but then his analogy falls apart. Microphones are single ended devices conducting energy from a single ended medium. Single ended amps may not be the most linear topologies, especially if the circuit isn't loaded well, but they primarily produce low, even order distortion of the sort that air and microphones produce. That's the reason people like the way they sound.
All of that said, I'm not sure there's a rational argument against some amount of low, even order distortion. I appreciate the technical and philosophical arguments that an amp should just reproduce the signal, but that doesn't translate well into a pleasurable listening experience too often. The character of an amp is defined by it's distortion character in response to a reactive load. Putting a death grip on that load, the speaker, and making it perfectly replicate the signal usually doesn't sound very good.
mashaffer
Super Member
Right now I am enjoying a bit of Strauss on a SE Tube amp driving my OB "table speakers" so I do appreciate the SE sound. After I get my preamp projects finished I would like to build a Class A PP 6EM7 amp to compare. Power output will be in the same ballpark as my SE KT88s.
AB amp with HCA circuitry
HCA (HYPERBOLIC CONVERSION AMPLIFICATION)
The Yamaha developed HCA circuit goes a step beyond the conventional Class A amplification generally used in a high performance amplifier. In a Class A amp, when output exceeds a limit determined by the idling current, operation degrades to Class AB, resulting in increased crossover and switching distortion. With the HCA there's less distortion and less heat generation.
Or in layman terms Class A/AB..
AB amp with HCA circuitry
HCA (HYPERBOLIC CONVERSION AMPLIFICATION)
The Yamaha developed HCA circuit goes a step beyond the conventional Class A amplification generally used in a high performance amplifier. In a Class A amp, when output exceeds a limit determined by the idling current, operation degrades to Class AB, resulting in increased crossover and switching distortion. With the HCA there's less distortion and less heat generation.
Or in layman terms Class A/AB..
There's lots of high bias class AB amps out there. And there are class A amps with active sliding bias schemes to get better efficiency and distortion. In my opinion, the little bump in distortion you get transitioning from class A to AB is insignificant and at such a high power level in my amp as to have no esthetic impact.
That transistion is well out of my normal listening level.. I'd never hear it.
I really meant to stay away, but I have to show my face again to admit that, on reflection, I think I was wrong on this point. (First time that's ever happened, of course...) I was conflating symmetry of non-linearities with an overall reduction in distortion. I'll go edit my post to recant my error if I can.
And I think I've caught on to the cancellation mechanism in a push-pull class A stage, though I'm doubtful that this is more important than avoiding the severe non-linearity around cutoff.
But as long as I'm here:
I sill disagree with this, though again, I think it's a nice shorthand description. The reason I disagree is that I maintain that the old-school definition of classes A through C in terms of conduction vs phase is still The Definition, and that AB is just something midway between A and B. In my book, both halves of a push-pull class AB stage are operating in AB. In my book, a class AB stage may have a single-ended topology (as may a class A, B, or C stage). Call me a cave man, but that's how I learned it. (From stone tablets. Well, not quite, but it was shortly after learning about vacuum tubes.)
None taken, and I hope that goes both ways.
Cheers,
chazix
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AB amp with HCA circuitry
HCA (HYPERBOLIC CONVERSION AMPLIFICATION)
The Yamaha developed HCA circuit goes a step beyond the conventional Class A amplification generally used in a high performance amplifier. In a Class A amp, when output exceeds a limit determined by the idling current, operation degrades to Class AB, resulting in increased crossover and switching distortion. With the HCA there's less distortion and less heat generation.
Or in layman terms Class A/AB..
Still a class A/B amp; not class A as the OP stated.
All the rest is Yamaha code which when translated means an amp for spec lovers and people that believe sales brochures.
There are myriads of better amps (even some from Yamaha) for people that love to listen to the beauty of recorded music.
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I can't see how you could make a single ended class B amp. Adding a small bias to a single ended class B amp is still going to produce enormous distortion. However, when I say a class AB amp is a conplimecompl pair of class B amps with a small bias, that's exactly what I'm calling a class B amp. But by definition, a class B amp has no bias.
In any event, class B and C are useless for the purpose of audio amplification. I'm not exactly sold on class D either given it's ugly low level distortion garbage.
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yes, but the Yamaha's implementation of HCA also sounds good
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Have you had the opportunity to listen to a MX-10000? I never heard anyone complaining that it does not sound good. On the contrary, most ppl who have the chance to listen to one are screwed for life, since it sets the standard too high for most of what else is out there.
The MX-1000 is no slouch either... very close to a wire with gain as it gets. Some ppl dislike these amps is because they tend to be too revealing / unforgiving.
Agreed, I love the V-fet amps and I think that the BX-1 Class A mono-blocks are fantastic....Yamaha set many standards and as a true engineering company, it was able to build pretty much any topology or type of amp, yet, it chose a class AB HCA amp for their Centennial signature amp. I do not buy that their target customer was only the spec lover.There are myriads of better amps (even some from Yamaha) for people that love to listen to the beauty of recorded music.
The VFET amps were nice amps with great parts, but they were pretty complicated circuits. Complicated circuits seldom sound as good or as organic as simple circuits. Class AB amps are virtually always more complex than class A amps, both in topology and technical requirements.
It's probably obvious I'm a fan of class A. I'm running a modified F5 at 31 watts. It is obscene how deeply I can listen into a piece of music. I've never heard a class AB amp like it. I don't subscribe to the notion an ideal amp behaves like a straight wire with gain .my amp is perfectly capable of making perfect 100 KHz square waves, achieving .003% distortion, and reaching out to 1,000 KHz in bandwidth. It sounds very interesting dialed in like that, but it lacks. It sounds better with some distortion.
It's probably obvious I'm a fan of class A. I'm running a modified F5 at 31 watts. It is obscene how deeply I can listen into a piece of music. I've never heard a class AB amp like it. I don't subscribe to the notion an ideal amp behaves like a straight wire with gain .my amp is perfectly capable of making perfect 100 KHz square waves, achieving .003% distortion, and reaching out to 1,000 KHz in bandwidth. It sounds very interesting dialed in like that, but it lacks. It sounds better with some distortion.
Agreed, it does not have to be as these amps require more "calibration" to the system they function within....are more "demanding" on ther rest of the components. Once setup with a good source, you will hear the music as it was recorded.
Edit: I should have mentioned that they are capable to drive any speaker load.
you should try to listen to a restored B-2 or a B-1 for that matter.
nothing against Class A. My very complex Class A design BX-1 mono-blocks are nothing short of fantastic.
