The JLH Gateway to Class-A :: 13

 Questions of Class-A -- 'Pure' and Otherwise

        After the previous post that surveyed a slew of class-A amplifiers, and then some, many a question has been raised by class-A enthusiasts and DIYers.

        Quite natural that they hinged on class-A and its merits. But more questions were raised about higher power amplifiers that 'claimed' they were class-A designs. Many readers were flummoxed by claims of class-A power going all the way up to nearly 100 Watts, and that too in small, light packages; they wanted to know if it was really "pure class-A watts". Questions and doubts galore, mostly triggered by the hyped and honeyed ad copy and reviews in glossy hi-fi mags. Forget about 'respectable' brands playing such misleading games; even designers have, so sad to note, got onto the bandwagon with a big 'CLASS-A' banner on it!

        Do we really have the 'garden-variety' class-A, and the pristine, 'pure class-A' in amplification?

Hype-fi

        Audio has all along been ruled to a considerable extent by advertising hype, and half-truths in the so-called 'reviews'. The term 'hi-fi' itself is tautological(in layman speak, unnecessary repetition), just as in the commonly used phrases like 'close proximity', 'new innovation' or 'free gift'.

        Fidelity means faithfulness to the original. Period. For us lovers of music reproduction, it means a playback (mostly at home) that is as close as possible to the original performance that has been 'canned'.

        Could fidelity then be 'normal', and also a bit higher than the normal? That is, when you pay big money for a 'high-fidelity' amplifier, rather than a mere run-of-the-mill amp. That would also mean that just a bit lower, 'low fidelity' exists. Ah, but then arises the question, could something lower than true fidelity be called fidelity??

        Be that as it may, the term has earned a place in the history of audio and we continue to use it without further thought. Sad to say, fidelity is an ideal concept at best, and in the real world, it has many degrees and levels. But then how could you label all of them 'hi-fi'? It is just a universal label that means not much, and tells you little about the product's real audible quality.

'Classy' Amplifiers

        In the earlier days of the emerging trend of 'hi-fi', amplifiers were 'classed' according to their operating points decided by engineering definitions. There were amplifiers of all classes -- class-A, class-B, class-AB, class-C. And each 'class' and its strengths and weaknesses were well known and clearly defined. Then some clever honcho in a company's advertising department discovered that he could gain 'extra mileage' for his product by labelling it a "class-A amplifier of 100 Watts" -- when the truth of the matter was that it was a humble class-AB amplifier that necessarily operated in class-A bias for the first watt or two, and slid into class-B for the rest of the output. This clever ploy caught on like wild fire, as we all know.

        Fidelity was truth in audio, and this sort of convenient blending of truth and untruth blurred the lines much. The unsavoury trend is followed these days even by 'respected' brands to hype things up and sell their stuff. Anybody except a nincompoop will know that a 300 Watt class-A amplifier will be, well, a near impossibility, given various practical considerations. Not that it is impossible to build one, but it will not be a practical solution within reasonable limits. (The humble DIYer knows the hassles of building a good 5 or 10 Watt class-A amp!) When you look in the audio Press, you get to see ads touting that, and more in dubious packages. Honestly, this cannot be done without adding a lot of "water to the milk", so to speak.

        A natural reaction to this hype from the opposite camp was with ad copy liberally laced with phrases like "pure class-A Watts" and such like, to distinguish their products from the 'super-inflated' products from the typical 'hi-fi' brands. Therein starts the tale of "pure watts" -- as if it was some kind of 'virgin stuff'.

Class-A is Class-A

        Hey, that is another tautological phrase, but here it means what it says! Class-A is class-A, and class-B is class-B, and never the twain shall meet! Except perhaps in the class-AB amplifier! But then it is a mere marriage of convenience, and little else. Funny that it is a strange animal -- class-A for a little while, but most of the time class-B, and never class-AB per se; really class-AB only in name!

        Come to think of it. Every hobbyist worth his/her salt knows that class-A amplification can be either of the two types -- Single-ended, or Push-pull, depending on their engineering topologies. Again, as we all know (or, should know!) that their harmonic profiles are not identical, which does make a difference when it comes to subjective perceptions. Anything other than these two configurations strictly operating in class-A bias conditions, cannot be called a class-A amplifier.

        You cannot have "pure class-A", and a somewhat "impure class-A". Either it IS class-A, or it is NOT class-A -- the engineering definitions and operating conditions are well defined, and 'purity' is NOT a factor in the equation. And suppose in the event that an amp is not 'pure class-A', then being 'impure' to what degree still makes it qualify as 'class-A' is a moot question.

        We must recall that class-AB was invented to overcome the inherent faults of class-B by blending in the continuous bias of class-A so that distortion at the cross-over point was reduced to inaudible levels. If you know how to design a class-B amplifier which could approach objective and subjective perfection in reproduction on par with a good class-A amplifier, well and good. But still that amplifier remains a class-B amplifier, and has to be called so -- probably a highly refined one! Just because it happens to be a refined, top-class amplifier does not make it deserve the moniker of class-A.

Truth in Audio

        We do understand it when companies and brands resort to cheap ploys to push their wares, though we do not subscribe to their points of view. But when seasoned and respected designers like Andrew Armstrong or D. Self starts labelling their high-bias class-B designs as a class-A amplfiers, I wish to draw the line then and there. Why couldn't that be called a highly refined, "class-A-beating" class-B amplifier if that is the reality? Mr Armstrong or Mr Self is not going to lose their design thrones just because they have designed very good class-B amplifiers. In fact, as able designers, it shows their mettle when they designs all classes of amplifiers that excel in performance! Ah, what is in a name? A lot, I must say ... quite a lot!

        We all go on believing that science and engineering has certainty and truthfulness. It is that belief that crumbles when a class-B amplifier 'masquerades' as a class-A amplifier, for whatever reason or purpose. It is time we ceased and gave up all that dissembling and started calling a spade by its real name. That is the day when we shall have 'true fidelity'.

        No more, no less !!

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