Class A amps

<< I've read a few articles on class A amps but still don't have a good understanding of how it affects sound quality. I've even seen amps which can be swithced into class A mode or AB. Does anyone have experience with this type of unit? Does class A have a true audible advantage or can it be detected only by test instruments? If it is audible, in what resepects? Thanks, Rick M. >> Class A amp will usually give you more detail and smoother midrange but less punch and dynamics. It all depends on what speakers you use and what type of music you like. I am so sure about that because I used to have a Gryphon Antileon power amp from Denmark. This monster amp has adjustable 50%, 75% and 100% class A knob which can be set during play.

Generally, the differences between single ended (class A) amps and push-pull units are very audible: the former have a much wider and more true-to-life soundstage. On the other hand, they tend to dissipate more energy as heat and are therefore usually less powerful than the latter units using the same output tubes or transistors. Tom

The sonic difference between Class A and AB is mostly because the Class A amps usually have better power supplies and regulation, and are also better built (they have to, as they run very hot). However, I have heard Class AB amps that sounded better than most of Class A amps. The switching noise is not hearable in any way with a good Class AB amp. Usually it is easier to make good sound with Class A, but again it only depends upon how well is the AB one designed. In my experience good class AB push-pull transistor amps usually sound better than SE units. The same is true with tube amplifiers: Class A is not necessarily better than class AB. Even when using the same topology or the same tubes, one amp can be world-class and can be mid-fi. As a conclusion: usually class A amps sound good, but not necessarily _very_ good. Speaker-cable-amp interaction is more important than the class of the amp.

In class a amp's amplification is don by just one transistor in the output stage, where class b amp's have two transistors sharing the job. One transistors handles the plus, the other the negative part of the sinus. There is, however, a small area where they both work. This can cause cross-over distortion. A class a amp will be cleaner, without this distortion. Dis-advantages are that they run very hot, do not have a high output (generally speaking) and are expensive. The difference between a good class a and a good class b amp should be quit audible though.

Rick: The sonic difference between Class A and Class AB amplifiers happens because transistors are not "perfect." It turns out that if you have an input voltage of less than about 0.6 volts, a transistor won't work at all; the output is nil even though there is an input. In a Class A amplifier, one ggets around this by "adding" a large constant "bias" to the input signal (about half of the maximum input voltage), so that the transistor will always be in the "active" region, where it amplifies the way one expects it to. In a Class AB amplifier, one uses a pair of transistors (or pairs, or more) to drive the output, one for the plus part of the signal and one for the minus part, as Michiel said. This way, there isn't a need for a huge constant bias, which wastes lots of power as heat when there is no signal. Instead, one just needs to add a little bias to get the transistors above the little part near zero when the transistors don't amplify. Unfortunately, it's near impossible to eliminate the little distortion just by biasing, and it will manifest especially in quiet, delicate passages. With the little Class B amplifier I built, this makes percussive elements sound like crumpling wax paper and things like flutes sound like kazoos. Certainly not acceptable, but fortunately it isn't anywhere near that bad in commercial amplifiers (or so I hope).

I have an Accuphase power ampliefier. If I play in class A. the music will be more clean and soft, but I can not play so laud as in class b

it amuses me when a class "a" amplifier does not generally have a high output. Tell that to krell .

All this discussion about operating class is really moot if it involves ASSUPTIONS. Since I have been designing amps for over 40 years I am somewhat of an expert on the subject. The most important thing is the OVERALL RANGE OF LINEARITY. This property is obviously much easier to achieve with a class A design albeit at great expense. In the last 25 years or so, this whole situation has become rather moot as the better designs by most competent engineers have long overcome the biasing problem. The sad truth of the matter is that the average audiophile layman has absolutely no way of verifying that any given unit has been correctly designed. One must un-fortunately trust the reputation of the designer and today even that is no guaratee as there are a lot of what I call dilletantes touting themselves as great engineers. The real truth is that everyone can't be "King of the mountain". James Bongiorno formerly of Dynaco, SAE, GAS, & Sumo.

listening to all of the above, all i can say is with all the amps i had a/b amps never came close. But theres one company that mad my jaw drop was sim audio, great product, i dont own any of sim,but i gotta say,it sounds good for a class a/b amp, and there intergraded amps too.like i say I may not be someone building electronics but I can say I have the ears of years hearing all kinds of components. so is class a amps better,to me yes,if you dont think so i guess your still in maze.there are a lot of a/b amps out there,very few sound good and are some that do a good job, class a is better.im just dieing to hear a digital amp make its way. well bye everyone enjoy listening.