Class A amps

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