Class A/B switching cause sonic problems?


I have heard different thoughts on this subject and was looking for some other opinions.
Spoke with Mike Creek at HE 2002 and he did not feel there was any degradation when you have a power amp that switches between Class A ( for the 1st watt) and Class B (for power over 1 watt). He though class A's inefficiency and heat generated were not worth whatever benefits there may be. Maybe modern A/B designs don't have problems like older designs did.
Then I saw an article somewhere on the web (darned if I can find it now) where another power amp designer was strongly against switching power supplies.
Is there any agreement on this subject as to who is right?
cdc
I can answer it as well.
1 watt of output power is measured according to a certain freequency probably 1000Hz. If it goes to the bass freequencies it would anyway switch since higher current is drown onto the load greatly increasing a slew ratio...
There are A/B amps where the switch to B occurs arround 25...30W where you normally listen to them in class A.
Cdc- There are many class A amps available, though probably more tubes than ss versions. There is a theoretical advantage to class A amplification, but there is the efficiency issue. In class A/B amps, all voltage and driver stages (that I'm aware of) are class A. It's only the output stage that is configured for class A/B. There are amps with higher biased class A/B output stages that run up to 15% of their output power in class A; the brand Symphonic Line comes to mind.

Obviously, if you need lots of power, class A/B amps will likely be necessary because of the efficiency. However, for absolute sonic reproduction with the fewest compromises, class A operation is usually first choice.
Remember, class of operation alone won't make up for compromises in the quality of parts used to implement the circuit design. There are some excellent examples of good sounding amps in either class of operation, though to my ear they are usually tube units.

Some of the newer, true digital amps, (Tact, PS Audio, etc) use a completely different class of operation. They are extremely efficient, and have garnered some very high praise sonically speaking. I've yet to hear them for myself, but that is another option for you to consider if you need high power.

As for switcher power supplies, lets not forget about one of the truly innovative engineers in audio, David Berning, and his designs. Bob_b has already stated the facts concerning this power supply type. As Ezmeralda11 has pointed out, if you're really interested in learning the technical info of different amp circuit topologies, there are several good books on the subject.
Enjoy.
No doubt that "crossover distortion" in A/B amps is a problem.

How big a problem is open to debate. In a well designed power amp it tends to be a small problem that may or may not be easy to identify except by really serious measurements. One poster mentioned Doug Self, his book really goes into deep detail on this subject, although his conclusions may or may not be correct.

So-called "Pure" class A is the solution to the switching problem in ultimate terms. But the price is cost, excess power dissipation, heat, and size (you get 25% efficiency)with 75% of the input power to the amp going away as heat and nothing else.

I use what is called a "high bias" class A/B in my large Mosfet amp where it is running around 35 watts of class A power sitting around, so in practice you are listening to a 35 watt class A amp 90+% of the time, with "free" headroom.

There is *still* a gain non-linearity where this switching takes place. In a typical AB design this non-linearity is in the 1 watt region, where much listening takes place.You can argue that it would be virtually impossible to detect at the 35 watt level.

Tube amps have the same issues, and more once a transformer is added into the equation...

Switching power supplies are another matter entirely.