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?
From all that I have read on this subject, my personal
opinion is that class A is sonically superior. Presently
I own a Bryston B-60R int. amp that I enjoy greatly, but,
I decided when funds become available I'll be going with a
Sugden A-21 Class A int. amp.(I've heard that amp w/Harbeth
HL-P3ES2 is a glorious match.) Bill
It appears that you're mixing up two different topics. Switching, sometimes called digital, power supplies (recent JRDG, Chord and others) is completely different from the class A/B switching controversy. Regardless, the general consensus is that amplifier designs where both halves of the waveform are handled by a single device is preferred.
Onhwy61, for the amp to perform in different classes of operation the DC power on active elements must be distributed differently so that the offset voltage is "located" at the very "bottom" of input "family" characteristics of a transistor or valve. Thus the switch of the power supply also takes place.

In my point of view that it's great to have either class B or class A.
Class B claimed to have less harmonic distortions theoretically but for real there is no ideal offset point so the positive-wave element will be also passing negative that will be added thereafter to the negative element and vice versa; creating unneccessary phase shifts as well which won't be present in class A.
The only point in class B is its efficiency and ability to fit into the small budget amps.
A/B amps due to the DC supply switching sort-of combine both cons from A and from B.
no text.
From experience I agree with Mike Creek in that an amp that has class A drivers with class AB outputs is certainly a legitimate design topology. I've used more than one solid state amp product that works this way & they sound just fine to me, and I am quite particular about sound quality. Of course a pure class A design is going to have a more purified sound than the hybrid design, but the tradeoff is a lot of wasted electricity & a hotter listening room. This extra heat isn't really an issue during cooler seasons, but on warmer days you'll certainly notice higher AC bills &/or a hotter house. Simply let your ears decide which you most prefer.
The amp doesn't normally "switch" back & forth though, this is simply driven by the input signal level exciting whichever stages at any given moment in time. One exception is the old Carver commutating power supply, but I wouldn't recommend that deisgn for any critical-quality applications.
Switching power supplies might be found in either type of design, & yes they can be noisy (although more efficient). In a properly designed component, either linear or switching power supply could sound equally good. I believe that Meitner, Rowland, & more recently TACT have manufactured examples of properly designed & executed "switchers".
Hi Bob. I guess I'm not totally clear on A/B amps. So you're saying the amp will switch even even I kept volume levels low so not to go above 1 watt output on the power amp? Aren't these amps supposed to put out class "A" for the first watt? Then "B" after that?
There don't seem to be any class "A" amps available anymore that I know of so maybe the market has decided for me what I want. But I do know ATC does use class "A" amps in their active speakers.
Thanks evryone for the help.
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.
Douglas Self's "Audio Amplifier Design Handbook" 2nd ed. covers it well.
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.
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.