"William Sommerwerck" wrote in message
...
Class D has always troubled me. It does not fit
with the accepted class of operation of an amplifier.

Given that you accept class D, but are not easy with it, what
other designation would you use to identify the switched-rail
concept as something which 'broadly fitted in with the scheme'
and allowed engineers to at least know what it was that they
were looking at?

The original concept of "class" related to the fraction of a cycle the
device was conducting.There's A (all), B (half), AB (more than half but
less
than all), and C (less than half). I can't think of any other meaningful
fractions.

There are no other classes. To call switching amps "class D", or to create
new designations for stepped B+ or stepped-bias designs thoroughly
confuses
the original meaning.


As soon as you start giving design concepts fancy names,
every manufacturer will pick his own, and no one will know
quite where they are at ...

They'll do it anyhow, for marketing. If Hitachi has a class-G amplifier,
then Toshiba, even though using the same circuit, will call it class H,
simply to look original.

How about just _saying_ what it is, in simple language? That would clarify
things for the technician, in a way that tacking on a
marketing-department-selected letter would not.



Again William, I hear what you're saying, and I am in broad agreement.
However, when the class lettering system was first used, the world of
amplification was a much simpler place. No one would ever have conceived of
fully digital amplifiers, or ones whose rails switched 'on the fly' as a
result of output stage demand. The class G concept has been around for a
while now, and I don't think that manufacturers have, in general, gone down
the route of all having their own name for it.

As we are all fully aware, language and linguistic interpretation changes
and develops all the time. It is a fact of life that we all accept,
otherwise we would all still be saying "thee" and so on, and "gay" would
still mean carefree and happy. The same is true of electronics. Meanings
change. The world moves on. "Class G" seems to have been accepted pretty
generally by manufacturers as the designation for the type of output stage
topology under discussion, just as "Class D" is now accepted as a fully
digital amplifier, where bias points don't come into it at all, unless you
consider 'hugely on' and 'hugely off' to be valid examples of the term.

I think it is just a case of the system being expanded and adapted to
encompass new ideas, and on that basis, other than for want of being an
historic purist, I really don't have a problem with it, nor do I see why it
should be such a huge problem for others.

At the end of the day, A, AB, C etc are just arbitrary letters to identify
particular amplifier topologies, based on the way they are biased. How the
letter related to the biasing scheme still had to be learnt, and I really
don't see why the system should not have been expanded in the way that it
was, to identify other topologies - even if they are just variants or
derivatives - based on something other than bias points.

Yes, you could say that this is "A class AB amplifier with switched rails",
but how much easier to just say that it's "Class G" ... ??

Arfa