Archived from groups: rec.audio.tech (
More info?)
<elephantcelebes@yahoo.com> wrote in message
news:1125278769.792161.243670@g47g2000cwa.googlegroups.com
> I would like to know what people consider the state of
> the art to be in the (hopefully) rapid obsolescence of
> Class-AB power amps. Given all of the apparent benefits
> of switching power amps, I am surprised that there are so
> few PA (pro audio, public address, whatever) amps with
> switching design. Any reasons? Is a Class-AB still
> cheaper to make, even with the big heat sink and fan?
The price performance advantages of class AB amps in certain
power categories, remains.
Switchmode amps are dependent on special ICs, high-speed
output devices, and in some cases complex analog power-level
output filters. They all cost money and the filters take up
space.
There is a third option - class H, that you don't seem to be
considering.
Switching amps aren't all gravy from a performance
standpoint.
Switchmode amps that are dependent on complex output filters
have problems with rising source impedance at high
frequencies, which results in an amp that is more sensitive
to the impedance curve of the speaker load.
Some switchmode amps are ugly-sounding when they clip. The
obvious response should be to simply use a larger amp, but
in some applications, clipping is not religiously avoided,
and so switchmode amps may have bad reputations.
I think the end game for power amps is apparent if you
consider the ubiquitous switchmode PC power supply. When PCs
first came out about 25 years, analog power supplies may
have been cheaper but they probably would have been larger
and run hotter. Due to continued development and immense
volume production over 25 years, the economic issues are
totally moot.