"Jim Lesurf" wrote in message

In article , David
Looser wrote:
"Trevor Wilson" wrote

**We're discussing Phase Linear and Perreaux amps from
the late 1970s and early 1980s.

OK, good. So this is nothing to do with MOSFETS in
general, merely one particular rather ancient amplifier.
Glad we got that clarified.

IOW, it is essentially OT to the OP and most of the discussion that followed
it.

Yes. If that is the case then it makes more sense to me
since I have also encountered some amps that 'sounded
different' because they had some flaw or limitation in
the design.

However, there's no reliable evidence that the amps that Trevor mentioned
have this kind of flaw.

So Trevor's proposed test is doubly irrelevant. It's not about the kind of
amps that this thread was created to discuss, and there's no reliable
evidence that the amps he mentioned actually have audible design flaws as
typically used.

Given some of the weirder designs that are
sold to 'audiophiles' I find it quite plausible.

Aside from that, there is a lot of audiophile lore and legend about certain
amps always sounding bad, when said amps in good operating condition
actually sound OK. Any amp that was sold in large volumes and may have been
prone to failure might be getting this kind of treatment. This is especially
true if the amp has a common failure mode that does not completely disable
it.

But it
may tell us nothing about MOSFET vs Bipolar as classes
when used appropriately within their limits.

Exactly. My audio club has examined this issue in some depth and no
surprise, we found that a properly-designed amp in good operating condition
sounds great, no matter which type of output device is used.

There is a precident for this. There was a class of SS output device that
was widely used and has completely fallen into complete disuse. But, that
did not happen to either MOSFET or Bipolar technology. I suspect that if
marketing stats were avaialble we'd find that there was a time when MOSFET
usage increased dramatically and obtained a fair market share. Since then,
MOSFET use has probably decreased, but there is still significant use of it.

The engineers I talk to say that linear (not switchmode) MOSFET amps tend to
be more costly and less efficient for a given power and performance level.
Note that a long-time advocate of FET power amps for audio, namely Hafler is
no longer in production. Haflers had a reputation for sounding great but
being costly and inefficient. Not all that inefficient, but audio can be a
very competitive business.