"Jim Lesurf" wrote in message
...
You can, of course, say the same about many individual technical specs
taken in isolation. Ideally, the amp should be 'adequate' or better on the
basis of a series of specs. This, in my experience thens to be what
mathematicians call "necessary but not sufficient" as a guide. i.e. if you
fail some specs you can expect the sound to be altered in predictable
ways.

In article , Iain M Churches
wrote:

As regards distortion, I have found that the amount of THD is not so
important as the distortion content - the way the THD is made up. For
example amplifiers with a small amount of 3rd harmonic sound less
pleasing than amplifiers with a larger amount of 2nd harmonic.

I have found that amplifiers with the most pleasing (this may not be the
most
accurate:-) sound seem to have a harmonic distortion decreasing gradually as
the order increases. This is perhaps one of the problems with NFB. It
cancels
the "benign" even harmonics, leaves exposed the more unpleasant odd
harmonics.

However my personal preference is for amplifiers that have minimal levels
of distortions at whever harmonics fall in band.

I have listen extensively to large Crown (Amcron) and Carver broadcast amps.
They have incrediblt low distortion figs which as a builder of valve amps I
can
only dream of. They may be incredibly accurate, but their sound leaves me
cold.

My main interest is in high quality valve amplifiers, which IMO are much
more of a challenge for a designer than SS (I also happen to like the
way valve amplifier can sound)

Depends what you mean. :-)

I am fortunate enough to be a recording engineer by profession, so I have
for
many years had the opprtunity on classical sessions to sit in the studio
during
rehearsals and hear the "real" sound, which can then be used as a reference
for what is coming out of the loudspeakers. Even in this digital age of
hard
disc multitrack systems, I still use a Radford STA100 .(UK built 1964)
for monitoring.

I'd agree that having to include the snags that o/p transformers and
valves
tend to bring do give you problems which solid state tends to sidestep.
:-)

Yes indeed. Generally speaking, the circuitry is more simple perhaps, but
the
problems are much more difficult to overcome. The triode would seem to
be the perfect amplifier stage until you come up against the Miller
effect:-))

However personally I am less concerened with 'challenge' than with getting
amplifiers that work nicely. Provided you take care and know what you are
doing, I think you can use either valve or solid-state. If solid state is
less of a challenge, fair enough, I'll use the time that frees up to
listen
to music. :-)

Perhaps I put too much emphasis on the word "challenge".


Although the above said, my experience was that it took years to design a
power amp (solid state) I was really happy with. Took a lot of work and
patience, but I am not sure it was a 'challenge'... ;-

Then you are a long way ahead of me. I have never been able to design
a SS amp with which I have been entirely satisfied.

Yes. The difficulty, though, is ensuring you make the relevant
measurements
and can interpret the results appropriately. One of my niggles with audio
reviews is that they often fail to do this and just give simple standard
values that don't tell us much.

I agree entirely. It may also be that on the test bench
we put too much importance on some
measurements and do not undestand the relevance of others. In valve
amplifiers for example damping factor has an enormous bearing on the way
the amplifier sounds. One takes a high DF for granted in an SS amp. In
a valve amplifier, a figure above twenty (which seems adequate in listening
tests) is not easy to achieve.


Iain