In article , Iain M Churches
wrote:

"Jim Lesurf" wrote in message
...
In article , Andy Evans
wrote:
Contrary to what Stewart and others think, I've spent 35 years
building and tweaking hifi with one aim in mind - to make the hi-fi
system sound like live music. I didn't use measurements for this, I
used my ears since I've been a professional musician for most of my
life.

Well, I've used both my ears *and* measurements. I find the
measurements to have been very useful in helping to identify what to
do when my ears weren't happy. Saved me a lot of 'flailing about' and
helped me to get an understanding of what it happening.

As both an engineer and a musician, I like the above approach. When I
build something that sounds especially pleasing, or perhaps not sop
pleasing, I take it to the workshop to find out why:-)

Over the years, several interesting factors have come to light. Extended
bandwidth (DC to daylight:-) is not necessarily a prerequisite for a
good sounding amplifier.

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.

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.

However my personal preference is for amplifiers that have minimal levels
of distortions at whever harmonics fall in band. Indeed, given
intermodulation distortion, I'd extend this to intermod in the audio range.
I am less personally less concerned with some harmonics being less
objectionable than others than with lowering distortion to the point where
it becomes audibly irrelevant.

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'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.
:-)

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. :-)

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'... ;-

It is probably true that measurement is not the complete story, as
amplifiers are designed to play music through loudspeakers, not
reproduce sine waves and spectral noise into oscilloscopes and spectrum
analysers. But being able to see what is going on, does tell one a
great deal, and points one in the right direction.

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.

Slainte,

Jim

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