"mick" wrote in message
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On Thu, 11 Nov 2004 06:34:47 +0000, Trevor Wilson wrote:


**Really? Can you provide your measurements to validate that fact? Here's
a few figures which your amps would need to meet, in order to provide
inaudible levels of distortion:

Frequency response: 20Hz - 20kHz (at, say, 1/3rd full power) +/- 0.1dB,
when operating into a real-world loudspeaker. Phase error: 20Hz - 20kHz -
+/- 5 degrees, when operating into a real-world loudspeaker.
Output impedance: Lower than 0.1 Ohm, from 20Hz - 20kHz (BTW: This is
where many run-of-the-mill SS amps fail)
THD: Less than 0.1% from 20Hz - 20kHz, at (say) 1/3rd maximum output.
IMD:
Less than 0.1%.


Trevor, I respect your point of view, but some research has been done (and
its not for me to judge how well) which shows that:

Frequency response - bottom end is limited by the volume of the room. Few
are capable of producing a fundamental tone down to 20Hz, although the
harmonics may be produced. The amp's and speaker's responses can't change
this - especially if they are "flat".

**Non-sequitur. Assume, for a moment, that I am still using my old KEF
T-lines, which were flat to 23Hz. The room I used them in was flat to 20Hz.


Phase errors are generally not easily heard unless a listener has
previous experience in spotting these. When they are detected it is
perceived as location information, not distortion.

**Phase errors MAY be very obvious to many listeners. More obvious than
frequency response errors.


Output impedence of the amplifier - controlling the speaker damping - is
also inaudible to the majority of listeners unless it is *really* bad.

**That would depend on the speaker. Some are insensitive to high output
impedance figures and some are not. Even the figure I quoted is too high for
some speakers. Like this one:

www.rageaudio.com.au/accu.jpg


THD is meanongless in the real world. It is a great method of producing
comparisons between amps, but there are so many other factors to be taken
into consideration that, below something like 5%, it is completely
inaudible.

**Bull****. Way back when I was a trainee tech, some of us experimented with
some pretty crappy speakers and discovered than 1% THD was audible. Other
experimenters have suggested that around 0.1% is a reasonable threshold for
average listeners. Critical listeners may be able to detect far less.


I'm not claiming that these are my own views. I generally don't consider
an amp bad unless I can hear the problems or it makes something smoke!


**Because many people imagine that because it has tubes, it must be
good. It is very important to show that this is not necessarily the
case. A valve amp may be good, or it may be bad.


Very, very true. Likewise a ss amp can sound absolutely appalling when
compared to a simple valve amp that has been designed and built well.
There are good and bad on both sides. IMHO some recordings sound better
via valves and some sound better via ss and for me the *sound* of the amp
is far more important than any figures attached to it. These preferences
may be a characteristic of my speakers!


**And I have never said anything of the kind. Except AM (though I did
build a superb, all valve, 4 stage TRF, with a triode infinite impedance
detector, when I was 16.).


And nothing sounds as nice as your own home-built stuff does it?

**Wrong. I built stuff for many years, 'till I heard my first commercial
amplifier. It was a sobering lesson to listen to a mighty Marantz 1200B. It
blew away everything I had ever built. My TRF was another story altogether.
I used to 'phone up the radio staion and complain about one of their
turntables having a worn stylus.

I've been
there, done that! (for many years). My first trf used battery valves & ran
from suitable 90v and 1.5v batteries!

**I'll betcha you didn't use an infinite impedance detector. Yours used a
standard diode one, right?



In fact, the last valve amp, I listened to, which I could easily live
with, was the Audio Research VT100. Trouble is, I regularly listen to
an SS amp which outperforms the VT100 at a significantly lower cost.



Lower cost - now we are getting to the point. Valves can't compete when
you talk of high quality watts per pound. I agree. But, you can't build
good, stable ss amps as easily as simple valve amps. The small size &
proximity of the components makes it far more difficult.

**That depends. If you're talking about building an amp from scratch, then
valves are easier. If you're tal,ing about buying off the shelf, or from a
kit, then the answer is not so straightforward.


I would recommemnd that anyone who wants to try the "valve sound" should
build a simple amp and give it a go. The cost can be reasonable, providing
that you are happy with 10W or less and are willing to make sacrifices
both ends of the audible spectrum. Remember that adult males tend to have
a top end hearing limit at about 16kHz (above this the frequencies give
"presence" information) so this isn't necessarily a great loss. This isn't
hi-fi, I suppose, but does that matter when you are enjoying the music?


**Nothing makes me happy. I'm a grump.

Ah! Get the soldering iron out & build a little valve amp to cheer
yourself up!
:-)

**No need. I use a soldering iron every day.


--
Trevor Wilson
www.rageaudio.com.au