[Karl Uppiano]

wrote in message
ups.com...
Since you two (Todd and Karl) are being so responsive to my questions,
I want to pull another one in.

I originally posted on rec.audio.opinion, but was suggested to move it
over here so I did. But I did get a response over there that I wanted
to quote here and ask about.


Trevor Wilson wrote:

Even if that is assumed to be true, what causes the tube to have a
steeper harmonic rolloff?

**Output transformer.

Is that due solely to the frequency response (higher freq. rolloff) of
the output transformer?

IOW, if you used an "ideal transformer" with a flat FR from 0-infinity,

would the tube amp's harmonic content be the same as a transistor amp
(with no xfmr) of the same topology?

Of course that would not make sense if the input frequency was
relatively low in the audio band (say, 1 kHz), because surely the
transformer would still exhibit fairly nice frequency response out to
at least 10 kHz if not higher....

I suppose now that I understand "WHY" harmonics are created as
whole-order multiples of the fundamental, now I'd like to consider
topologies of audio amplifiers and their harmonic content differences.

And here I'm not quite sure the questions to ask, so I'll just put back
out there again that "I read somewhere" that a class-A tube amp (with
output xfrmr) has a steeper harmonic content rolloff than a
transistor-based push-pull amp with no xfmr. Granted there are at
least three variables here (tube/transistor, class A/class AB, and
xfmr/no-xfmr) if not more, but I'd like to dive in and learn what I can
learn...

This starts to get into areas where I do not have specific knowledge about
specific devices. Triode tubes and transistors have remarkably different
transfer characteristics (bipolar junction transistors and field effect
transistor curves are shaped a bit more like tetrodes, but you can't even
take that to the bank). The differences in transfer characteristics alone
are enough to give rise to different harmonic content. That is a reasonable
starting point, anyway.

My personal opinion (flame bait) is that both amplifier types (tubes or
transistors), when linearized using properly-designed negative feedback
should have such low distortion characteristics as to be indistinguishable.
Perhaps theoretical or measurable, but my opinion (again, flame bait) is
that if you can actually *hear* a difference between two amplifiers of
similar power and bandwidth, then one of the amplifiers is poorly designed.
:-)