Distortion... why/how is it created?
(It was suggested that I bring my question over here....)
While so many people run around with their hands in the air talking
about this amp and that amp, their distortion measurements,
tube-vs-transistor, yadda-yadda-yadda, I'm concerned with something
much more fundamental.
If the phrase is true "all amplifiers cause distortion," which I
believe is the case, my question is simple...
How is it created?
For instance, let's take the scenario of an all-analog, all pure
class-A staged amplifier.. My *assumption* is that in an ideal model,
this scenario would generate no distortion, but in using real-world
components, distortion is still generated.
I understand that there exist what are called "nonlinearities" in the
amplifier, where at some input levels, a change of the input voltage
causes a particular change in the output voltage, but at some other
input level voltage, the same change in voltage (just offset from the
original) would cause a different amount of change in the output.
So is distortion's root this nonlinearity?
And if so, why does this nonlinearity always manifest itself as n-order
harmonics?
And how does clipping come into the picture?
I've read that class-A tube distortion is "more pleasing" because most
of its generated harmonic content are low-order fundamentals with a
steep rolloff (n 5), but push-pull (transistor-based but even
apparent in push-pull tube) topologies have a less-steep rolloff, with
harmonics still of decent amplitude even with the higher-order
harmonics (n10).
Even if that is assumed to be true, what causes the tube to have a
steeper harmonic rolloff? One article I read seemed to imply it had to
do with a tube being a "high impedance" amplifier. Not sure what that
means, if you compare a 30W tube amp to a 30W transistor amp, what's
different? Could you adapt a transistor-based circuit topology to act
as a higher impedance amplifier?
Some quick background-- I've got an EE degree in electrical and
computer engineering with emhpasis on the digital realm of circuit
design. But I've been trying to go back and "fill in the details" in
the analog world due to my heavy interest in audio. So while I easily
understand some EE topics, others I may not have as fundamental a grasp
on.
Any and all input would be greatly appreciated!
...dane
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