Yes, yes, to be more precise I should’ve said: “Why tube amps sound different than solid-state ones”, but I used the word “better”, because lots of audiophiles prefer the tube (or tube-like) “euphonic” sound ;-) One of the usual explanations is even vs odd harmonics, but still it’s not clear why we prefer even harmonics.
These two excerpts make it clear:
1. By Paul McGowan
Voltage amplifying devices (like FETs or tubes) produce more even tones and current amplifying devices (like bipolar transistors) produce more odd tones.
2. By Elk
Those of you musically inclined probably already understand that even order harmonics (e.g., tube distortion) begin with octaves, than a perfect fifth. Starting with a 1,000Hz note, 2,000 Hz is an octave, 4,000 Hz is two octaves higher – both the same note of the scale. 6,000 Hz is two octaves up plus a perfect fifth, the beginning of a pleasing chord but so much lower than the first two that it barely matters. 8,000 Hz, vanishingly low is three octaves up.
Oddly tape distortion is odd-order and, thus, does not have any second harmonic. 3,000 Hz, the loudest distortion component of tape, is an octave and a perfect fifth higher. Musically a different note, but the beginning or a chord. 5,000 Hz is two octaves plus a perfect third, a nice major chord but musically even further from the original note. Now it gets ugly. 7,000 Hz does not correlate with a musical interval but lies directly between two notes – like a dreadfully out of tune piano.
Simple, eh? ;-)