Some other variables that affect the sound of an amplifier:
Humans are relatively insensitive to even-ordered harmonics and astonishingly large amounts are usually not objectionable. Even ordered harmonics tend to add 'bloom' or 'fatness' (in the bass) and will obscure detail if in large amounts.
Humans find odd-ordered harmonics much more objectionable, in fact higher orders (about the 7th and beyond) are used by the human ear/brain system as loudness cues. Transistor amps with high feedback tend to have very low distortion except for higher/odd ordered harmonics, which is why many transistor amps will have a harder sound. Tube amps, particularly those with low or zero feedback, will have very little high/odd ordered harmonics and will have a softer sound.
Bandwidth plays another role. Generally, due to phase shift/group delay effects, the cutoff frequency of many amps can be audible. For example a 10Hz cutoff will introduce audible artifacts to about 100 Hz, resulting in a bass shyness. Amps that cut off higher, for example 20Hz, will have cutoff artifacts to 200Hz. High frequency cutoff issues generally follow similar rules- to 1/10th the cutoff frequency. A 50KHz cutoff will introduce artifacts down to 5KHz. These are all frequencies that humans can hear very easily! -and is why so many manufacturers strive for wide bandwidth.
There are a number of other influences, but it is getting late and these are good for starters. .
Humans are relatively insensitive to even-ordered harmonics and astonishingly large amounts are usually not objectionable. Even ordered harmonics tend to add 'bloom' or 'fatness' (in the bass) and will obscure detail if in large amounts.
Humans find odd-ordered harmonics much more objectionable, in fact higher orders (about the 7th and beyond) are used by the human ear/brain system as loudness cues. Transistor amps with high feedback tend to have very low distortion except for higher/odd ordered harmonics, which is why many transistor amps will have a harder sound. Tube amps, particularly those with low or zero feedback, will have very little high/odd ordered harmonics and will have a softer sound.
Bandwidth plays another role. Generally, due to phase shift/group delay effects, the cutoff frequency of many amps can be audible. For example a 10Hz cutoff will introduce audible artifacts to about 100 Hz, resulting in a bass shyness. Amps that cut off higher, for example 20Hz, will have cutoff artifacts to 200Hz. High frequency cutoff issues generally follow similar rules- to 1/10th the cutoff frequency. A 50KHz cutoff will introduce artifacts down to 5KHz. These are all frequencies that humans can hear very easily! -and is why so many manufacturers strive for wide bandwidth.
There are a number of other influences, but it is getting late and these are good for starters. .