Ralph,Part of this is speed and part of this is what kind of distortion is being generated. The trick with distortion is to do everything you can to make sure the circuit is linear. What we've done for decades on now in our amps that is a bit unusual (other than the fact that the amps are OTLs) in that they are fully differential and balanced from input to output. This causes the even ordered harmonics to cancel at each stage of gain throughout the amp. Because this is the case distortion isn't compounded to the degree that it is in a single-ended circuit.
Because distortion isn't compounded as much, as the order of the distortion harmonic is increased, its amplitude falls off at a faster rate than in a single-ended circuit. In addition the 3rd harmonic is the primary distortion component. It is treated by the ear the same as the 2nd (IOW its innocuous and contributes to 'bloom' and 'warmth') and is present at a much lower level than the 2nd is in a single-ended circuit. Because it is significantly higher than the succeeding orders though, it masks them from the ear. So the amp sounds smooth on that account, and because the distortion is inherently lower, also more neutral.
The output section is exceedingly fast- it has linearity to well past 20MHz. We've actually experimented using versions of the circuit as linear RF amplifiers! The bandwidth is intentionally limited by the driver circuit. In a nutshell the amp is very fast in terms of risetime; that in combination with field coil drivers makes for very high speed reproduction (field coil drivers can have speeds similar to ESLs and for the same reason- the motive field does not sag when the driver is asked to do work) that is low distortion as well.
Because the amp runs zero feedback, to have low phase shift it is essential that it be wide bandwidth. So it has unmeasurable squarewave tilt at 20Hz (IOW no phase shift at 20Hz which can rob an amplifier of impact, owing to 2Hz full power response) and less than 1degree of phase shift at 20KHz as well. This is important in two ways- the ear can percieve phase shift of a group of frequencies (although it cannot if only a single frequency) because it uses phase information to help ascertain the soundstage. The other way the ear perceives phase shift is as a tonality; a rolloff close to 20KHz can cause the amp to sound dark. Filter theory tells us why; the phase shift components when dealing with this kind of rolloff can be detected to 1/10th the cutoff frequency or 10x the cutoff frequency depending on which end of the spectrum we're talking about.
why does the volume aspect always feel strange, It never feels loud enough even though the room is hitting 100db ++ i