Tone response at different volumes?

[andy474x]

Lately I've been noticing that there seems to be a big difference in the way my SE30 responds at higher volumes, compared to other amps I've used. I know this isn't the "SE" amp section, but this is just me wondering about different amps in general, not SE amps specifically. Anyways, some amps I've tried seem to get brighter and more harsh at high volumes, and I end up turning the tone and treble down, whereas the SE30 tends to want the tone controls turned up higher at max volume to get those frequencies back. Kind of like the old Plexi's, I've noticed guys always play them with the tone stack all turned up. So what is it that makes some amps behave this way? My guess would be either the transformer or the position of the tone stack in the signal chain, but I really have no clue. Maybe it's just the quality of the amp. Thoughts?

PS - for the record, I do prefer having to turn up the tone controls, I hate amps that get harsh when you crank them up!

 

[Em7]

Amps do not get brighter as you turn them up. The increase in brightness has to do with how the human ear responds to sound pressure. At low sound pressure levels, one has to crank up the bass and treble controls to achieve equal loudness with the midrange frequencies. As sound pressure rises, the equal loudness contours flatten, which is why we have to re-EQ an amp when we crank it up. The contours that describe how the human ear responds to sound pressure are known as the "Fletcher-Munson" curves.