The amps I have owned (and still own) only had a treble knob and some a bright switch which I never used. True hard to please everyone. I am not complaining just saying that it is too confusing for me. I am a simple guy! Most off the times I only touch treble and presence because the bright switch makes it too harsh and noisy for me.
If you want some of effect of the bright switch, but not as much as happens by default, adjust the value of the bright cap. With this value you can control how much bright the bright cap gives you. This is a very powerful parameter when you use the bright switch.