I have a circa 1978 analog amp with a detented volume knob marked in dB. All of the way up, it is marked 0 dB and at the bottom end it is marked -infinity with -60 as the first detent up.
I always assumed that this approach was probably decided by an engineer.
Whereas we tend to think of using a volume knob to increase sound, from the electronic standpoint a volume knob restrains the signal!
Replace a volume knob with a straight piece of wire and you would get 0dB alteration (the signal is not restrained). The volume control is then used to throttle back the signal.
For my old amp, I presumed that they chose an average speaker efficiency (for that time period) and assigned the markings accordingly.
Many of today's amps go up to 0dB, then continue to +10dB. I don't know why, but would guess that it was a marketing decision.
