Amplifiers; amplifiers being audio apparatus; audio amplifiers; electric amplifiers (current); electric amplifiers (signal); electric amplifiers (sound); electrical amplifiers for sound signals; electrical amplifiers for use with musical instruments; electroacoustic amplifiers; electrodes with amplifiers; electronic amplifiers; guitar amplifiers; keyboard amplifiers; power amplifiers for use in sound reproduction; power output amplifiers; signal amplifiers; sound amplifiers; stereo amplifiers