sentence: Electronic amplifiers have to be connected to electrical current or a battery to work.
sentences_before: Electronic amplifiers make a signal from the radio or electric instrument louder and stronger by using transistors or vacuum tubes.
sentences_after: Once the signal from the radio or electric instrument has been made louder and stronger, the signal needs to be connected to a loudspeaker so that people can hear it.
concept_name: electronic amplifier
headings: Amplifier How it works
categories: Electronic musical instruments Electronics Audio technology