In electricity:
* Insulator: This is the most common opposite, as it prevents the flow of electricity.
* Resistor: This is also relevant, as it restricts the flow of electricity, though not completely blocking it.
In music:
* Performer: While a conductor leads the orchestra, the performers are the ones actually creating the music.
* Composer: The composer writes the music, the conductor interprets it.
In other contexts:
* Leader: A conductor leads, so the opposite could be a follower.
* Guide: A conductor guides, so the opposite could be a lost person.
To provide a more specific opposite, please clarify what kind of conductor you are referring to.