The Conn-Dupont operation lasted until 1879 when Conn regained full control of his company.

They subsequently formed the Conn-Dupont company, and started production of the Conn Four-In-One cornet, playable in four different keys. In 1876, convinced that he needed specialist help, Conn persuaded a skilled French instrument maker, Eugene Dupont, to leave his employ at the Distin company in England and bring with him a small team of craftsmen. Having developed a process to vulcanize rubber to metal, Conn soon started manufacturing his mouthpieces, at first in humble premises over a drugstore in Elkhart, Indiana. The story goes that Conn devised his original mouthpiece after suffering a split lip in a bar brawl and, wanting to continue to play cornet in a local band, came up with a rubber rimmed mouthpiece ('a cushion for the lips,' Conn called it) that enabled him to play comfortably. As a 21 year old Civil War veteran, Conn invented a brass mouthpiece in 1874 for which patents were soon granted. Charles Gerard Conn was born in upstate New York in 1844.

Conn trumpet serial number n18733