J. DAddario's first factory was in Lynbrook, New York, and the initial staff consisted of only five employees. It was a real family operation with John, Sr., John, Jr. and James DAddario leading the company's growth and business plans. In the early 1980s D'Addario complemented its successful fretted line with the acquisition of the Kaplan Musical String Company, a long-established manufacturer of classical instrument strings. The brothers embarked on a rigorous program of research and development and created a world-renowned line of products in the field, establishing D'Addario as a premier manufacturer of instrument strings.
D'Addario pioneered the use of nickelplated steel for electric guitar.