Mr. Brohn (rhymes with “bone”) viewed his role as supportive of the composer’s intentions.
“That music is the reason for your existence at this moment, and the central focus for you is to help the composer say what he wants to say,” he wrote in an essay in “The Alchemy of Theatre” (2006), edited by Robert Viagas.
He recalled in the book that he was hooked on “The Secret Garden” when its composer, Lucy Simon, played some of the music on his piano, and that he cried when Claude-Michel Schönberg sang songs in French from “Miss Saigon,” which he wrote with Richard Maltby Jr. and Alain Boublil.
“Bill was a crier,” Mr. Schönberg said in a telephone interview. “He was highly emotional and cried with enthusiasm about everything.”
Mr. Brohn surprised him, he said, particularly in sections of songs where his brass and string orchestrations “didn’t make sense if you listened to them separately.”
But, he added: “When played together they were perfect for the emotion and the message. It was distorted and it was beautiful.”
The current Broadway revival of “Miss Saigon” is faithful to 95 percent of Mr. Brohn’s original orchestrations, Mr. Schönberg said.
William David Brohn was born on March 30, 1933, in Flint, Mich. His father, William, worked in the automotive industry, and his mother, the former Ottilia Pleger, was a nurse.
As a teenager, he said, he was transfixed when he heard the overture of Rodgers and Hammerstein’s “South Pacific” on the original Broadway cast album. The orchestra, Mr. Brohn wrote, “soared on the wings of orchestrator Robert Russell Bennett.” Mr. Bennett, who collaborated with George Gershwin, Richard Rodgers and Jerome Kern, became a mentor to Mr. Brohn in the mid-1960s.
Mr. Brohn graduated from Michigan State University, where he studied music theory, and earned a master’s in composition at the New England Conservatory. He played the bass and conducted early in his career, but eventually turned to orchestrating and arranging full time.
In addition to his work in musicals, he orchestrated the music for a few movies and television shows and for ballets by Agnes de Mille and Twyla Tharp.
After a rehearsal of “The Informer,” Ms. de Mille’s ballet about Anglo-Irish violence, Mr. Brohn praised her attention to orchestral sounds. “When she asks for drums, she wants military drums to convey a threat hovering in the air,” he told The Los Angeles Times in 1988. “As for the bell, she wants a church bell to suggest funerals, not a chime or a synthesizer.”
Mr. Brohn collaborated 11 times over nearly 30 years with the British producer Cameron Mackintosh, from “Miss Saigon” in 1989 to the revival of “Half a Sixpence” currently running in London. A sudden illness last year while Mr. Brohn was working on “Half a Sixpence” forced him to return to the United States. It was his final project.
While the two worked on a revival of the musical “Oliver!” in London, Mr. Mackintosh said that he was displeased that the brass section in the song “Consider Yourself” sounded as if it were playing “Seventy-Six Trombones” from “The Music Man.”
Mr. Mackintosh said in a telephone interview: “Bill completely got it. A light bulb went off, and he figured out the difference between English music hall music and American vaudeville. And that’s why he was able to do ‘My Fair Lady,’ ‘Mary Poppins’ and ‘Half a Sixpence’” — all of which Mr. Mackintosh produced. “They’re all rooted in the music hall.”
Mr. Brohn, who lived in Clinton, Conn., is survived by a sister, Marianne Viau, and two brothers, Paul and Fritz.
He attended the opening night of the Broadway revival of “Miss Saigon” in late March in a wheelchair.
“I told him,” Mr. Mackintosh said, “that the music was as fresh as the day he picked up his pen.”