Barry Manilow

The cast of "Harmony" at the CTG/Ahmanson Theatre. (Craig Schwartz / July 11, 2012)

Barry Manilow is accustomed to working in rarefied settings: the glittering showrooms of Las Vegas, for instance, or the high-end recording studios in which he made such inescapable soft-rock standards as "Mandy," "Looks Like We Made It" and "Can't Smile Without You."

And then, of course, there is the colorful Cuban nightclub — "the hottest spot north of Havana" — he describes in "Copacabana," the Grammy-winning 1978 smash that's come to signify an idea of campy razzle-dazzle.

On a recent afternoon, though, Manilow was soaking up the grungier atmosphere at a rehearsal space in downtown Los Angeles. Standing behind a table littered with soda cans and a half-empty bag of trail mix, the ceiling above him checkered by water stains, the 70-year-old singer and songwriter nodded intently as he conferred with a choreographer.

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"I can't believe I'm saying this after all these years, but this is my favorite part," Manilow said. "The nuts and bolts of the thing, figuring it all out."

The occasion was a run-through of "Harmony," a new musical by Manilow and his frequent writing partner, Bruce Sussman. Or a semi-new musical, let's call it: Set to open Wednesday night at the Ahmanson Theatre, the show has roots that stretch back nearly two decades, including a 1997 premiere at the La Jolla Playhouse and a planned Broadway run that stalled out in 2003.

Manilow's sustained enthusiasm for "Harmony" is perhaps unexpected for a pop star who's reached the age at which many in his position begin to coast. But more surprising still is the show itself, which shares little with wildly successful jukebox musicals like "Jersey Boys" and "Mamma Mia!"

Inspired by a German television documentary that piqued Sussman's interest when he saw it in 1991, "Harmony" tells the real-life tale of the Comedian Harmonists, a Berlin-based vocal sextet that rose to international acclaim in the early 1930s, yet later was all but forced to disband by the Nazis because several members were Jewish.

The musical, which Sussman says depicts "a quest for harmony in what turned out to be the most discordant chapter in human history," doesn't shy from that story's dark edges — or from its potential for dark comedy. One line, from a song satirizing a cartoon Hitler, rhymes "Anglo-Saxon" with "hair is flaxen."

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And though it occasionally offers up a schmaltzy melody, Manilow's music hews closer to the sound of traditional Broadway than to his signature brand of easy-listening pop.

"Those golden-age musicals with a book that you could bite into — 'Fiddler on the Roof,' 'Gypsy,' 'West Side Story' — those are immensely appealing to us, and they're done not that often these days," Sussman said at the rehearsal space after a recent run-through. Revivals of the classics are common, he was quick to acknowledge, but "it's become so unusual for a new show to do what the old ones did."

"My heart is in writing songs about specific characters," said Manilow, who puffed an electronic cigarette as he spoke, a pair of mirrored sunglasses resting on the table before him. He added that he'd started out wanting to write for the theater and only ended up in pop — penning endless variations, he said, on "I love you" and "I miss you" — as a kind of "detour." So the jukebox approach, he went on, holds little allure. "I think it's the easy way out."

Yet you can imagine that the easy way might've seemed enticing at various points during "Harmony's" slow journey to the stage.

The musical was first produced in 1997 in La Jolla, where it received lukewarm reviews. Writing in The Times, Laurie Winer called Manilow's music "beautiful" but said "key sections are completely unbelievable"; the Comedian Harmonists' story, she decided, "is not told well here." (A different musical based on the German group, "Band in Berlin," played briefly in New York in 1999.)

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Six years later, a retooled "Harmony" was on the cusp of a Broadway run when its producers shut it down just weeks before a Philadelphia tryout because of a lack of funds.

"We've had bad luck," Manilow said, adding that the show's money troubles are hardly unheard of in the theater world. "But because Barry was involved," Sussman said, "everyone knew about it."

For years afterward the men kept "Harmony" "in a drawer," Manilow said. "It was too hard."

Eventually, though, the singer decided he "wanted to see the show one more time before I croak." So after regaining the rights to the musical from an earlier producer who didn't want to surrender them, the two searched for fresh investors with mixed results.