Back in the 1960s, when Warren Hellman was a hotshot investment banker, he decided to master the banjo. And being a hotshot investment banker, he decided to take lessons from the best.

So he called Pete Seeger.

“I called him two or three times,” recalls Hellman. “Finally I got a call back from Pete’s manager, who asked what I wanted. I said I’m a big-time investment banker and I’d like to take lessons. He said, ‘I’d like to hang up.’ ”

He never did take lessons from Seeger, though Hellman, 75, kept his banjo close by. He became wealthy, as a banker at Lehman Brothers, then with his own company, Hellman & Friedman. He also became a philanthropist and Jewish community leader, currently chairing the endowment committee of the Jewish Community Endowment Fund.

Hellman may be a financial leader, but in the world of American folk music, he has a ways to go. His passion for traditional American folk music, however, has never wavered.

That’s why, in 2001, he started (and sponsors) the Hardly Strictly Bluegrass Festival — San Francisco’s popular free music fest at Golden Gate Park. And why he formed his six-piece bluegrass band, the Wronglers.

That’s not a misprint. They are called the Wronglers due to Hellman’s affinity for cowboy lore, and because the band sometimes plays the wrong notes.

Warren Hellman (upper right) and the Wronglers. photo/krista martin

That’s getting more rare. The band debuted at Hellman’s Hardly Strictly fest a couple of years ago, then went on to do professional gigs all over the region.

Their next concert takes place 5 p.m. Sunday, Aug. 16 on the turf lawn at the Peninsula Jewish Community Center in Foster City.

How does Hellman define the Wronglers? “It’s simple music from complicated people,” he says.

No doubt. His bandmates include former JCC executive Nate Levine, bassist Colleen Browne (an employee at Hellman & Friedman), fiddler Krista Martin, mandolinist Bill Martin and Hellman’s wife, Patty Christina Hellman.

“Perhaps because we’re kind of exotic, we do seem to have a lot of dates,” says Hellman. “But we have a very weak banjo player.”

His bandmates would beg to differ.

“Warren is an extremely passionate, dedicated guy,” says guitarist Nate Levine, former executive director of the JCC of San Francisco. “He has a wonderful mix of intensity, humility and a great sense of humor. His playing is strong and getting stronger.”

The band got its start five years ago when each of the members was a student of local traditional music master Jody Stecher. He suggested his pupils try jamming together, and thus a band was born.

Their repertoire features bluegrass and Old Time classics, as well as the occasional original, such as Hellman’s “White Lady,” a popular tune on the bluegrass circuit.They  also put a bluegrass spin on tunes such as “Titwillow” from Gilbert and Sullivan’s operetta “The Mikado.”

This weekend, the Wronglers will even take a crack at a couple of Jewish liturgical tunes, “Kol Amar” and “Ein Keloheynu.”

Why funnel songs like these through a banjo and fiddle? Says Levine cryptically, “If you’re holding a hammer in your hand, pretty soon everything looks like a nail.”

Hellman is no picker-come-lately. As a youth, he loved groups such as the Kingston Trio, and later fell for the music of Bill Monroe and Flatt and Scruggs.

But there’s a difference between being a fan and playing  music professionally. For Hellman, a lifelong athlete and competitive businessman, it’s all about achievement.

“One of my theories is that as you get older, almost everything you’ve done you get worse at,” he muses. “I’m not going to run a 38-minute 10K anytime soon again, or a three-hour marathon. So if you find another thing you’re capable of improving on, it’s very fulfilling. Also the relationships between the members have been  wonderful.”

Levine echoes the sentiment. “We’ve all become very close friends,” he says. “My favorite part is getting together to practice twice a week. It’s made me get a lot better at music making.”

The same is true for Hellman, who is a pretty fine frailer, despite his self-deprecating humor. When asked what draws him so much to this kind of music, he quotes from the legend hanging over the Country Music Hall of Fame.

Says Hellman, “The sign says ‘Country music: three chords and the truth.’”

The Wronglers perform with Margot Leverett & the Klezmer Mountain Boys 5 p.m. Sunday, Aug. 16, at the Peninsula JCC, 800 Foster City Blvd., Foster City. Tickets: $8-$20. Information: (650) 378-2702 or www.pjcc.org.