Neil Diamond, Burt Bacharach Croon for Obama Volunteers in Los Angeles (Exclusive)

Iconic balladeers Neil Diamond and Burt Bacharach made a visit to the Obama campaign's Culver City call center Sunday to surprise the phone bank volunteers with an impromptu concert.

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Southern California DNC co-chair Ken Solomon told The Hollywood Reporter that "the place went crazy" when Diamond and Bacharach plugged in their microphones and started to sing "Sweet Caroline."

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"They wanted to do something to thank the volunteers," said Solomon, who helped organize the singers' visit with friend Chuck Lorre. "It was like the '60s or something. Everyone was singing along. It was amazing."

Solomon said he was scheduled to fly back to campaign headquarters in Chicago on Sunday, but he decided to change his flight when Bacharach mentioned that he wanted to do something special for the Obama volunteers. Bacharach made a quick call to his friend Diamond, and soon they were on their way to the westside phone bank, set up on a large soundstage at the Culver Studios.

After the sing-along, Diamond decided to stay to make a few phone calls for campaign. He tweeted: "Working the phones for Obama... If I call you, don't hang up. It's really me and I need you."

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About 150 volunteers were at the call center when the Bacharach and Diamond arrived. They also took to Twitter to express their excitement.

"As if making calls for @barackobama wasn't rewarding enough…@neildiamond & #burtbacharach sang us out! #ofaculver," wrote volunteer Erica Rich.