There was sweet soul but no harmonizing with Mavis Staples, Patty Griffin and Amy Helm

The Sweet Harmony Soul Tour – featuring Mavis Staples, Patty Griffin and Amy Helm – was a case of more is less on Sunday night at the Minnesota Zoo.

There were 50 minutes from Staples, who was in fine form. There were 50 minutes from Griffin, who was rather low-key. And there were 25 minutes from Helm, who was encouraging.

But there was nothing from all three of them together – or any collaborations of any sort.

Where was "Waiting for My Child To Come Home," the duet that Staples and Griffin recorded when they met in 2009? How 'bout having Helm come out to sing a verse of "The Weight," a Staples staple that Helm's father, Levon Helm, wrote and sang with The Band? No, we simply got Staples and various members of her band each singing a different verse – as she always does.

Staples, a zoo regular, even made a little speech about what a joy it was to tour with Helm and Griffin. "They can sing for such tiny little girls," Staples said near the end of her closing set. "I used to be that size loooooooong ago."

She accepted birthday wishes from fans (her 76^th was Friday) and a cake backstage from her cousin Regina. "She can make the best rum boogie cake," Staples declared. "But you gotta be careful if you eat it. You will boogie."

The Rock and Roll Hall of Famer boogied in her inimitable way, praising the Lord in song but eschewing the verbal testifying that has characterized some of her longer sets in the Twin Cities. She was focused on singing, with her excellent band (her sister Yvonne was not there, for a change). Staples' usually raspy voice was a little clearer than usual. No complaints there. And, having recovered from knee surgery, she's no longer using a cane. Amen to that.

Staples opened with "If You're Ready (Come Go with Me)," the 1973 smash for the Staple Singers, dusted off the Staples' enduring civil rights anthem "Freedom Highway," and delivered the traditional "Turn Me Around." She got fired up for "The Weight" repeating "put the load" over and over, building to a gospel frenzy. She received a standing ovation.

The capacity crowd sang along to the Staple Singers' signature "I'll Take You There," which was soul stirring as always. But Mavis never took the crowd there with Griffin and/or Helm.

Griffin didn't demonstrate much personality during her set of Americana tunes, seasoned with various shades of gospel and some swampy blues-rock that suggested Bonnie Raitt.

Helm showed a strong voice, as she previewed material from her July 24 solo debut, "Didn't It Rain." She and her two-man band closed with a gospel medley of "Gloryland" a cappella and "Ain't That Good News" with instruments – performances that suggested that she and Staples and Griffin should be singing together on this 12-concert tour. That would be good news, indeed.