Just a year after he formally reopened the legendary Minnesota studio that hosted Nirvana’s “In Utero” sessions, Twin Cities recording guru John Kuker died unexpectedly Monday in Los Angeles. Friends say a heart attack was the suspected cause of death. He was only 40.

The Anoka-reared music expert hosted classic recording sessions by the likes of Semisonic and Jonny Lang in the late 1990s and early 2000s at his earlier studio, Seedy Underbelly in Minneapolis, and is credited for giving many local bands a boost.

After losing his lease a decade ago, he relocated his operations to Los Angeles but never lost touch with his Minnesota roots. Proof came in 2012, when he jumped in to save the crumbling Pachyderm Studios in Cannon Falls, buying the property for about $370,000 and investing more than that during the past two years to renovate it.

“He was the obvious, right guy to save [Pachyderm] because he was so knowledgeable and invested in his work,” Semisonic’s Dan Wilson said. Wilson remembered Kuker lending Semisonic gear to record its door-opening “Pleasure” EP even before the original Seedy Underbelly was built “because that was his thing, helping local bands however he could.”

“He was always a super generous, sweet guy — helpful and kind, which really says a lot when you’re in the hard business of running a recording studio,” Wilson said.

Darren “Kid Dakota” Jackson recorded some tracks just a few weeks ago with Kuker at Pachyderm, about 45 minutes south of the Twin Cities. He said you could see the pride that Kuker took in reviving the rural studio, whose 1990s heyday also generated top-selling albums by PJ Harvey, Soul Asylum and Live in addition to Nirvana’s studio swan song.

“John put so much time and energy and thought into putting the place back together, he just seemed so perfect for the job,” said Jackson, who first recorded with Kuker in 2001. “He was always very generous with us, letting us use his space and his gear. We all learned so much from him over the years.”

Local recording engineers, including Jacques Wait and Alex Oana, also learned from Kuker. “I’ve not met a friendlier, funnier, more generous guy in the business,” said musician-turned-producer Kevin Bowe. “A true gear nerd of the highest order.”

Bands who recorded at Kuker’s Minneapolis studio ranged from Lifter Puller, the Soviettes and the Hang-Ups to D.C. alt-rockers Girls Against Boys and even soft-jazz duo Tuck & Patti. After relocating to Los Angeles and starting an offshoot space in New York, Kuker’s client base jumped exponentially to include the Yeah Yeah Yeahs, Jonas Brothers, Jimmyeatworld and Nick Cave’s Grinderman.

Still, his heart remained close to home. He said in a 2012 Star Tribune interview about purchasing Pachyderm, “I’ve been bouncing all over the map, but I do hope this [studio] will get me back to Minnesota on a more permanent basis.”

His idea seemed to be working. Since its reopening last winter, Pachyderm has hosted album-making sessions by Trampled by Turtles, Motion City Soundtrack and buzzing newcomers Hippo Campus, who just returned there a week or two ago.

“John has been very happy these last few months over how well it was going there, which just makes this all the more sad,” said Nick Tveitbakk, his longtime engineering partner.

Tveitbakk has been talking to Kuker’s family and believes Pachyderm’s future is safe. “They want to keep the momentum going and believe that’s what John would’ve wanted.”

Kuker leaves behind a wife, two sons, a daughter and stepdaughter. Information on a memorial is not yet available.