EXCLUSIVE

Lee Dorman -- the bassist for the acid rock band Iron Butterfly -- was found dead at his home in Orange County, CA earlier today ... TMZ has learned.

70-year-old Dorman was an original member of the group -- and played during their famous 17 minute recording of the rock classic "In-A-Gadda-Da-Vida."

Law enforcement sources tell TMZ ... officers responded to Dorman's home around 10 AM this morning ... and he was found sitting in his car.

We're told cops do not believe there is anything suspicious about his death.

Dorman reportedly had a history of heart problems -- and according to some reports, the medical issue forced him to retire from music.