Son of a Preacher Man was never recorded by Janis Joplin. Not in the studio, not live, now anywhere. I doubt she would even have hummed along to it.
Why don't you remove this error from your site. It perpetuates an Internet and urban legend that is simply not true.
Janis would roll over in her grave if she knew..
How do you know? Have you talked to her lately?
Lyrics taken from http://www.lyricsmode.com/lyrics/j/janis_joplin/son_of_a_preacher_man.html