Mantom scored nine goals in 47 appearances last season, as the Midlands side earned a place in the League One play-offs.
He was with them permanently for three seasons following two loan spells there. Overall, he made 153 appearances and scored 19 times.
Sam began his career as a trainee at West Bromwich Albion, and also enjoyed loan stays with Oldham Athletic and Tranmere Rovers.
He is our second signing of the summer, along with fellow midfielder Josh Morris from Bradford City.
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