“The Sing-Off,” NBC’s a cappella singing contest of which Newton’s own Sam Weisman is executive producer, is coming back to television Monday. Weisman tells us he’ll be watching from home this year because the entire series has been taped. (The show’s judges — Ben Folds, Shawn Stockman, and newcomer Jewel — will be in the audience for Monday's live episode of “The Voice,” which leads into “The Sing-Off” premiere.) The show — which exposed the Tufts Beelzebubs to the world and helped a cappella act Pentatonix make it big — features no Boston groups this year, but Weisman did tell us a local story about the season. Monday’s episode features a medley of songs by Fun., a band that’s never licensed its music for competition. Weisman got permission to use the hits after befriending the band’s local producer, Dalton Sim , whose Nettwerk Music Group is in Cambridge.