The BOSS DF-2 SUPER Feedbacker & Distortion effect pedal, produced from September 1984 to April 1994. Originally labeled "SUPER Distortion & Feedbacker", BOSS later changed the name so as to not compete with DiMarzio's "Super Distortion" guitar pickups.

While HUM's guitar tones and textures venture into beautiful, soaring feedback territory (e.g. "Suicide Machine" and "The Scientists"), the feedback function of the DF-2 is used sparingly live, if ever at all in the studio. That said, for an example of how that mode might sound in a recorded, HUM-like / adjacent context, give the Honcho Overload track "Stereoblaster" a listen, from their album Pour Another Drink.

For those that might be looking for a lovingly crafted, modern update (or for a replacement) of the classic DF-2 distortion pedal - which are likely to be slowly but steadily more difficult & costly to acquire in the future - consider the HUM Along recreation pedal, hand built by the good folk of Leyland Pedals, over yonder in the UK.