Subwoofer Isolation Transformer / Ground Loop Hum Eliminator, Blue Jeans Cable brand, made in USA Most, but not all, problems with a humming subwoofer are caused by ground loops. If your powered subwoofer hums due to a ground loop between amp and sub, this transformer will fix the problem by breaking the ground connection while allowing the signal to pass through. This transformer will NOT fix hum caused by other causes, e.g., power supply issues within the sub, ground loops between devices other than the amp and sub, induced hum from power cabling placed too close to the subwoofer cable. See troubleshooting tips, below. Comes with instruction sheet describing causes of hum, and how to track it down and eliminate it. If this transformer doesn't fix your hum issue, this means something other than a ground loop between amp and sub is responsible for the problem -- and you're welcome to return it for a full refund. Works with any powered subwoofer with an RCA-type (unbalanced) input; no separate power required. Made in the USA.