Marantz DLT-1 digital line transformer 

The Marantz DLT-1 digital line transformer is an inline transformer (plus a few loading resistors) designed to go between CD player and amp. The Marantz DLT-1 actually increased the output slightly, but it helped to filter out RF mush coming out of many CD players twenty years ago.

Its Philips sister is the Philips L-300 audio line transformer