On Lines work good on a CDP with a captive power cord.
I use one on my Sony W222ES CDR recorder. I can hear a difference in a recorded CDR with and without the On Line on the power cord.
I was just about ready to get rid of the Sony because the copies made on it sounded cold and sterile lacking depth.
The On Line makes the copy sound more analog sounding when played on my Arcam Alpha 9 CDP.
Placement of the On Lines on the power cord is at the equipment end.