I also bought 3.5 mono to RCA adaptors....they sort of worked but the ground portion of the 3.5 plug shorts to the tip portion of the 3.5 mm plug when inserted into the adaptor...tried several 3.5 mm plugs and they all did the same thing especially if you move the cord when the 3.5 plug is fully inserted
The adapters convey RCA monophonic audio to both channels of a 3.5 mm stereo jack. It would also combine 3.5 mm stereo audio to a single monophonic stream. In my application, I feed the left channel of a line level audio stream out an RCA plug, through this adapter, two both channels of a 3.5 mm stereo connector. My monophonic audio is presented to both left and right channels of my amplifier. Just what I needed.