Single Stereo to Mono Converter, RCA Audio stereo to mono adapter summing box RCA L/R
5 Pack 2x RCA Stereo Converter to 3.5mm Mono by Keple, Audio Adapter, Y Splitter, 3.5mm One Ring Male Jack Plug to 2 x RCA Phono Female Connection | Keple.com
Amazon.com: OSD Audio SMC21 Stereo to Mono Converter – Gold-Plated RCA Connections and 1:1 Ratio Audio Transformer : Electronics