Review on 🔌 Sewell Sound Link: Bi-Directional Audio Extender up to 2000ft over Cat5e/Cat6, with 3.5mm & RCA Inputs/Outputs - Black by Mitchell Watson

OK, that's a really isolated balloon! I disassembled it just in case (see photo) and here they are: isolation transformers. You can also see in the photo that the traces are surrounded by a good ground plane with lots of vias to shield the signal. Don't confuse this product with $10 devices that plug RCA connectors directly into CAT twisted pairs. These cheaper devices don't protect your signal! These isolating transformers "float" in your audio signal so that it is no longer dependent on other potentials. This means your audio signal is not disturbed by stray magnetic fields or ground potential differences between your transmitter and receiver devices, both of which can be significant over long distances. It's worth the extra money to avoid that 60Hz hum or other noise in yours Also, these baluns are passive, so you don't need to connect to a power source.