"Actually, unless I miss my guess, which is highly unlikely, there are no wires inside a Sony Walkman."There are. Depending on the model and your acceptance of the word "wire", easily all of them have it.
Just a quick look at some of the models...
http://www.hembrow.eu/personal/sonywmd6c.html
and...
https://www.eevblog.com/2015/06/10/eevblog-752-original-sony-walkman-tps-l2-teardown/
and, for those who were not present at our most recent lecture,...
https://www.sony.com/electronics/walkman/nw-wm1z