I remember the sound, the song and Joe South, but I don’t think I knew how he made the sound. Mine is a Rogue STR-1 electric guitar/sitar. The sympathetic strings have their own pickup;
Back in the 70s, I had an autoharp that I turned into a tuned resonator, sort of a string reverb. And on a larger scale, I had an old upright piano that I would remove the lower panel from and expose the strings and sounding board that I also used as a reverb and a percussive instrument to be played with drum sticks. Strings are fun.