Aaron- this doesn't answer your question about effects. However, there is an interesting story behind the sound.
Are you referring to the boom-chicka chicka- boom sound that was the vintage Cash signature?
I read that he wanted a snare sound in his song. But only had the Tennessee Two as back up (doghouse bass and hollow-body rhythm). He used to tear off a piece of bar coaster to place behind his strings to muffle them. [ "Cash tore off the edge of a drink coaster and used it as a pick. He damped the vibrations by sticking a piece of paper underneath his strings, creating a short, percussive sound that felt like the Morse code he listened to night after night." (while in the Air Force)]. When learning to play the guitar, he attempted to emulate his friend, Pete Barnhill's guitar playing style of playing the rhythm and lead with his thumb, and dragging a finger to accentuate the beat. Hence the chicka-chicka-boom. I have been scouring YouTube to find a clip that I watched that showed Cash's guitar with the card in place.
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Start with a single repeat at about 100ms and adjust the time to taste. If you go too low it will lose its separateness and start to change the tone by phase interaction.
cool thanks. i just got a record player and have been listening to a lot of my dad's old johnny cash records lately, and really liked the percussive delay sound.