https://www.youtube.com/watch?v=WWc4eNtUy2I
https://www.guerrilladigital.cc/2021/03/10/i-spent-the-last-two-weeks-researching-and-making-endless-cassette-loop-tapes-and-this-is-what-i-learned/
was used in broadcasting so it's a good quality but pretty expensive now, good for all kinds of audio mods here's a good example of a tape delay and other mods https://www.youtube.com/watch?v=ABU-psBnmxk
Echo-Matic circuit (Stompbox coockbook)