WARNING: this mod will void your warranty and can possibly damage or even break your headphones! Read carefully and make sure that you can follow each step BEFORE you order, disassemble, solder or cut anything!
This replacement-cap for the Superlux HD-681 headphones enables you to install a 3,5mm audio-hack instead of the original far-too-long 3m cable!
Installation is straight forward: you unscrew the original (remove the cover with a knife our your fingernails to get to the screw), unsolder the original cable, then re-solder to the audio-jack THROUGH this printed cap, glue the audio-jack in, screw it tight and you are done :)
Additional parts needed: - Neutrik Rean NYS 240 BG audio-jack (other plugs may work, I used this one; throw the black part away) - some thin short cables for re-wiring - a slightly longer screw than the original (I found one in my spare-part-box, it's 10mm incl head, 2mm thick) - glue for the plug
For the proper wiring, use this helpful thread: https://www.head-fi.org/threads/need-help-wiring-superlux-hd668b.877749/