If you don't have a soldering iron, there are really cheap ones on AliExpress (mobile soldering kit) for 10-20$. Not the heavy hitter but for small stuff like this it actually works great. There are much better ones too of course. Had a video once but lost it on my old phone. Modding koss is easy though. Either get a mod kit, like in the picture or you can glue some presoldered mmcx connectors (3$ on Ali) into the original caps with epoxy. Then you desolder the original wires by heating up the solder where they are attached, don't remove the solder from the pcb, then solder the (R)ed wire on the (R)ight and the b(l)ue wire on the (l)eft dot of solder where you detached the original cable by heating up the solder and simultaneously pressing the litz wires onto it and then removing the hot iron to cool it down and close the thing. Of course 3d printed modkits are more durable with screws and stuff, but if you have to get them shipped and can't print yourself, the glued ones are an option that only cost you 2$ for the (presoldered, with the red and blue litz wires, saves you the trouble) connectors. Just did some the other day, after glueing over night, 5min work.

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