Hey, it's not a headphones sub if there's no Koss-post. And since it's the brand that brought the first stereo headphones to the world. Why not start with that.
These are mine, had several. Usually broke the cable, sometimes used the life-long warranty to get free parts.
As i got more interested in headphones, the portapro wasn't quite good enough for in-door listening as it used to be. So i made "wireless" mod so i could have something decent while running.
They are perfect, the tuning actually works better outside.
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The mod was "designed" so that nothing was broken to archieve it. The cable is intact.
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The BT-adapter is switchable, i have another one for instant full battery.
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Adapter is in a weird angle to keep the if off my head. Found out fast how the head blocks signal and in wide spaces the audio would hiccup.
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Headband has an adjustable locking mod, keeps from eating hairs.
Nicely done! Have you thought about shortening and re-terminating the 3.5mm cable, or do you like having the full length in case you want to occasionally use them as wired headphones?
I've been planning on maybe clipping the cable on my broken older pairs and remaking this. Keeping the original cable intact on these means that i can reverse them in the future. I like having one pair with a flawless cable.