I wanted to give wireless headphones a try without buying a new set of headphones - I already had several wired pairs I was quite happy with. For the sacrificial test, I used a pair of headphones I hadn’t used in a while, Sennheiser HD-201. I took a cheap bluetooth stereo speaker from e-waste recycling, where it had been discarded due to a li-ion battery that had dropped below it’s BCM’s low-end cutoff. I modified the main PCB from the speaker to better fit inside one of the headphone’s ear cups (moved capacitor, extended charging port, removed aux in port) as well as replacing the buttons with taller-profile buttons. I removed the existing cable from the headphones, attached the local audio driver, soldered twisted-pairs from some scrap CAT cable to run to the other side for the other audio channel as well as a much extended battery. The headphone cup was drilled to allow the buttons to be accessed, and I engraved their indicators on the housing plastic with a scriber. The result was quite good, and I was especially pleased to find I was able to use the headphones for over 40 hours without needing a charge (all day, every day at work, and charged only on weekends).
This project eventually led me to repeating a similar process on other pairs of headphones as well - it turns out true wireless is quite convenient indeed!
