imageLike most phones these days my Cingular 3125 (aka, HTC StarTrek, aka QTek 8500) uses a combined headphone/charging port preventing the use of regular 3.5mm headphones.

What’s less common is that it’s impossible to get a simple headphone adapter for it. The only adapters I can find have an 80cm long cable ending in a combined volume control/3.5mm socket. When you add in the length of your regular headphones that’s a serious amount of cable!

The 3125 is a pretty decent media player and great for places like the gym. I decided to I’d take the headphones that came with the phone and perform a little surgery to make my own compact adapter :)

Requirements;

  • A 3.5mm Jack from Radio Shack (~$2)
  • A soldering iron and basic skills
  • Fine wire strippers
  • A set of helping hands
  • Patience

The first step is to decide where you want the adapter to be. You can either have it after the volume control/mic which allows you to retain that functionality but results in a lot of cable, or you can place it a lot closer to the Micro-USB plug which gives you a more compact adapter (but is harder to solder).

Attaching the jack after the volume control is the simplest option. Snip off the ear buds and trim the black rubber (a scalpel works best) to expose 1cm of the inner wires. Each cable should have one gold wire (-ve) and one colored wire (+ve). Unscrew the 3.5mm Jack (remembering to thread the cable through the casing!) and solder one colored wires to each of the inner posts. Then solder both of the gold wires to the outer band. Tightly screw the Jack back together and you should be good to go.

Attaching the Jack before the volume control is a little more tricky. Snip the cable somewhere below the volume control (I left about 2″ from the USB plug) and carefully trim the rubber casing on the outer wire to expose the inner micro-wires. This time one outer wire will have four micro-wires and one will have three.

The way I figured this out was to crack open the volume control and examine the inner wiring, but if your headphones are the same as mine then;

The collection of four micro-wires are the ones we are interested in and are;

  • Red - Right Audio (+ve)
  • Red/Gold - Left Audio (+ve)
  • Gold - Audio (-ve)
  • Red/Green - Audio (-ve)

The collection of three should be trimmed and sealed, but they are

  • Green - Data
  • White - Mic(+ve)
  • Gold - Mic(-ve)

Soldering the four micro wires is quite tricky and you will need a good set of helping hands to hold the parts in place.

The Red and Red/Gold wires must be attached to the two inner posts and I found it easiest to do these first. The best way to solder this type of wire is by “tinning” it - E.g. first applying a small amount of solder to the end of the wire, then soldering the wire to the surface.

After you have soldered the inner wires you must solder the Gold & Red/Green wires to the outer band. Again, first tinning the wires is the best approach here.

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The outer band is at the top

 After soldering all four wires plug in a set of headphones and test the sound quality. It should be clear and crisp. If there is any crackling or drop out (particularly when you gently shake the jack) then there’s a bad solder contact that must be redone.

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 And hey presto! Your very own mini-headphone adapter for the Cingular 3125.