Whether you need a sound card in a system that has none, your onboard sound is broken, or just want better sound and less interference noise than the average onboard audio setup, detailed here I explain how you can create an external USB DAC from an old or broken USB headset or even some USB speakers.

My old USB headset's one speaker was working sporadically, so I replaced it with a new headset that uses 3.5mm connectors that plug into my onboard sound.

I was disappointed in the flat sound and low max volume so I started looking around for affordable external DAC/Amplifiers but the price range and availability didn't suit me as I realised it would have been cheaper to spend a little more on a headset that connects via USB and uses it's own DAC (Digital-to-Analogue Converter).

I got the idea of using the old USB headset's DAC as the sound was decent, to output to my new 3.5mm headset. I wasn't sure how much I would gain but I gave it a shot.

I was pleased enough with the result that I decided to post it on here.

Step 1: Parts and Tools

The parts were easily acquired from my local electronics shop for very little money:

Case - These are generic, but you can get creative by using mint tins or the like. If using a metal case, line it with sponge or tape to avoid short circuits.
3.5mm Mountable female jacks, 1x stereo for the speakers and 1x mono for the mic. If you can't find a mono for the mic, you can use a stereo jack, but you might have to bridge the two non ground contact.
Some wire
Heat shrink tubing. You might not need this, but in my case, the USB ground was exposed when trimming so i used this as an insulator. You can also put this over your jack contacts if shorting is of concern.

Tools needed can be as basic as you want, I used a few extra to make the process easier:

Soldering iron
Solder sucker
Soldering wire
Wire cutter
Screw drivers
Vernier scale
Drill
3rd hand
Multimeter

Step 2: Old or Broken USB Headset or USB Speakers

Find an old or broken headset.

It wouldn't be financially viable to buy a headset for this purpose, so if you don't have an old one lying around, ask your hoarder friends or colleagues.

Step 3: Find the DAC

Some headsets have the DAC in the USB plug part, and some have it inline as was my case.

Look for screws, in this case they were hidden behind the sticker, others might use clips or glue. Whatever the method of sealing, be careful not to damage the circuit board when opening the casing.

Step 4: Analyze the Wiring

Have a look at the circuit board. In this case, the board was conveniently marked for the two mic wires as well as the speaker ground/left/right connections.

If your's doesn't have these markings, disassemble the headset carefully and trace wires back, in most cases they should be the same colour all the way through.

I illustrated this by writing down the mic wires' colour mapping as well as the speakers'. Note the common ground for the speakers.

NB! Not all headsets use a common speaker ground. If it uses distinct ground wires, be sure to pair them correctly.

Step 5: Soldering Your New Wires

As is often the case with headsets, the existing wires for the mic/speaker connectors were very fine and easy to snap so I soldered on new thicker wires. When doing this and your circuit board isn't marked, make sure to note down what colour wires you are replacing with which.

On the USB side, take a picture or take notes of which wire colours should go where on the circuit board, then desolder them as the wire will need to pass through the case when installing the board into the case.

Step 6: Install Into Case

To accurately measure using a vernier scale, I put masking tape over the casing so the pen ink would take and be visible. I made small pilot holes with the tip of the soldering iron, then drilled them out using the same size bit as the threaded neck on the female 3.5mm jacks for a tight fit.

Solder the mic and speaker wires to the respective jacks.

I found the L and R channels of the speaker jack by plugging my headset into the jack then using the continuity setting on my multimeter, I touched the ground wire on the screw neck ground part and tapped the other two points taking note of with side of the headset makes a click sound to establish L and R.

Note how the L and R contacts on the mic are bridged, as in almost all cases you'll have a mono mic setup.

Mount the jacks into the case, push the USB cable through the hole you made in the other side, and solder the wires back on the circuit board referencing the notes or photo you took for correct mapping. Use a cable tie to ensure the USB cable doesn't pull out.

Note that I shortened the USB cable as I don't need it to reach far.

NB! If your USB cable has a ferrite bead, do not remove this as it will aid in minimizing interference.