Tuesday, June 4, 2013

Replacing a bad hardwired speaker cable with a jack

I have a pair of Logitech X-230 computer speakers that have served me well for close to 10 years now.  One issue is that the cable that runs from the speakers to the computer is hardwired in.  Recently, a wire failed and I was left with mono sound.  While this was fine for fireside chats, music sounds much better in stereophonic sound.

I decided to open up the speaker and see how feasible adding a jack would be.  The layout was simple enough.  I identified where the wires connected to the circuit board and used a multimeter to determine which wire went to which part of the plug (tip, ring, bottom).  I labeled the circuit board with my findings.

I then closed up the speaker and debated what to do.  I could have easily just spliced in a new wire.  The problem was I didn't like the idea of ruining a new wire, and I liked the idea of a jack for future flexibility.

The problem was I hadn't soldering in 10 years, and even then I had no idea what I was doing.  I decided to learn how to solder and attempt this as a first project.

I was making a large electronics purchase from Sparkfun, and so included a soldering iron and 3.5 mm stereo jack in the order.

If you read the comments on that jack they are pretty bad.  The only other choice at Sparkfun was this jack.  Note that the first one is panel mount which meant it had a nut to hold it in a hole drilled in a panel.  The second one would have to be held in place internally somehow.
This animatronic parot gave its life
so I could listen to Manowar

I watched a lot of soldering tutorials, and read some stuff.  Then I found some solid wire from some old network cable I had, as well as some stranded wire from an old talking parrot toy I had.  I made some splices and soldered them.  With that I declared myself the world's foremost authority on soldering *.

The first order of business was removing the hot glue holding the audio cable in place.  Following some internet advice I used some acetone and it released the cable immediately.

I cut the cable giving myself about 8 inches to work with inside the speaker.  I tested the part that would remain inside the speaker to make sure the broken wire wasn't in there.  I also stripped the ends of the other part so that I could use it for testing.

A quick note, there are three wires in a stereo audio cable.  Right and left channel, and then a common ground.  The ground is often bare wire twisted around the outside of the other two wires which serves as a shield.  I just twisted up that part of the ground wire, with no regard for interference inside the speaker.

Now I had to install the jack.  I drilled a hole in the side of the casing and put the jack in.  However, as the comments had forewarned, the jack was not deep enough to fit through the wall.  Actually it was just about perfect depth to fit, but with no space left over for the nut.

I thought about gluing it in place, but ended up drilling a slightly larger hole and then by pure luck having the nut fit perfectly in there.  I then could screw in the jack to the nut.  Once it was screwed in it was pretty much locked in place.  This meant I had to do the soldering inside the speaker.

For some reason only the ground tab had a hole to thread the wire through.  I probably should have drilled holes for the other two.  It took about 3 hours to solder the wires on.  Including soldering the first one on the wrong tab and then having to unsolder and then resolder it.  The angle of the case made it very difficult to get the iron in a good position.  The ground and another tab were quite close and I kept getting bridges between them.  The ground wire with its holey tab took about 10 minutes.

I did a final test with the multimeter to make sure there were good connections from the solder points on the circuit board all the way to the bare ends of the audio cable.

I closed everything up and just about had a heart attack when an audio test revealed the left and right channels to be mixed up.  Then I remembered that I don't care about the channels being correct, and as a result the speakers are physically on the wrong sides.

I must say the end result is about a billion times more professional looking than it should be.

Secret soldering expert?
* Note "the world" is the name I call my house.  Even then this is a tenuous claim, as I believe my cat may have substantially more soldering knowledge than it is letting on.

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