3.5mm 5.1 Surround Sound Switch / Splitter Box

I had a problem which needed solving.

I've just bought a Dell 2709w Monitor which takes DVI and has 5.1 output using the standard PC solution of three 3.5mm jacks, coloured Green, Orange and Black. I had hooked up my Xbox 360 via HDMI to the monitor, and the sound comes out of these (unfortunately only in Stereo since it's in Dolby Digital, but that's another story). This would be great, however there is no similar input, meaning that I have the issue that I had to keep swapping the jacks on my subwoofer if I wanted to get any sound from my PC or the Monitor. Having carried out much searching on the internet, I was unable to find a box that does this, and while many people seem to have similar problems, very few people have a solution.

My first test was to simply try a headphone splitter in reverse on each individual subwoofer channel. This didnt work, since the computer's output always took presedence over the monitor's output. It was then that I came across the following article on Bl3nd.com - 5.1 Audio Switch. It's at this point that I decided to contact Joey Hazlett, the owner of the site to get some information and increase my knowledge on building such a device, with a mind to do it myself. I have to say that Joey was masses of help and the following guide wouldn't be possible without him.

So, I was going to build a splitter box which takes two 3 x 3.5mm Inputs and allows you to switch between them to one similar output.
This would be suitable for connecting two 5.1 surround sound PC cards / PC's to the same subwoofer.

Step 1: Tools and Parts

To complete this project you will need the following tools:

Soldering Iron
Insulating tape
Drill and various sized bits
Stanley knife
Ruler

You will also need the following parts:
Speaker Wire (I already had this)
1 x Box
9 x 3.5mm Sockets
3 x DPDT Switches

Thanks to Rapidonline.com for the parts - I really struggled to find these in the UK!

Step 2: Designing the Circuit

Initially, I wanted to do ths project with a single switch, but after not being able to find one big enough, I decided to separate the channels out. This turned out to be a better solution anyway, since i can have two different audio sources on at the same time.

So, in the end I came up with this circuit.

G, O, B stand for Green Orange and Black, the three channels, and L, R, G stand for Left, Right and Ground. The things in the middle are three DPDT switches (Double Pole, Double Throw), which basically allow you to take two sets of 2 contact inputs and join them to an output.

Step 3: Making the Box

The next step is to actually drill the holes for the box.
This is fairly simple, just make sure you measure everything to lay them out neatly and start with a smaller hole and work bigger so as not to crack the plastic.

I didnt have a large enough bit for the switch holes (and if i had it wouldn't have fitted in the drill!), so I needed to drill smaller holes and file out the remainder.

Step 4: Building the Circuit

Basically, all that happens now is that you solder everything together, fit them into the box and it works! The only thing that is tricky is making sure the wires all match up on the correct channels.

The only place that this gets particularally difficult is on the 3.5mm socket. You need to look at this and work out which is which. On a 3.5mm jack, the tip is the left channel, the shaft is the right, so look at the connector and you can work out which point is which.

Also, when looking at the switches, think of them as two sets of 4 points (with the middle 2 being in both set), and that each side of 3 is independent. When the switch faces one way, you are getting those 4 points connected, and when it faces the other, the other 4. This will help you to work it out.


The final thing to remember is that every single one of the grounds needs to be joined together in one big clump! My grounds were all labelled with insulation tape so i knew which they were.

Mostly, it's a doddle, if a little fiddly...

Step 5: Optional Extra Step

In addition to the initial premise, I also decided to take a dual phono connector in. This was to allow my Wii to connect into the same box. I also wanted this to duplicate the front channels on the rear (with the option of turning the rear off). This in fact turned out to be the hardest part. A phono connector looks like this, with simply one wire and the ground coming out, so after buying some phono sockets from ebay and another DPDT switch from Maplin (although I'll only use one side of it), I did the following

I had to split each phono cable into two - one for the back channel and one for the front. I then took the back channel ones (one from left (white), one from right (red)) and attached them to one side of the DPDT switch. The middle of the switch went directly to the back channel switch on the side of input 2 - this allowed for the breaking of the back channel for just this input. The reason I went to input 2 is because this is coming from the Monitor (i.e Xbox) and I will not be using the Wii and Xbox together. The other two leads went directly to the switch for the front channel.

Once again, join the grounds with everything else.