# How to make an audio 5.1 switch?

I'd like to make a 5.1 audio switch to enable my 5.1 audio system (+mic+headphones) to be available for any of the 4 computers it can be connected to.

So I guess I would have :

• INPUT : 4 (computers) x 5 cables (x2 wires (stereo) ?) - 5 cables are 3 for the 5.1 audio, 1 for microphone, 1 for headphone
• OUTPUT : 1 (audio system) x 5 cables (x2 wires (stereo) ?)

And I don't see the beginning of a way about how to do that properly.
By properly I mean, first do it, second avoiding current issues like current going back to the system or interferences that could damage the electronics.

Note : I'm used to solder electronic components, but I know nearly nothing about electronic theory.

I found this as a starting point / reference, but it is only for 2 inputs, and it uses RCA connectors instead of jacks.

Could you help me ?

• HDMI switches are available. I bought an unpowered one once and it was terrible. It attenuated the signal so badly that some devices did not even recognize that a signal was present. I also tried a powered one, it was better but still not good. Jun 22, 2020 at 11:14
• @badjohn this isn't HDMI though Jun 22, 2020 at 11:28
• Sorry, when I needed to switch multiple 5.1 sources, I was using HDMI. Is your requirement analogue? I expect that similar switches are available. I used to have a tape switching unit. Only stereo and two devices but I expect that more capable ones exist. Jun 22, 2020 at 11:32

Hm, while you can technically do this with analog switch ICs, you'll have a lot of fun with ground loops, reference levels, and control.

Sounds like a job for a lot of relays, that you control with a power source connected to a rotary switch. That's costly.

Or: really just a get a RaspberryPi or similar, a decent 5.1 USB sound card to attach to that, and network cabling instead. You can get network sound infrastucture that works on basically any operating system (including exotic ones like microsoft windows) as client and on linux on the pi as server. I'd look into JACK audio.

• The cheapest DPDT relays on Digikey were about $1 each when I looked and you could use 12 of them to make this switch. 8 channels (5.1 + 1 + 1) x 1.5 relays per channel (3 relays needed to select from 4 inputs, but one set of relays can do 2 channels because DP) = 12 relays =$12 (maybe \$25 if I'm wrong). Not too bad, if you live in the Western world anyway. The advantage of relays is they're completely foolproof. Jun 22, 2020 at 9:52
• @user253751 fair point! I'd still prefer the software solution for the higher degree of flexibility, and the fact you're not pushing low-level audio signal over greater distances, but what you describe would definitely be more foolproof and it seems in fact cheaper. Jun 22, 2020 at 11:26

"ABCD" boxes use wafer switches to enable the user to operate a single control to choose between 4 options for large numbers of conductors.

• Okay, but how can you get or make one for 5.1+1+1 audio? Jun 22, 2020 at 11:28
• if you're looking to buy an appliance ask elsewhere. Jun 22, 2020 at 11:43
• Then why does your answer point to a type of appliance which could be bought? Jun 22, 2020 at 11:49
• @user253751 to illustrate the principle. Jasen is right. Also, you're asking a "how to make" question, and not a "what to buy" question (and that's good, because that would be off-topic here, indeed). Jun 22, 2020 at 11:57

As Marcus mentioned, you will have lots of troubles with hum and buzzing and hissing (high frequencies, down-converted) because of the several power supplies involved, each with their non-audio-friendly switching power supply.

Thus avoiding the ground loops is key.

Instead of trying to use differential amplifiers, that must handle 50 volts common_mode of high_frequency spikes, I suggest you consider audio transformers.

You will still have spikes/trash coupled from primary-to-secondary, through the overlapping winding capacitances.

You have 10 individual signals from millivolts to volts going in two directions, so an all-electronic solution probably is beyond your skill set. Your link shows the right approach - relays. I think this will be more reliable than something with a gigantic multi-pole rotary switch.

An ABCD box might work, but I think crosstalk between the 5.1 signals and the mic signals will be a problem. Also, you will need one meant for printers, with 25 pin connections. For true isolation and to prevent the ground loop problem mentioned in another answer, you need to switch each signal and its ground. That's 20 signals per computer.

There are many audio switch products on ebay. Here is one that is a 4 x 2. If you don't want to build anything, a stack of these would handle all of the signals. Because of its open-frame construction, one could come up with a control circuit to drive multiple board's relays in parallel with a single switch or switch array.

Search ebay for "stereo audio switcher".

https://www.ebay.com/itm/Audio-Signal-Switcher-4-Input-1-Out-hifi-stereo-RCA-Switch-Splitter-Selector-Box/114144550330?hash=item1a938b9dba:g:bNAAAOSwbLpeZnZJ