My car stereo has only one 'Aux' input, but I have several gadgets that I like to hear on a trip without swapping cables: MP3 Player, talking GPS, Blackberry, XM player, Kindle, etc.

I couldn't find a commercial solution, so I came up with this little passive audio mixer that takes 1/8" headphone outputs from up to four devices and safely mixes the signals into one line that can feed a car stereo Aux input, powered speaker or any other amplifier that can take 1/8" stereo output.

No batteries are required, it's sonically transparent and most audio gadgets have their own volume control so the mixer can be done very simply and cheaply.

This little mixer also works great for connecting multiple computers to one set of amplified speakers and has many other possible uses. Note that this device is NOT RECOMMENDED FOR HEADPHONES!!!! Whatever you plug into the output needs to have its own amplification, or the volume will probably be too low.

Note: Soldering is required. If you don't know how, please search for Instructables on how to solder, as that's beyond the scope of this project.

Step 1: Materials

Qty 1    ---       Altoids Tin. See Note 1.
Qty 5    ---     1/8" (3.5mm) Stereo input Jacks, Radio Shack part 274-249 or equiv.
Qty 8    ---      1k ohm Resistors, Radio Shack part 271-004 (5-pack) or equiv. see Note 2.
1 foot   ---      22-30 gauge solid hookup wire, stripped bare

Note 1: A normal Altoids Tin can take 4 or more inputs, this example assumes 4 inputs. The Altoids Gum tins can fit 3 inputs comfortably. Adjust the number of jacks according to:

       # of Jacks = 1+ # of inputs

and number of resistors by:

       # of Resistors = 2 * # of inputs

Note 2: All resistors (2 per input channel) should have the same value, which can be anything between 1k  and 10k ohms. Higher values result in a higher volume drop. Also, the resistor power rating can be 1/8 or higher. This circuit runs no power through it, so there's no need for bigger than 1/8 w, but use whatever you have handy. Bigger power rating = bigger size.

<p>It works!!!</p>
Hah! that's a crazy-looking tin, I like it! Good job, glad it worked.<br><br>Rich
I made a new passive mixer based on your ible. Thank you so much for the awesome instructions !
<p>that I can use my PC headphone output as input 1 &amp; a low level source as input 2? I know PC output is amplified, but thought you may have any suggestion. I know I can use car audio HI-Low adapter, but like to use your idea for a compact box, Thanks </p>
I would suggest just trying it first, if there is too big a difference in the input levels, you may need to lower the resistor values for the low level signal. You can do this either by replacing the resistors or by soldering resistors in parallel. The formula for the resulting resistance is (r1 x r2)/(r1 + r2)<br><br> Good luck
Great box! Thanks for sharing the pictures!<br> <br> Rich
<p>This was exactly what I was looking for. Thank you for making the instructions clear and actually including a circuit diagram that wasn't made in MS Paint. It works perfectly for what I need, and every input comes out the other end crystal clear, even when multiple sources are playing at once.</p><p>I ended up using a Radioshack project box instead of an Altoids tin, mostly because I just didn't have one sitting around and the box was actually cheaper than a tin of Altoids. This also makes the drilling significantly easier and prevents any unintentional shorts. </p><p>Thank you again for taking the time to make this useful, clear and concise guide.</p>
Hey, nice job! Glad you were successful and thanks for posting the pictures!
<p>works pretty nice! great idea!!!</p>
<p>Nice job! I like the jacks you used, where did you get them?</p><p>Rich</p>
<p>hi from Germany. I found the Jacks at www.conrad.de but I will make an other one with 6,2mm jacks :-)</p>
<p>thanks for the great idea! I did a mixer/splitter for an experimental music project</p>
<p>Hey Vanderaalle, great job!! Looks like you're using 1/4&quot; jacks and I *love* the tin (although not a smoker myself). Hope this works well for you.</p><p>-Rich</p>
Made one and it works great. Thanks.
<p>why did you put the resistors , can we do it with out them ?</p>
Please read FAQ on step 15. You can do anything you like, but unless you want to use this as a signal splitter, leaving out the resistors is a bad idea.
Wow, really nice job! Good idea to use resistor networks!<br /> <br /> Would you care to share the artwork?<br />
Jacks are Mouser 161-3508-E. Resistor networks are Mouser 652-4608X-1LF-1K 1k ohm. Other resistor values are available. Board was fabricated by ExpressPCB.com.
Can this image be used to have a board made or do we need the ExpressPCB file?
Looks like a 2-sided board with the silkscreen mask drawn in so you would either need the file or just reproduce it on your own. It isn't mine and I don't have it. Maybe chipmonger would nice enough to provide if you asked.
This is a 2 sided board and I don't know if the image is scaled correctly once you download it. I do have the ExpressPCB file if you want it. Email me at steve&quot;at&quot;PowerSwitchTail&quot;dot&quot;com.
Thanks for the artwork and again, really nice job!
I made mine. Not as pretty as yours but sure gets the job done! Stuck with the 1k resistors. Thanks for the great 'structable!
Thanks for posting. Here is my version,&nbsp;it works perfectly.<br> <br> C3-PO is an old ball mouse. After removing the guts there was plenty of room for the wiring. For the triple input audio jack I used parts from an old motherboard's sound card. They have five leads on each; 1) ground, 2) closed tip, 3) open tip, 4) closed ring, 5) open ring. When a plug is inserted, the part that touches the tip moves from the open tip lead to the closed tip lead. This must be how a computer knows when a plug is inserted. I used the closed tip/ring leads, leaving the open/tip leads alone. I wonder if the the open leads could be used for anything.
Nice! Good recycling!
Thank you. I used pulled parts from trashed sound card and a &quot;Smalls&quot; tin.... I love Old school point-to-point wiring...and Hot glue.
Here's my version of the mixer, using a Lucky Stars Candy tin. I plan to add a &quot;floor&quot; above the wiring so that I can store a short 1/8&quot; patch cord inside as well.
Nice! I particularly like the 'Hello Kitty' motif ;^) Thanks for sharing the picture.<br><br>Rich
Made one in less than an two hours, including trip to radio shack for parts, and safeway for MINI altoids tin. Used 1k resistors. Very Small, works fine.
Nice job!<br> <br> Good idea to run the connectors out of the bottom of the mini altoids tin.<br> <br> Looks like you used heat-shrink tubing for insulation as well. Heat-shrink is one of the best things ever for building things and professional wiring repairs.<br> <br> I'm glad it worked for you and thanks for sharing the picture.<br> <br> - Rich
<p>May be a silly question. Would it be possible to do this with 3.5 mm TRRS input jacks? As to use it with headphones that also have a microfone.</p><p>Thank you</p>
Hey Jo&atilde;oS38,<br> <br> No such thing as a silly question, only silly people, I always say ;^)<br> <br> Seriously though, keep in mind: this is a passive mixer with no amplification on the output at all. Plugging any kind of headphone (TRS) or headset (TRRS) into the output isn't going to work very well -- you won't get much volume and really need an amplification stage after the output.<br> <br> Fortunately, there are lots of inexpensive headphone amp boards out there now. I've played with <a href="http://www.parts-express.com/sure-electronics-2x2w-at-4-ohm-class-d-audio-amplifier-board--320-306" rel="nofollow">this one</a>&nbsp;(Sure Electronics&nbsp;AA-AB32131) and it works pretty well -- could be battery or USB powered.<br> <br> To your specific question: what are you trying to do? Would you be trying to use the microphone, mixing mics of 2 headseats or just plugging in a TRRS headset to use as headphones (not using mic)?<br> <br> Either way I think you'd need a TRRS output jack -- I haven't had any luck plugging a TRRS plug into a TRS jack (e.g. smartphone headset plugging into a stereo output device). The other way works fine of course, plugging a TRS/stereo headphones into a TRRS output.
<p>I'll explain my situation, maybe there's an easier solution for it. Although this is way out of the subject of your instructable.</p><p>I have Teamspeak on my Android phone, and I'm connected there with headphones (with mic). But at the same time, I'd like to mix in the audio stereo input from my Playstation 4 controller. As you can imagine, this is not easy to manage.</p><p>My bad solution atm is to use the the single ear piece + mic, that comes with the PS4, on one ear connected to my phone (TS), and wear headphones connected to the PS4 controller to get the game's audio.</p><p>Cheers</p>
<p>2nd answer: re-read your comment and noticed you mentioned sound through the controller... The mixer/amps I mentioned have to plug into the console, since the mic from your headset is routed to the USB audio interface. Also you'd have to get game sound into the TRS cable... So on the downside, you'd have to be wired back to the console, on the plus side, the cord is long and there are independent volume controls (game,USB chat) on the amp itself close to you... If you have to have wireless (I.e. Plugged into controller) it would take a little thinking...</p>
<p>Thank you for your replies. I'm going to take a look at your suggestions and see if I can make them work for what I need. Cheers!</p>
<p>Joao: Thought about this some more and added a step to the end of the Instructable for variations (step 16) -- look at the schematic I added. It's easy to mix the game sound and voice chat, but you *really* need to amplify the resulting mix for the headset (you *could* try using smaller resistors like 100ohm ... not sure how well that would work). For the mic, the easiest thing would be only have one jack with the mic routed. This way two devices wouldn't be trying to power the mic... that's likely to be noisy. If you had to have mic to going to both smartphone and game controller, I'd route the mic to one directly and connect the other via a capacitor to block the DC bias voltage it's trying to send to power the mic. I think this might work pretty well! Also, you might be able to use a TRS cable from the game controller since you're ignoring the mic.. not 100% sure on that. Good luck and please let me know how it goes!! Rich</p>
<p>yeah, ok I understand exactly what you're trying to do. I do this on PS3 -- Skype/TS/mumble on ipad mixed with game sound. I use a headset mixer/amp that came with a Turtle Beach PX22 -- it mixes audio from a 3.5mm TRS plug (usually game sound) a built-in USB audio interface (usually chat/mic) and has an extra input for a TRRS cable to go to your smartphone/tablet. There's a single 3.5mm TRRS output for your headset. Look on eBay for 'px22 amplifier' you'll find them for $15-20 (amp/mixer alone, no headset). The first-gen Plantronics Rig has a similar amp/mixer that's even a little nicer. Now, the question is: will this work with PS4? I think so, but will have to try it (have PS4 but don't play anything that requires chat at atm). These are great and you can't build anything equivalent that cheap (and compact). Good Luck! Rich</p>
<p>I made it and it works like a charm thank you for the awesome instructions!</p>
<p>Thanks for the pictures, nice job! That's quite a rig you have there!</p>
<p>Very nice! Do you think it is possible to modify the project to give inputs a priority so that if an input is active the lower priority inputs are muted?</p><p>Andrea</p>
Hi Andrea,<br><br>Not really, since it's a completely passive circuit. What you want is called ducking and it requires active circuitry (battery power, transistors, etc).<br><br>Sorry,<br><br>Rich
<p>Very nice!!! Do you think it is possibile to modify the project to give inputs a priority so that if an input is active the lower priority inputs are muted?</p><p>Andrea</p>
<p>First time soldering since I was at school, and it came out perfectly.</p><p>Thanks to the clear instructions this is ready for a road trip.</p><p>:D</p>
If you only want to connect mono instruments together, just build one channel of the circuit instead of building both left and right channels. This way you'd have mono inputs and a mono output. If you want to mix stereo inputs with mono, the easiest thing would be to connect the mono input to both L and R channels via resistors
<p>This looks so cool, and something I can do as a first DIY audio project.</p><p>I guess it would turn just fine if I use 1/4, 1/8, stereo and mono combined?</p><p>Thanks.</p>
The size of the connector doesn't matter at all, so yes, you can mix 1/8&quot;, 1/4&quot;, etc stereo connectors with no problem. Mixing mono and stereo is not as simple. What are you wanting to do?
Thanks for replying. I'd like to plug my Casio VL-1 and SK-1, both have mono outputs.
<p>I just did my soldering today! It's my first electronics project, and it's pretty messy, but it works. I even found a place in Melbourne (Australia) that sells Altoids.</p><p>I made mine to have three inputs, two straight through and one with its own volume control (for my Apple TV, as it doesn't have its own volume control).</p><p>Thanks for the great instructions!</p>
<p>Thank you for this thread! I've spent a while Googling for answers to questions I had regarding multiple signals, risks and protection! <br><br>Many people think it's risk free using Y-cables with adapters or crossing connections unprotected which to me is just bonkers!<br><br>Being new to audio I was just going to use diodes so I appreciate you explaining the futility of this method! <br><br>I have a question regarding values! <br><br>You specify 1k to 10k and from what I can see from your photos you selected 4.7k, does this have specific advantages? I only ask as previous searches, 4.7k and 10k seem to be popular choices with audio mixers!<br><br>Many thanks!</p>
Hi chuchunezbee,<br> <br> thanks for the nice comments, glad this is helpful. Here's the tradeoff:<br> <ul> <li> higher resistor = more&nbsp;volume loss, lower possible distortion&nbsp; <li> lower resistor = less&nbsp;volume loss, higher possible distortion </ul> OK so, how to pick the resistor for best tradeoff? For a circuit designed to drive a 32ohm headphone, a 320ohm load is only 10% of full load, while a 3.2k is only 1%<br> <br> 1k seems like a good tradeoff at about 3%, but you could probably go down to 320 or so with no bad effects -- up to you.<br> <br> Good luck,<br> <br> Rich

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