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.

I made a new passive mixer based on your ible. Thank you so much for the awesome instructions !
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>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
Hello! <br>Thank you so much for getting back to me and so quickly too! Really appreciate your help with this, I found so many other threads on other sites with bad info! I found your instructions very educational and really helpful!<br><br><br>Regards<br>Pete :D
<p>Thanks for the instructions! Thanks Rich! Used 10k resistors, have 2 outputs and 5 inputs!</p><p>Wanted to follow your link to make an active amp to try and remove problems I am having with ground loops, still didn't get rid of them but I'm better off then with my original Y splitter!</p>
<p>This is an awesome project. I am going to do it when I get solder.</p>
Cool project, think im going to have a go this weekend!<br><br>I need a passive mixer to combine two preouts from an amplifier to feed a powered 2.1 speaker set with only one input. Would 2k resistors be appropriate for two input sources carrying 1v with 1.2k impedance?
I think you'd be fine with 1k, but it's not super critical. Transmission line theory says maximum power transfer happens when the source and sink have the same impedance. 2k would be fine also.
<p>I want to mix two signals, and then split the mixed signal into two outputs. Should I only put resistors between the two inputs? Thanks a lot!</p>
Yes, you don't need resistors between the outputs.
Hi rich can I use the box the other way around meaning , use the 1 output as a input and the other 4 jacks to plug 4 headphones
<p>Hi Ashley,</p><p>What you really want is a headphone splitter (which you can buy very cheaply) but if you want to build your own (and you don't ever plan to mix active signals together), then yes. But in this case, I'd recommend building without the resistors, because they'll reduce your headphone volume and provide no benefit.</p><p>HTH,</p><p>Rich</p>
Hello rich I just checked out your projects last night thank you for your detailed instructions with pictures , I just want to know if I use the output jack as an input eg. Plug my phone using aux cable can I plug 4 headphones and listen to them through the other 4 jacks , just want to find out bro thanks
<p>Wouldn't diodes be better and also eliminate need for additional amplification?</p>
Please read the FAQ on step 15. In short, no, audio is an AC signal, you're thinking DC.
This is perfect. Is there a way to add power into the circut safely so this can be used with headphones or is there a separate device that i can build which amplifies the signal?
Yes, there are a lot of options: <ol> <li> Search for CMOY headphone amp and you'll find lots of plans, kits and finished products online. <li> search for &quot;headphone amplifier kit&quot; on ebay, you'll&nbsp;find many, many options (mostly from China). <li> I've built a USB-powered version with my &quot;Double-wide Altoids Project Tin&quot; and this board:<a href="http://www.parts-express.com/stereo-2-x-150mw-class-ab-lm4881-headphone-amplifier-board--320-321?utm_source=google&utm_medium=cpc&utm_campaign=pla" rel="nofollow">&nbsp;http://www.parts-express.com/stereo-2-x-150mw-class-ab-lm4881-headphone-amplifier-board--320-321?utm_source=google&amp;utm_medium=cpc&amp;utm_campaign=pla</a>&nbsp;the main picture on the Double-wide project page shows the Sure Electronics board in one of the tins. Eventually, I'll do an instructable on this. <li> Small commercial headphone boosters like the &quot;Boostaroo&quot; work pretty well, but are overpriced for what they are IMO. </ol> Good luck, HTH<br> <br> Rich
<p>It works great! Anyone knows how i should get a 2nd OUTPUT for recording in place? </p>
Just put in another 1/8&quot; stereo jack and wire all of the signals directly in parallel with your existing output jack, e.g.<br><br>GND - GND, Left - Left, Right - Right

About This Instructable


406 favorites


More by richfiddler11: Universal Chat Mic -- DIY Gaming/Comm Headset Double-wide Altoids Project Tin Altoids Tin 1/8" Stereo Mixer
Add instructable to: