Picture of Altoids Tin 1/8

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.

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Step 1: Materials

Picture of 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.

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operationkhaos made it!4 months ago

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.

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.

Thank you again for taking the time to make this useful, clear and concise guide.

richfiddler11 (author)  operationkhaos4 months ago
Hey, nice job! Glad you were successful and thanks for posting the pictures!
syberdiver10 months ago

works pretty nice! great idea!!!

richfiddler11 (author)  syberdiver10 months ago

Nice job! I like the jacks you used, where did you get them?


hi from Germany. I found the Jacks at but I will make an other one with 6,2mm jacks :-)

vanderaalle made it!1 year ago

thanks for the great idea! I did a mixer/splitter for an experimental music project

richfiddler11 (author)  vanderaalle10 months ago

Hey Vanderaalle, great job!! Looks like you're using 1/4" jacks and I *love* the tin (although not a smoker myself). Hope this works well for you.


chipmonger4 years ago
Made one and it works great. Thanks.
DSCF0056 compressed.JPG

why did you put the resistors , can we do it with out them ?

richfiddler11 (author)  costumatx1 year ago
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.
richfiddler11 (author)  chipmonger4 years ago
Wow, really nice job! Good idea to use resistor networks!

Would you care to share the artwork?
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
Mixer PCB artwork.jpg
Can this image be used to have a board made or do we need the ExpressPCB file?
richfiddler11 (author)  jkotecki1 year ago
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"at"PowerSwitchTail"dot"com.
richfiddler11 (author)  chipmonger4 years ago
Thanks for the artwork and again, really nice job!
EET19821 year ago
I made mine. Not as pretty as yours but sure gets the job done! Stuck with the 1k resistors. Thanks for the great 'structable!
everend2 years ago
Thanks for posting. Here is my version, it works perfectly.

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.
2013-03-23 13.15.30.jpg2013-03-23 13.15.58.jpg
richfiddler11 (author)  everend2 years ago
Nice! Good recycling!
Thank you. I used pulled parts from trashed sound card and a "Smalls" tin.... I love Old school point-to-point wiring...and Hot glue.
fergusontea3 years ago
Here's my version of the mixer, using a Lucky Stars Candy tin. I plan to add a "floor" above the wiring so that I can store a short 1/8" patch cord inside as well.
richfiddler11 (author)  fergusontea3 years ago
Nice! I particularly like the 'Hello Kitty' motif ;^) Thanks for sharing the picture.

rand0mmm4 years ago
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.
Screen shot 2010-08-11 at 3.37.48 PM.PNG
richfiddler11 (author)  rand0mmm4 years ago
Nice job!

Good idea to run the connectors out of the bottom of the mini altoids tin.

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.

I'm glad it worked for you and thanks for sharing the picture.

- Rich
FrostyManiac made it!5 hours ago
I made a new passive mixer based on your ible. Thank you so much for the awesome instructions !

It works great! Anyone knows how i should get a 2nd OUTPUT for recording in place?

Just put in another 1/8" stereo jack and wire all of the signals directly in parallel with your existing output jack, e.g.

GND - GND, Left - Left, Right - Right
Jayve Montgomery made it!6 days ago
Thanks a bunch for the knowledge. I built my version with an aluminum RadioShack project box because all I could find were 1/4" stereo jacks. I used Sugru to solder and added a 5th input. I even had to 'stretch' a resistor using some of the solid wire because my placement was a bit spaced and all is well. One lovely solution to mix my family of Korg devices. Do it folks!
KausikK1 month ago

I want to be able to connect the mixer's output to my headphones, so would this amp be fine:
richfiddler11 (author)  KausikK1 month ago

Yes, the Boosteroo will work fine. I'm also working on another instructable that uses this board as a headphone amp. I've built one and it works pretty well.

Oh, I looked at that board before but it looked hard to use. Good luck though!

FrostyManiac2 months ago
Hi :) Love your tutorial and decided to build it myself with 3 inputd and also added an audio-taper 10kOhm pot master volume before the output jack. But I have ran into a problem. When I tested my circuit after soldering the first of the three inputs I noticed that the right channel is FAR more quiet than the left. The pot shouldnt be crappy quality (ie. the tolerances between the gangs shouldnt be too much). Can I fix it by putting a smaller value resistor for the left channel output ?
richfiddler11 (author)  FrostyManiac2 months ago
Hey, sorry you're having this problem. you need a volt-ohm meter. Measure the resistance between the center-tap and ground for each channel at about the level you expect to listen at.

If there's a big difference, put a similar resistance value between the ground tap and ground of the *quieter* of the two channels.

You *could* also try tacking different values between the center tap and ground of the *louder* channel. This will be very tricky to get right though.

If you got an earlier message saying something else, please disregard, this is correct.
Thanks for the heads up, Im going to try to put different value resistor for the quieter channel to raise its volume. I've tried earlier to measure the resistance between the two channels and the difference is about 0.2-0.5kOhm

would this work for a mic? i would like to use a basic clip-mic with several devices: my 2 phones and my computer.

richfiddler11 (author)  isaac.christie3 months ago
Hi Issac,

As it stands, a mic wouldn't work, but with a few mods it could happen. What are you trying to do exactly?  Have 1 mic send audio to 3 devices at once?

I did a variation so my son and I could play minecraft together and record our (hilarious) commentary from 2 headset mics along with the game sounds -- worked well, but not quite what you're looking for.

Also, I'm thinking of doing an instructable for a pc gaming headset mixer that would combine game sound, incoming voice chat from game/skype/teamspeak and outgoing mic from 1 or more mics/headsets. This will require power and active amplification. Stay tuned on that.

Hi Rich,

Thanks for your reply, will def be keeping a lookout for your next Guide. After some consideration I now believe a simple switch to choose which output the mic gets sent to is better than mixing it, rather than a constant feed to all devices.

On a diff note, I'm already talking to a couple of CMoy builders on making a a setup for me which includes your passive mixer which I will use to mix my laptop, iphone, ps4 outputs to 1 pair of earphones.

And I'll get 1 mic make a switch to direct it to my laptop, iphone, ps4.


Great article great project.i read through all the comments but couldn't find an answer to my following question....I'm trying to connect an external bluetooth for my BlackBerry through the aux input on my car radio and recently I'm trying to add an external xm radio through the same input. I've tried using a dpdt switch to disconnect the 2 sources (I have all the grounds tied together....but I still get a bit of feedback when I switch to the BT. XM works great! Any ideas?

richfiddler11 (author)  edward.wolofsky4 months ago
The best troubleshooting advice I can give is:

try changing things around, one thing at a time, while paying attention to conditions when the noise appears and disappears. Swap cables, remove mixer altogether and direct connect, etc. This will help eliminate variables.

What Bluetooth device (receiver?) are you using and how is it powered? Is it really feedback or just noise? (trend is to use these terms interchangeably, but they're very different!)

As soon as a charger/power supply is connected to most devices, audible (and annoying) noise is introduced into the audio. It's because the switching converters used to go from +12V car power to +5V  USB are *very* noisy and hard to filter out. If your Bluetooth device has a battery option, try that and see if the noise goes away.

Proximity to the mobile phone itself can introduce noise, e.g. if my mobile phone is next to my office desk phone, audible noise in present, but it tends to come and go.

Good luck, this type of thing can be tough to get rid of, or you might get lucky and find the cause.

I'm using a Kinivo BTC450 Bluetooth Hands-Free Car Kit for Cars with Aux Input Jack .... no noise when plugged in directly and I noticed minimal noise with the car in the ACC position. Sometimes it's there ... sometimes not when I have the 2 units plugged in ... the power source (the 12 volt plugs) may not be the problem - it could be a shielding issue from the aux input (located in the arm rest) to the radio.
I did come across this unit (saw it on Amazon) :
PAC Ground Loop Isolator for 3.5 Mm Applications - what are your thoughts on that? They want $17.00 on line ... can probably build on for a lot less. Tnx for your feedback (pun not intended!)
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