Altoids Tin 1/8" Stereo Mixer

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: 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

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.

chipmonger3 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)  costumatx2 months 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)  chipmonger3 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)  jkotecki6 months 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)  chipmonger3 years ago
Thanks for the artwork and again, really nice job!
EET198211 months 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!
everend1 year 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)  everend1 year 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.
fergusontea2 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)  fergusontea2 years ago
Nice! I particularly like the 'Hello Kitty' motif ;^) Thanks for sharing the picture.

rand0mmm3 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)  rand0mmm3 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
syberdiver13 days ago
Hi, thats awesom! Really simple and verry usefull. Now i can connect my computer, my mediaplayer and my guitar and have more fun. Great job , and great instruction!
vanderaalle made it!1 month ago

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

costumatx2 months ago
tanks man , do you have a nice an simple schematic for a active mixer
richfiddler11 (author)  costumatx2 months ago

Most powered computer speakers have a 1/8" headphone jack on the front -- just use that, or just buy a headphone amp. There are tons of opamp mixer designs on the web, but by the time you buy all the pieces it's probably cheaper to just get a Behringer (or other cheap brand) pro audio mixer -- easily had for $50-$100 and easy to find used. Unless you just want to make something...

costumatx2 months ago
well i have built your disign and there is big volume drop
richfiddler11 (author)  costumatx2 months ago

Yes, a volume drop is to be expected, as explained in the project text.

In the past, most folks who have complained about the volume drop didn't bother reading the instructable text and were trying to drive passive headphones or speakers, neither of which works very well. This is meant to drive a powered speaker, preamp or headphone amp which in most cases can more than restore the volume drop.

You don't say what your inputs and outputs are or what you're trying to do, so it's hard to help you.

I have Two Pcs and one earphone what do you think is the best solution

Thanx Alot
richfiddler11 (author)  costumatx2 months ago

Get yourself a set of powered computer speakers with a headphone jack or some type of headphone amp and you'll be fine. Again, this mixer has no amp or batteries and is not meant to drive headphones!

Good luck

costumatx2 months ago

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

f6point33 months ago
This is an outstanding project and I modified it slightly for a larger tin, because I wanted to use it as a passive mixer for dynamic microphones in a home studio. So the jacks are mounted in the lid and labeled "In 1" through "In 4" and "Out". I've weighed it down with two bags of dollar-store marbles inside the tin, for stability.
Stephen3044 months ago
I've had a problem with trying to connect 2 computers to 1 set of speakers. I was using an audio splitter to merge the audio, but when computer 1 played audio, it would mute the second computer for 30 seconds after the sound stopped from computer 1. I assumed this was because the audio from computer 1 was messing with computer 2 when it went through the splitter. I built this with 1k resistors, but the audio from computer 1 still gets sent to computer 2 as well as the speakers, causing the sound to cut out again. Any ideas? I added images of my mixer because I like my layout lol.
2013-12-18 16.14.50.jpg2013-12-18 12.44.50.jpg
richfiddler11 (author)  Stephen3044 months ago
I like your construction as well! Very nice job!

You know, I think some PCs (laptops in particular) try to be smart and detect what is plugged into the 1/8 stereo output jack. Often times you will get a pop up saying what has been detected. That's the only thing I can think of.

I would check your mixer first with 2 "dumb" sources to make sure everything is OK. If that checks out, then look at your sound settings to see if there's a way to turn the detection off. Good luck!
Stephen3044 months ago
I don't understand why I can't find these in stores. I have a couple computers I need to merge audio so they all use my sound system without having to re plug everything when switching computers. I use an audio splitter but it causes problems like one computer cutting out when the first computer plays sound.

Will be building this soon.
wes10996 months ago
If i did something that looked like my diagram below would i be able to use headphones with this mixer? And another question, will i be able to have multiple inputs playing at once without any issues?

Altoids Tin Mixer Output
Cmoy headphone amp
richfiddler11 (author)  wes10996 months ago
Yes to both questions. The CMOY is made to drive headphones and my little mixer is made to combine multiple inputs safely into one stereo output. If you're building your own CMOY, it might be possible to put both functions in one tin, but I don't know if there's space for any extra inputs in a CMOY. That would be nice though.

Yeah i tried to find a way to put both functions into one tin but there isn't enough room because most of the space is taken up by the CMOY pcb, its parts, and the 9v battery.
wes1099 wes10996 months ago
So I just built mine, and it can actually power my headphones decently without an amp, but the amp is still necessary, and my cmoy kit won't get here for a while. I used these 1k ohm 1/8 watt resistors and these 3.5mm jacks, both of which are from radioshack, a Altoids Cinnamon Chewing Gum tin, and some 24 AWG copper wire I found in my grandparents garage. I will post pictures tomorrow.
wes1099 wes10996 months ago
richfiddler11 (author)  wes10996 months ago
nice! I like the size of Altoids gum tins. hope it works well with your cmoy!
cfishy8 months ago
I made another one using a 10 cent plastic container (10 pack in a dollar store), resistor network and liquid tape. Works great!
richfiddler11 (author) 9 months ago
Very hard to debug problems like this remotely -- doubt it has anything to do with the resistor values, but you didn't say what size you used..

OK, so with the following 3 scenarios, which ones have the 20 minute behavior you're talking about?

1) media center -> Bose speakers
2) media center (only) -> mixer -> Bose speakers
3) media center and TV tuner -> mixer -> Bose speakers

- You already said the problem shows up in #3.

- if it shows up in #1 then it's obviously a problem with the media center on it's own.

- if it shows up in #2 (and not #1) then you might have a wiring problem or perhaps a resistor value issue.

The Bose speakers are powered, yes?
roady0019 months ago
I just finished mine, easy with this great tutorial. However something isn't like it supposed to be: I have 1 TV tuner and 1 media player as input, and Bose PC speakers (2.1) as output. The TV tuner is fine, but when using the Media Player, every now and then (+/- 20 minutes) there is a short load noise 'tick' (like quickly connecting an electric guitar to an amplifier) after which the volume drops with 15%. Then after another +/- 20 minutes, again shortly the noise 'tick' is sounding and the volume is restored. This happens in cycles.

Any ideas? Should I be using bigger resistors?
cfishy10 months ago
Thanks! my first altoid tin project, saves me $100 for a SONY XA-300 module! I used Radio Shack protoboard 276-0150 and it fits!

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