# 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

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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chipmonger says: 3 years ago
Made one and it works great. Thanks.
richfiddler11 (author) in reply to chipmonger3 years ago
Wow, really nice job! Good idea to use resistor networks!

Would you care to share the artwork?
chipmonger in reply to richfiddler113 years ago
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.
richfiddler11 (author) in reply to chipmonger3 years ago
Thanks for the artwork and again, really nice job!
rand0mmm says: 3 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.
richfiddler11 (author) in reply to 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
fergusontea says: 2 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) in reply to fergusontea2 years ago
Nice! I particularly like the 'Hello Kitty' motif ;^) Thanks for sharing the picture.

Rich
AM Industrial says: 11 months ago
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.
everend says: 8 months 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.
richfiddler11 (author) in reply to everend8 months ago
Nice! Good recycling!
EET1982 says: 6 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!
jkotecki in reply to chipmonger2 months ago
Can this image be used to have a board made or do we need the ExpressPCB file?
chipmonger in reply to jkotecki2 months ago
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) in reply to jkotecki2 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.
wes1099 says: 1 month 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
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\/
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\/
richfiddler11 (author) in reply to wes10991 month 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.

Rich
wes1099 in reply to richfiddler111 month ago
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 in reply to wes10991 month 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 in reply to wes10991 month ago
richfiddler11 (author) in reply to wes10991 month ago
nice! I like the size of Altoids gum tins. hope it works well with your cmoy!
cfishy says: 3 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) says: 5 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?
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?
cfishy says: 5 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!
cfishy in reply to cfishy5 months ago
Here's mine, with the RadioShack 276-0150 protoboard. Works GREAT!
richfiddler11 (author) says: 9 months ago
I don't speak spanish, I only know how to use http://translate.google.com

Here is the schematic. Stereo potentiometers potentiometers are 1K or 5K (logarithmic). You can omit the fixed resistors or use 200 or 300 ohms. Good luck.

---
Yo no hablo español, sólo sé cómo utilizar http://translate.google.com

Aquí está el esquema. Potenciómetros potenciómetros son estéreo o 1K 5K (logarítmica). Puede omitir los resistores fijos o utilizan 200 o 300 ohmios. Buena suerte.

pogodike200!!! says: 9 months ago
y si quiero ponerle potenciometros a cada entra de señal de cuantos kilos podria ser??????????
you speak spanish???
richfiddler11 (author) says: 9 months ago
I don't speak Spanish but google translated your comment as: "and if you want to control the damn one of those audio inputs as hagosi no potentiometer. stupid"

There is a schematic in the FAQ with stereo potentiometers if you want volume control (5k ohm, audio taper) . Many devices (ipods, etc) have their own volume control and in that case it is best to build the simple, cheap version.

Here is a google translation back to Spanish, no idea if it makes sense or not:(i no hablan traducción española, por google):

No es un esquema en el FAQ con potenciómetros estéreo si usted desea tener un control de volumen (5k ohm, conicidad audio).Muchos dispositivos (iPod, etc) tienen su propio control de volumen y en ese caso lo mejor es construir la versión simple, barato.
pogodike200!!! says: 9 months ago
y si quiero controlar el maldito audio de alguno de esas entradas como lo hagosi no hay un potenciometro . estupido
jamoiholland says: 10 months ago
Would it be possible to modify this to have 2 simultaneous (as opposed to switched) outputs? My ultimate goal is 2x 3.5mm inputs and 2x 3.5mm outputs! Thanks
richfiddler11 (author) in reply to jamoiholland10 months ago
Absolutely, yes. You can split signals without resistors, it's only in combining sources that you need resistors between channels. Just put in an additional output connector(s) and wire it/them straight to the original output (i.e in parallel, no resistors between them). You could also buy a commercial headphone splitter and use that. Good luck.
xhedos says: 1 year ago
Hi,

Thank you for laying this out. It makes perfect sense. Question - could the 1/8" jacks be replaced with xlr plugs for microphones? Obviously the altoids tin would no longer be a suitable host. But, would the wiring still work out?

//s
richfiddler11 (author) in reply to xhedos1 year ago
It would need some mods and some ground-rules or assumptions to be met. For the simplest case:
1. All the inputs are at a similar mic-level
2. All the inputs are balanced (a.k.a. differential, which xlr mic signals are).
3. None of the mics require 48vdc phantom power to operate (i.e. they're either dynamic or battery-powered condenser type)
In this case, you would want to lower the resistor values to maybe 50-100 ohms. Also, you would probably want variable resistance instead of  fixed. For the original design, it assumes that each device has its own volume control, but microphones do not, so without a way to adjust the mix the mixer would be semi-useless.

It might be better to use an XLR-to-1/4" mono transformer/adapter for each input and build a mono version of the mixer with volume pots.

In reality, you can buy a decent XLR mixer for \$50-100 new and by the time you buy the parts, it's probably not worth the effort, unless you really want to make your own.
xhedos in reply to richfiddler111 year ago
Thank you for the response!
Ohem says: 1 year ago
I'd like to do 2 custom mixers, 1 for when I'm at friend(s) with my iPad (Skype, for teamplay with other friends at distance) and 360/PS3/Wii playing games. And a 2nd (for home) to combine the sound from PC (incl mic) and many other consoles. Why i'd like to do this is for one simple reason - convenience. It's way more convenient having the sound in the headphones instead of speakesr in which I'm not a fan of. I'd like to make a mixer with 1x3-poles input (PC/Console) 1x4-poles (iPad) and 1x3,5mm stereo output and 1x3,5mm mic input (leading to iPad mic in).

I understand there's a difference in volume levels in iPad/iPhone/handheld and PC/consoles, so how do i balance it out correctly and how do it know what resistors to use in order to max the volume in headphones? is pre-amp necessary? what to use?

I have, although a bit limited by age, soldering skills.
richfiddler11 (author) in reply to Ohem1 year ago
The microphones will be tricky since they are getting DC bias voltage from the device (iPad,iPhone,PC,etc). Keeping the dc power sources separate, while still powering the mics and mixing the mic signals will be a pain and I'm not sure what it really buys you. It could be done, but I'm not very interested in designing it, sorry.
Ohem in reply to Ohem1 year ago
Maybe an "Operational amplifier" powered through USB?
richfiddler11 (author) in reply to Ohem1 year ago
If you want an active amp, google on 'cmoy headphone amp' and you'll find tons of kits, plans, how-tos, functional products, etc. just put my mixer on the front end of the cmoy headphone amp.
richfiddler11 (author) says: 1 year ago
Honestly, I've built quite a few of these and never had any problems with shorts -- the resistor leads are rigid enough not to flex much on their own, even with a pretty decent shock. Even if there was a short, it would not cause any permanent damage.

But ...  if you're the sort of person who stays awake at night worrying about this sort of thing, you could also try these alternatives:

1) "spray on electrical tape" http://www.plastidip.com/home_solutions/Liquid_Tape

2) Potting: The ultimate in shock-proofing.

'Potting' in electronics means to fill in the air space in the circuit enclosure with a suitable compound (non-conducting, non-corrosive, etc). Electronics-grade epoxy is used as a potting compound in military, automotive, aircraft, etc. This stuff is expensive and bullet-proof (figuratively speaking ;^)