Instructables

Altoids Tin 1/8" Stereo Mixer

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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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syberdiver2 months ago

works pretty nice! great idea!!!

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richfiddler11 (author)  syberdiver2 months ago

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

Rich

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

vanderaalle made it!5 months ago

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

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richfiddler11 (author)  vanderaalle2 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.

-Rich

chipmonger4 years ago
Made one and it works great. Thanks.
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why did you put the resistors , can we do it with out them ?

richfiddler11 (author)  costumatx5 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)  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 ExpressPCB.com.
Mixer PCB artwork.jpg
Can this image be used to have a board made or do we need the ExpressPCB file?
richfiddler11 (author)  jkotecki10 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)  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!
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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.
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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.
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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.
lucky_stars.jpg
richfiddler11 (author)  fergusontea2 years ago
Nice! I particularly like the 'Hello Kitty' motif ;^) Thanks for sharing the picture.

Rich
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.
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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
RobbOlson2 days ago

First of all Rich, Great job on the write-up and your willingness to respond to comments. I came across this when trying to figure out how to add an additional aux input jack in my truck and I was so impressed that I signed up to the site to give you kudos and ask my own question.

I am currently building a console and am incorporating the docking station (pictured below) to charge my phone as well as connecting it to the aux jack but I want the wires to be run inside the console to keep it tidy looking. Ideally, I want an input jack inside the console but I would still like to keep the original jack below the radio available though too in case I have someone riding with that may not have an iphone and can then plug into that jack. I have done some searches but am only finding splitters for audio outputs (for 2 headphones) rather than 2 inputs and am wondering if what you did here would work for my application.

Also, I am new to all this electronic stuff and am just learning about capacitors, diodes, resistors, and such. I was hoping you might explain how this device works (eliminating interference between inputs or how it determines which device to use for the output signal)

Thanks again for the great write-up!!

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DJAWB1 month ago
I have a question, is there some way i could make say two sound systems in two separate cars play in unison? The idea of an aux splitter is possible but i have no experience in sound or electrical.. Any suggestions? Thanks in advance
richfiddler11 (author)  DJAWB1 month ago

Hey DJAWB, yes you're correct, your question really has nothing to do with the mixer, but I'm truly curious (i.e. don't read this question with a harsh tone)-- why on earth would you need the two cars to get the audio at exactly the same time?

Without knowing anything about what you're trying to do, what fidelity level is needed (voice or music), whether the cars are close vs. across country, etc. it's hard to say.

If both drivers have smart phones and good data plans, some type of network streaming would probably make the most sense. I'd do some research on setting up an IP-radio server. Maybe you could just use skype on your mobile phones?

If the cars are very close together, you might be able to use some kind of wireless technology like an FM transmitter (might need to be hacked for more power), CB radio, bluetooth, wireless guitar transmitter/receiver, or maybe just power a wifi router in your car so the other car could connect without using 3G data..

DJAWB1 month ago
I know this has nothing to do with this instructable but i can't find anything on this topic so i thought i'd ask in the comment box where people with experience with these things could help
JKPieGuy2 months ago

A few years ago I made a headphone splitter resembling this project. It worked great for when you wanted to share music with your friends without bothering anyone else. Though I was thinking of one day having the feature to switch from "Splitter-Mixer" with the flip of a switch (or a small circuit that would sense it and switch automatically). Was also considering adding a small amplifier circuit to it with a max volume shunt, to prevent people from adjusting it to high and bursting their ear drums. I'll let you know if I ever come though with either one of the two ideas.

piergap2 months ago

Question: do not the volumes go too low? i expected operational amplifiers and a 9V battery needed (.... then turning into an active mixer).

i tried to connect two media players like that (just through resistors), but the output was really low....

richfiddler11 (author)  piergap2 months ago

Hi piergap, please read through the instructable text and discussion, this is addressed many times. If you have questions after reading, let me know and I'll be glad to explain anything that's not clear. The short answer is when driving line-level devices like self-powered computer speakers, the loss is not a big deal. OTOH, when driving devices like normal headphones that require power, the circuit in this mixer will not work well -- there is no free lunch and you have to understand the limitations. In the right scenario, this is an extremely handy little device.

thanks and apologize.... i admit, was at work and was stealing a bit of salaried time. did not went too deeply into the project, apart looking at the pictures!

driving headphones was what i am looking for, then you ansered.

syberdiver3 months 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!
costumatx5 months ago
tanks man , do you have a nice an simple schematic for a active mixer
richfiddler11 (author)  costumatx5 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...

costumatx5 months ago
well i have built your disign and there is big volume drop
richfiddler11 (author)  costumatx5 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)  costumatx5 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

costumatx5 months ago

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

f6point37 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.
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Stephen3047 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.
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