Altoids Tin 1/8" Stereo Mixer

15 Steps
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: May 28, 2010. 2:17 PM
Made one and it works great. Thanks.
richfiddler11 (author) in reply to chipmongerMay 31, 2010. 7:03 PM
Wow, really nice job! Good idea to use resistor networks!

Would you care to share the artwork?
chipmonger in reply to richfiddler11Jun 1, 2010. 9:15 PM
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 chipmongerJun 10, 2010. 1:02 AM
Thanks for the artwork and again, really nice job!
rand0mmm says: Aug 11, 2010. 3:38 PM
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 rand0mmmAug 12, 2010. 5:20 PM
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: Oct 17, 2011. 5:41 AM
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 fergusonteaOct 17, 2011. 7:25 AM
Nice! I particularly like the 'Hello Kitty' motif ;^) Thanks for sharing the picture.

Rich
everend says: Mar 23, 2013. 11:47 AM
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 everendMar 25, 2013. 5:13 AM
Nice! Good recycling!
EET1982 says: May 20, 2013. 4:20 PM
I made mine. Not as pretty as yours but sure gets the job done! Stuck with the 1k resistors. Thanks for the great 'structable!
richfiddler11 (author) says: Feb 25, 2013. 7:41 PM
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: Feb 25, 2013. 7:49 AM
y si quiero ponerle potenciometros a cada entra de señal de cuantos kilos podria ser??????????
you speak spanish???
richfiddler11 (author) says: Feb 23, 2013. 12:24 PM
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: Feb 23, 2013. 9:24 AM
y si quiero controlar el maldito audio de alguno de esas entradas como lo hagosi no hay un potenciometro . estupido
jamoiholland says: Jan 18, 2013. 4:37 AM
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 jamoihollandJan 18, 2013. 6:56 AM
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.
AM Industrial says: Dec 17, 2012. 12:39 AM
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.
xhedos says: Oct 12, 2012. 11:22 PM
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 xhedosOct 13, 2012. 9:43 AM
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 richfiddler11Oct 31, 2012. 10:36 PM
Thank you for the response!
Ohem says: Oct 9, 2012. 5:11 AM
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 OhemOct 13, 2012. 9:57 AM
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 OhemOct 9, 2012. 10:52 AM
Maybe an "Operational amplifier" powered through USB?
richfiddler11 (author) in reply to OhemOct 13, 2012. 10:01 AM
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: Oct 9, 2012. 9:53 AM
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 ;^)

Electronics-grade silicone RTV is a cheaper alternative: http://www.amazon.com/Clear-Electronic-Grade-Silicone-Cartridge/dp/B0063U2RPW/ref=sr_1_3?ie=UTF8&qid=1349801014&sr=8-3&keywords=electronic+grade+silicone

And cheaper yet would be to fill the box with melted candle wax (parafin).

With any of these, make sure your circuit works perfectly before applying the insulator and wrap your connectors with tape to keep insulator out of the contact area.

Or, just build it, see that it works fine without insulation and forget about it.

Rich
Krayzi99 says: Oct 7, 2012. 9:24 AM
I will be making this, though it'll be without the enclosure, as it will be for my multi-channel synth. Also. I recommend using a pcb. Theyre more difficult to do, but they keep your mixer from having a short. theyre are several PCB ibles out there.
matricha says: Sep 20, 2012. 1:21 PM
I have found that lengths of plastic insulation from stripped wire slipped onto the leads does a fine job of insulating.

It takes a while but is easier than wrestling tape.
Bshorty says: Aug 24, 2012. 2:46 PM
Hi,
I have the same issue for multiple sources except mine are coming from both RCA Audio as well as 1/8" audio jack. The 3 sources are:
1. Overhead DVD Player
2. IPAD (via 30 pin to audio/video out)
3. Android phone/ iPod using 1/8" earphone jack.

I do not wan't all these signals mixed but rather switched, in other words only one source used at a time but a clean permanent solution (except the phone/iPod).

My question is wether the outputs from the other two devices need to have a different setup then the one you built because of different levels or does this even matter at all.
Thanks for sharing :)
richfiddler11 (author) in reply to BshortySep 4, 2012. 11:00 AM
Hi Bshorty,

Sorry for the delay in answering -- not 100% sure I understand what you're asking or trying to do, but I can make a few (hopefully) relevant comments that might help:

1) Even though this is technically  a mixer, I almost never have more than one source playing at a time. Rather than make a complicated device to do switch automatically, I just play one device at a time. This gives the "clean" setup you mention with the added bonus that you can hear occasional notifications from a phone, iPad, GPS, etc.

2) Whether the audio comes from an 1/8", 1/4", RCA or whatever type of plug, you can substitute the required connectors and it should work fine.

The levels coming out of all devices should be similar, e.g. able to drive headphones. If you try to mix in a lower level signal (one that normally goes into a preamp) along with headphone level signals, you'll find that there will be a huge mismatch in the volume levels.

Hope this helps, feel free to ask followup questions.

Rich
mlee47 says: Apr 2, 2012. 9:34 AM
This is almost what I have been looking for. But I want to use headphones to listen to my GPS and MP3 player on my motorcycle. I've ordered 10 ohm and 20 ohm resistors and going to give it a shot. There is a 'commercial" motorcycle version for \$179, or spend \$500-700 on a new waterproof motorcycle GPS w MP3 player, and a \$200 bluetooth helmet speaker system. I'll try this for \$15 and see first....
Mukumbu in reply to mlee47Aug 7, 2012. 8:56 PM
I use mine on my motorcycle with a boostaroo connected to a bt transmitter. Works perfect!
richfiddler11 (author) in reply to mlee47Apr 2, 2012. 8:21 PM
It won't hurt to try with those values, but you might be happier with the mixer and a headphone booster like this: http://www.radioshack.com/product/index.jsp?productId=2732095

Boostaroo-3 I think it's called, it has a high impedance input and can drive a few sets of headphones.
andystills says: Jun 19, 2012. 10:25 AM
Awesome instructable! Have mine made and it works. Question: Is it possible to prevent this from acting as a splitter? I am using mine to allow multiple hookups to a set of living room powered speakers... however, my home computer, one of the source, is also hooked up to the desktop powered speakers. When another source is playing through the living room, the altoids mixer acts as a splitter and sends the audio to the desktop speakers. Any way to prevent this?

Thanks again for a super useable instructable.
richfiddler11 (author) in reply to andystillsJun 20, 2012. 5:13 AM
Hi Andy,

Not sure I understand how you've got things hooked up.

The way I build the mixer there are 4 inputs and only one output, but you're talking about 2 output devices (livingroom and desktop speakers).

Normally, the outputs of all your sources would go to the inputs of the mixer and the output of the mixer would go to the input of the powered speakers. But that only accounts for signal going to one set of powered speakers.

How are the desktop/computer speakers even getting any signal at all?

If you can tell me exactly how things are connected I might be able to help you. A sketch/diagram is always easiest to understand.

Rich

Boredinschool says: May 3, 2012. 8:24 AM
Could you make it like a head-phone splitter by using 2 resistors and putting them on the side that has 1, plus adding volume controls and a better power source (besides the device your using) ?
pongping says: Mar 15, 2012. 2:21 PM
richfiddler11:

I am only an amateur with electronics and soldering. I just wanted to say thanks for an easy and practical project. I have a KVM switch connecting my computers which does not support audio. The KVMs that do have audio do not work that well, in my opinion. Typically, they switch the audio and if you have a process running on another machine that is not in focus, the sounds are not played on the speakers. This is a great alternative!

tlebrell says: Mar 4, 2012. 1:37 PM
I'm making a homemade stereo practice guitar amp out of some beefy powered PC speakers. I know that by itself, it doesn't have enough pre-amp to "work", but I plan on using it with a digital effects processor (Zoom pedal unit) 100% of the time. The Zoom has stereo headphone out with gain comparable to a headphone output on anything else. Tested and works great.

I haven't made the control panel yet, because what I'd really like to do is drop in an aux stereo input for hooking up an iPod to jam along with. It looks like I could pull this off just with an extra jack and four 1K resistors (two for the ZOOM side, and two for the iPod side). If I wanted to get fancy and add a mixing knob for the aux input, could I simply replace the aux-input's 1K resistors with a 1K stereo POT? Could it have any negative consequences for either device?

Thanks!
hang4 says: Jan 19, 2012. 2:51 PM
cool set up. i'm trying to do something similar, but different. I am a hang glider pilot and take in flight videos. I also have a ham radio that I use to talk to my chase driver. I have a mic and speakers wired into my helmet with a three conductor jack that has mic, speaker and ground connections. The mic is keyed with a PTT switch that runs down my sleeve.

What I would like to do is be able to record the radio transmissions in both directions by splitting out the mic and speaker wires to a second jack that I can connect to a voice recorder. What would be a real plus is if I could also use the mic to narrate when I am not transmitting. Any thoughts from anyone???? Thanks
lespaul55 says: Nov 23, 2011. 10:44 AM
Could you use 1/4 female jacks? If yes then can you mix between the 1/4 inch and 1/8 inch jacks?
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