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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Signing UpStep 1Materials
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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Would you care to share the artwork?
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
Rich
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
Do you see any problem in this combination such as the impedance of the PC amplifier, etc.? Would the 1 ohm resistors still be a good choice?
Thanks,
drluv
You should try feeding the output of the mixer straight into your car stereo input before even bothering with the additional stage in between. If this is an Aux input and is fairly high impedance (normal line-level input) you probably don't even need additional amplification.
Rich
I swear my buddy built one with diodes that worked like a charm. Two sources each a computer sound card... into a box with this circuit and one output to powered speakers.
I'll have to look further.
I assume the reason you don't want to use resistors is because of the signal attenuation. Keep in mind that resistors are highly linear and introduce virtually no distortion, meaning the signal is still a clean copy of the original with a little less amplitude. Amplification can bring this back with a very high degree of fidelity to the original signal.
Diodes are non-linear and once the damage (clipping) to the signal has been done, you can't undo it later on. That's why I would never use diodes on an audio signal unless I was intentionally trying to distort it.
But hey, knock yourself out and try it. You won't hurt anything and maybe you won't be able to tell the difference. But I bet if you do compare the resistor and diode approach side-by-side, you will notice which one sounds better.
For a headphone splitter you would be better off not using the resistors. The resistors are only required for mixing multiple sources together.
Rich
Ps: sorry for any grammer and errors
If you want to experiment (at your own risk) and as long as you don't take the resistor values below the resistance of a typical set of headphones (again, 16-32 ohms), then you shouldn't cause any damage to either players or headphones and you can gauge the sound quality/volume trade-offs for yourself.
http://www.roccat.org/Products/Gaming-Sound/ROCCAT-Kave-5-1/ is the headset, im guessing 10KOhm as it says on the tech specs but im not sure. im looking to fuse together the 5.1 3.5mm outputs on both my PC and a decoder box from my xbox, and also the headset signal from the xbox controller through the fronts.
Thanks
i have a tin that hopfully ill be able to put 4 different circuits in, 1 for each channel. yeah ill have 9 inputs in total as ill have an extra input on the front speakers from the output of my xbox controller, on a adaptor i have for it.
Thanks for uploading the instructions btw :)
I am currently working on alittle electrical project that I've put off for months due to the fact of not exactly knowing what I'm doing and I was wondering if you could help me out. I saw your project you made with the "Altoids tin audio mixer" on Make Magazine awhile ago and I had thought it would make a good headphone splitter if you reversed the way the audio was going into. (Basically one input feeding 4 outputs.) The problem is that I want to add alittle LED indicator light that automatically turns on when you plug some thing in and I don't know how to exactly wire it so that it could do that. Another question I had is do you still need the resistors if I make it into a headphone splitter instead of a mixer and could it be backwards compatible, like say I wanted to use it as a mixer one day instead of a splitter? I was possibly wondering if there was a way to amplify the signal that wasn't to costly (but if you can't help me out with that it's ok.)
If you could answer my questions I'd really appreciate it.
Thanks.
1) Regarding the LED -- Yes, in theory this could be done but I don't see the point. The project is entirely passive, so there are no batteries to either A) power an LED or B) die and require replacements or require anything to be switched off.
If you added an LED, a battery would have to be added and would only serve to light the LED.
If you're dead set on adding an LED, google on 'LED indicator circuits' or something like that and you'll find loads of information and circuits online.
2) regarding splitting vs mixing -- the ideal construction of a splitter is to use no resistors, while the ideal construction for a mixer requires resistors.
If you plan to split a signal to drive several high-impedance inputs (e.g. powered speaker inputs) then turning the mixer (with resistors) into a splitter will not be a problem. If you're trying to drive several pairs of headphones, then you will not want the resistors.
Cheap headphone splitters are readily available, while cheap, small mixers are not.
3) Regarding amplification -- I've pointed out several times in previous answers that you could easily add this mixer circuit a front-end to a CMOY headphone amp, which also happens to be built in an Altoids tin. Google on 'CMOY headphone amp' and you'll find tons of info.
I have a question. Could I use a 4 stereo jacks and a mono one, and still use the 1K resistors? Thanks!
2) There is one solder point near the output jack where my solder point on the output jack and my solder point where I soldered the 2 resisters together accidently got soldered together (So basically, what should be two solder points are now one). I hope that was a thorough explanation. Also, I am confident that it is the output jack which is the problem, because I tried all of the inputs and they are all working the same. Thanks for any information you may have.
If you are driving an input to a powered speaker, aux input, etc this is no problem (these are examples of high impedance inputs). If you're trying to drive a headphone, speaker, etc (examples of low-impedance inputs) you are not going to be very happy with the sound level.
I'm curious as to why you'd want to do this, but that aside:
Assuming you have 2 stereo inputs, you would first need to mix each stereo channel down to a mono signal. Do this by tying the L and R channels together with 2 resistors in series (1K or so each), then feed the middle tap of the resistors to the L or R output mix.
Yeah, I might not have explained what I meant in the clearest way. I'll try an ascii art picture and if that doesn't work maybe I can draw a real schematic. Here's what I was talking about. This is assuming the input is coming from the left:
left >----------|
|
1K Resistor
|
+---------------------> mono mix output
|
1K resistor
|
right>--------+
You would tie the mono mix of one input to the L output mix and the other to the R output mix. This is equivalent to panning one input hard left and one hard right.
If you wanted to get *really* fancy, you could implement adjustable panning (i.e. audio positioning) so you could adjust each input's position in the stereo mix. I'd have to think about this but it would probably require a stereo potentiometer on each input channel.
Try the simple case first though -- that will give you the largest separation and if that doesn't make the 2 conversations more intelligible, then there would be no point in adding adjustable panning.