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.
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 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.
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
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.
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.
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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.
you speak spanish???
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.
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
- All the inputs are at a similar mic-level
- All the inputs are balanced (a.k.a. differential, which xlr mic signals are).
- 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.
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.
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
It takes a while but is easier than wrestling tape.
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 :)
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
Boostaroo-3 I think it's called, it has a high impedance input and can drive a few sets of headphones.
Thanks again for a super useable instructable.
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
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!
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!
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