Altoids Tin 1/8" Stereo Mixer

Step 13 Done! Testing and Troubleshooting.

Congratulations, you should now be done. Close up the Altoids tin and test the mixer:

- attach the output jack to a known good powered speaker
- attach an working mp3 player to each input in turn.

Problems?
If something doesn't seem to be working check these things:
1) Do you get sound with mp3 player, cable(s) and powered speaker without the mixer?

2) Double check wiring. Is everything wired correctly, per instructions?

3) Any cold solder joints? (solder joints that look good but don't really connect) Try resoldering any suspect connections.

4) Any shorts? Shorts are accidental connections caused by wires touching each other. Look carefully and pull apart wires that look like they might be touching.

Comments

[Boredinschool]

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) ?

[rsmith56]

I would love to use this with my 4 wired lav mics (atr-3350 small battery powers it). Two questions - is it possible to add volume to each input? Would you need to power it? and what about a 3 way switch that would allow left/both/right for each? Would that be very hard to do?

[richfiddler11]

Self powered lav mics would work fine. For volume control see circuit in FAQ section, step 15. power is only required if you add an active preamp circuit. Yes, you can add a left/right switch, I'd probably use a SPDT switch.

[heinsickle31]

Ok, I got both speakers to broadcast (apparently the resistors aren't allowed to touch the can, but if you guys have any info on the volume level, that'd be great.

[richfiddler11]

With a passive design you will always lose some volume. What are you trying to drive? A powered speaker?  A passive speaker? Headphones? The lower the impedance of the load you're trying to drive, the bigger the volume loss will be.

[heinsickle31]

Headphones. Actually, I am currently using it as a headphone splitter if it makes a differance, but the loss happens when I use it as a mixer also. I don't mind the loss of volume, I wouldn't put it much higher anyway, but I would like the possibility to though.

[richfiddler11]

Yeah, if you read the notes and comments, this is not at all recommended as a headphone splitter. The impedance of headphones is in the 8-32 ohm range (quite low) and this mixer is not going to perform well unless your driving something with an input impedance of 1k ohm or above, like a typical powered speaker input.

For a headphone splitter you would be better off not using the resistors. The resistors are only required for mixing multiple sources together.

Rich

[guywith2names]

im not an expert in electronics and i would like to use this with headphones w/o amplifying it.... what if i lower the resistors to lets say 500 ohm or lower? would that work. Im trying to have 2 3.5 input sound run to 1 pair of headphones. i know if i used a headphone splitter to COMBINE 2 sound sources, and i turn BOTH volumns all the way up, it may damage the equipment. what are you thoughts of doing this?

Ps: sorry for any grammer and errors

[richfiddler11]

In order to run headphones, you'd have to go lower than 500 ohms. Most headphones have an impedance of between 16-32 ohms and typically you want the source (i.e. amplifier) to have a lower impedance than the load (i.e. headphones).

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.

[TAYLOR1337]

what sort of resistors would i need for a powered headset?
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

[richfiddler11]

1 kOhm would still be fine. You typically want the impedance of the source (mixer output) to be much higher than the impedance of the load (headphone). It's good that you're using a powered headphone. Interesting headphones, do you plan to mix 2 sources for each of the 5.1 channels? In other words you'll have 8 (10?) inputs and 4 outputs?

[TAYLOR1337]

another quick question, does it matter what way round the resistor goes? like gold ring towards the input or output etc..?

[TAYLOR1337]

yeah thats what im looking to do :)

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 :)

[heinsickle31]

Sorry for being a little late, but I can't seem to find the problem with mine. I can only get it to play out of the right speaker and it is only about half volume. I did everything that the instructable said and I can't find any shorts. There are only two things I can find that might be an issue. 1) I used different terminals. The link for them are here: http://www.radioshack.com/product/index.jsp?productId=2103452
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.

[chorpie]

 what if you used a terminal strip inside the open area?  might make the wiring a bit cleaner and avoid some possible areas for shorts.  or... i am a big fan of heat-shrink tubing.

[richfiddler11]

Sure, that would work great.

I was just trying to keep it simple & cheap, and honestly I've been using one of these in a car for several years and have never had a short. With the lighter resistors

But I don't blame you for wanting to make it neater/more rugged -- go for it!

I thought it would be cool to pour melted paraffin in to ruggedize it, stick a wick in there and have an emergency candle too.

[chorpie]

 might i ask why the resistor body needs to be close to the jack? is it just in order to keep things out of the way?  this is, by they way, a cool instructable :)

[richfiddler11]

Thanks, there's no electronic reason for suggesting that the resistor body is close to the input jack. There are 2 reasons I said that:

1) makes it a little easier to connect all the output sides of the resistors together in 1 "solid" wire.

2) I consciously decided not to include a schematic in this project, since it is so easy to build and it might intimidate some folks. So I thought positioning the resistors that way would keep some builders from getting confused about which side the next resistor should connect to.

So do whatever you want, as long as the circuit is equivalent.

[Tchnclfl]

xD the lack of schematic was kind of putting me off because I didn't feel like reading the whole thing, I just wanted to build it my way :). But now I read it and I understand how it's all working.

[richfiddler11]

Hi Tchnclfl,

Being an EE myself, I appreciate what you're saying: a schematic is the most concise way to describe a circuit and in your place as a consumer of someone else's how-to (which I frequently am) I would also prefer a schematic to a blow-by-blow account.

As the writer in this case, I choose an approach I *thought* would be accessible to a wider range of instructables.com readers. At the same time, I did put a schematic diagram in the FAQ section for the cognoscenti -- did you see that? Maybe it should have been under a more obvious heading like "Schematic", huh?

Glad you kept at it,

Rich

[Tchnclfl]

I actually didn't notice that, but thanks!

No, I completely get the approach, and I can appreciate it, I would probably have done the same thing too.

[tackdetack]

 I seem to only get audio out of one channel at a time. Same for all 4 inputs.. The Channels work, but not at the same time.. Any ideas?

[richfiddler11]

Wow, that's really tough to debug without  looking at it.

Do your jacks have switched contacts on the tip and ring by any chance? There would be 5 terminals  on the jack instead of 3. That could cause some weird problems if you picked the wrong terminals...

The best I can recommend is to double check your wiring against this schematic, there's not really a lot that can go wrong if the wiring is correct.

[danderrick]

Thanks for the schematic. I couldn't get the right to left and then center and dosy doh. Dan Derrick

[richfiddler11]

Hi Dan,

So I hope that means you got it working?

Rich

[danderrick]

Ah, I have all the parts handy but the tin. I didn't quite understand until I saw the schematic. Now I'll tackle it with confidence. Probably just stick it on a wooden ruler and make sure everything is grounded. Thanks for the reply, Dan Derrick

[tackdetack]

Hey, It turns out my cable was dead, I just bought some new ones and it works perfectly!

thanks for this great instructable!

[kyismaster]

is it good to have the copper touch the metal casing? or is it just because no other wire is touching the casing, i would have used electrical tape religiously.

[richfiddler11]

Hi,

You have to understand that the bare copper wire and the case are already connected together electrically  on purpose.  So it doesn't make a bit of difference whether the wire touches the case randomly  or not.

The ground tabs of all the jacks are tied together through the case and you could almost get away without the copper wire. However, a good solid ground is critical for quiet audio circuits and the connection between the jack and the case is not reliable, so the copper wire is there to provide a rock solid return path.

OTOH, if any of the resistor leads touches the case, you will definitely have a problem.

Let me know if this is not clear,

Rich

[kyismaster]

quite interesting, pretty surprised there isnt really a built in amp powered by a battery to "power" the out put, usually being speakers. then again, not sure if those inputs are powered or not, are they coming from outputs?

if thats true, then basically this is like a passive "mixer" yes?

[richfiddler11]

> if thats true, then basically this is like a passive "mixer" yes?

Yes, it's not only like a passive mixer, it is a passive mixer.

And if you read through the text, you'll see that it's not meant to drive low-impedance devices like speakers or headphones, only high-impedance inputs. Amplification is done after the mixer.




 

[Vaughanabe13]

If you intend to only have one audio input "active" at any given time, would distortion still be an issue or not? I'd like to do this for my PC desktop speakers so I can switch multiple audio sources to the same speakers without having to unplug/replug the 1/8" speaker cord every time. In this use case, only one device would have a signal on it at any point, so are resistors necessary?

[richfiddler11]

Hi,

It doesn't make any difference at all if the other inputs are active or quiet, you still need the resistors.

Here's why: When you tie several outputs together directly, each one "sees" the others as a low-impedance load, and what's worse, each additional device you add lowers the total load impedance seen by each device (parallel resistances or impedances divide).

Why is this bad? The lower the load impedance, the more power the device's output must try to provide. That's where distortion and/or destruction come in.

Here's an example to understand the basic relationship:
  - put a 1k ohm resistor across a 9V battery:
         high impedance->low current->low power->no problem
  - put a piece of bare wire across the same battery:
         very low impedance->high current->high power->bad things/smoke

If you only want to use one input at a time and have some objection to using resistors, you might be better off making a selector switch using a 2-pole multi-position rotary switch like this:

http://www.radioshack.com/product/index.jsp?productId=2062536&CAWELAID=107598141

[participant]

Is the procedure the same if you want to create a mixer with a combination of 1/4 and 1/8 inputs?

[richfiddler11]

Yes, no difference at all except the size.

[codongolev]

oh, cold solder joints... I love getting electronics from people that are "broken", then opening them only to melt a few solder joints and it turns on.

[techman9]

 amen to that, me to lol

[nagoia1984]

lol I know exactly what you mean haha

[forty0z310]

From one Rich to another,
thanks for the fun weekend project.
Two thumbs up.

[flakeman2]

 How about having the ability to act as a splitter?  One audio in split into 4?