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Converting stereo sound to mono from an mp3 player or other similar devices? Answered

I am makin a small project where i need to input mono sound. almost all mp3 players output stereo channels. 
in my circuit i have a TS connector where mono sound need to be input. 

if i connect a TS connector in a TRS socket., will the output be automatically be mono or i will only get one channel out of the stereo output from the mp3 device????

thxs in advance



Best Answer 6 years ago

If I were you, I would create a mono bridge. However, there are a few things to remember:
1. If your Mp3 player has short circuit sensing circuits, it might mistake the bridge for a short. (It's not, but it can fool the circuit into thinking that it is)
2. By creating the bridge, you will basically double your output volume, which can cause clipping.

To create a mono bridge, take both of your positive leads, and solder them to the positive post of a mono ts jack. Then take both (if you have more than one) or just the one negative (if you only have one) and solder them to the negative post of your ts jack. Congratulations, you now have a mono bridge.

This is mostly used in pro-audio (which I do as a side job), so be careful if you are using consumer equipment.

do i have to add a resitor in each line (L & R). so that it doesn't fool the player.

can this connection damage the player???

I have never heard of it damaging the player. The only reason to add resistor into the lines would be to lower the output gain. If your player does have short sensing circuits (which I highly doubt), adding a resistor will not stop it from being fooled.

I have made a mono bridge many times, and the only problems I have ever had was clipping, and once an amp thought it was a short.

You shouldn't use a straight Y cable to sum a stereo signal to mono. It's bad for the output opamps. Just add a couple inline 1K resistors. See the Rane note. http://www.rane.com/note109.html

It probably won't work as you wish. In some cases you may damage your equipment.

Download "Audacity" for free.  Then load your stereo music into it and pick "convert to mono" in the menu then save to a new number.

The conversion is instant and really works nice.

That will only convert the sound file, and not your connections.

A humble voltage divider, consisting of two resistors, can be used to add two signals together. The attached picture assumes that V1 and V2 are ideal voltage sources, and the result is that the open circuit voltage in the middle of the divider is V3 = (R2*V1 + R1*V2)/(R1+R2).

The only drawback to doing this is that the output resistance seen by whatever follows this thing is the parallel resistance of R1 and R2 .  ( Call it R3 = R1*R2/(R1+R2). 

So if you use big resistors for R1 and R2, then the output resistance of this circuit will be large.  But that's not a big deal if the next stage in your circuit does not care about wimpy output resistance.

I suggest  picking R1 and R2 both with resistance, in ohms, greater than or equal to the rated impedance, in ohms,  of the headphones the mp3 player is expecting.  Usually this is pretty low, something like 8 ohms, or 16 ohms, for each speaker.  So maybe R1=R2=47 ohms?  Assuming you want equal amounts of each channel added together.

The expected impedance of the headphone speakers is pretty low (circa 8 or 16 ohms), and it ?might? be the case that the designers of your mp3 player made it so that you can actually short  (connect 0 ohms across) the outputs of the headphone jack without hurting it.  I don't know if that's true or not for your mp3 player, but maybe you want to err on the side of caution, and if you use couple of resistors you know are larger than the usual impedance of the speakers, then you know you won't overload it.  Even if possibly they made the thing so you can't overload it, not by plugging anything passive into it.

Anyway,  this talk of shorting the outputs reminds me of your question of what happens when a mono (Tip, Sleve) plug gets inserted into a stereo (Tip, Ring, Sleve) jack, I decided to actually try this with some of the junk I've got in my workshop here.  I looked at what-got-connected-to-what using an ohmmeter.

The result of the this experiment was that Ring and Sleve usually wound up shorted to each other while Tip went through.  I think that means if you plug a mono plug into the stereo jack on an mp3 player, that one of the channels ( the right one, I think) will get shorted to ground, while the other will connect through to your output.  The pictures should make this clear.


+1 and +1

Now for my take...

If you are running the signal into preamp, use a pair of summing resistors. How big depends on the gain of the preamp and the input impedance. I'm going to refer back to my thread over at the Nuts n Volts Forum (yet again...) wherein I get confirmation on the exact same (almost) question.

If you are using headphone out to line level, I have used stereo to mono Y cables/adapters for years without any apparent damage. Just make sure the signals don't connect to ground within the cable. Do not just plug a stereo TRS into a mono TS plug, you'll have one of the signals going straight to ground or not connect at all, depending where the contact is within the jack.

If you want to use only jacks, put a stereo jack at the input and tie the Tip and Ring together (for the positive part of the signal) and connect the Sleeve to ground as normal. This way, you can use either stereo OR mono plugs for the source.


Use a couple of op-amps.