I have a circuit board which have four poles to audio out, R+ R- L+ L- is there a way to combine L- and R- into ground so it would be possible to solder it into a 3.5mm plug?

 

You want a three pole audio out signal like, LEFT, RIGHT, GND. It occurs in multiple place that I'm aware of so it must be OK.

 

You want a three pole audio out signal like, LEFT, RIGHT, GND. It occurs in multiple place that I'm aware of so it must be OK.

Yes, but I want to know how I convert L- and R- to GND. From what I know it's not as simple as just solder them together.

 

AFAIK (I'm not an expert), it depends on the amplifier. Some have differential outputs, and connecting the grounds together may shut down the amplifier. This link is the story of someone who tried to connect the grounds together and could not get their amplifier to work.

 

It depends on whether those outputs are balanced outputs or not. With unbalanced outputs, the L- and R- would both already be tied to ground and would be totally safe to join together. With balanced outputs, the L- and R- would be signals with reversed polarity relative to L+ and R+. You wouldn't want to tie those together, although I don't think it would damage anything; it would just reduce your stereo width.

Odds are good that it's unbalanced, but I thought I'd throw this out there just in case.

 

Yes, but I want to know how I convert L- and R- to GND. From what I know it's not as simple as just solder them together.

You have to show us the schematic diagram of your board. It would also be helpful to know what you are connecting it to.

 

Isn't there a circuit I could make that could convert the outputs into R, L, and GND? or would I need a small computer (Raspberry Pi?) to convert the signals into what I want?

 

You have to show us the schematic diagram of your board. It would also be helpful to know what you are connecting it to.

The board comes from a broken pair of wireless headphones, but the board itself still functions properly. But it means I don't have a schematic diagram for it. My idea is to install a 3.5mm female plug/jack so I could use it with any non-usb headset. I know I could just buy a new wireless headset, but I like to re-use what I can from broken electronics.

 

Isn't there a circuit I could make that could convert the outputs into R, L, and GND? or would I need a small computer (Raspberry Pi?) to convert the signals into what I want?

We can't answer your question without seeing what you have. A circuit might be necessary or it might not, we just can't tell from the inadequate verbal description. Maybe you could create a schematic by looking at the board and tracing out the runs.

 

measure the resistance betweeen the two - terminals. if they are very low resistance, it should be ok to connect them together for a common.

 

measure the resistance betweeen the two - terminals. if they are very low resistance, it should be ok to connect them together for a common.

Agreed! This is the simplest solution. If the resistance reading is not very low, then things get more complicated!

 

Agreed! This is the simplest solution. If the resistance reading is not very low, then things get more complicated!

The simplest solution might be a transformer?

 

A pair of transformers I think... but that's still more work than just soldering the two negatives together. If the OP has a multimeter and a few seconds to use it, transformers may turn out to be unnecessary.

 

A pair of transformers I think... but that's still more work than just soldering the two negatives together. If the OP has a multimeter and a few seconds to use it, transformers may turn out to be unnecessary.

Oops. I meant the simplest solution for the situation where L- and R- can not be tied together. Sorry for the confusion.

 

Ah, understood. In that case, I think you're probably right.

 

measure the resistance betweeen the two - terminals. if they are very low resistance, it should be ok to connect them together for a common.

Sorry it took some time before I replied, I bought a multimeter which measures 0.5 ohms between L- and R-

 

I come more from the "try it" side than the "sketch it" side of things. 0.5 ohms from L- to R- is interesting, but I'd be reading all angles of those points. If everything reads under 1 ohm for example, you're probably learning more about your multimeter and how you've set it than about your circuit being tested. If that L- to R- reading is noticeably lower than the other combinations, you may have found something. You could connect R- and L- through a fairly low value resistor, to limit current, and if you get good results try it with a much lower resistor, or none at all, and test again.

Also don't get the impression that "ground" is ground. It's usually only a common point within an isolated system. And I mean isolated! "ground loops" are a lot of fun for analog audio guys (if any others of us still exist) .

With the info we have here, we're all guessing at this. Our guess is that "insufficient information" isn't a reply you'd like or have much use for. Most of us like this "blind man and the elephant" game.

Best of luck!

 

I did some other tests and gets in ohms
L- R+ = 3.7M
L- L+ = 3.8M
R- R+ = 3.8M
L+ R- = 3.7M
L+ R+ = 13.4M
L- R- = 0.5

Granted the values jumped around quite a bit. But L- R- was always the lowest and R+ L+ was always the highest.

EDIT:
I just notice something, when I was taking pictures of the circuit to post here. It seems L- and R- already is connected on the board.
https://dl.dropboxusercontent.com/u/4506031/Pictures/Internet/board.jpg

 

Ha! That's awesome and not surprising. So you don't even have to join them, cause it's already done. That's great. Just hook your trs sleeve to the shared negative, ring to right, and tip to left.

 

Ha! That's awesome and not surprising. So you don't even have to join them, cause it's already done. That's great. Just hook your trs sleeve to the shared negative, ring to right, and tip to left.

What I think is odd is how they where separate on the board, even when the are connected. But oh well.