# Stereo to Mono Adapter



## leashy (Nov 29, 2009)

I need some advise. I am wanting to combine the R/L channels on the headphone output on my computer into one channel, making it mono, so that I can hear both channels in the single speaker I have it plugged into. But I want to do it safely without damaging the output on the computer. How can that be done?

I know I can buy a cheap stereo to mono adapter from Radio Shack that would in essence just short the two channels together. Could that possibly causes damage to the output?

Another idea I had is maybe plug a cheap headphone amplifier into the headphone output first and then plug the stereo to mono adapter after that. Seems like that might isolate it off the computer output at least, removing any possibility of damage there.

Any ideas??


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## brucek (Apr 11, 2006)

> I know I can buy a cheap stereo to mono adapter from Radio Shack that would in essence just short the two channels together.


That's exactly what it would do. You're not allowed to short outputs together. You require a combiner.

brucek


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## leashy (Nov 29, 2009)

brucek said:


> That's exactly what it would do. You're not allowed to short outputs together. You require a combiner.
> 
> brucek


Where could I find a combiner?


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## brucek (Apr 11, 2006)

> Where could I find a combiner?


Well, you would be looking for a stereo passive combiner (or mixer as they're often called). Radio Shack use to sell one, but I don't know if they still do.

It's quite easy to fabricate your own with a couple resistors if you don't mind messing around with that kind of project.

I won't tell you how to mount this arrangement, but with the two left and right line level signal cables you will short the shield (grounds) together and connect each hot (positive) to a 10kohm resistor (Radio Shack). The free ends of the two 10kohm resistors are now connected together. Connect the shorted end of the resistors (mixed mono signal) and the shield to an appropriate RCA connector and your good. 

This mixer will have an input impedance of 10Kohms and an output impedance of about 5kohms. It will have an acceptable insertion loss of about 6db. This arrangement is basically what's inside a passive mixer you would purchase if you didn't want to make one. Since you're not concerned about crosstalk, you could drop the resistors down to 5Kohms.

brucek


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