Stereo to 2-channel mono question

I posted this last week in sci.electronics.design but got no responses. Probably it's too basic. Anyway...

I'd like to make a small male/female patch-cord that would passively mix-down stereo headphone output to two-channel mono.

Assuming typical MP3 player drive levels, is this circuit OK?

Plug > -- to -- > Jack ~~~~ ~~~~ Left __[R1]___.__.__ Left Right __[R2]___| |__ Right Common _______________ Common

R1 = R2 = 1000 ohms

Thanks for any advice!

What do you mean by "two-channel mono"? It may be me but I don't know what you want to do.

Tom

I want to plug one end of the patch-cord into an MP3 player and then plug earphones into the other end of the patch-cord. Then, at *each* ear-piece I'd like to have an L+R mono signal.

"Two channel mono" == monophonic on a stereo plug?

That should work, as long as the input impedance of the 'mono' device is high enough.

The cheap 'ear bug' sitting on my desk has a resistance of ~ 30 ohms. So with 1 k's I think you'll need some gain after the mixing. If you wanted to do it without any post amplification then I think you could pick some 'mixing' R's that match the resistance of the head phones you are using. You throw away 1/2 the signal that way, but it's simple.

George H.

Yes - L+R at each output channel.

OK. The mono device is just headphones.

My main concern was loading and/or cross-connection of the MP3 player's output drivers - that's why I picked 1K mixing R.

Thanks for the reply!

Why?

Thanks, Rich

Yes. That's how it's done.

At work, it's better to keep 'one ear open' and since my MP3 player(s) don't have a stereo/mono select, this seemed like a good work-around.

Ah, got it. :-) Rich