The cable is to be used to take the output of an mp3 player and present it as a mono signal via a 1/4" phone plug.

If we've all read the white paper, we know the two channels can't just be soldered together, as some output stages connected this way will distort. So... there must be a 100 ohm to maybe 750 ohm resistor in series with each channel before they're connected together, and this must all be molded into the cable.

This has to be a molded cable because it's to be used on stage in a performance setting, where little plastic boxes or the like can easily get busted.

Anybody know of a company that makes this?

I haven't looked for anything prefab'd, but I'd build my own, using 1/8 Watt resistors, into the phone plug, then fill the void in the plug with epoxy. If you use a metal case plug and good technique, the assembly should survive any trauma that the raw cable can survive.

Or, a little clunky, instead of using a little plastic enclosure, use a short section of copper tubing and build a "bulge" into the cable. Again, you can fill the whole assembly with epoxy. Enclose the whole assembly in shrink tubing. Use three pieces of two different sizes of tubing if the diameter difference between the cable and tube is too large for a single section of tubing to shrink around.

Thanks, buzz.
This cable would plug into a Direct Box. If I'm going to shift the channel summing away from the mini plug, it might be easier to modify the input phone jack on the direct box. The only problem would be that the input then could not take a balanced signal (now it can take balanced or unbalanced). Since I don't have any balanced signals on phone plugs, that might be acceptable.

There's a pretty good cable guy on this site. I would reach out to Brent.

Thanks, Jeff, will do. That never occurred to me since this is such simple stuff.

in that case id swap to di that take care of tis for you.

Radial stage bug sb5 has a 3.5mm TRS cable built in
[Link: radialeng.com]

radial pro av 1 or 2 is more versatile and will sum and serve as a DI

[Link: radialeng.com]

The Radial Engineering products do look like they'll do what I need. They have a fancy term for their stereo to mono function, "automerge." That makes me think they're going to charge me twenty bucks for four resistors. But still....

Budgets matter, so you've got to keep in mind that swapping means taking one out and putting another in. You're not recommending that, you're recommending BUYING additional equipment, and shelving what we have, so it's not just swapping.

With molded plugs? Never seen one. Usually, the resistance is about 470 Ohms series and 10K parallel (it's in the Rane document) and it works.

Is this going to a mixer?

Edcor makes a summing transformer and it's not too big. Not expensive, either.

[Link: extron.com]

[Link: atlasied.com]

We've used both before and they work fine.