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[Dan Richardson]

I have a cable wired 1/8" stereo to 2 XLRs, for plugging my whatever into a desk that only has XLR inputs.
Someone mentioned that phantom power will blow up an iPhone's output stage.
That would be bad.
Yes, I can turn off the phantom on most desks, but things happen.
I don't want to carry around a pair of DIs just for this application.
Is there a safe way to wire this?
What happens if I leave the XLR pin 1 open, and wire pin 3 to shield and pin 2 to signal?
Is this a reasonable electronic solution?
Are there boards with phony balanced inputs where this will cause issues?

[Geoff Doane]

What happens if I leave the XLR pin 1 open, and wire pin 3 to shield and pin 2 to signal?
Is this a reasonable electronic solution?
Are there boards with phony balanced inputs where this will cause issues?

That should work, although the two pins-3 will be common to each other (still shouldn't be a problem that I can see).

If you run into an unbalanced XLR input (very rare these days, I think), it shouldn't be a problem either, as long as the XLR is wired pin-2 hot.  If it isn't, it just won't work.  It shouldn't damage anything.

Building an adapter with a 10 μF, 63V cap in series with pin-2 might be an even better idea.  Connect pin-1 and -3 to the shield of the TRS.  This might cause current to flow from pin-3 to -1, but that's only a problem with transformer inputs (could magnetize the transformer), which are also rather rare these days.

GTD

[Gareth Marsh]

I made the same cables, and used to use them with inline transformers to prevent this happening.

One day, I was on a system that had far greater issues and the transformers were used somewhere else. House techs had global phantom on (without any input needing it), I hooked in my macbook without thinking, and that was the end of the headphone output.

I have just been very careful since then, but I have thought about blocking caps, or even if I could cram a transformer into an XLR shell somehow (this would also help with noisy laptops).


Gareth

[Josh Bennett]

are you connecting this in a way to get stereo? XLR(L) pin2 to 1/8" tip, pin3 to 1/8" sleeve; XLR(R) pin2 to 1/8" ring, pin 3 to 1/8" sleeve. That would work against phantom damage, but will insert any ground noise from your laptop or other device directly into the signal stream.

[Frank DeWitt]

What your suggesting should work OK on battery powered devices. such as a I-pod. (Keep the output low, as earphone output is close to line level.

I can imagine some strange things happening with any powered device such as a laptop.  (If both are properly grounded, then you have reconnected pin 1)

A DI box provides protection and ground isolation and gets the level right for a mic in so it is a very nice solution.  If you only need Mono you could build a 3 resistor summing cord,  http://www.rane.com/note109.html  Then you would just need 1 DI box, and some of them are quite small.

Disclaimer, I build and sell DI boxes.

Frank   http://lbpinc.com/DI.html

[Fred Dorado]

why not just a stereo di, it would give you more options, you would only need to carry one, it would provide protection and the ability to use 1/8 or even rca connectors is nice, I think some even do 1/4 along with the others.

This is what we use, it's cheap, small and would protect equipment and you would need a specialty cable, allowing the xlrs used for this to be use somewhere else when not needed

http://www.audiopile.net/products/DI_Boxes/DBRC-2A/DBRC-2A_cutsheet.shtml

[Dan Richardson]

The re-grounding pin 1 issue is the kind of thing I was afraid I was missing.
My pack is frequently insanely tight for both size and weight.
A couple pounds and the size of most DIs is actually an issue.
I'd also rather not have a mediocre xformer inline where a straight wire could be,
and good xformers cost money.
That said, both the DIs presented were interesting options. Frank, that box of your is lovely. Have you got room in there for another xformer and another XLR?

Meantime, I'll scrounge up a couple of caps and give that a try.
Thanks, all.

[Weogo Reed]

Hi Dan,

How about this? :

 http://www.galaxyaudio.com/JIBR.jsp

Stayin' warm up your way?!

Good health,  Weogo

[JamesButera]

Didn't check the weight, but if you can fit it the Radial JPC is a great DI that you can use for more than just iPod.

http://www.radialeng.com/di-jpc.htm

[Daniel Cash]

Unless you are sending the signal a long distance, why hassle with balanced connectors with a risk of phantom power? Just use the 1/4" line inputs.   I use a cable like this for the job, and never had a problem.   Am i missing something obvious?

[ProSoundWeb Community]