XLR-RJ45, what am I not understanding?

[shufflebeat]

A couple of months ago I picked up some RJ45-XLR(x2) adaptors so I could send a L/R signal over distance for a coming project.

Plan:
source L/R > XLR(f)x2
> rj45 > rj45 >
XLR(m)x2 > destination L/R

However, on sticking a meter across the pins I find that the 2 XLRs on the adaptors are parallel connected to each other, meaning L/R will be summed at the first adaptor and undermining the whole process.

So - two questions:

Am I missing something, or possibly going stupid?

Is there any scenario where this setup is useful?

Confused of Lancs.

[Hugh Robjohns]

There are 4 separate pairs in an ethernet cable, capable of conveying four balanced audio signals.

Plenty of 4 channel XLR-RJ45 adapters exist and are used for this everyday. I've used them myself.

So... it seems likely that you haven't bought what you think you have — as in a product designed for a different application — or you've bought something badly designed/constructed that isn't fit for purpose.

Want to share some clues as to what you actually purchased?

[shufflebeat]

This is the closest thing I can find until I hunt down the link:

https://www.amazon.co.uk/gp/aw/d/B0B6G4 ... ETRH&psc=1

Now, I realise this one is sold as a DMX connection rather than audio, but surely in DMX there would be no use for a second XLR, possibly on output splitting duty (dodgy) but DMX combiner? I don’t get it.

[Hugh Robjohns]

In the product notes from that amazon page (my emphasis):

...3 Pin XLR male / Female to RJ45 Adapter Extension Cable, flexible PVC jacket, nickel-plated connectors provide reliable contact, which can provide stable transmission and high-purity audio signals.Note:Gives a double mono signal instead of stereo.

So it appears designed to be parallel wired.

Not suitable for intended purpose. Return for refund.

[shufflebeat]

Well spotted, that man, that’s obviously what I missed. Thanks, Hugh.

So, second question. In what scenario is this useful?

[edit]

Just re-read the notes, that does seem to have been snuck in, unless there is an actual use-case for this that I can’t think of. Never heard of “double mono” before.

I’ll be holding on to them to chop up and adapt for the role intended but many thanks for the spot.

[Wonks]

Any live situation where you might want to provide a single signal to two sources over a distance - which could be a common DMX signal to two lights with no through outputs, or a signal to tops and a sub where the top has its own high pass filter and the sub its own low-pass filter.

I admit it's pushing it a bit to find a really common application, but sometimes these niche products do have a use.

[shufflebeat]

Any live situation where you might want to provide a single signal to two sources over a distance - which could be a common DMX signal to two lights with no through outputs, or a signal to tops and a sub where the top has its own high pass filter and the sub its own low-pass filter.

I admit it's pushing it a bit to find a really common application, but sometimes these niche products do have a use.

That explains the parallel outputs, and each of these can be used as such (audio = XLRm, DMX = XLRf) but these are sold in pairs, suggesting one is an input and there’s a Catxx cable between them.

I suspect someone has made without a design brief and the marketing dept. did what we are doing, i.e., searching around in the mud for potential uses.

I may be wrong, I often am.

[Wonks]

I suppose it is up to you how you use it. Whichever type of connection you use as the input, you can always cut the other one off; keeping the two output connectors intact.

I was wondering about maintaining the 100 ohm characteristic impedance of DMX cable, but Cat 5/5e/6 also has a 100 ohm characteristic.

[Hugh Robjohns]

...which why it's also suitable for conveying raw AES3 (being close enough to 110 Ohms for jazz... and other musical genres).

[Folderol]

Cat 5, etc. is proving to be the Swiss army knife of cables

[shufflebeat]

This is all true and good to be informed, but surely I could do all this with one XLR, or twice with two if they weren’t parallel wired.

Still not getting it.

[ef37a]

That does seem a very stupid product!
I have a pair of boxes similar to these, https://www.kenable.co.uk/en/networking ... 45134.html

I got mine from CPC some time ago but they don't seem to stock them any more. The transformers in the adapters are not of course of very high quality but I just needed to get signals from a Xenyx 802 mixer from a bedroom (mics in the garden) across the house to my living room for recording. The route is a tortuous one, goes through a patch bay and even with a mix of shielded and unshielded cable the noise level is still very low. Be fine for a comms link/talkback system.
While searching I found a two channel XLR to RJ45 box. You can of course just send low impedance balanced pairs and not have the limitations of transformers. You do not get galvanic isolation in such a case.

If you are of a DIY bent you can put 4 Xlrs or TRS jacks in a standard 13A double back box and run that on a single CAT 5X cable. Must be shielded if only to allow phantom power.

I have in fact just bought 50 shielded CAT5e plugs for about a tenner*. I have the AMP tool and a couple of lengths of shielded cable left so is you wanted a couple of 2m cable to play with Shufflebeat, PM me!

*I doubt they meet the very stringent requirements for full speed performance but they LOOK fine and crimp on quite nicely!

Dave.

[shufflebeat]

That’s very considerate, Dave, thanks, but I have a couple of kilometres of various feline cable pedigrees lying round, if I bring any more in I may be sleeping with the actual cat.

I’ve got a few experimental projects in mind, one of them being a single 13a style back box and blank front with XLR sockets and rj45. This episode might motivate me towards B&Q fairly soon.

[Hugh Robjohns]

Canford do a nice plastic hexagonal box that takes three standard D-sized connectors:

Box:
https://www.canford.co.uk/Products/49-3 ... E-Box-only

Universal D-size connectors:
https://www.canford.co.uk/Search?q=Universal+connectors

So you could slot in two male or female XLRs and a universal D-sized RJ45 connector or ethercon socket, and wire up as you please.

If you only want two channels of audio, that's what I'd do... I have several of these hexagonal boxes as break-outs and splitters. They're excellent, and easy to work with.

[shufflebeat]

Ooh, that’s quite Space 1999, I like it.

I’ve made a few 4ch drop-snakes with these in the past:



…coupled with a blank panel. Good screening with handy earthing connector and readily available cable glands with cut-outs.

If screening isn’t a major issue then those Canford boxes do look good.

[Hugh Robjohns]

It's intended for line-level or speaker level signals, but I have used one in an emergency for mic level signals and had no RFI problems...

For line-level connections, you've got 50-60 mm of screened cable in there linking the connectors, with the only unscreened bits being the few mm of wire at the back of each connector.

I guess it depends on the local RF environment, but I've never had a screening issue. If you are really concerned, you could line with stick-on copper foil...