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Author Topic: 3-pin DMX - What the hell??  (Read 10731 times)

Geri O'Neil

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3-pin DMX - What the hell??
« on: December 09, 2010, 08:42:41 am »

(Admittedly coming from a guy with an audio background. That means that if I had to make a light come on with something like a Grand MA or an Avolite Pearl, I'd still be in the dark)

So is there a move afoot in DMX world to move from 5-pin XLR connectors to 3-pin? For the past couple of years, the lighting department will send a slip to my desk..."Need 4 pairs of 5-pin to 3-pin adapters for this weekend"...or "Need 8 more pairs of adapters" to the point that we are now up 36 (that I'm aware of) adapters of this nature. And for under-20ft connections between fixtures, they just grab mic cables, which is bad because (A) even I know that using mic cables for DMX fixtures might or might not work reliably (I know, I know, I know, a lot of guys do and proclaim "No problems, I get it already) and (B) when I have 4 or more audio shows going out, one of them a symphony show, I run out of mic cables pretty quickly. And since we rent a lot of the various fixtures that we use, we see several different brands and models of fixtures.

I guess this is rhetorical question since we've ordered a couple of thousand ft of DMX cable to build out a bunch of under-50ft 3-pin XLR, the idea being to run 5-pin from the control (FOH or other) to the dimmers and splitters and to use just a few adapters to get into the 3-pin runs.

But why are some manufacturers using the 3-pin XLRs when I've read little notes to the effect of (paraphrasing) "The DMX communications standard is viable only when DMX-spec cables are used with 5-pin XLR connectors. Use of any other cable or connectors can significantly reduce integrity and reliablility of DMX control."? While I'm not making notes or documenting what I'm seeing, I think I've even seen a mixture of 3-pin and 5-pin conenctors between models of the same brand.

Any rhyme or reason to all of this?

Geri O
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Chad Costanzo

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Re: 3-pin DMX - What the hell??
« Reply #1 on: December 09, 2010, 12:01:06 pm »

I think the biggest reason has to do with cost. DMX has never been really fully used and 2 on the pins are un-used.  So 3 pin cable is cheaper and easier to come by.  (I know ashop who had 5 pin connectors with 3 pin cable, cost savings) I agree it and become a pain with all the 3-5 adapters and such.  I own more than I care to own. Alot of my 5 pin fixtures I just leave 3-5 adapters in the case and if they need them they are there to use
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Chad Costanzo

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Duane Massey

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Re: 3-pin DMX - What the hell??
« Reply #2 on: December 09, 2010, 01:21:09 pm »

Another factor was the reluctance of the major manufacturers (High End, Martin, etc) to change from their own protocol which already used the 3-pin. Once the majority of fixtures on the market, especially the lower$$ gear, established the 3-pin as the norm there was no going back.

With very few exceptions there is no advantage in using 5-pin connectors, as long as the cable is the proper spec.
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Rob Timmerman

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Re: 3-pin DMX - What the hell??
« Reply #3 on: December 09, 2010, 08:18:27 pm »

As the DMX standard was intended to drive interoperability, it specifies a (single) connector and gender scheme.  The connector specified by standard is a 5-pin XLR.  Virtually all varsity-level gear has 5-pin XLR on it (although some also has 3-pin).

The current trend towards 3-pin XLR appears to be driven by the manufacturers of low-end fixtures targeted at the DJ and club market that may already have an inventory of cables with 3-pin XLR.  Conceptually, this really isn't any different than the use of Microplex dimming (intended for use with mic cable) or strobe controllers with 1/4" plugs on them.  

The problems with 3-pin XLR being used for DMX are many - the 2 big ones in my mind are the implication that mic cable is fine for DMX, and the freedom the manufacturer now has to ignore other parts of the DMX spec.  I've flamed plenty about the former in other threads; the later is borne out in some of the reports of incompatible in other recent threads.  And the price difference between the different pin count connectors is quite small, so there really is no excuse for using the wrong connector.

In the eyes of the DMX standard, nothing that doesn't have a 5-pin XLR connector is a DMX device.  It may output or accept data that looks very much like DMX data, but it's still not DMX.  Me, I'd convert any 3-pin fixtures in my inventory over to 5-pin, and factor that cost into the cost of the fixtures.  But YMMV.
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James Feenstra

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Re: 3-pin DMX - What the hell??
« Reply #4 on: December 12, 2010, 12:45:54 pm »

as both the 5 and 3 pin connectors are 'd' size anyways, they should be incredibly easy to swap in and out in fixtures

I can think of a few quality moving lights that only take 3 pin

notably high end studio color 575s...and I think the 575 spots are 3 only as well

any lighting shop *should* have a decent inventory of both kinds of cable anyways, and the only place 523 adapters should be necessary would be coming out of the console into fixtures that only take 3 pin
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James Feenstra
Lighting, Audio and Special Effects Design

Rob Timmerman

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Re: 3-pin DMX - What the hell??
« Reply #5 on: December 12, 2010, 12:50:00 pm »

James Feenstra wrote on Sun, 12 December 2010 12:45

as both the 5 and 3 pin connectors are 'd' size anyways, they should be incredibly easy to swap in and out in fixtures




Except there's a very good chance that the connectors are mounted to a PC board that is laid out and drilled for a 3-pin connector.
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James Feenstra

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Re: 3-pin DMX - What the hell??
« Reply #6 on: December 12, 2010, 01:11:11 pm »

true enough, although removing the entire pcb and using wire to replace the leads is generally pretty simple

rarely do i see an xlr in a fixture connected directly to a main pcb...it's usually a smaller i/o board with a connection into the main
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James Feenstra
Lighting, Audio and Special Effects Design

Scott Raymond

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Re: 3-pin DMX - What the hell??
« Reply #7 on: December 14, 2010, 09:08:36 pm »

Geri O'Neil wrote on Thu, 09 December 2010 07:42


Any rhyme or reason to all of this?

Geri O


Of if only you knew!  That's the reason the lights end up in the audience all the time.  People don't stick to the standard and the lights go all wonky.  Twisted Evil Wink

In reality I do seem to remember some older lights that actually used both pairs.  I believe it was feedback from lights that had been slaved, or feed back for programming the firmware in other fixtures.  Some of the early HES stuff had their own controllers available but I don't know if those needed five.  As for the DMX standard I can't speak to whether that specified two way communication, but DMX transmission itself is basically RS485 or RS422 electrically with added opto-isolation if I remember correctly.  Just an old computer standard (twisted pair) modified for ground isolation.

FWIW, probably not a lot.

Scott
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James Feenstra

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Re: 3-pin DMX - What the hell??
« Reply #8 on: December 15, 2010, 01:43:35 pm »

pins 4+5 are generally for data confirmation

I can only thing of a handful of lights that actually require those pins, and those lights generally like cat6 instead
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James Feenstra
Lighting, Audio and Special Effects Design

Geri O'Neil

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Re: 3-pin DMX - What the hell?? Update...
« Reply #9 on: December 17, 2010, 07:26:56 am »

well, obviously, we will built more 3-pin DMX cables with the proper spec cable. Yes, James, the plan is to run the usual 5-pin DMX snakes to the stage, hit the dimmers and splitters, then to the fixtures and start with the turnarounds as necessary.

And when someone smarter than me designs a fixture and sez "use this kind of cable for the best results", I tend to listen to that person (that's why I scour the fruited plains for any available processor settings from the manufacturer of a particular speaker cabinet. You guys know, the big black box that makes noise and is usually in the way of a Genie leg....I'm so sorry, that was a joke...Very Happy).

And I swear, 2 hours after I made the original post, I got a phone call from one of the newer light guy on a set-up that "the last fixture in a string of 6 is acting wonky (Mega-bars, I think). we need another one" ME: "What kind of cable are you running?" THEM: "we just grabbed a handful of your mic cable". ME (after pounding the desk) "Get thee to the workbox, get a handful of turn-arounds, and run DMX cable  between the fixtures". THEM: "But we don't have any short runs..."..

Me:"JUST DO IT!!!!!.

Them: "Wow, it works now..."

I hung up them.

Thanx for the discussion guys, and putting up with me...

Geri O
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James Feenstra

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Re: 3-pin DMX - What the hell?? Update...
« Reply #10 on: December 20, 2010, 05:45:24 pm »

Geri O'Neil wrote on Fri, 17 December 2010 07:26

You guys know, the big black box that makes noise and is usually in the way of a Genie leg
yeah those things ALWAYS block sight lines

now if I could get the musicians and backline out of the way everyone could sit back and enjoy the light show

Wink
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James Feenstra
Lighting, Audio and Special Effects Design

Geri O'Neil

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Re: 3-pin DMX - What the hell?? Update...
« Reply #11 on: December 21, 2010, 06:51:10 am »

James Feenstra wrote on Mon, 20 December 2010 16:45

Geri O'Neil wrote on Fri, 17 December 2010 07:26

You guys know, the big black box that makes noise and is usually in the way of a Genie leg
yeah those things ALWAYS block sight lines

now if I could get the musicians and backline out of the way everyone could sit back and enjoy the light show

Wink



Ahh, so you've seen the Trans Siberian Orchestra, then? They do that quite nicely.... Laughing  Laughing  Very Happy

I always enjoy reading your postings, James. Take care,
Geri O
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len woelfel

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Re: 3-pin DMX - What the hell?? Update...
« Reply #12 on: December 21, 2010, 09:25:42 am »

James Feenstra wrote on Mon, 20 December 2010 16:45

Geri O'Neil wrote on Fri, 17 December 2010 07:26

You guys know, the big black box that makes noise and is usually in the way of a Genie leg
yeah those things ALWAYS block sight lines

now if I could get the musicians and backline out of the way everyone could sit back and enjoy the light show

Wink



Without lights it's just radio.

James Feenstra

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Re: 3-pin DMX - What the hell?? Update...
« Reply #13 on: December 21, 2010, 02:00:49 pm »

Geri O'Neil wrote on Tue, 21 December 2010 06:51

James Feenstra wrote on Mon, 20 December 2010 16:45

Geri O'Neil wrote on Fri, 17 December 2010 07:26

You guys know, the big black box that makes noise and is usually in the way of a Genie leg
yeah those things ALWAYS block sight lines

now if I could get the musicians and backline out of the way everyone could sit back and enjoy the light show

Wink



Ahh, so you've seen the Trans Siberian Orchestra, then? They do that quite nicely.... Laughing  Laughing  Very Happy

I always enjoy reading your postings, James. Take care,
Geri O

they're in town thursday actually...too bad i'm doing another gig Neutral

brian usually does a pretty good job
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James Feenstra
Lighting, Audio and Special Effects Design

Geri O'Neil

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Re: 3-pin DMX - What the hell?? Update...
« Reply #14 on: December 22, 2010, 06:38:39 am »

James Feenstra wrote on Tue, 21 December 2010 13:00

Geri O'Neil wrote on Tue, 21 December 2010 06:51

James Feenstra wrote on Mon, 20 December 2010 16:45

Geri O'Neil wrote on Fri, 17 December 2010 07:26

You guys know, the big black box that makes noise and is usually in the way of a Genie leg
yeah those things ALWAYS block sight lines

now if I could get the musicians and backline out of the way everyone could sit back and enjoy the light show

Wink



Ahh, so you've seen the Trans Siberian Orchestra, then? They do that quite nicely.... Laughing  Laughing  Very Happy

I always enjoy reading your postings, James. Take care,
Geri O

they're in town thursday actually...too bad i'm doing another gig Neutral

brian usually does a pretty good job


Oh, yes, no doubt. We got to spend a day with Brian when he was doing a (no doubt a short and temporary) stint with a Nashville group several years ago. Good guy to hang out with. And he definitely stepped up nicely, ya reckon?... Very Happy

Geri O
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