Control/Dimming DMX Help!/Wire colors

[Crysalis]

Hey all! Brand new here, and lookin for some help.

Just installed a brand new lighting system for my local church. We have an elation scene setter (24 channel) which runs (4) four channel DMX dimmers. These are connected with a 3-pin DMX cable.

Gepco DLC224 250 250 ft. High-Bandwidth, 24 AWG 4-Conductor DMX Cable Wire | Full Compass

(this is the cable we bought)

I put neutrik connectors on them. 1 - white, 2 black, 3 red. I left the shield un-soldered.

We cannot get the signal from the controller to the dimmers to work. The cable we pulled (through conduit, walls, etc) is not working for the lights. However, as a test, we did continuity testing (as well as using a regular microphone to our mixing board) and the cable seems to be fine. We then took 2 mic cables and plugged them in directly from the controller to the dimmers and everything works perfectly. However, something is up with the cable that we pulled.

Interference? How to get around it? Do I need to terminate? What did I do wrong?

I appreciate any and all help. I will be working on this all day every day until I get it resolved as we have a big production going on this week and need this to get working!

THANK YOU!

 

[Sony]

You left the sheild unsoldered....that is your problem right there most likely, the sheild has to be soldered to Pin #1. The DMX Pinout is Pin 1) Shield, Pin 2) Data 1-, Pin 3) Data 1+, Pin 4) Data 2-, Pin 5) Data 2+. This pinout is the same for both the male and female sides of the cable and YES the sheild is required to be soldered the ONLY pins that are "Optional" are pins 4 and 5.

 

[theatre4jc]

Typically the shield is soldered as the ground. Don't think not using it would be a problem, per-se, but my first thought would be that it could be interfering. Did the shield get completely cut away? Could the line have a couple breaks in it where the shield could be crossing the lines? If you can run 2 mic cables from the board to the dimmers and it works just fine, then I would highly doubt that you would need a terminator.

Since the lines have continuity and will work through an audio console obviously the lines are good, which is strange to me. Did you check the continuity verses the other pins? I'm basically just thinking out my thoughts because nothing jumps out to me as an issue.

 

[JD]

Yea,
Case= no connect,
Pin 1 = Shield,
Pin 2 = white,
Pin 3 = black.

Do not use the other two conductors if you are using the 3 pin connectors. (or, connect them to pin 1 as well.) Whatever you do, do not connect anything to the case ground of the connector. White and black can be assigned the other way around, but pin 2 must always connect to pin 2 on the other end, same with pin 3.

 

[SHARYNF]

are you SURE that you checked continuity testing correctly? I have seen people take both ends of the cable and forget that the male and female are MIRROR images of one another, and that what they have done is it actually wire up a cable with the pins 1 and 2 reversed

3 Pin XLR Wiring Diagram

Sharyn

 

[Crysalis]

I got it guys. Thanks for the replies. The shield wasn't soldered like I was told it was (I had someone else on other end of the cable). I Re-soldered both ends and made sure the shield was soldered and it works beautifully. Thanks for
the help... Much appreciated.

 

[Footer]

I got it guys. Thanks for the replies. The shield wasn't soldered like I was told it was (I had someone else on other end of the cable). I Re-soldered both ends and made sure the shield was soldered and it works beautifully. Thanks for
the help... Much appreciated.

TRUST..... but verify.....

 

[pathway]

What wasn't mentioned here was the importance of connecting pins 2 & 3 with a twisted pair. The installed cable probably has a black/white pair and a black/red pair, so your original connection may have inadvertently been pins 1 & 2 for the first pair and pin 3 with the red lead from the 2nd pair. That arrangement would have passed a continuity test but as the cable length increased, signal distortion (and the likelihood of corrupted data) would as well. The mic cables, although made with wrong type of cable for DMX, would work better since pins 2 & 3 used a twisted pair .

I would double-check that your installation really does have a twisted pair on 2 & 3. Connecting the shield to pin 1 got things running, but you can't be sure that didn't just improve the quality of the line enough to get the signal from one end to the other more or less intact. You could still see annoying glitches in your dimmer outputs when you least need them. A properly connected and terminated DMX cable installation gives you 100% rock solid reliability, and anything less can cause no end of trouble that you'll blame on your board or whatever else because, after all, what could possibly be wrong with the cable?

 

[derekleffew]

Good point, pathway. More than once I've accidentally gotten my wires crossed. I really dislike cable that doesn't have all unique wire colors.

However,

Gepco International, Inc. -- Audio and Video Cable Products --

According to the manufacturer, the pinout should be:

Recommended Pinout for 5-pin XLR:
Pin 1 - Shield
Pin 2 - Black
Pin 3 - Red
Pin 4 - Blue
Pin 5 - White

So Crysalis should be correct if he disconnected the white wire and attached the shield to pin 1. For an XLR3 the blue and white wires should be insulated and unterminated.

See also the thread DMX Wiring, in which case the pinout I posted would be wrong for this Gepco cable.

 

[SHARYNF]

For the sake of clarification and information, I decided to ask around a question that some folks might be thinking but have not asked:

Question is why is twisting so important, if there is a shield. So we asked Milton Davis at Doug Fleenor and here was a very good answer

I think there have been religious wars fought over this subject.

Both aspects of the cable (shielding and twisted pairs) contribute to its effectiveness. The shield prevents outside interference *above 7MHz* from causing problems. Shielding does absolutely nothing to stop magnetic interference below 7MHz (such as fields generated by 60Hz devices). The twisting of the pairs actually buys us more in terms of a robust signal. The twisting insures that the data plus and data minus signals are equally exposed to the interference. If the outside influences are induced equally onto both signals, we can easily subtract out that component leaving only the data represented by the difference in voltage between the two signals.

If I had to choose between being shielded or having twisted pairs, I would choose the twisted pairs in most cases. For another real-world example, look at CAT5 cable. It is available in shielded versions, but in the US you rarely see it. However, *all* CAT5 cable uses twisted pairs.

SO this is a technical explanation as to WHY you Need to have it be twisted and WHY you need to make sure you are using the correct pairs.


Sharyn

 

[ajb]

That's a good point to bring up Sharyn. The original balanced twisted pair is the telephone system:

The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits. In the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, which had the incidental benefit of reducing attenuation, hence increasing range.

As electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, shared the route with electrical power lines. Within a few years the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles. In this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, or six per mile. Such open-wire balanced lines with periodic transpositions still survives today in some rural areas.

Wikipedia- Twisted pair - History.

Keeping balanced data on twisted pairs also keeps the wires in a pair in close proximity even when bundled with many other pairs, which means the respective magnetic fields of each wire in a pair largely cancel one another out, which helps to reduce crosstalk between pairs in a bundle.

 

[JD]

Good point, pathway. More than once I've accidentally gotten my wires crossed. I really dislike cable that doesn't have all unique wire colors.

However,

Gepco International, Inc. -- Audio and Video Cable Products --

According to the manufacturer, the pinout should be:


So Crysalis should be correct if he disconnected the white wire and attached the shield to pin 1. For an XLR3 the blue and white wires should be insulated and unterminated.

See also the thread DMX Wiring, in which case the pinout I posted would be wrong for this Gepco cable.

So, the problem I have with the wire you pictured (and I have seen this a lot) is that the four conductors are NOT independently twisted, instead, all four are twisted together! In the current DMX, only two conductors are used so no big deal, but why would they claim it is DMX cable if the two pairs share the twist ??

 

[SHARYNF]

So once again getting assistance from Milton here is the response

From reading the spec sheet (FOR THE GEPCO DLC224), it appears that the cable has two twisted pairs. Those two pairs may also twist around each other. I don't know how they could manufacture a cable with all 4 wires in a single twist and still control the impedance. Note that their data sheet does call out a black/white pair and a red/blue pair. If you're holding a piece of this stuff you are more able to see its construction than I can from the spec sheet. Until you get into running significant distances (over 500 feet), the twisted pairs or 4 wires twisted probably won't matter much.


Regards,

Milton Davis, Engineer, ETCP-CEE-RT

 

[derekleffew]

Now I'm confused.

... Milton:

Note that their data sheet does call out a black/white pair and a red/blue pair.

...

If these are in fact the pairs, this would appear to violate the DMX pinout on the same page.

Recommended Pinout for 5-pin XLR:
Pin 1 - Shield
Pin 2 - Black
Pin 3 - Red
Pin 4 - Blue
Pin 5 - White

IIRC Icewolf08 uses this particular cable, perhaps he can tell us which colors belong to which pairs?

 

[SHARYNF]

I agree I was just also looking at the spec sheet....
\could be a type in the pairing (would not be the first time the sheet does not fit the product) ))


Sharyn

 

[JD]

Re: DMX Help!

When I think of two pair shielded cable, I think of what I have pictured below. Two pairs, each twisted and each shielded. This is an OLD piece of long run arcnet cable, about as flexible as a water pipe! (110 ohm) Didn't want to cut open any of my DMX, but the construction is the same.

 

[SHARYNF]

Datapoint ARCNET now you REALLY are showing how long you have been around. Next you will be showing a section of Golden Rod ;-))))

Sharyn

 

[church]

For more information on twisted pair check out the following link

Twisted pair: Definition from Answers.com

 

[epimetheus]

I can confirm that the Gepco DLC224 does in fact not have 2 individual pairs. The 4 insulated conductors have a common twist. Needless to say, I was not thrilled to discover this, but luckily I only bought 80ft. We bought some Horizon/Rapco DMX cable at my church that does have 2 individual twisted pairs.

 

[SHARYNF]

I am not sure why for DMX that would be an issue, since you are only using one pair and the shield. The extra two wires are really not used This probably means that there is not problem with selecting 2 any of the 4 for use

Sharyn