plainman007 Posted March 18, 2012 Share Posted March 18, 2012 Hello, Theres no one in my area that provides proper DMX cable. So I had no other option to buy the best quality mic XLR cable they had. And the store keeper told me that svereal DMX users are using this cable. My run is going to be 120' long and with 10 moving heads and 10 color changers on that line linked. Will I have any problems ? Im planning to use a terminator at the end and would lke someone to give me a link to pic where they show how to sloder the XLR cable to the XLR 3 pin connector. Thanks Link to comment Share on other sites More sharing options...
david.elsbury Posted March 18, 2012 Share Posted March 18, 2012 You will probably find it works fine with this cable. With 20 devices on it, you are within the specifications so that should also be fine. Can you clarify what you mean with regards to showing you a picture of how to solder the XLRs on? http://www.hometheatershack.com/forums/attachments/remotes-cables-accessories-tweaks/24153d1286917907-how-solder-illustrated-diy-guide-making-your-own-cables-XLR-soldered.jpgThe screen goes to pin 1, make sure you keep the wiring the same on each end for the other 2 pins. A terminator is definately a good idea, just solder a 120ohm resistor between pins 2 and 3 of an XLR plug Link to comment Share on other sites More sharing options...
plainman007 Posted March 18, 2012 Author Share Posted March 18, 2012 The pic youve shown is what I was meaning to see. How to solder the wires onto the connector. This pic explains it well. Thanks. The only thing is my DMX connectors dont have numbers next to the pins. Or is it normally not numbered. Ive got to judge visually and based on their position I guess ? When you say the screen goes to pin 1, whats the screen, is it the shield ? There seem to be 2 wires in the central core and another which is a bunch of wires forming a fine sheath, Thats the screen ? So theyve go tot be twisted together and soldered on pin 1 ? I was planning on soldering a 120ohm (half watt) resistor between pins 2 and 3. Is the half watt part imperative ?? Thanks & RegardsJoshva Link to comment Share on other sites More sharing options...
springgrove Posted March 18, 2012 Share Posted March 18, 2012 The pic youve shown is what I was meaning to see. How to solder the wires onto the connector. This pic explains it well. Thanks. The only thing is my DMX connectors dont have numbers next to the pins. Or is it normally not numbered. Ive got to judge visually and based on their position I guess ?The numbers are often tiny, but this link will help. When you say the screen goes to pin 1, whats the screen, is it the shield ? There seem to be 2 wires in the central core and another which is a bunch of wires forming a fine sheath, Thats the screen ? So theyve go tot be twisted together and soldered on pin 1 ?The screen is the shield, i.e. the 'bunch of wires forming a fine sheath'. Yes, twisted together, as you say. I was planning on soldering a 120ohm (half watt) resistor between pins 2 and 3. Is the half watt part imperative ??It is not dissipating any power, so the power rating (watts) doesn't matter. You'll want one that fits in the case. Nigel Link to comment Share on other sites More sharing options...
boatman Posted March 18, 2012 Share Posted March 18, 2012 The pin numbering of 3-pin XLR connectors is like this picture. Remember that this is the view from the front of the connector, not the solder side. http://upload.wikimedia.org/wikipedia/commons/thumb/8/81/XLR_pinouts.svg/300px-XLR_pinouts.svg.png There's much more info on XLR connectors on Wikipedia. Ahh, too slow with the typing. Link to comment Share on other sites More sharing options...
Brian Posted March 18, 2012 Share Posted March 18, 2012 It is not dissipating any power, so the power rating (watts) doesn't matter.It most certainly is and most certainly does. Link to comment Share on other sites More sharing options...
plainman007 Posted March 18, 2012 Author Share Posted March 18, 2012 Brian > If it does matter, then is the half watt resistor the correct one to use ? Or something else ? Regards Link to comment Share on other sites More sharing options...
dbuckley Posted March 18, 2012 Share Posted March 18, 2012 It is not dissipating any power, so the power rating (watts) doesn't matter.It most certainly is and most certainly does. Indeedy. That 120 ohm resistor has 5V across it, so using the formula every sound engineer should have engraved on his heart, Watts is E (E is voltage) squared R. so %V squared is 25, and 25/120 gives 0.20W. So a minimum of a quarter watt resistor, my recommendation is the 0.6W metal film resistors available from the likes of Maplin. Another application of that formula is finding the voltage across a speaker wire. For your subs you have 2500W into a 4 ohm load, whats the voltage on the wire? E = square root of watts times ohms, so root of 10,000, so 100V. Enough to give you a decent belt when the kick is hit. Link to comment Share on other sites More sharing options...
plainman007 Posted March 19, 2012 Author Share Posted March 19, 2012 Dbuckley > That was totally too complicated and mathematical. Just let me know if a half watt resistor would be fine for a DMX terminator. I have no subs. :) Thanks Hey Guys, A quick check. If the cable run is 360 feet. But still with the same 20 fixtures only on it, will I still be within specifications and my mic cable will still hold good ? I was wondering if I didnt want people stamping on the wires laying on the ground then I should raise it to ceiling level and then send the signal to each truss. Can you tell me if instead of 120 feet I were to use 360 feet. Would this high quality mic cable still work ? Thanks Link to comment Share on other sites More sharing options...
Ynot Posted March 19, 2012 Share Posted March 19, 2012 Dbuckley > That was totally too complicated and mathematical. Just let me know if a half watt resistor would be fine for a DMX terminator. I have no subs. :)Actually it's NOT that complex. And as pointed out, something that is extremely useful to know - one of the most basic formulae around and one with SO many applications in theatre. That formula, and it's derivatives, helps with the above, it will help you work out how many lanterns you can run off a 13A supply, or 63A supply, and conversely how much curent the lanterns you have in the rig will consume, and all sorts of other things. If you're anything near a serious technician I would spend a bit of time researching Ohm's Law as it WILL stand you in good stead. Link to comment Share on other sites More sharing options...
revbobuk Posted March 19, 2012 Share Posted March 19, 2012 The longer the cable run, the more the difference between mic cable and DMX cable will become apparent. Mic cable has a higher capacitance, and the effect of this will be to attenuate the higher frequencies more as the cable length increases. DMX signals are digital, and the effect of high-frequency attenuation on a digital signal is to 'round off' the sharp rising and falling edges of the waveform. This can introduce timing errors, or at worst cause the signal not to be detected at the receiver. So you are much more likely to have problems with a longer run. And the problems may be intermittent, and hard to track down. Cat5 cable, if that's available to you, would be a better compromise for a longer run. And it's cheaper! Link to comment Share on other sites More sharing options...
Nicktaylor Posted March 19, 2012 Share Posted March 19, 2012 I appreciate the problems about operating in another part of the world but nothing posted here resembles anything that a competent person should not either know or be able to work out before using kit that is obviously having mains into it. Good luck with the project though. By the way can you not buy DMX cables on the international market? I guess Ebay will find you ones from China or Germany and if you need enough the shipping would end up free'ish Link to comment Share on other sites More sharing options...
plainman007 Posted March 19, 2012 Author Share Posted March 19, 2012 There are a few suppliers in my country that offer correct DMX cable. When I called them. Out of stock. All of them. The thing is they rarely buy the expensive cables and keep them because here every pro lights and audio hirer just uses the cheapest crap you can lay your hands on. They arent bothered about accuracy etc. So I will have to suffer these side effects invariably. Im designing the show from a creative point of view. And because theres nobody here who can help me with these things im doing it myself. None of the largest stores having so called 'tech engineers' have heard of a DMX terminator. One of them said "what terminator,,,theres nothing called terminator, I think you dont know much about lighting". Just because your on the other side of the world where this is a bigger and recognized and organized industry, you cant assume that these things are available here and im purposely not using them. This is all the resources I have, now its upto me, I can either do the project or not do it. These things are obstacles, im trying my best to learn and overcome them. No point telling a disabled guy that he's disabled and that he cant do this and he cant do that. I know that. Thats why im asking such simple questions. Link to comment Share on other sites More sharing options...
timsabre Posted March 19, 2012 Share Posted March 19, 2012 Why don't you run out your 360ft of mic cable on the ground and try it.I would expect it to work fine.As Revbob says, if it's for permanent install then cat5 would be a better cable to use. Link to comment Share on other sites More sharing options...
Brian Posted March 19, 2012 Share Posted March 19, 2012 Brian > If it does matter, then is the half watt resistor the correct one to use ? Or something else ? David has provided the long technical answer. The shorter one is that the USITT Recommended Practice document calls for a 1/2W resistor. A larger one (1W etc) will also work fine. Link to comment Share on other sites More sharing options...
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