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6-pin xlr comm hack

Discussion in 'Sound, Music, and Intercom' started by reddawnman, Jan 13, 2008.

  1. reddawnman

    reddawnman Member

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    Hey all:

    Love the forum. After reading the intercom design pdf and taking off a couple cover plates, i figured I'd post something here.

    I am dealing with a school that has hard-wired intercom lines in the walls that are 6-pin XLR ports that I think were originally supposed to be part of a 2-channel telex system. For whatever reason the school never bought the transmitter hardware and have a bunch of 6-pin male receptacles just sitting in the wall / floor / backstage panels that should be able to be used for intercom ports hanging in a bunch of convenient places around the theatre, as they should be. This system is also wired into the TV production studio upstairs (about 150' away) so if needed they could use it for live shoots and such. As far as I know, they've never used the wall outlets for lack of transmitter hardware and / or 6-pin xlr ends.

    Trouble is, the 6-pin xlr system doesn't work, and never has to anyone's knowledge because the guys that did the wiring were never called back. so, they have a porta-com (Theoretically clear-com compatible) 3-pin XLR intercom system that is jerry-rigged in to plug into the patch panel and a field microphone input. So, to have intercoms backstage you have to take a precious microphone input backstage and patch it into the patch panel to the intercom system.

    Ive looked at the pinouts for 6-pin xlr, and after unscrewing some wall plates, I've determined that the plates are wired up, and it looks as though the grounds et al are wired in correctly - we should have continuity.

    I then got a 6-pin female and soldered the pins out (according to standards in the intercom systems pdf) to 2 3-pin XLR's. Plugged it into my clearcom base station, into the wall, then went to another one of the wall plates and plugged in another one of my 6 to 2x3 xlr adapters to a clearcom headset. I heard a pop when connecting the xlr, so I know at least I was getting power. However, no audio or ability to talk out.

    I know that ideally you need to have a pro come in and check out connectivity on all the plates in the house, and that it really should use the same 6-pin IC headset system that was supposed to be spec'd originally. However, this is a cheap high school (reading this board it seems to be a common theme) and there's no way they are paying anyone for this. This is just kind of a side project that would be nice to get working.

    I'll see if i can get into the school on monday and post some pictures. They also have nice things like a 25lb pig hanging by aircraft cable and duct tape keeping tension on aircraft cable that was originally hooked onto a cyc batten extension. We tell people not to stand under it... *sigh*
     
    Oldman likes this.
  2. museav

    museav CBMod CB Mods Departed Member

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    Occupation:
    Acoustical, audio and audiovisual consultant
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    How long ago was this installed? Did the installer leave any drawings and other documents? If not, then shame on them for not doing it and shame on the school for letting them.

    If this was wired as a two channel, party line system, then it should just simply have all the 6 pin XLRs wired in parallel. The receptacles may be physically wired in parallel or may be brought back to some common point and paralleled there (I personally prefer the second approach, if you end up having to troubleshoot the wiring you'll soon see why). As far as checking continuity, you could probably make up a plug that shorts pairs, insert it into one intercom jack with nothing else hooked to any of the other intercom jacks and then go around with a multimeter or continuity checker and verify that the same open and shorted pair combinations show up everywhere. You could also use a signal generator and inductive amplifier, something like this http://www.triplett.com/product_info.php?cPath=28&products_id=72, to verify the wiring.

    Just to verify your breakout cable wiring, the standard Clear-Com 6 pin connections are Pin1 is ground, Pin 2 is +VDC, Pin 3 is Channel B audio, Pin 4 is Channel A audio, Pin 5 is PGM+ and Pin 6 is PGM-. So a typical breakout cable would have one 3 pin XLR wired as Pin 1 to Pin 1 (GND), Pin 2 to Pin 2 (VDC) and Pin 3 to Pin 4 (Channel A audio) with the other 3 pin XLR wired as Pin 1 to Pin 1 (GND), Pin 2 to Pin 2 (VDC) and Pin 3 to Pin 3 (Channel B audio). Pins 5 and 6 on the 6 pin would not normally be wired to the breakouts. I have seen 6 pin systems wired as two separate 3-wire channels but that would be non-standard.

    While apparently not directly relevant, from what I can tell the Anchor Audio Porta-Com systems are RTS two-wire compatible rather than Clear-Com compatible. They use three wires for two channels; Pin 1 is ground, Pin 2 is both Channel A audio and VDC power and Pin 3 is Channel B audio. Clear-Com is three-wire with Pin 1 as ground, Pin 2 as VDC and Pin 3 as the audio. The physical wiring used may be the same in either case, but based on the online manuals you can't directly connect Clear-Com devices to a Porta-Com system.
     
    reddawnman likes this.
  3. reddawnman

    reddawnman Member

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    No drawings or anything at all. I believe that the installer has some sort of political connections in the district and is wired in to the Old Boy Network... School was built in 97 I believe

    Looking at the back of the receptacles, I am pretty darn certain they did it the half-arsed way and daisy chained the receptacles. instead of making a common somewhere. I haven't had a chance to look behind all receptacles, but judging by the "quality" of other connections I'd say the whole job was done the friday afternoon before a 3-day weekend.


    Hadn't thought of that - excellent idea. I was assuming I'd need to buy a signal generator to verify, but since the job doesn't pay and since the administration doesn't care, I will short and use my multimeter's continuity tester.


    Yep, that is how I wired them, and they only give me a "click" on connect / disconnect. However, all 6 pins are wired in the back of the sockets, and I am worried that they MAY have wired it non-standard. I believe I'm going to have to make a shorting device and really go around and make sure that the pins are wired correctly. It is more than possible that the installers didn't know what they were doing and just wired in cable from pins to pins without any crossovers or common grounds so they could say that all 6 pins had continuity...


    I misspoke... No, you can't as I called up portacom and was told in no uncertain terms that I was a bad boy for asking if they would interface with a competitor's product, heh.

    What I meant to say was that the headsets / beltpacks DO work with a clear-com system if powered by a clear com base station. The headsets are 2 channel, but as long as they are set on channel "b" they work just fine with a clearcom compatible system.

    Thanks for the help. I will keep everyone informed.
     
  4. Chris15

    Chris15 CBMod CB Mods Premium Member

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    OK... I'm an engineer so I am obliged to seek out a more complex solution than is required :mrgreen:. If you are wanting to check the wiring, what I would do is first check there are no shorts between any of the pins and then I'd be grabbing the nearest plugpack not currently in use and 5 say 10K resistors. If you wire the plugpack across pins 1 & 6 and the link 1 -> 2, 2 -> 3, 3 -> 4, 4 -> 5, 5 -> 6 with a 10K resistor in each case. You then should be able to go to any of the wired comms point and of you stick a meter probe into pin 6 and then step through pins 1 -> 5 and get a decreasing voltage in pretty even steps.

    Worst comes to worst, instead of making adapters, why not just convert the points to 3 pin? You could either parallel conductors or just leave the spare 3 behind the plate for future use.

    Whatever you do, document it...
     
  5. icewolf08

    icewolf08 CBMod CB Mods

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    I take it that your 2 channel belt packs do not have 6-pin inputs, hence why you are trying to make breakouts. If this is the case, I wouldn't bother with the standard wiring, as the standard assumes that you are connecting to the belt pack with a 6-pin connector. You may consider making making a breakout where the first XLR-3 connects to pins 1-3 of the XLR-6 and the second XLR-3 connects to pins 4-6, no harm in that, and you have two truly separate channels.

    The other thing about 3-to-6 "Y" adapters, especially for Clear-Com is that you really should install diodes inline on the voltage conductor. Why? Because in a two channel system, both channels have discreet power. If you parallel them at a connector and one channel shorts it can take out the the entire system. With diodes in place a short on channel A won't affect channel B. The key is installing the diodes in the correct polarity.

    One other thing to consider, do you have proper termination?
     
  6. reddawnman

    reddawnman Member

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    The 2 channel belt packs are RTS packs that use 3 pin inputs, and generally I use them with the RTS transmitter hardware (also 3 pin 2 channel). The Clear-Com part was just to let everyone know about a hack i use on occasion with those particular headsets, whereby you could connect them to a clear-com network, set the headsets to channel "b" and they will function just like 1 channel Clear-Com compatible headsets. I use this on a large live-shoot when we have something like 8 cameras and 4 Clearcom headsets and 4 porta-com headsets.

    The question about the 6 pin wiring is totally different. I'm just trying to get 3 pins of it working so I can either:

    a: connect the 3-pin 2 channel RTS system up to the pre-wired 6-pin intercom slots so we don't have to keep using mic inputs.

    or

    b: Connect 1 channel of a 3-pin ClearCom transmitter up to the 6-pin intercom slots so we can use that hardware.

    or (icing on the cake)

    c: get all 6 pins working for a 2-channel clear-com setup.

    The wires in the wall are just that - wires. as of now all they do is connect to the pinouts on the receptacles, and I need to determine if there is a short or not.

    I am only running 1 channel at a time from my 6 to 3 y adapter, and yes, I know I have correct termination at the base station. Are you saying that if I paralleled the grounds all to pin 1 it would short out, or are you saying that if something in the 6-pin shorts from say 3 to 4 or 2 to 3 I could end up shorting both channels?

    Keep it coming, guys. i go to the site tomorrow with my multimeter.
     
    Last edited: Jan 15, 2008
  7. icewolf08

    icewolf08 CBMod CB Mods

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    Paralleling the commons won't cause a short, but if there is a short somewhere in the system on one channel then having the two channels paralleled will short the entire system. You would only use the diode setup i mentioned on the DC voltage line, as sound is inherently AC a diode would not allow sound signals to pass correctly. Thus the diode prevents a voltage short over to the other conductors once paralleled. I know that most people just make 6 to 3 adapers and have no problems, this is just a safer solution.
     

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