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Author Topic: Wiring XLR to RCA  (Read 11789 times)

Tom Roche

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Wiring XLR to RCA
« on: May 14, 2004, 04:19:37 pm »

My church needs to run an audio feed from the board to a TV located in a "crying" room.  The TV has RCA audio inputs while the board outputs are all XLR.  Is there a way to wire this so it works?  Thanks,

Tom
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Rob Timmerman

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Re: Wiring XLR to RCA
« Reply #1 on: May 14, 2004, 06:44:09 pm »

This should be in the Study Hall, but for some reason it isn't.

http://www.rane.com/note110.html
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Michael 'Bink' Knowles

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Re: Wiring XLR to RCA
« Reply #2 on: May 25, 2004, 01:40:10 am »

Tom R. wrote on Fri, 14 May 2004 13:19

My church needs to run an audio feed from the board to a TV located in a "crying" room.  The TV has RCA audio inputs while the board outputs are all XLR.  Is there a way to wire this so it works?  Thanks,

Tom


First off, the Rane notes don't cover this case. The thing is, I bet the run from the mixing board is longer than, say, 20 feet. If that is the case, you need to run the line balanced up to the TV and then unbalance it for the RCA jack. The way to do this is with a transformer. Also, your RCA jack will not be able to take +4 line level signals and will either need to be A) padded down with resistors, B) stepped down via a special transformer or simply C) turned down at the console. If the crying room has its own send you can turn it down. If it's tied to some other send (you are using a wye cable or splitter) then you will need to pad it or step it down by 12dB. 10dB or 15dB pads are much easier to find.
http://www.sescom.com/audio/images_audio/il19.jpg
Here's what I would do: Get a 10dB or 15dB XLR inline pad and an inline 1:1 transformer. You don't need the best freq response (it's a TV ferhevvinsake!) nor high-signal-level compatibility from the transformer so the Sescom IL-19 will be fine.
http://www.shure.com/photos/a15as.jpg
For the pad you can get a 15/20/25dB switchable pad from Shure (the A15AS), a fixed 10dB pad from Whirlwind (IMP pad), a fixed 15dB pad such as the Sound Devices XL-15 cable or roll your own 12dB H-pad with matched resistors in a project box. 12dB of padding is the goal but 10dB will do if you run your mixer outputs conservatively. 15dB of padding keeps you safe from hot console levels. An inline XLR pad is what I'd use because I always try to anticipate changes to the venue and the inline XLR pad is useful everywhere you put it even after the crying room upgrades to a full sound system and doesn't need padding.

How to hook it all up: when you are in the crying room take the line from the console and plug it into the pad. Take the pad and plug it into the transformer. Then take pins 2 and 3 from the transformer XLR and adapt them to the RCA with pin 2 going to the RCA center pin and pin 3 going to the RCA shield ring. The XLR pin 1 doesn't connect to anything.

Other devices to consider are the Sescom TR-135 stepdown transformer which I've never used, the Rane Balance Buddy (BB 22) or the Whirlwind Line Balancer. The latter two of these units will require you to adapt them with a female-female XLR barrel so that you can plug a male XLR console output into the male XLR transformer output. Don't worry! Running a 1:1 transformer 'backwards' is fine; I do it all the time. Further choices include powered units such as the Henry Matchbox II but now you are getting into more expensive options with higher audio qualities that overmatch your TV's little speakers.

Hope this helps!

-Bink
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Tom Roche

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Re: Wiring XLR to RCA
« Reply #3 on: May 25, 2004, 02:14:08 am »

Wow Bink, that's a lot of info you provided.  Thanks.  The crying room is directly behind the FOH booth and required about 30' of cable that passes through the back wall.  I found a couple of web sites that showed (in their opinion) the correct way to wire up the XLR to RCA without transformers.  Since I had to rig something up really fast I went that route, at least to see if it would work.  XLR pins 1 and 3 to RCA sleeve, pin 2 to tip.  Output is from the DSP.  It worked out fine.  We get sound out of the TV monitor's right channel speaker only, but it's clean.  After setting the monitor volume to its midway point, I had to increase the output gain on the DSP by 4 db, but this is only for voice, no music.  I will look into a transformer if it means getting sound to both monitor channels.  Thanks again,

Tom
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Too Tall (Curtis H. List)

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Re: Wiring XLR to RCA
« Reply #4 on: May 25, 2004, 11:02:21 am »

Tom R. wrote on Tue, 25 May 2004 02:14

Wow Bink, that's a lot of info you provided.  Thanks.  The crying room is directly behind the FOH booth and required about 30' of cable that passes through the back wall.  I found a couple of web sites that showed (in their opinion) the correct way to wire up the XLR to RCA without transformers.  Since I had to rig something up really fast I went that route, at least to see if it would work.  


>XLR pins 1 and 3 to RCA sleeve, pin 2 to tip.

Hi,
   This particular setup is most useful when you are trying to feed an unbalanced 2-conductor OUTPUT (like the RCA out from a CD player) to a balanced INPUT (XLR input to a mixer channel).
You are doing the reverse. Feeding a balanced output to an unbalanced input. My feeling is you got lucky. I used a small Ramsa mixer that had a balanced 1/4" TRS (Tip, Ring, Sleeve 3 conductor) output for an aux.
If you plugged a 1/4" 2-conductor unbalanced phone plug into this output thereby shorting ring and sleeve (pin 1 and pin 3) it distorted nastily.
If you are up for the work I would run a 3 conductor (2 wires and shield, typical mic cord) from the XLR output of the DSP to the TV and then wire-
Pin 2 > RCA tip
Pin 3> RCA shield (ground)
Pin 1> unconnected at the TV end. (Cut it back a ways for working)

>Output is from the DSP.  It worked out fine.  We get sound out of the TV monitor's right channel speaker only, but it's clean.  After setting the monitor volume to its midway point, I had to increase the output gain on the DSP by 4 db, but this is only for voice, no music.

>I will look into a transformer if it means getting sound to both monitor channels.

If the present setup is working I would just buy a 1 female to 2 male RCA Y-cord from radio shack to feed both channels.
Going with a balanced system and transformer is great, but I don't see a need in this case.
Going "Balanced" reduces noise and adds 6dB of output. If you happen to go past something making a great deal of EM noise it is invaluable, but what usually kills you for long runs of 2 conductor lines is the top frequencies roll off. This has nothing to do with being "balanced" and everything to do with the impedance match of the output and the input it is driving. That is why you often hear of something as being " Balanced low- impedance".
So if you are lucky enough to have an output that is low impedance (and a friendly input match) and nothing that causes a great deal of noise where the wire run is you might be able to run unbalanced for 200 feet and have a usable signal for something as low fidelity as a TV. (I've done it more then once).
OTOH Murphy makes sure it does not happen often and it is sure to hum and buzz loudest when you need it most
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Too Tall
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Tom Roche

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Re: Wiring XLR to RCA
« Reply #5 on: May 25, 2004, 02:56:43 pm »

Thanks Too Tall.  Just a note: the TV monitor input is a single RCA.  I didn't see a stereo/mono switch on the TV either....kind of weird I suppose.

One of the web sites I read also recommended pin 2 to tip, pin 3 to sleeve, and pin 1 unconnected.  Since I'm already using 3 conductor wire it would be easy to disconnect pin 1 wire from the RCA sleeve.  But in the end I'm concerned with a better, permanent hook up that gets the signal to both TV speakers.  Thanks again,

Tom
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Michael 'Bink' Knowles

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Re: Wiring XLR to RCA
« Reply #6 on: May 25, 2004, 04:28:11 pm »

Tom, I wonder if the TV has only one speaker. I've seen this on economy models that have only one RCA audio input. Time to consider putting someone's old home stereo speakers in the crying room...

The point about snipping and taping off the pin 1 balanced shield at the RCA jack is that now you won't be slamming your console's pin 3 output straight to ground. Shorting pin 1 to pin 3 does this! You can tie pin 1 to pin 3 and get through a gig or two, but you lose clarity and you put undue stress on the output chip in the console. It will overheat and won't last as long.

Going the other direction (from RCA output to XLR input) you DO tie pin 1 to pin 3. The XLR balanced input circuit isn't at all bothered by this. Confused yet?  Razz  The Rane note mentioned earlier covers these and other wiring schemes.

I would keep the idea of a transformer alive on the back burner just in case the TV starts to buzz from the video system's ground connecting to the audio system ground. If this happens, the transformer will take care of you and cut the buzz.

-Bink
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Tom Roche

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Re: Wiring XLR to RCA
« Reply #7 on: May 25, 2004, 06:52:36 pm »

Excellent.  Your explanation of the consequences of tying together pins 1 & 3 put it in clear perspective for me.

As for the TV, perhaps it has only one speaker.  Since there are two speaker grills, one on each side of the screen, I assumed there are two.  I'll take another look-see to verfiy.  Again, you guys have been great help.  Best regards,

Tom
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Too Tall (Curtis H. List)

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Re: Wiring XLR to RCA
« Reply #8 on: May 27, 2004, 11:34:36 am »

Tom R. wrote on Tue, 25 May 2004 18:52

Excellent.  Your explanation of the consequences of tying together pins 1 & 3 put it in clear perspective for me.

As for the TV, perhaps it has only one speaker.  Since there are two speaker grills, one on each side of the screen, I assumed there are two.  I'll take another look-see to verfiy.  Again, you guys have been great help.  Best regards,

Tom



   After reading Bink's reply I realized it can be put much more simply.

   As a rule you can always short an INPUT. By taking the hot to ground all the input sees is there is no voltage coming in. Many input volume controls do just that when turned all the way down.

   On the other end it is NEVER a good idea to short an OUTPUT to ground!
In the old days if you shorted the hot output of a power amplifier to ground you would immediately "let the smoke out". Depending on what device you are using some can take it forever and some will blow up or sound like crap as soon as you short the output, but it is always a baaaaad idea.
Too Tall

PS- I know you "got" this from reading Bink's reply, but someone else may appreciate the explanation. I know I did when an old friend explained it to me the first time.
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Too Tall
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Phil Ouellette

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Re: Wiring XLR to RCA
« Reply #9 on: May 27, 2004, 12:13:55 pm »

Too Tall wrote on Thu, 27 May 2004 11:34

On the other end it is NEVER a good idea to short an OUTPUT to ground!


Unless it is a transformer isolated output, in which case you have to short the minus output to ground to get a signal.

This whole issue is due to the differences between transformer outputs verses electronically balanced outputs.  My opinion is why bother with it, if a manufacturer can't use a transformer then they should just tie the cold output to ground through a resistor that matches the build out resistor in the hot output and be done with it.  This gives you the same hum rejection into balanced inputs as the electronically balanced version and makes wiring to an unbalanced input trivial.

Phil

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That's "newbiesque" to my friends.
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