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Old October 19th, 2004, 03:45 PM   #1
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Infrared Receiver to XLR input

I will be recording (pro bono) an event in a hall where getting a direct cable connection from the sound system to my camera is impractical. The hall has an infrared audio transmitter for the hearing-impaired. It appears that the best way to get an audio feed directly into my PD170 is to connect one of the infrared audio receivers to an XLR jack on the cam, using the receiver's headphone jack.
I'm thinking of buying a male mini-jack to male XLR cable, or using my old Studio 1 box in reverse with a male-to-male XLR converter (something Mike Rehmus suggested in a post here last year).
Sound needs to be adequate, not top quality. In addition to the feed, I will use my AT835 shotgun mounted on the camera, recorded on separate tracks so I'll have a backup soundtrack.
Will this setup work? Anything simple I can do to improve it?
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Old October 19th, 2004, 04:20 PM   #2
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You need to determine if the receiver puts out a stereo or two-channel mono signal, versus a single-channel mono signal. This will determine how your cable or adapters need to be wired in order to prevent cancelling the signal when going to the camera's balanced input or potentially losing half of the stereo sound.
Examine the headphones that are used with this system. Do they have the standard headphone TRS 3-conductor plug? If so, then does the IR transmitter for the system take a stereo or mono feed from the house system?
Let us know and we can go from there. The key is you don't want to send the same signal to pins 2 and 3 of your XLR input or you'll get cancellation. You also don't want to lose either the left or right signal if this system is stereo.
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Old October 20th, 2004, 04:47 PM   #3
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Thanks for the info, Jay.
The IR receiver is mono. The jack accepts a male mono mini-plug.
What type of adapter/connector do you recommend?
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Old October 21st, 2004, 09:57 AM   #4
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I'll recommend two methods and you can decide based on what you have available.
The simple way would be to obtain or make a cable that has a male mono mini to an XLR male. The tip of the mini should be wired to pin 2 of the XLR. The sleeve of the mini should be wired to pin 1 of the XLR. Pin 3 of the XLR shouldn't be connected to anything. (That's the important part!) I also wouldn't connect the XLR shell to anything.
Unfortunately coming up with a cable so simple isn't always a simple task depending on where you live and your time frame.
So the alternate method would be to obtain a mono mini male to mono 1/4" male cable. Then obtain a direct box. Both these components are available anywhere there's a Radio Shack for the cable and a music or guitar store for the direct box. Radio Shack also sells a 1/4" female to XLR male transformer. This would probably work too depending on the headphone output level of the receiver, but it wouldn't give you other controls such as grounding and attenuation. The direct box or transformer will convert the unbalanced mono signal from the receiver to a regular balanced signal that you can input directly into your camera. You'll have to experiment with the correct level setting of your camera input (probably line or mic ATT) and the receiver volume. Make sure if you do use a mic setting on the camera that you turn the phantom power off.
If you need to place the receiver at a distance from the camera to ensure good IR reception, then the unbalanced cable should be short with the transformer close by, and the XLR cable should then travel the greater distance.
All these components are available online too, but making certain you get the correct "unbalanced mono mini to XLR male" cable in a correctly wired version can be a hassle.
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Old October 21st, 2004, 11:09 AM   #5
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Jay,
B&H has a mini-male to XLR-male cable made by Comprehensive. The mini-jack is mono. Shouldn't this be wired correctly for mono signals? Here is the link:
http://www.bhphotovideo.com/bnh/controller/home?O=WishList.jsp&A=details&Q=&sku=133521&is=REG

For your alternate method, would my Studio 1 XLR adapter do the job of the direct box or transformer?
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Old October 21st, 2004, 11:31 AM   #6
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That cable "should" work. I have found cables like that with occasionally incorrect wiring so you should test it ahead of time.
I think it would be much better to try this cable than to try your Studio 1 in reverse.
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Old October 25th, 2004, 09:03 PM   #7
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No go

I tested this with the mini-to-XLR cable, and got either a constant hiss or no sound, depending on which switch settings I use on the PD170 (mic/power off results in hiss, line and mic att don't provide any sound). I tried various combinations of the switches and volume settings on the receiver and my cam, and was not able to obtain good sound from the mic.
Guess the headphone-out jack on the IR receiver doesn't have the power for a mic connection.
Instead, I will see if the venue will allow me to set up an additional mic on the podium, connected to my wireless system.
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Old October 26th, 2004, 08:51 AM   #8
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It may be due to some kind of interaction between the headphone jack and the balanced input. Can you test the connectors on the cable and tell me what conductors on the mini are connected to what conductors on the XLR?
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Old October 26th, 2004, 11:04 PM   #9
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Jay,
I won't be using the IR system, as the venue has okayed my placing a wireless mic on the podium, so the cable is a moot issue now for me. Just for information, is there a way to test the jack connectors without special cable testing equipment (my situation)?
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Old October 27th, 2004, 09:42 AM   #10
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Any small multitester ($10 and up) that can test for continuity can be used to check the cable wiring.
Simply clip one probe to the tip of the mini and use the other probe to touch the XLR pins and shell one at a time. Make note of what is connected.
Then repeat with the first probe connected to the sleeve of the mini. Again make notes.
To go a step further you can test the tip and sleeve of the mini to see if they are shorted together (bad).
You should also check the pins and shell of the XLR to determine if any of them are shorted together too. Make notes of all these results and keep it with the cable for future use.
Behringer makes an electronic cable tester and tone generator for about $50. Very handy to have and it can also latch onto intermittent problems with a cable.
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