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Old July 30th, 2010, 12:29 PM   #1
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Help! Major audio cable problems

Ok, I'm testing equipment for a shoot which starts in 1 week. I tested all the equipment a few weeks ago, and everything was perfect.

I have AT899 microphones and NX5U cameras. I'm using phantom power.

I'm using LiveWire XLR cables to connect the microphones. They're 20 feet long. I have 3 that I got about 5 years ago and one new one. The new one seems thicker and more rubbery, the older 3 are thinner and feel more like vinyl. The connectors all look the same.

Now, when I hook everything up, I get a very loud 60Hz buzz. The one new (thicker) XLR cable is perfectly, and I mean *perfectly* quiet, not even the suggestion of a noise. The 3 older ones buzz very loudly. But everything was perfect when I tested it about 3 weeks ago, not a peep.

I tried switching microphones, I tried switching cameras, it all seems to come down to the cables.

I don't get it, how can I have 3 bad cables? Is LiveWire a bad brand? Or is something else going on?

If I switch the two cables (same microphone, same camera), the buzz goes with the cable, the other system is perfectly quiet with the one "good" cable.

I just tested 2 shorter cables I have, one is another LiveWire and the other is a cheapo one that came with something, and those two are also perfectly quiet.

I thought XLR was supposed to get rid of the 60Hz buzz. And I don't get how I could have *3* bad cables.

Are there different types that are wired differently or something? And I don't see how I could have missed this in my previous testing...

One last thing... If I plug in ONLY the cable (with no microphone on the end), the 3 "bad" cables buzz so loudly that I can hear the headphones across the room, but the 3 "good" cables don't even have a hint of 60Hz while wearing the headphones with the volume all the way up. It doesn't make a difference if phantom power is on or off.

Help!
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Old July 30th, 2010, 12:58 PM   #2
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So first, how and what are you connecting? Microphone>cable>cam input? or is there more to it?

If you are having problems with just the mic>cable>cam, and the problem follows the cable used, then yes you seem to have several bad cables or a remote possibility of a bad connection inside your camera connector. Does wiggling the connections on both ends of the "bad" cable affect any change? If there are more items in the chain, then certain combinations could reveal a problem that may or may not be a bad cable.

Do you have a cable checker, or a simple volt-ohm meter? I would start with checking each pin of the cable for continuity, and to make sure there are no shorts between pins or shell. Compare your findings to a known good cable. Wire can break down over time resulting in shorts or non-continuity. Kinking the cable sharply or crushing (ever run over one with your car?) can cause problems in the wire sometimes. If you find a problem you can disassemble the ends and inspect the connections within. XLR is pretty simple, and I find a quick soldering job will usually cure any problem identified.

Good for you for checking things ahead of time. Always easier to deal with a problem when the camera isn't rolling...
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Old July 30th, 2010, 01:05 PM   #3
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Is the camera running on battery or the ac adapter? Is the venue you are checking the cables in the same as the previous check? Perhaps the three cables aren't shielded as well as the others and during the prior test, there wasn't any electrical noise present?

Just one layman's thoughts....
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Old July 30th, 2010, 01:36 PM   #4
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This is why we have cable testers. At the very least, use a meter to test the bad cables. In particular, it sounds like the cable shield has become disconnected from the XLR pin 1 ground. This is a rather common failure mode and the solution is to simply repair the broken connection. Its not rocket surgery. If you were here in PDX, I would offer to fix them for you. Shouldn't take 10 minutes to fix all of them.
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Old July 30th, 2010, 01:39 PM   #5
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Venue is the same (my living room), and the cameras are running off AC (I've never even charged the batteries that came with them).

Wiggling things doesn't seem to make any difference.

The cables have never been abused, they've been in storage almost all of the 5 years that I've had them. I don't kink or run over them.

Yes, it is just microphone>cable>camera. Actually, as I said, the problem occurs with just cable>camera, you can't get much simpler than that. I tried both inputs on both cameras, same thing happens, 3 bad cables and 1 good cable. Phantom power on or off, same thing. I can hear the buzz change if I move the cable, so it's picking up interference from the room.

The cables seem to be ok, except there doesn't seem to be any shell-to-shell continuity (the big metal outside part of the plug), although the good one doesn't have that either. It's hard to make contact with the female side, but the probe on my meter is much smaller than an XLR pin.

I did leave them plugged into the microphones while in storage, do you suppose that stretched out the contacts? Perhaps electrolytic corrosion? That couldn't be the problem though, since even just a cable has the problem, with the female end unplugged.

I opened one of the plugs, and the soldering is sloppy but still looks like it makes a good connection.

I guess I'll just buy new cables and hope for the best. Any suggestions for a brand that's better than Live Wire?
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Old July 30th, 2010, 01:46 PM   #6
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Ok, I think I found the problem. It looks like the shield is in fact connected to pin 2 instead of pin 1. In the "good" cable it's connected to pin 1.

So, I'll never buy LiveWire again. Can you guys tell me a brand that doesn't suck?

Thanks for the help.
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Old July 30th, 2010, 01:54 PM   #7
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I'm still trying to figure out how I missed this during testing... I think I was using one of the shorter cables for one of the cameras, and didn't check the audio when I was using one of the mis-wired cables. I'm glad I decided to do a final "dress-rehearsal" test in the exact configuration I plan to use.

Curse LiveWire! Curse them!
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Old July 30th, 2010, 02:19 PM   #8
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Quote:
Originally Posted by Richard Crowley View Post
This is why we have cable testers. At the very least, use a meter to test the bad cables. In particular, it sounds like the cable shield has become disconnected from the XLR pin 1 ground. This is a rather common failure mode and the solution is to simply repair the broken connection. Its not rocket surgery. If you were here in PDX, I would offer to fix them for you. Shouldn't take 10 minutes to fix all of them.
Do you think your tester would have detected this mis-wiring? It would take more than a continuity test.
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Old July 30th, 2010, 03:10 PM   #9
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If the cable was mis-wired at BOTH ends a tester would not have picked it up, but if only one end was mis-wired it probably would. In a straight XLR M->F cable, pin 1 goes to pin 1 (shield), 2 to 2 (signal hot), 3 to 3 (signal cold) is correct.
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Old July 30th, 2010, 05:35 PM   #10
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Yes, it was mis-wired at both ends. That's why it sort-of worked, and made it hard to figure out.
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Old July 30th, 2010, 09:06 PM   #11
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Which is why i suggested taking a look inside...never know what your gonna see in there. And yes it would have passed a simple continuity test, but you were having problems none the less. There's always an answer for audio issues-sometimes they are very difficult to find.

So why buy new cables? just resolder to the correct pins and be done with it...the best brand here are the ones i make from scratch ;-) but when pinched for time I've bought from speakerrepair.com, the GLS stuff. bought the first batch as disposable for a high risk job but am still using them. cheap and not to bad. YMMV.
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Old July 30th, 2010, 09:48 PM   #12
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Originally Posted by John Meeks View Post
Yes, it was mis-wired at both ends.
That reminds me of an experience at NAB, back in the mid-80s.

As a Grass Valley engineer, I had developed a prototype distribution amplifier for parallel D1 signals. It used a 25-pin connector that included ten twisted pairs. We had loaned a couple to Sony for the show. Unfortunately, there were problems in getting the signal from end to end. All the tests, including cable checks came up clean.

Finally, we figured it out. The cable was wired with perfect connectivity. However, the twisted pairs were all mixed up. Bit 0+ might be twisted with Bit 7- and so on. Talk about a brain scratcher! Once the pairs were matched (Bit 0+ with Bit 0-), it worked like a charm. :)

The lesson learned: never trust a cable - even when the ohm-meter says it's golden.
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Old July 30th, 2010, 09:52 PM   #13
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Awesome cables:

Audio-Technica 3-pin XLR Male to 3-pin XLR Female AT8314-25 -
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Old July 30th, 2010, 11:02 PM   #14
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Quote:
Originally Posted by Jon Fairhurst View Post
That reminds me of an experience at NAB, back in the mid-80s.

As a Grass Valley engineer, I had developed a prototype distribution amplifier for parallel D1 signals. It used a 25-pin connector that included ten twisted pairs. We had loaned a couple to Sony for the show. Unfortunately, there were problems in getting the signal from end to end. All the tests, including cable checks came up clean.

Finally, we figured it out. The cable was wired with perfect connectivity. However, the twisted pairs were all mixed up. Bit 0+ might be twisted with Bit 7- and so on. Talk about a brain scratcher! Once the pairs were matched (Bit 0+ with Bit 0-), it worked like a charm. :)

The lesson learned: never trust a cable - even when the ohm-meter says it's golden.
This can happen with ethernet, since the twisted pairs act as their own shielding, and there are cable testers that can check for it. I think they start around $4,000. They can even tell you things like how long the cable is, how much of it is untwisted at the connection at each end, exactly where it's kinked (even if it's not broken), and a bunch of technical stuff.
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Old July 30th, 2010, 11:32 PM   #15
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Originally Posted by John Meeks View Post
So, I'll never buy LiveWire again. Can you guys tell me a brand that doesn't suck?
There is no brand that can guarantee that a mis-wire like that won't escape from the factory. This is a fluke. LiveWire is generally regarded as being a very sensible brand where you get excellent value for the price.

I make all my own cables because its fun and I'm cheap, but if I had to buy them off the peg, A brand like Live Wire (or Redco or Whirlwind, etc.) would certainly be preferable to the high-price rip-offs like "Monster" or the low-ball stuff like Hosa, et.al. A failure like this would NOT put me off buying LiveWire again. I can practically guarantee that LiveWire will take it back and either repair or replace it. Nobody wants to see that kind of thing happen.
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