How long for audio cable

CClub wrote on 4/3/2008, 6:16 PM
For an upcoming concert, I'm thinking of putting my Rode Videomics on stands in front of a stage, then run a cable back to my V1U's. Videomics have 1/8" male, I currently have 25' cables that connect 1/8" female into XLR inputs in the V1U, and I've never had problems at all with that. If I were to add 25' extension to that, would there be a problem with the audio signals?

Comments

TGS wrote on 4/3/2008, 6:22 PM
If it's all low impedance, shielded XLR cables, I thought you could go almost forever.
I've seen 100 footers for sale. I'm speaking of regular singing mic cables, but I don't think there would be a difference.
If I'm wrong, there should be some quick corrections from others.
Chienworks wrote on 4/3/2008, 6:24 PM
If those 1/8" plugs aren't balanced then the entire run is unbalanced, so length can be a big problem. Of course one could put an impedence matching transformer between the mic's 1/8" plug and the XLR cable. If that's done then thousands of feet are probably fine.
CClub wrote on 4/3/2008, 7:09 PM
Thanks for all the info. In looking just now at the impedence matching transformer, all I found were transformer such as http://www.amazon.com/Shure-A95UF-Impedance-Matching-Transformer/dp/B0002GZORQ/ref=sr_1_2?ie=UTF8&s=electronics&qid=1207274589&sr=8-2This[/link]. If this has a female 1/4" adaptor into female XLR (as it appears), then I'd have to go from the 1/8" male of the Rode Stereo Videomic, into a female 1/8" to male 1/4", into the transformer before going to the cables. Would that adapter negate the benefit of the transformer?
musicvid10 wrote on 4/3/2008, 7:34 PM
1) You should connect your mic using the shortest length of unbalanced cable possible with the 1/8" plug into a 1/4" adaptor.

2) Plug that into a suitable direct box. For a mic level signal I recommend an active DI. If you are on a budget look at something like the Ultra DI-1000.

3) Be sure to push the "Ground Lift" button on the direct box.

4) Run any length you need of XLR to your camera inputs.

This is the accepted commercial configuration and will work fine for you.
CClub wrote on 4/3/2008, 7:48 PM
Great info, again. Okay, this leads to another question. I found a Direct Box (Live Wire ADI Active DI Direct Box, $59 @ Guitar Center). I like the fact that it can be powered by 9V battery or 48V. BUT, if I click on the 48V on my V1U XLR controls, I assume that it'll power the Direct Box, but would that cause a problem with my Stereo Videomic? The Videomic requires its own battery power, and I've been told that it could cause damage to the Videomic if I also switched on the 48V phantom power on the videocamera. Or would the Direct Box take all the power for itself and not send it on to the Videomic?
riredale wrote on 4/3/2008, 8:14 PM
Just ran 80' of RadioShack stereo SHIELDED 1/8" cable (sold in 20' lengths) from my AT822 (stereo miniplug) to my mixer for a band recording two days ago. No external noise, even with the mic turned off and the gain on the mixer cranked up. Setup was in a high school theater with lots of overhead lighting, so I am less than convinced that balanced XLR is the only way to run a mic signal. I suspect that cabling is a lot better these days than decades ago. The 1/8" connections are much more delicate, however.
Steve Mann wrote on 4/4/2008, 8:44 AM
You got lucky.
musicvid10 wrote on 4/4/2008, 2:27 PM
The 48V Phantom power from your camcorder is applied to the balanced XLR chain. The unbalanced DI inputs are electronically isolated from the outputs. You have nothing to worry about.

You will need to provide whatever power is needed for your mics from their normal source. Also, if you have two microphones, you will need two DI boxes, or a 2-channel "stereo" DI.

In some cases, even six feet of shielded cable from an unbalanced mic introduces unacceptable hum in the recording. I just mixed down a show that had this very problem from a stereo mic, and ended up putting over 20 notch filters in Vegas to bring it down to tolerable levels, which of course affected the overall shape of the audio.

The purpose of an active direct box is to isolate the source from the destination, break any potential ground loops, and provide just enough signal boost to maintain unity gain over long cable runs. The slight hiss that may be introduced in the active gain stage is eminently preferable to the noise, signal loss, AC hum, and THD that are introduced by other methods, anecdotal experience notwithstanding,