Dirt in the mic in Port (Maybe)

[Bruce Dempsey]

During a concert yesterday I tried to get clean sound from the Concert board xlr thru my 2 channel xlr rolls cam mixer to the 1/8 mic input on a sony 550v = noise 60 hz buzz. I think maybe the port is physically dirty. What to poke in there? to clean it up before a bit of deoxit
thaks

[Zoran Vincic]

If the connector was REALLY dirty there would be a possibility of an intermittent signal but 50/60 Hz hum usually indicates an issue with the power supply and/or grounding (ground loop to be more specific).

[Bruce Dempsey]

thanks zoran
should I use batterys to supply power to the rolls cam mix rather than ac?

[Gary Nattrass]

A battery power supply may be best but it might be an idea to invest in a transformer Isolation box, I personally use the ART make but there re others from Rolls.

They also have the advantage of being able to ground lift the audio circuit but isolating via the transformer will be of great advantage.

[Bruce Watson]

Originally Posted by Zoran Vincic

If the connector was REALLY dirty there would be a possibility of an intermittent signal but 50/60 Hz hum usually indicates an issue with the power supply and/or grounding (ground loop to be more specific).

Agreed. RF noise can get in a bunch of ways, but the two biggies are the power cable (fix is to use batteries if you can), and the unbalanced mic line (fix is balanced XLR cables all the way to the camera, which is why they exist).

If your camera doesn't have XLR audio inputs, you can still run XLR cables right up to the camera. Then you have to convert from balanced to unbalanced audio, and from XLR to 3.5mm mini-plug. This requires a http://www.bhphotovideo.com/c/product/772496-REG/Sescom_SES_LZSLHZ_XF14_SES_LZSLHZ_XF14_Low_to_Low_High.html and an adapter. There are of course many ways to do this, and that link is just one example.

My point is that you can minimize the length of your unbalanced cable. IOW, minimize the size of the "antenna" that's picking up the stray RF noise.

[Bruce Dempsey]

thanks
Never did understand why I always had obnoxious noise when plugging into professional mixing desks at theatres
looking thru ebay and other places for 2 - 9v rechargables and a charger, and noting that the usual suspects are not in the market place . Was hoping enerloop had a 9v setup but no luck

[Rick Reineke]

If you are going from a mixing board's XLR, it iwas likely +4dB. (though the Mackie VLZ series mixers had a mic/line switch)
As was stated, you need the proper cables and interface box and/or attenuation to feed your unbalanced mic level input.
I can only imagine the distortion, EMI and other nastys that were present..

[Jay Massengill]

If you are using the Rolls MX36 cam mixer, it has Mic/Line level switches on both the XLR inputs and the 1/8-inch output.

Make sure you don't have phantom power activated on the Rolls, and since you can't turn off the Plug-In Power on the Sony's mic jack, hopefully the Rolls is successfully handling this voltage since it's specifically made to mount under small video cameras (and has capacitors on the output shown in the schematic).

You may want to try another 1/8-inch TRS cable between the mixer and camera, making sure you clean the connectors and then avoid touching them. Also plugging, gently twisting and replugging to get a good connection.

Anything that is AC-powered in your system, including an external video monitor attached to the camera, can create hum when connecting to a house mixer that is AC-powered from a different location.

So your choices are to use the exact same power circuit as the house mixer, isolate your signal connections with transformers, or power everything with batteries.

Also use a cable tester that can latch onto intermittent wiring faults to check all your cables.

[Rick Reineke]

As Jay stated, plug all video/audio gear should go into the same AC circuit. This should eliminate ground inconsistencies. (aka, loops) Obliviously, lighting should be distributed accordingly, as it draws lots of power.

[Zoran Vincic]

Originally Posted by Bruce Dempsey

thanks zoran
should I use batterys to supply power to the rolls cam mix rather than ac?

Try and see. If a ground loop between the main desk and cam mix causes the hum it should be eliminated by using batteries.

[Bruce Dempsey]

Thank you everyone
I now have a much better understanding of the issues relating to the ingesting of clean audio to a camcorder from house sound.

[Bruce Dempsey]

Originally Posted by Jay Massengill

If you are using the Rolls MX36 cam mixer, it has Mic/Line level switches on both the XLR inputs and the 1/8-inch output..

Any idea how long a continuously powered up mx36 would run on 2 - 9v alkalines?
I've ordered Soshine 500mAh 9V Lithium ion Rechargeable Battery X2 Battery Charger | eBay
which should perform for at least as long

[Paul R Johnson]

When you have a balanced output provided, it's always worth using an XLR M/F barrel with no connection on pins 1 - lifting the ground completely. If the levels match and the connectors are correct it often cures it. you can also use this technique to convert to unbalanced, using just pins 2 and 3.

[Bruce Dempsey]

That's a cool notion
Do I doctor a barrel myself by removing pin 1 or can I get one storebot?

edit I see a hosa
http://www.markertek.com/Audio-Equip.../GLT-255.xhtml
ordered one on ebay

[Rick Reineke]

"Do I doctor a barrel myself by removing pin 1 ?"
- You would NOT physically remove the pin, just disconnect the shield / wire going to it. Make sure the XLR's shell is not tied to it as well.
Normally when going from balanced to unbalanced, Pin-3 is tied to shield/ground. This will not attenuate the signal though.
The Hosa connector should work also. But a DI would be better, and most have a ground lift switch built in.
The Rolls DB25b is a transformer balanced, passive direct box is affordable and has a variable pad build in. You would still need an XLR to 1/8" adapter however.

http://www.markertek.com/Audio-Equip...on/DB25B.xhtml