60 hz hum/buzz in audio section of V1U?
 

Hello

I've noticed when plugging in XLR cables into either mic input that occasionally I get a hum that I can describe as a 60 cycle or 60hz hum. The hum seems to be able to be reduced if I reorient the cable and also seems to vary according to location. In some locations I can't produce it, in others it is quite evident, but can vary from quite noticeable to nonexistent with a re-orientation of the cable or even by putting my hand on the camera.

I've experienced this exclusively in outside locations. I cannot reproduced it in my house, for example.

Considering the XLR input is balanced it would seem any outside-induced noise would be cancelled. I've also found that if I completely remove any cable from either XLR input, I'm not able to get the camera to produce the hum by locale or orientation of the camera. I suspected the cables, but I've tried a number of them, from short to long with about the same reproducibility and results.

I have experienced this problem in the past with unbalanced signals or poorly shielded or grounded equipment, but this happens with the V1U when battery powered, there is no possibility of ground-loop induced hum in the 120v AC system.

I live fairly close to major radio towers and most recently it happened within a mile or 2 of the tower. I've also experenced it probably 3 miles away from that. It doesn't seem that the tower is the cause, but you never know.

Has anybody else noticed this and is it inherent in the camera, is that a way you've found to reduce it, or is there something defective with my unit?

Thanks in advance for any advice.

Regards,

-Keith

you sure you don't have an open ground on the cable? I don't get any hum on any of the V1's we've got; that certainly doesn't mean someone else' wouldnt'.

I've tried it with 4 different XLR cables, all premium quality. One 1' with a right angle, one 1' Y cable, and two longer XLRS. They don't have an open ground. One thing about the noise is that it has a pretty high harmonic content as most 60hz hum does with a 'buzzy' quality.

But why would you expect a 60 Hz hum (or harmonic there of) if you are (presumably) powering the camera from its battery? Batteries are great because they usually eliminate such hums... Seems to me that the hum has to be originating from some AC source - if it is really 60 Hz.

Brian, I actually don't know if it is a 60hz or its harmonics, it just sounds exactly like hum I've experienced in electronics that are not well shielded or have 'ground loop' problems. Obviously it cannot be from a 60hz AC source as it is battery powered. It could be another frequency. The loudest component is certainly not 60hz, it is not low enough to be that, but possibly a high harmonic. I've attached a .mov, .wmv and .wav files of the sound.

60 hz hum
 

It sounds like maybe RF is getting in there. Are your outside shoots around communications facilities, cell phone towers, radio towers, satellites, 911 call centers, etc.? Other than that, I'm baffled.

You might try taking a piece of aluminum foil and wrapping it on each end of the cable. See if that helps. I would think a good quality cable would be adequately shielded, but who knows.

John

As the attached spectrograph shows this isn't hum, RF breakthrough is the most likely culprit. Probably not having the camera or the microphone cable's shield actually earthed might be contributing to the problem.
The problem can occur because at RF frequencies the mic cable just acts as aerial, even the shield. The 'balanced' inputs might not be so balanced at these kinds of frequencies, so the RF gets rectified and ends up in the audible spectrum.
If earthing the shield of the mic cable kills the noise a more practical solution might be to add some RF filtering, something like this:
http://www.canford.co.uk/commerce/Pr...oductID=20-766

Or if you're handy with a soldering iron a 500pF capacitor between pin 2 & 1 and pin 3 & 1 in the plug end of the mic cable might kill the problem.

Thanks to everybody for the advice. Indeed some of the shoots are relatively close to major radio transmission towers (within a mile), although I have experienced the buzz fairly far away (2-3 miles) but still within "line-of-sight".

I'll try the fixes suggested. In addition the capacitor fix, I do also have some ferrite cores that clamp around cables that are supposed to suppress RF. Perhaps these would be the simplest and most versatile fix if they work. I'll report back on my findings.

Thanks again.

-Keith

I just had this problem on a shoot this weekend. I was shooting a movie short over on Maui in a suburban area of Kihei (small town) where I don't think there is much of anything that would be emitting strong RF. It did happen twice in the same neighborhood where we shot most of the scenes and hasn't happened before. Everything was running off of battery and we weren't near any fluorescent lights and I know my cell phone was turned off. The first time it happened, I shut the camera down and it went away when I restarted. The second time it happened I didn't catch it because we were doing some quick pickup shots in a car and I forgot the headphones. It came in at about -20db so I thought the levels were okay as we had a lot of car noise and the speech was coming in at about -10db. Fortunately, it isn't a problem but I know I'm going to listen better when you guys tell me things like I should always wear headphones.

The more I think about it, I'm wondering if our location not too far off the landing path of the Kahului airport might be a factor. The noise was very steady and lasted too long to be a passing airplane, but that is all I can think of that would be sending out RF. Any ideas? I'm hoping it's just a random problem and not a defect with my camera.

Airports + Communications = RF. As it has been mentioned, any communication transmissions can cause an RF problem. Airports have very sophisocated communication systems. You know; you should always wear those headsets...lol.