October 27, 2014 at 8:47PM

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Audio hum when using an external monitor

I'm getting a constant "hum" in my audio when recording sound into the BMPCC with an external monitor attached. Up until now, I've been able to get clean audio out of the BMPCC using the Rode NTG-2 into the JuicedLink RM202 into the camera. I just recently added a SmallHD DP4 to this setup, however as soon as I turn on the monitor, I get a hum. Interestingly, the hum gets slightly softer when I touch the preamp or the camera body.

So far, I've tried the following to resolve the problem:
- Replaced the cable from the preamp to the camera
- Replaced the HDMI cable from the monitor to the camera
- Tried using a different monitor
- Tried using the DP4 running off batteries / plugged into the wall
- Tried both "Line" and "Mic" settings in the camera
- Tried using a Rode VideoMic

Using the VideoMic made the hum go away, however I would like to make this setup work with the preamp and understand what the problem is. Perhaps this is caused by some type of grounding or signal issue?

4 Comments

Some times the problem is the blackmagic camera cinema. The important thing is use a preamp like a zoom h4n. Is a recorder too and now cheap.

October 28, 2014 at 10:00AM

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Ragüel Cremades
Film producer and director
7599

Here's a link to the JuicedLink Riggy manual...
http://www.juicedlink.com/pages/riggy-micro-user-manual

Check out the section titled "Mounting, Grounding, Ground Loops, and the ENC GND Switch", which talks about using the "ground lift" switch on the JuicedLink preamp to eliminate hum or buzz.

October 28, 2014 at 4:54PM, Edited October 28, 4:54PM

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Guy McLoughlin
Video Producer
30803

usually comes from bad cables or contacts. meaning cheap aluminum or steel. you will notice the better cables will have gold plated connections, and also the cables them self at the minimum tripple threaded copper.
Best is silver cable with gold (cost performance wise) at about 60~90 a foot. Mogami also does platinum cables that are kind of way too.
expensive, but they are cleaner sounds.

my recommendation for cables are
Mogami
Canare
Horizon's Silver line

October 30, 2014 at 10:00AM

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Kazu Okuda
Filmmaker
1328

Sounds like a grounding issue IMHO.

November 25, 2014 at 3:59PM

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AARON T
LEAD DESIGN/AUDIO ENGINEER
86

I have had this issue, but it has turned out to be mains-induced noise from poorly shielded cables. The human body picks up mains hum: if you wrap your hand around the audio cable and you get an audible increase in hum then this is the issue.
I have found that changing to a much better shielded cable makes all the difference in this situation. I have also found that having headphones plugged in to an output on a camera will not give audible noise (directly) in the headphones as the mains-induced noise is too low a level, but this low level noise signal is carried back into the camera and for whatever reason makes it onto the low level input signal where it is significant. So I now have the habit of checking the audio levels with the headphones, looking on the level meters then unplugging the headset and monitoring only on the level meters (which seems to work fine for me).

May 15, 2015 at 9:14AM

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Thomas Dove
DoP
119

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