Question concerning the Internal Coiled Cables used in Boompoles:

[FantomPwr]

Hi Everyone - I'm a new member here, and I'm hoping that one of you can help me solve a problem I'm experiencing with my first boompole.  I do volunteer audio capture work for a local acting group in Ashland, MA that has recently begun creating short films.  Here is what I'm currently using for gear: a Zoom F8N Field Recorder, a pair of Sennheiser MKE 600 shotgun mics with Auray DUSM-1 shockmounts, an Auray BP-59A 9.5-ft boompole with internal coiled cable and side-exit XLR-M, Bose QC-25 noise-cancelling headphones, and several Kopul Series 5000 mic cables of various lengths.

 

Here's the problem.  When I have one of the mics atop the boompole (internal cable plugged in), a good mic cable connecting the boompole's side-exit XLR to a mic input of the recorder, and the recorder powered by its AC adapter, I get a nasty 120-hz hum about 30db below the dialog I'm trying to capture.  Other info: (1) If I touch the boompole, the hum increases; if I also touch the recorder, the hum decreases.  (2) If I unplug the AC adapter (i.e., run on the AA cells), the hum disappears.  Nice workaround, but the best lithium AA cells won't get me thru an 8-hour shoot.  (3) If I reconnect the adapter and bypass the boompole's internal cable, the hum disappears.  (4) I ordered and replaced the internal cable, but that had NO effect on the problem.  (5) Using the phantom power of the recorder or the AA cell inside the mic also has no effect.

 

So, I realize that Auray isn't considered a premium brand, but I am disappointed to discover that these coiled cables aren't properly shielded.  Are K-Tek's coiled cables likely to have this problem too?  Might the problem be solved if I just jumper pin 1 of the XLR to the body of the boompole?  

 

 

[Derek H]

I would try a different AC adapter first. I think that's most likely the problem is you have a cheap and noisy one. Unless you can solder trying to troubleshoot the cabling will be challenging. The only thing with the XLR (including inside the pole) cable you could check is if pin1 and the shell of the XLR are connected. Sometimes having it connected or not connected can make a difference for certain combinations of gear.

 

Another option.. get a big rechargeable battery to run the Zoom so you can avoid the AC adapter entirely. Professional sound mixers would choose rechargeable NP1 type batteries or Smart batteries like from Inspired Energy but you could probably come up with something cheaper from Anker or another quality battery brand. Like a big power block that has USB and 12V outputs. Just make sure it has a connector with the correct voltage for your Zoom. The pitfall there is some of those things are designed for phones and other smart tech and might put itself to "sleep" in certain scenarios.

[Rick Reineke]

You can check if the AC power supply is the problem by temporarily running the F8n on it's internal AA back-up batteries.
Does the inference occur in all locations?

[Paul F]

" If I touch the boompole, the hum increases;"  That suggests that the shield on the cable is not properly terminated or non-existent. 

 

120Hz - that will be the bridge rectifier in the AC adapter. Nothing you can do about that.

 

Going with batteries may solve the problem today, but there is an underlying problem that may turn up again since this suggests that the setup is vulnerable to interference of another kind. I suggest an inspection of the cable and it's terminations. Does the cable have a shield?

 

I think you should consider a battery solution regardless as you plan to do short films. So AC power does not seem practical in that case. Many of us with F8s use Sony NPF batteries and a battery plate.

[OB1]

I agree on the AC versus battery. Try both and see if the noise is still there. If not, I'm betting it's the cable for sure.

120hz is generally in the bridge area but other anomalies can also cause noise in this range.

[Tim Norris]

12 hours ago, FantomPwr said:

Are K-Tek's coiled cables likely to have this problem too?

 

Not all boom poles are created equal.

 

I recall experiencing intermittent electrical interference with my first internal coiled cable Vdb pole, and always at one particular spot on The Magnificent Mile in Chicago, above an electrical vault. In January 2000, covering the Iowa Caucus, I bought my first internal coiled cable K-Tek pole to replace the Vdb pole, mostly because it was much longer and candidate Bush didn't like to get close to the press. I first noticed a reduction in all handling noise as well as a reduction in wind noise, which I had attributed to the wind protection on my Schoeps mic.

 

You will likely be pleased with a top of the line K-tek pole.

 

Cheers,

Tim

[Patrick Farrell]

The fact that you can bypass the boom cable with an external XLR and the noise goes away is pretty telling. I'd get a multimeter and check the wiring of the internal cable, all pins in relation to the others as well as to the XLR shell. Then compare that to the wiring of your known good working cable and you should have your answer. (Definitely wouldn't advise jumping pin 1 to the boom pole as you suggest. The pole and consequently your hands should stay isolated from the audio path.)

[The Documentary Sound Guy]

Only thing that hasn't been mentioned is you could try plugging the AC adapter into a ground lift and wear rubber soled shoes while you are booming.

But a better boom cable and better battery system is what you really need.  The F8N should accept up to 15V in via the hirose plug, so power it via a proper external battery pack.  Ditch that AC connection ASAP, it's a hazard in more ways than one.