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Ferrite bead for EMI/RFI screening?
Old 10th January 2010
  #1
Ferrite bead for EMI/RFI screening?

Hello,
I'm looking for ways to be prepared in advance for RFI/EMI problems when doing classical music location recordings. I've heard that the new Neutrik EMC screened XLR connectors where good, but they were around 4 times as costly so I opted out since I haven't had any problems so far with other equipment.

However, I'd like to be prepared when the day comes. What do you think of something like this? Would it work to clip onto a standard mic cable?
The cables I have are either 10,2 mm diameter or 6.5 mm.

Thanks, people!
Old 11th January 2010 | Show parent
  #3
Very good, thanks.

However, I lack the technical knowledge in these matters to decipher which products would be suitable for me. The clasp/bead construction seems useful since it would be rather more visually appealing than the loose ferrite core.

What specs do I need to look out for? What impedance is required to block out common sources of interference?

Thanks for your time.
Old 11th January 2010 | Show parent
  #4
Lives for gear
 

Jensen has a DIY RFI insolation box:

http://www.jensen-transformers.com/as/as073.pdf

they sell the beads too
Old 11th January 2010 | Show parent
  #5
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Hi
It would be good to be really technical and do loads of calculations but I expect you have a pile of different gear and will be using a range of mics so unless you are really going to work out all the details, which will change from 'gig' to 'gig', you won't get any recording done.
I would suggest buying a number of the clamp on ferrites you showed from ELFA and keep them in your 'toolkit', fitting as many as you need when the time comes.
They should be able to be properly clamped (snap shut) around your cable although it does not need to be 'tight' onto the cable itself.
These are quite cheap and you should get a decent collection if you are really worried.
You could also invest in 2 or 3 of the 'inline' filters which ought to be a bit more effective for the really troublesome situations.
Good luck
Matt S
Old 11th January 2010 | Show parent
  #6
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Another thing to remember is if the opening is large enough for two passes of cables you'll get more attenuation by making a loop and clamp around the two
cables.

Remember also that it may be more effective at one end or the other. It's not always easy to determine which piece of gear is being affected by the RF.
Old 11th January 2010 | Show parent
  #7
I'm very thankful that you took yourselves the time to answer my questions. I will purchase some of the beads and keep them ready.

Thanks to all contributors!
Old 11th January 2010 | Show parent
  #8
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Quote:
I lack the technical knowledge in these matters to decipher which products would be suitable for me.
Johannes -

The pdf document I linked to contains a picture of what you want to build and I gave you a link to Mouser Electronics with the specific part you want. Take some mic cable and wrap it around a toroid as in the picture. If you are not skilled at making mic cables, perhaps you know someone who is?
Old 11th January 2010 | Show parent
  #9
Thanks Chris,
I saw the toroid drossel construction and while it seems effetive it's both permanent and a bit visually disturbing. I have put some toroids on order with the beads as well, though.

Great help!
Old 11th January 2010 | Show parent
  #10
Lives for gear
 

Hi
The items from ELFA in Sweden just clip on so you don't need to solder at all.
You cold then chose to leave them on some of the cables but if not they can be carefully opened and removed. The plastic clips will fail eventually but you always have your 'Gaffer tape'.
Matt S
Old 11th January 2010 | Show parent
  #11
Quote:
Originally Posted by Matt Syson View Post
Hi
The items from ELFA in Sweden just clip on so you don't need to solder at all.
You cold then chose to leave them on some of the cables but if not they can be carefully opened and removed. The plastic clips will fail eventually but you always have your 'Gaffer tape'.
Matt S
Yes, that was my understanding and past experience. I've used this kind of peripheral before but I've never had to select what specs it should meet and order one - that's why I posted here and you've been very helpful!

(For the record, while I'm no wizard of the arcane soldering iron, I'm not a complete newbie either when it comes to cables. )
Old 11th January 2010 | Show parent
  #12
Lives for gear
 

Hi
I presume you don't want to be getting your iron out while the concert waits?
Make it easy!
Matt S
Old 11th January 2010 | Show parent
  #13
Quote:
Originally Posted by Matt Syson View Post
Hi
I presume you don't want to be getting your iron out while the concert waits?
Make it easy!
Matt S
You SO get me
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