RF Choke rings. Do you use them? Do they work?

[roonsbane]

Hey all,

I have known guys that carry them with them on remotes, those small magnetic donut rings. I have never used them myself and am wondering how effective they really are. I want to eventually get a pair of 4006TL's and have used them enough to know that they can be succeptable to RF. Should I invest in some of these? Do you stick them on the output end of the cable? What kind of reduction in RF can I expect with them?

Cheers!

Cameron

[XLR2XLR]

I am also interested in this so bump.

[roonsbane]

Anyone------ Anyone-------Bueller-------Bueller-------bump!

[rufus13]

They do the job. Best used inside equipment that might get used professionally, because they are brittle. You can zip-tie them in place just inside an input connector. I've bought thousands of small cores at surplus for cheap (couple cents each by the pint or pound).

Cheers.

[Remoteness]

Originally Posted by rufus13

They do the job. Best used inside equipment that might get used professionally, because they are brittle. You can zip-tie them in place just inside an input connector. I've bought thousands of small cores at surplus for cheap (couple cents each by the pint or pound).

Cheers.

Yeah, you see these on a lot of OEM cables.

I concur, they do the job for sure.

I've also seen folks tie wrap them individually inline on the inside of an I/O panel.

If I had a chance to buy buckets of these for cheap I'd install them in a New York minute.

[David Rick]

I have a pair of large ferrite donuts that travel in my supply box. They are big enough to fit an XLR connector through. If I have RF trouble on site, I wrap several turns through them. I've also retrofitted the cables of certain gear that seems RF-sensitive by heat-shrinking a ferrite right next to the connector.

Not all ferrite is created equal. If you can find out the manufacturer's part number, you can often find performance curves on their web site. If you know what frequency range you're having trouble with, you can pick a part with high resistance in that band. If in doubt, go with ferrite material #31.

I highly recommend that you read AES convention paper #6564 by Jim Brown.

David L. Rick
Seventh String Recording

[absrec]

Originally Posted by David Rick

I have a pair of large ferrite donuts that travel in my supply box. They are big enough to fit an XLR connector through. If I have RF trouble on site, I wrap several turns through them. I've also retrofitted the cables of certain gear that seems RF-sensitive by heat-shrinking a ferrite right next to the connector.

Not all ferrite is created equal. If you can find out the manufacturer's part number, you can often find performance curves on their web site. If you know what frequency range you're having trouble with, you can pick a part with high resistance in that band. If in doubt, go with ferrite material #31.

I highly recommend that you read AES convention paper #6564 by Jim Brown.

David L. Rick
Seventh String Recording

Where do we buy them?

-Aaron

[David Rick]

The low-frequency and broadband #31 material that Jim Brown likes is made by Fair-Rite, and their stuff is rather hard to get.

Fair-Rite

A typical part for heatshrinking on mic cables (0.388" ID) would be Fair-Rite part number 2631626402. The snap-on version of this is part number 0431167281.

I know of one distributor that will sell Fair-Rite parts in small volume:

Amidon Inductive Components

Unless your RFI problem is caused by AM radio, you probably don't need #31 material, and you'll have an easier time fixing the problem. Ferrite cores from Steward are widely available. For example, you can order them from Digi-Key.

BTW, if you don't want to pay for a copy of Jim Brown's AES paper, check out this on-line paper by Brown that has much of the same information.

Understanding How Ferrites Can Prevent and Eliminate RF Interference to Audio Systems

David L. Rick
Seventh String Recording

[Remoteness]

David,

Thanks so much for the information and links you provided.

[XLR2XLR]

yes thanks just got back to the post !

[David Rick]

Originally Posted by Remoteness

David,

Thanks so much for the information and links you provided.

Happy to be of help, Steve. This thread should be done, but I must tell you that I just spent the whole day working in a $200/hr facility. The session started at 8:00 AM, and I had to pay for it in advance. The control room was very noisy, and the main room, although impervious to radio signals, was not only dark, but very nearly anechoic! It had the biggest turntable you've ever seen. While the house engineer took me to lunch, the second engineer tried to break my gear. Can you guess where I was?









I was at a radio frequency test facility!

The test room was a steel box, about 18' x 30' x 12', and was semi-anechoic between 80 MHz and 1 GHz because the entire inside was covered with ferrite tiles! I was there to look for Electromagnetic Susceptibility problems in a piece of equipment I'm working on. It turned out there was a serious problem around 100 MHz. Fortunately, they had a big kiosk full of different ferrites, mostly Steward #28 material. It took me eight hours of experimentation, two ferrites, and a surface-mount capacitor, but in the end I improved the problem by 30 dB. Now you know how I can afford all those nice mics in the picture.

David L. Rick
Hach Company (the day job)
Seventh String Recording (sleepless nights)

[Remoteness]

Awesome!