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[Kelvin Gryder]

A few years ago we picked up radio interference on a faulty piano pickup. It was a good excuse to get a good set of mic's for the piano.

[Frank DeWitt]

I just tripped over some info on this.
http://www.audiosystemsgroup.com/SAC0305Ferrites.pdf
http://www.audiosystemsgroup.com/AES-RFI-SF08.pdf

And the list
http://www.audiosystemsgroup.com/publish.htm

[Frank DeWitt]

A few years ago we picked up radio interference on a faulty piano pickup. It was a good excuse to get a good set of mic's for the piano.

I did some reading of the above and of http://www.audiosystemsgroup.com/AESPaperFerritesASGWeb.pdf

I found some bad news and some good news.  Foil shield with a drain is not good for RFI problems Nothing can be done about that now. It takes a lot of turns around the Ferrite to be effective for AM frequencies,  He found 14 turns to be best.

The good news?  A short distance between the Ferrite and the mixer is important but it is less important at AM frequencies.   It might be easier to make up a bunch of short cables with XLR, 14 turns around a Ferrite, XLR at your bench and then plug them in on location.

My other thought is that as a stop gap before Christmas you could borrow your X32.  Connect it at the platform.  Shorter cables, equal poor antennas, an mix with a remote. 

Another work around would be to place a multi channel preamp on the platform and send line level signals down the snake to the line inputs of the EV mixer.

Those are just temporary patches. Your Ferrites on each line are permanent and clearly better.

[Matthew Donadio]

... They are using the wiring installed by a reputable church sound contractor for the original congregation about 5 years ago. It is comprised of 30 some runs of good quality 22ga twisted pair with foil shield and drain wire plenum cable running through the basement ceiling of the wood framed church. The wiring is all properly terminated, good quality steel floorboxes, Switchcraft connectors, heat shrink over the shields, no connection of pin one to connector housings, good workmanship evident throughout. ...

FWIW, I had a problem with an AM radio station getting into my condensor mics a few years ago.  I tried ferrites, but those didn't fix the problem.  Following Klaus Heyne's advice from http://repforums.prosoundweb.com/index.php/topic,1152.0.html did the trick, part of which is ensuring that pin 1 is connected to ground and that the connector shell and mic housing make contact.

[Frank DeWitt]

FWIW, I had a problem with an AM radio station getting into my condensor mics a few years ago.  I tried ferrites, but those didn't fix the problem.  Following Klaus Heyne's advice from http://repforums.prosoundweb.com/index.php/topic,1152.0.html did the trick, part of which is ensuring that pin 1 is connected to ground and that the connector shell and mic housing make contact.

If you do this, make sure that the shells in patch panels and floor pockets are not mounted in conductive panels.  Other wise you have ground loops. You also need to be carefully that connectors laying on the floor don't touch one another.

[Bob L. Wilson]

I did some reading of the above and of http://www.audiosystemsgroup.com/AESPaperFerritesASGWeb.pdf

I found some bad news and some good news.  Foil shield with a drain is not good for RFI problems Nothing can be done about that now. It takes a lot of turns around the Ferrite to be effective for AM frequencies,  He found 14 turns to be best.

The good news?  A short distance between the Ferrite and the mixer is important but it is less important at AM frequencies.   It might be easier to make up a bunch of short cables with XLR, 14 turns around a Ferrite, XLR at your bench and then plug them in on location.

My other thought is that as a stop gap before Christmas you could borrow your X32.  Connect it at the platform.  Shorter cables, equal poor antennas, an mix with a remote. 

Another work around would be to place a multi channel preamp on the platform and send line level signals down the snake to the line inputs of the EV mixer.

Those are just temporary patches. Your Ferrites on each line are permanent and clearly better.

My research uncovered that as one would expect four factors are important in the performance of a ferrite. Material, geometry, installation, and placement with the first two being of preeminent importance. I chose toroids made of Laird Low Frequency material that are 1.5" long and only have a .5" ID which means I will need to remove every XLR connector to install them. It also means they achieve over 2600 ohms at my 1.2mHz target with only five wraps and as a bonus nobody else can take them off once installed. I will try to get some before and after photos of the meters on the board to show reduction in interference.

[Thomas Lamb]

My research uncovered that as one would expect four factors are important in the performance of a ferrite. Material, geometry, installation, and placement with the first two being of preeminent importance. I chose toroids made of Laird Low Frequency material that are 1.5" long and only have a .5" ID which means I will need to remove every XLR connector to install them. It also means they achieve over 2600 ohms at my 1.2mHz target with only five wraps and as a bonus nobody else can take them off once installed. I will try to get some before and after photos of the meters on the board to show reduction in interference.

As you say "as a bonus nobody can take them off" which may be what you want however, out of convenience I have seen them as a "multi piece" unit too that can be installed no matter what the connector. I wonder if the fact that they are not 1 piece effects their effectiveness. They Shirley would be more convenient.

[Bob L. Wilson]

Before and after of the same channel with and without ferrite.

[Bob L. Wilson]

After

[Mark McFarlane]

After

So does it sound as good as it looks?

[ProSoundWeb Community]