RF issues at live venue – attenuators?

[DCtoDaylight]

Has anyone had experience with the RF suppression products that Shure and Neutrik make to go on mic cables? Shure has a little in-line attenuator, and Neutrik makes special XLR connectors that supposedly do the same thing:

Shure

Neutrik

An orchestra I record will be playing all their concerts this year at a church sanctuary that has nice acoustics but a nasty RF problem. On the two occasions I’ve recorded there I’ve picked up a good bit of radio on my recordings (I’m pretty sure it’s AM – music and news/talk). My portable setup (MacBook Pro, Metric Halo ULN-2, Redco cables with Canare Starquad, two high-end Toa SDCs) has had no RF issues anywhere else, but this church is located right near the building that has most of the TV and radio broadcast antennas for our city.

I’ve tried swapping and rearranging cables, and also completely disconnecting my recording setup from wall power. In the heat of the moment I didn’t have time for anything more extensive.

I’m going into the space on a non-performance day to do some experimenting. I figured I’d try swapping out mics, cables, and my interface with alternatives to see if any of those are the problem, but it would be great if all I needed was an add-in attenuator or new cable with the Neutrik connectors – advice is most welcome!

[PDC]

Originally Posted by DCtoDaylight

Has anyone had experience with the RF suppression products that Shure and Neutrik make to go on mic cables? Shure has a little in-line attenuator, and Neutrik makes special XLR connectors that supposedly do the same thing:

Shure

Neutrik

An orchestra I record will be playing all their concerts this year at a church sanctuary that has nice acoustics but a nasty RF problem. On the two occasions I’ve recorded there I’ve picked up a good bit of radio on my recordings (I’m pretty sure it’s AM – music and news/talk). My portable setup (MacBook Pro, Metric Halo ULN-2, Redco cables with Canare Starquad, two high-end Toa SDCs) has had no RF issues anywhere else, but this church is located right near the building that has most of the TV and radio broadcast antennas for our city.

I’ve tried swapping and rearranging cables, and also completely disconnecting my recording setup from wall power. In the heat of the moment I didn’t have time for anything more extensive.

I’m going into the space on a non-performance day to do some experimenting. I figured I’d try swapping out mics, cables, and my interface with alternatives to see if any of those are the problem, but it would be great if all I needed was an add-in attenuator or new cable with the Neutrik connectors – advice is most welcome!

RF can come in through any cable. I would put RF chokes on everything and then run on a battery power supply.

[John Willett]

I am changing over to the Neutrik EMC connectors as standard now as and when I change cables.

But I use the Canford Audio RF in-line XLR RF Filter and always have some in the kit.

[Remoteness]

I purchased a bunch of the Neutrik EMC connectors.
I'll let you folks know how they worked out once we build and test a few of them.
We're starting on the 100' lengths first.
We're also going to build a few XLR EMC barrels for our kits.
Marketek builds them with standard Neutrik EMC connector.
We're going to do the same.

[mixedupsteve]

They make a panel mount EMC also for racks.

[DCtoDaylight]

Originally Posted by John Willett

I am changing over to the Neutrik EMC connectors as standard now as and when I change cables.

But I use the Canford Audio RF in-line XLR RF Filter and always have some in the kit.

Hi, John, and thanks so much for the input - it sounds like these Canford devices have successfully solved RF problems in the field, or else you wouldn't carry them around, right?

Assuming this is the case, I'd order a couple of the Canfords today, except that it's an international sale for me here in the US; the Shure versions are much more readily available. Is there any reason to think that the Canfords would be way better and thus worth the extra hassle?

[DCtoDaylight]

Originally Posted by Remoteness

I purchased a bunch of the Neutrik EMC connectors.
I'll let you folks know how they worked out once we build and test a few of them.
We're starting on the 100' lengths first.
We're also going to build a few XLR EMC barrels for our kits.
Marketek builds them with standard Neutrik EMC connector.
We're going to do the same.

This will be interesting info! I want to get a 2-channel snake (more of a worm, really) for my flown stereo pair, and that would seem like a pretty ideal application for these guys.

And that's a clever idea, to make barrels out of them.

[Remoteness]

Originally Posted by mixedupsteve

They make a panel mount EMC also for racks.

Sweet!
I should look into those when we're ready to deal with the wiring for the Cosmo build out project.

Originally Posted by DCtoDaylight

This will be interesting info! I want to get a 2-channel snake (more of a worm, really) for my flown stereo pair, and that would seem like a pretty ideal application for these guys.

And that's a clever idea, to make barrels out of them.

Worm - I love that description for stereo pair snake!
LOL

Yeah, making your own barrels would be a lot cheaper than buying them off the shelf.

[chris319]

That RF could be coming in anywhere. The fact that you've disconnected your system from AC power tells us something. Did you have your Metric Halo running off Firewire power from your Macbook? All you can do is keep disconnecting things until you isolate the source of the RFI (quite likely your mic lines). With RF, so many times the solution is arrived at simply by trial and error.

Here is a document showing how to build RF filters out of ferrite toroids:

http://www.audiosystemsgroup.com/SAC0305Ferrites.pdf

Mouser carries an assortment of FairRite toroids. You could build a box with XLR ins and outs and a heap of toroids inside.

[DCtoDaylight]

Originally Posted by chris319

That RF could be coming in anywhere. The fact that you've disconnected your system from AC power tells us something. Did you have your Metric Halo running off Firewire power from your Macbook? All you can do is keep disconnecting things until you isolate the source of the RFI (quite likely your mic lines). With RF, so many times the solution is arrived at simply by trial and error.

Here is a document showing how to build RF filters out of ferrite toroids:

http://www.audiosystemsgroup.com/SAC0305Ferrites.pdf

Mouser carries an assortment of FairRite toroids. You could build a box with XLR ins and outs and a heap of toroids inside.

Hey, thanks for the thoughts, Chris! And yeah, that's exactly how I tried powering things - off the MacBook battery. Didn't make any difference from wall power, alas.

What I figured I'd do during my experimentation time is just what you say - try swapping things in and out. I guess my big fear is that this place is swimming in enough RF energy that none of my stuff will work, hence the question about the attenuators.

Thanks very much for the link to the paper on toroids! That does seem like it would be an industrial strength solution, and may be what I have to fall back to....if nothing else, a box like you describe would be handy to have in the bag.

Once again, I'm incredibly impressed with the knowledge here.....

[chris319]

What I figured I'd do during my experimentation time is just what you say - try swapping things in and out.

NO! You don't want to do that! You must work systematically! Work from the Macbook out. Make a recording with the Macbook on batteries, then plug it into the wall, then add the interface, then plug a dynamic mic directly into the interface, then a condenser, then add a short length of mic cable, then a long cable until you find out where the interference comes in.

I suspect you can rule out the AC even if the Macbook is plugged in because I believe the Macbook battery will filter out any RF that might come in through the wall. I also suspect you can rule out the Firewire link as it is digital.

[DCtoDaylight]

Originally Posted by chris319

Work from the Macbook out. Make a recording with the Macbook on batteries, then plug it into the wall, then add the interface, then plug a dynamic mic directly into the interface, then a condenser, then add a short length of mic cable, then a long cable until you find out where the interference comes in.

I hear what you're saying - start with a clean slate and work outward. I'll experiment ahead of time to see if any of my mics will plug directly into the interface; I've never tried that!

Thanks again for the input - and I'll post a report on how this all evolves.

[chris319]

If none of your mics will plug directly in, just use as short a mic cable as you have. If the problem enters at that stage you'll know it.

Do you own an ohm meter and have you used it to make darn sure all of your cables are properly wired and balanced?

[DCtoDaylight]

Originally Posted by chris319

If none of your mics will plug directly in, just use as short a mic cable as you have. If the problem enters at that stage you'll know it.

Do you own an ohm meter and have you used it to make darn sure all of your cables are properly wired and balanced?

Actually, I realized I could use an XLR-to-quarter-inch adapter and plug in a mic *almost* directly that way.

I do have a good multimeter; I'd tested all my cables before the last recording with a cable tester and they came through fine even with jiggling and all, but I suppose it can't hurt to check them again and make sure they're operating at spec in terms of resistance.

The thing is that I go from having no problem in either channel in other locations to problems in *both* channels at this location, even with different mic cables; it seems unlikely that four cables would all have the same problem, but not impossible. And, as you wisely said, the watchword here is "systematic."

Thanks again for lending your brain to this - I'd really like to beat this RF down!

[chris319]

What do you have, four mic cables going into an interface or mixer of some sort? Any or all of those mic cables could be acting as an antenna. It only takes one, and your interface/mixer could be detecting the RF signal.

[DCtoDaylight]

Just wanted to close the loop on this thread - I got to spend some time experimenting at the venue today, and determined that the RF is getting in through the electronics module of one mic.

I also learned, thanks to Chris319, something about toroidal ferrites, which seem really worth keeping in one's bag! I had gone in expecting to use them as chokes on the main mic cables to see if that would help, but they came into play upstream, instead.

These particular mics have their capsules in a separate module from the electronics; the capsule has a short cable attached to it that plugs into the electronics. Both capsules worked fine with one set of electronics and had RF issues with the other, so the second electronics module is the culprit. (I also swapped out mic cables and channels on the interface and tried an RF choke on the mic cable en route to the diagnosis)

The interesting part is that if I wrapped a turn or two of the short capsule cable around the ferrite "donut" to make a choke, it completely eliminated the RF problem, just as the paper that Mr. 319 linked to above described. It was incredibly satisfying - I swapped it in and out a few times just to hear the talk radio voice be eliminated.

My guess is that there's a defective shield or ground connection on or near the jack in the electronics module. And since I don't have time to get the mic worked on before the next recording I'm doing, I think I'll make use of the ferrite on the night as an interim measure (with backup mics on hand, of course).

So - thanks once again to the Gearslutz community, especially Chris319. And for $7, I'd say the Fair-Rite 2631803802 is a heck of deal:

2631803802 Fair-Rite EMI/RFI Suppressors & Ferrites

[Audiop]

Originally Posted by DCtoDaylight

My guess is that there's a defective shield or ground connection on or near the jack in the electronics module.

And/or poor input filtering of the circuit (possibly none at all).


/Peter

[DCtoDaylight]

Originally Posted by Audiop

And/or poor input filtering of the circuit (possibly none at all).


/Peter

Hmm - that sounds like it would be a design issue, right? In that case, wouldn't both electronics modules exhibit the problem?

[leddy]

I had some older Avenson STO's that were very susceptable to RF. The newer ones are not. Brad can also mod the older ones I believe.

I was going to suggest that it might be a mic and not the cables but you found that out before I read this thread.

[chris319]

Well how do you like that? Congratulations on so cleverly tracking down the problem, but who would've suspected that would be the source? And only one or two turns fixed it! Can you tell us what kind of mic it was?

A common problem I'm finding with your typical soda-can-with-screen mics is that there is no electrical bonding between ground and the body and the wire mesh, and all are coated with non-conductive paint. I recently recorded a string section with a Heil PR40 which was 2 -3 feet away from a fluorescent light and I got a major buzz. I brought it home, hooked it up and held it up to a light dimmer. It picked up buzz from the dimmer, but if you put your ear up to the dimmer it was totally silent, ergo, the buzz was not acoustical at all but was being picked up by the mic inductively. The only thing you can do is modify the mic by scraping away some of the non-conductive paint and soldering a wire to points on the screen and the body.

[DCtoDaylight]

Originally Posted by chris319

Well how do you like that? Congratulations on so cleverly tracking down the problem, but who would've suspected that would be the source? And only one or two turns fixed it! Can you tell us what kind of mic it was?

Hey, you were the one emphasizing a methodical approach! I hope I would have gotten there anyway, but it was good to have nudge towards planning - I wrote up a whole list before going in.

The mics are a long-discontinued model, the Toa KY. Toa had a short run in the high-end mic world in the late '80s or early '90s; when they bailed you could get these mics for $125 each, when the original list was over $700. They're very nice SDCs - gold plated diaphragm, accurate but not clinical, and at home in a very wide variety of situations. Best gear deal I've ever gotten.

[toddboyle]

The Fair-Rite website says the part. 2631803802 seems to be a HUGE chunk of metal, 2.4 inches outer diameter, 1.4 inch inner and 1/2 inch long. I was thinking of getting one for a lapel mic. that has RF problems, until I saw the size!!! can you confirm? thx.

[chris319]

There are many sizes of 31 material toroids available. Just click on the "31 material" tab in the Fair-Rite catalog.

[DCtoDaylight]

Yep, the ferrites I got are kind of big - the idea is that you can use them on a regular mic cable, passing the connectors through the hole in the middle. But as Chris notes, Fair-Rite has a wide selection. You have to spend a few minutes with the data sheet to figure out the various dimensions, but odds are they have something that'll work. Of course, you then have to find someone who'll sell them to you in a reasonable quantity, but Mouser is a very good place to start.

Good luck!

[chris319]

It helps to wind a choke, i.e. several turns of mic cable through the toroid.

[tourtelot]

The Neutrik connectors work very well, under extreme conditions. My Sanken shotguns were terribly susceptible to the strong RF from wireless video transmitters mounted on the film cameras on my last TV show. The Neutrik connectors at the mic end only (!) made the strong RF field invisible to the recorder. I can't recommend them enough. A little tricky to install but not too bad.

D.

[chris319]

Both Neutrik and Switchcraft make XLR connectors with ferrite in them. Probably not as effective as a toroid but better than nothing:

Neutrik, Connectors, XLR, Speakon, Audio

Switchcraft

[JonesH]

I recently ordered some multicable and was weighing long on whether to buy ECM Neutrik XLRs or not. In the end I chose not to, since they were very much more expensive and I haven't had bad experiences before, but I am definitely interested in getting some clip-on toroids if those can help. has anyone found a reliable (preferrably european) source that fits on mic cables?

[DannyL]

I have a few mics (UMT70, UMT800) that are susceptible to RFI.

Following GPrime's suggestion I used Gotham audio 3 conductor w/ shield cable, and created a "drain" On the Female connector (switchcraft worked best) I connected the case to the green wire, pins 2/3 as normal and the shield to pin 1. On the other end I connected pins 2/3 as normal and tied the green wire and the shield together at pin 1. I have to use these cables to connect any M7 capsule phantom mics, even if I need to extend the xlrs with another piece of cable. This proves to be an effective RFI supressor.

On my MV692's (they are A/B powered with separate supplies from the 60's) I needed to modify the connectors so that I have a small (10pf) capacitor connecting the signal wires to earth, with ferrite beads before the the caps. All this is done inside the teuchel connectors. This is fairly effective though I still have problems occasionally.

Danny

[MichaelPatrick]

advice?

use transformers