Topic: picking up radio station with CA mics???

[SBW]

Has anyone ever had a problem with the wires on the CA-14 mics acting as antennas and picking up a radio station?  Unless I have the wires totally bundled up, I can distinctly hear a radio station in the background. 

I'd like to try recording w/ the omnis but I have to spread the wires out to to get stereo and the radio station shows up.  Is there any kind of shielding I can use???

Any suggestions welcome

SW

[jagraham]

Were you using mics directly into recorder or a pre/battery box?  This came up sometime recently in a thread.

[John Willett]

This is something that can happen with unbalanced microphones, especially if the unbalanced cable is long and especially in areas with a strong RF signal.

This is why professional microphones are balanced.

[LikeASong]

I would like to hear a sample, if possible

[SBW]

I had the mics plugged into the CA 9100 preamp.  I can't change the mic wires because they're permanently connected to the mics. 

This sounds crazy but if I plug in some grado labs SR60 headphones directly into the output of the preamp, crank up the gain, it sounds like I have a walkman.  However, if I wrap the microphone wires around the preamp itself, then the radio station goes quiet.

[ilduclo]

google is your friend here, there's a lot of discussions out there on the subject. I used to pick up a neighbors HAM signal over my speaker wires, when I upgraded to heavier more shielded wires it went away...

[DigiGal]

The FCC requires radio stations to perform a station identification every hour, which will help you identify the station and thus its frequency.  Additionally there are still low power analog television transmitters in operation and again they are required to perform a station identification.  HAM operators could be tougher to identify.

Balanced mics/cables perferably StarQuad with Neutrik EMC XLR connectors would do wonders to eliminate it.

[SBW]

I don't know if you've ever seen CA mics but I think the wires are soldered straight on to the mics and the cable is tiny - like 20 guage or so.  Would these cables be balanced or unbalanced?  I have no idea.

[adrianf74]

I don't know if you've ever seen CA mics but I think the wires are soldered straight on to the mics and the cable is tiny - like 20 guage or so.  Would these cables be balanced or unbalanced?  I have no idea.

1/8" connectors are unbalanced... at least in the case of any of these small mics.   The only way to try and avoid this is to run three-wire mics (such as a mini-XLR terminatre pair of AT853's) or to not use a preamp and stick with a battery box.

[LikeASong]

I don't know if you've ever seen CA mics but I think the wires are soldered straight on to the mics and the cable is tiny - like 20 guage or so.  Would these cables be balanced or unbalanced?  I have no idea.

1/8" connectors are unbalanced... at least in the case of any of these small mics.   The only way to try and avoid this is to run three-wire mics (such as a mini-XLR terminatre pair of AT853's) or to not use a preamp and stick with a battery box.

Why would using a BB instead of a preamp solve the problem? I have no real opinion towards or against that - just curiosity

[adrianf74]

Why would using a BB instead of a preamp solve the problem? I have no real opinion towards or against that - just curiosity

I say this because I'm basing it on a similar issue some people have had with cellphone interference being picked up during recordings on a preamp.  I believe it has to do with a battery box providing a fixed voltage and as soon as a preamp (with variable voltages being introduced) is involved, these secondary problems can creep up when using unbalanced gear.

I've had cellphone hits on various preamps using 1/8" connections and *NEVER* had an issue when using the battery box.

[LikeASong]

Why would using a BB instead of a preamp solve the problem? I have no real opinion towards or against that - just curiosity

I say this because I'm basing it on a similar issue some people have had with cellphone interference being picked up during recordings on a preamp.  I believe it has to do with a battery box providing a fixed voltage and as soon as a preamp (with variable voltages being introduced) is involved, these secondary problems can creep up when using unbalanced gear.

I've had cellphone hits on various preamps using 1/8" connections and *NEVER* had an issue when using the battery box.

Aha, I understand you. There must be some serious Physics explanations behind this issue but I'm a chemist

[absnj]

Why would using a BB instead of a preamp solve the problem? I have no real opinion towards or against that - just curiosity

I say this because I'm basing it on a similar issue some people have had with cellphone interference being picked up during recordings on a preamp.  I believe it has to do with a battery box providing a fixed voltage and as soon as a preamp (with variable voltages being introduced) is involved, these secondary problems can creep up when using unbalanced gear.

I've had cellphone hits on various preamps using 1/8" connections and *NEVER* had an issue when using the battery box.

Aha, I understand you. There must be some serious Physics explanations behind this issue but I'm a chemist

So could an alchemist change unshielded cables into shielded without having to re-wire the mics?

[capnhook]

Yep.

The alchemist in me sez you should use lead pipe. 

[SBW]

Sweet, I will try the ferrite bead trick and see if it works.  Also, what exactly is the difference between the CA9100 and a battery box?  Also, do you know where to buy them? 

Thanks

[SBW]

Oops, I meant where's the best place to buy battery boxes or do you just literally hook up a battery to the wires and stick it in a box?

[SBW]

Success!! I found a snap-on ferrite ring from an old 28.8 modem I had.  I wrapped the pair of cables around it a couple times and the radio station is gone!!

Thanks for all your help

SW

[LikeASong]

Congrats.

And a big to Jon     

[Chuck]

Are there any negatives to using the ferrite bead?
That's a nifty trick I didn't know about.

[Fatah Ruark (aka MIKE B)]

Are there any negatives to using the ferrite bead?
That's a nifty trick I didn't know about.

That is pretty cool.

Anyone know if that would help reduce cell phone noise? I've had that happen a couple of times in tight quarters.

[DigiGal]

Neutrik's EMC connectors integrate a ferrite bead as part of their design.

Link to Neutrik EMC Series XLR Connectors

[Chuck]

DG, have you made your own cables with those? The assembly instructions are intricate!

[DigiGal]

DG, have you made your own cables with those? The assembly instructions are intricate!

Yes, I installed the EMC connectors on my Gotham GAC 4 low capacitance star quad cables.  They are easy to work with, I wouldn't recommend attempting to chop them though if that's in mind.

[it-goes-to-eleven]

Ferrite beads are available in countless different sizes and configurations.   Some devices incorporate them, and other RF control features, into their design.

They can interact with a/c signals, creating an impedance load.  They can be modeled in Spice.

There is no freelunch

[it-goes-to-eleven]

And I'm wondering how a ferrite gives a DVD "deeper colors" . . . that's a real puzzle as I did not know that ferrite could change an optical storage medium's data and even understand its encoding algorithm!

Jon, you must- must! - offer these magic beads on your products.  You'll clean up, pun not intended.  It'll be the biggest thing since output transformers...

[stepeanut]

I recorded Beth Orton on Wednesday night, at the Brudenell Social Club in Leeds, UK.  Sadly, my recording is plagued by interference.

I was running my usual rig: AT853s (terminated to a single mini-jack by Darktrain) > CA Ugly II (set at +15 dB) > M10.  Since I began running the Ugly II, I have experienced the odd, low-level burst of interference.  I've only ever heard it on recordings of quiet, acoustic gigs, and usually only between songs.  It doesn't happen much -- at some gigs not at all -- and so far I've been able to live with it.

My Beth Orton recording is a different story.  The interference can be heard multiple times throughout the set, and for sustained periods of up to ten seconds at a time.  Initially, I put it down to cell phone interference, but it has just struck me that there is a minicab firm located next door to the venue.  Could it be that their radios caused this unusually severe interference, rather than cell phones?

[adrianf74]

Would love to hear samples of what you're referring to but I'm willing to bet the minicab firm is the source of the interference -- any of their "calls" would have to be strong enough to get around the service area so I could see this as being the case.

[stepeanut]

I'm heading into town right now, on another taping mission, but I'll see about posting a sample tomorrow.

[yates7592]

I only ever had mobile phone interference issues using a CA Ugly preamp (version 1) with my B3's terminated with a miniplug. When I stopped using the ugly and just used a (CA) battery box the problem went away.  Don't know if it's the mics or the preamp or a bit of both......in fact I tested with my mobile ringing right next to the mics/recorder at home and this confirmed that the preamp was the "culprit" - the BB gave no interference at about 1 inch from the mobile, but the pre gave big interference - however I do believe that if mics are properly shielded then the problem also goes away.....

[kleiner Rainer]

Hi stepeanut,

I had a hum/buzz/RFI problem with my M10 - Rode Stereo Videomic combo and a 5m cable while recording near 15kV AC railroad catenaries. During nightfall, I had shortwave reception. Replacing the interconnect with a homebrew cable with thick copper braid (not foil shield with drain wire!) and Neutrik connectors at both ends cured the problem once and for all. The fault was a rather high shield resistance so that the disturbance current flowing on the cable shield generated a voltage drop that was added to the microphone signal (remember, no symmetric mic!).

Ferrites are fine, but from two decades of EMC lab experience, I can tell you that you need the correct type of ferrite for your problem. There is not a single type of ferrite that you slap on and that will always solve your problem. But it sure would look strange if you show up at a venue with your rig and a box full of ferriite samples and start testing 

Your problem could also be a susceptibility of your preamp for certain RF frequencies. You should ask the manufacturer, maybe he has a cure at hand that can be retrofitted (in fact, every electronic device sold in the EU has to be tested and certified for EMC compliance!).

Maybe you have a ham radio operator near you who could help you with this issue. Hams have to solve this type of trouble on a regular basis, and they have access to transmitters for testing the effectiveness of the shielding/filtering of your rig. They also often know where to buy well-shielded teflon coax (expensive, but still cheaper than the "High futility" stuff  )

Battery boxes are less problematic in RFI situations, because they are passive devices. Most Recorders are FCC and CE approved, so their EMC compliance has been tested (immunity and emissions, electrostatic discharge).

So here is your to-do list:

- improve the shielding of your mic cables
- immunize your preamp against RFI (shielding, filtering)
- test

Greetings,

Rainer

Design engineer, EMC/RFI guy and ham radio operator for the last 20 years...

[Church-Audio]

Success!! I found a snap-on ferrite ring from an old 28.8 modem I had.  I wrapped the pair of cables around it a couple times and the radio station is gone!!

Thanks for all your help

SW

Glad you found a solution. My gear is all shielded. With copper foil depending on how old your preamp is. They may not be 100% shielded. You can certainly bring the gear back to me. 

Chris