Radio reception with an sm58...

Wayfarer · Post by **Wayfarer** » Sun Jan 11, 2009 1:37 am

Hello and hi. I am using a ProFire 2626 as my interface and mic pres. I have been using only a condenser mic with it, until tonight. I have discovered that plugging in an sm58 gives me a radio signal. How does this happen, and how do I stop it?

I would appreciate any education about this phenomenon...

Thanks!

CurtZHP · Post by **CurtZHP** » Sun Jan 11, 2009 8:21 am

Have you tried a different SM-58?

digitaldrummer · Post by **digitaldrummer** » Sun Jan 11, 2009 9:15 am

or another cable - could be a bad ground somewhere

Wayfarer · Post by **Wayfarer** » Sun Jan 11, 2009 10:16 am

I just have the one 58. It very well be the mic; I swapped out the cable twice and still pick up the radio station. It's neat to catch up on the latest news (it's a news station), but...

I've never had this happen before, hmmm....

CurtZHP · Post by **CurtZHP** » Mon Jan 12, 2009 6:58 am

It's likely an AM station. I had a similar situation happen once when I was hot-rodding a cheap little solid state preamp. Whenever I shorted the input, I'd hear the local AM talker big as life on the output. The cable basically acted as an antenna at that point.

Does the 58 work otherwise?

Wayfarer · Post by **Wayfarer** » Mon Jan 12, 2009 7:09 am

CurtZHP wrote:It's likely an AM station. I had a similar situation happen once when I was hot-rodding a cheap little solid state preamp. Whenever I shorted the input, I'd hear the local AM talker big as life on the output. The cable basically acted as an antenna at that point.

Does the 58 work otherwise?

Yes, it works fine, but for the back-up group. The radio station is maybe 1/3 as loud as just speaking into it, and I only hear it when I touch the mic or it is aimed in certain directions...

dave watkins · Post by **dave watkins** » Mon Jan 12, 2009 8:14 am

that sucks i had a wah wah pedal that picked up a mexican radio station once when i was a kid, i wanted to record it but i couldn't ever get it to do the same thing again. moral of the story: record and entire album with your radio antenna sm 58, it'll be grand!

chris harris · Post by **chris harris** » Mon Jan 12, 2009 9:32 am

Wayfarer wrote:
CurtZHP wrote:It's likely an AM station. I had a similar situation happen once when I was hot-rodding a cheap little solid state preamp. Whenever I shorted the input, I'd hear the local AM talker big as life on the output. The cable basically acted as an antenna at that point.

Does the 58 work otherwise?
Yes, it works fine, but for the back-up group. The radio station is maybe 1/3 as loud as just speaking into it, and I only hear it when I touch the mic or it is aimed in certain directions...

Sounds like a grounding problem with the circuitry of your sm58. A when you touch the mic, your body acts like a giant antennae.

CurtZHP · Post by **CurtZHP** » Mon Jan 12, 2009 9:36 am

My guess is that something is goofed up with the transformer in the SM58, and it just happens to manifest itself when connected to the simple solid-state preamps in the Profire. (I'll go out on a limb and assume that the preamps are of the capacitor-coupled, single chip differential amplifier variety, which can be very susceptible to RFI.)

suppositron · Post by **suppositron** » Mon Jan 12, 2009 10:16 am

Isn't there some mod you can do by adding a capacitor across the leads of the cable thus shorting the rf signal to ground? I think it's supposed to be a small value like a few pico farads.

Studiodawg · Post by **Studiodawg** » Mon Jan 12, 2009 11:16 am

You may be able to ground the electronics to the body of the mic...I recently sent my Avalon U5 back to them for this mod because it was picking up our FM station (92.9)...it's not AM-only.

CurtZHP · Post by **CurtZHP** » Mon Jan 12, 2009 1:22 pm

suppositron wrote:Isn't there some mod you can do by adding a capacitor across the leads of the cable thus shorting the rf signal to ground? I think it's supposed to be a small value like a few pico farads.

I think you can get away with a .1mf ceramic disc capacitor between each signal pin (2 and 3) and pin 1.

Rather than mod the cable (and having to worry about which cable it is later), you could back the XLR connector out of the mic and put the caps there.

Or you could just send the thing back to Shure and tell them to fix it.

digitaldrummer · Post by **digitaldrummer** » Mon Jan 12, 2009 3:16 pm

or if this is the same Profire that keeps giving you trouble (re: your other post about really low output with the AKG C1000) then maybe the Profire has a grounding problem. Without a proper ground that could be why your other mic has really output too.

digitaldrummer · Post by **digitaldrummer** » Mon Jan 12, 2009 3:17 pm

or are you by chance located in the Bermuda Triangle or just outside Area 51?

CurtZHP · Post by **CurtZHP** » Mon Jan 12, 2009 8:38 pm

digitaldrummer wrote:or are you by chance located in the Bermuda Triangle or just outside Area 51?

THAT'S IT!! Wayfarer just needs to replace the hat in his avatar with one made of tinfoil! Fixed!

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Radio reception with an sm58...

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