recording a radio station...help!

[devilution]

I just bought a used v69me tube microphone off of ebay, and it's picking up a radio station!! It's very soft, and I have to turn up the volume a lot to hear it, but I know it's the mic because other mics plugged in the same way don't do it. And it doesn't even get good reception. Before plugging it in, I opened it up and saw that the previous owner had replaced the tube. I don't think I'm doing anything dodgy with the audio or power cables. Is this normal? Is it possible that when he replaced the tube, he created this problem? Is it possible that when I opened it up, I caused this problem?

Thanks so much.

 

[dgatwood]

I just bought a used v69me tube microphone off of ebay, and it's picking up a radio station!! It's very soft, and I have to turn up the volume a lot to hear it, but I know it's the mic because other mics plugged in the same way don't do it. And it doesn't even get good reception. Before plugging it in, I opened it up and saw that the previous owner had replaced the tube. I don't think I'm doing anything dodgy with the audio or power cables. Is this normal? Is it possible that when he replaced the tube, he created this problem? Is it possible that when I opened it up, I caused this problem?

How close are you to the radio station in question? Something in the device is acting like a rectifier and is basically stripping off the carrier from a fairly close radio station. I'm guessing you're within a mile or two of the tower.

The cause could be just about anything, but I doubt it has anything to do with opening it up. You might make sure that all the screws are tight. If the cage around the element isn't sufficiently electrically connected to the rest of the body, you could get that sort of problem. Could also be any number of failed components in the mic, a bad microphone cable (improperly connected shield), etc.

If it goes away or diminishes when you touch the metal part of the connector on the cable, try a cable that actually connects the grounding lug to the ground wire at the microphone end.

 

[ittam]

You can put Rf filtering caps somewhere in the chain, obviously
near the mic. Might help and then not. And the better screening your cables have the better.
Matti

 

[devilution]

Thanks a lot for the replies. I've messed around with it a little and have some more details, and hope I can get just a little more help.

I'm picking up at least 3 radio stations, depending on where I position the cables. The cables being used are the 2 Mogami cables that came with the mic. One is an XLR cable, and when I switch it out for a cheaper XLR cable, the problem gets worse. The other is a 7-pin cable that I think is made specifically for the v69 microphone, and I think it is only available in the one variety.

When I touch the capsule, the RFI does diminish considerably. Also, the connection at between the 7-pin cable and the microphone is kind of tempermental: if I touch it lightly in one direction, the RFI gets a LOT louder, as though I've flipped a switch. I assume this means simply getting a better XLR cable won't solve anything? Does it indicate that the problem could be 7-pin cable?

Thanks a lot.

 

[dgatwood]

Thanks a lot for the replies. I've messed around with it a little and have some more details, and hope I can get just a little more help.

I'm picking up at least 3 radio stations, depending on where I position the cables. The cables being used are the 2 Mogami cables that came with the mic. One is an XLR cable, and when I switch it out for a cheaper XLR cable, the problem gets worse. The other is a 7-pin cable that I think is made specifically for the v69 microphone, and I think it is only available in the one variety.

When I touch the capsule, the RFI does diminish considerably. Also, the connection at between the 7-pin cable and the microphone is kind of tempermental: if I touch it lightly in one direction, the RFI gets a LOT louder, as though I've flipped a switch. I assume this means simply getting a better XLR cable won't solve anything? Does it indicate that the problem could be 7-pin cable?

Thanks a lot.

Is your house properly grounded? My gut says probably not. Go out and check.

 

[devilution]

Problem solved! Thanks so much for the replies, though the problem turned out to be something a lot stupider. I'm posting what happened, hopefully some other impulsive idiot whose midnight eBay purchases land them in electronic troubles well beyond their understanding will benefit from this story.

The solution was, simply, that I put my USB stuff on the floor.

The rest of the story is this: I'm recording on a laptop with a Line6 Toneport UX1 (a cheap, plastic USB unit--very cool if you don't really know what you're doing). It is possible that my building is poorly grounded, and there are definitely a lot of radio towers in my neighborhood. I actually had the same problem of RFI with some computer speakers, and it started as soon as I moved here. I asked my landlord if she knew anything the quality of the building's grounding and she said she did not.

Moving any components of the chain affected which radio stations I was picking up, but didn't really affect the overall strength of the RFI. I moved the UX1 around a little and it was the same thing. Today i put it on the carpeted floor (out of necessity, while stretching power cords to test if other outlets solved the problem) and suddenly the problem was solved. I guess somehow that grounded it? Perhaps the mic input had a floating ground or something, because the box was intended only for cheap dynamic mics? Regardless, after it was on the carpet, the RFI was gone, and even manipulations of the other cables wouldn't bring it back.

 

[cusebassman]

You wouldn't be grounding something based solely on setting it down on carpet, as far as my limited knowledge of electricity tells me.

However, I have had plenty of experiences where moving cables away from electric cords and into different patterns of travel from one device to another either made RFI better or worse.

As for the 7-pin cable, it is a commonly used cable for tube microphones. My Rode K2 uses the same type. Happy recording!