Amp picking up radio signals?

rsimper · #1 02-28-2002, 08:22 PM

I KNOW this happens to some people...it has happened with both of my acoustic amps...the marshall and the carvin, and I am wondering why? Is it just a result of a particularly strong signal in the area (seems unlikely due to the fact that I am on a college campus in Vermont, and it picks up a signal from 45 miles away rather than the college station broadcast from 45 yards away)

Is it the pickups? The amp? Any suggestions to what I might be able to do? Too bad I just cant tune the amp to 88.3 FM...why did it have to choose 93.7??? At least its a somewhat decent station but SHEESH...I wanna hear my 510, not third eye blind!

jmeinel · #2 03-01-2002, 01:14 AM

OMG!!!! It's so nice to know those weren't voices in my head!

I don't play much with an amp, but every once in awhile I'll plug into my dad's California Blonde and I'll hear this spanish radio station. I can't seem to get rid of it, and it gets hard to play competing with the radio. It would be one thing if it was playing contemporary music that I knew because then I'd just play along, but I don't know any spanish music.

Someone please help Ryan and I with this little dilema. Or at least tell us how to switch stations. If I have to listen to a radio on my amp I want to at least decide the station I'm going to be competing against.

Jennifer

Aruthas · #3 03-01-2002, 09:17 AM

I am not an expert on guitar amps, but here I go anyway. The pickup itself is most probably not the cause of this, being a piezo-electric transducer. There could be some problems with the sensitivity of the Fishman preamp, but then you would hear radio no matter what amp you plug into. My guess is that it is a combination of the amp input stage being very high impedance, and the cable between the guitar and the amp being too long and/or of poor quality.

A long cable connected to a high inpedance input is in fact an antenna. Maybe trying a DI box near the guitar, and connecting it to the amp in a balanced input would be the solution. Please, anybody, correct me if I speak through my hat again.

John712 · #4 03-02-2002, 09:21 AM

Hey--hams out there--how about helping Ryan with his case of RFI?? I've been out of it too long myself, but if you can't isolate and eliminate the source, you install a radio frequency filter (RF) in the offending line. The power line to the amp or the cable from the guitar are your only two cables unless your running an effects box. If the cable from the guitar to the amp is shielded, it should NOT be the problem. It could conduct a signal being picked up in the bridge or Fishman though. That's the limit of my limited knowledge. I'll post a note on the general discussion--maybe some of the more technically savvy hams and recording pros will have a solution. Good luck!

ScottyMac · #5 03-02-2002, 08:06 PM

Well, I'm not a technically saavy ham, but I am a ham, and I worked in radio for 20 years.

Ryan...do you know if you live close to a translator of the station you are hearing? Is there an 'antenna farm' somewhere nearby?

Secondly, the post regarding a high impedance input is valid...check to make sure all your grounds are working. Make sure the ground on the wall outlet is intact, and make sure your cords are all grounded properly.

I'd be curious to know if this happens in all outlets in your home or, er, dorm. You might also try using different cables too.

It's not likely, but it's not totally impossible that the station you are picking up is broadcasting out of legal spectrum with some harmonics...it's happened before. The tech term is spurious emmissions.

Since it happens with two different amps, I doubt a problem there.

My knowledge has been exhausted.

Gutch · #6 03-02-2002, 11:26 PM

Proper grounding is the best way to minimize the problem. Unfortunately, it may be difficult to track down the house's ground.

A decent alternative is the use of a torroidal choke on the AC line and, if necessary, on your input cable. Go to Radio shack and ask for an RF choke kit. Clip it over the AC input line at he point that it enters the amp. They may also offer you what looks like a donut-shaped magnet. If you get this, wrap the ac line thru the middle hole and around the outside of the donut several times. This would actually be the more effective method. Plug it back in and see if there is an improvement.

Hope this helps,
Dave

rsimper · #7 03-03-2002, 09:10 PM

Thanks for the suggestions everyone!

John712- thanks for your specific help and plea on my behalf

I think when i get some time (maybe this next weekend) im gonna try it all out and hopefully ill stop hearing Matchbox 20 when Id rather hear my 510

W5BLT · #8 03-04-2002, 06:51 PM

First of all, GUTCH is correct. The torroidal choke should "help" the problem, but, most likely won't eliminiate it.

However, there is an avenue of help. As with stereo's, TV, VCR's etc., the manufacture must provide reasonable protection from RFI. This is an FCC rule. Not state, not local. By simply calling, writing or emailing the manufacture, they are required by law to provide you (free of charge) any modifications necessary to eliminate RFI.

As a ham operator, I've had countless neighbors banging on my door demanding that I shut my station down because they can hear me over their TV's or telephones. Heck, one lady even called the cops on me. As a federally licensed operator and because I was operating within my stations limitations, they have absolutely no authority in the matter. Only the FCC does.

That being said, again, the problem can most likely be easily resolved by contacting the amp manufacture and providing them with a polite explanation of the problem. Don't think that this is new. It isn't. If they begin to get snotty with you, let them know as nice as you can that your next call will be to the FCC. That tends to get folks attention.

Good luck and don't blame the ham or the radio station. They're probably in full compliance.

BTW: As I live in CA., the same neighbors that were banging down my door when they had RFI problems, became fast friends when we had earthquakes or some other disaster that they couldn't get out on their telephones. You see, I never lose power. I keep a standby generator available at all times. Ironic, huh?

leftydude · #9 03-05-2002, 08:38 AM

I think the professor from Gilligan's Island is responsible. He started this whole thing.

Gutch · #10 03-05-2002, 09:16 AM

.

Gutch · #11 03-05-2002, 09:17 AM

THAT'S IT!!! Wrap the amp in coconuts and bamboo and it should work great! (Just make sure there's no one around wearing a red shirt and a goofy cap!)