I forgot how amps pick up radio signals

[Lavahead]

The search option sucks, we all know that.

Now, sometimes when I've had my ear to a cab listening to the sound of the speaker I've heard some radio interference coming through. It's happened a couple times.

I was just recording some acoustic guitar in my hosue with my roommate (all hardwood floors, 15 ft ceilings, wide hallway. thats all you need by the way, just a good acoustic enviornment. thats what this house has taught me), and we had one Baby Blue about 5 ft up and it was the only open mic to the monitors..and we were getting radio bleed through the monitors. We switched mics to an MC012, no radio. Switched back to the BLue, radio.

What is the explanation here? I remember having it explained to me once, about the guitar amp bleed, but it just seemed weird with an open microphone. Although there is still a preamp stage and then an amplication stage, and then some sort of monitor (speaker)...thoughts?

Thanks!
Mike

[fremitus]

There are usually two grounds in an electronic system. One is for power and one is for signal. The power ground is always noisy, and usually the case of the system is grounded to it. The signal ground is a clean ground. It is used as a voltage reference for the music signal. You don't want this ground to be connected to the power ground. It will cause your signal to be noisy, and it is possible that the case will act as an antenna imposing radio signal on your guitar signal.

all that being said, i would question the wiring of the baby blue...
of course, it could just be the shape of that weird little guy, it does LOOK like an antenna...


p.s. - steely dan still sucks

[soundguy]

Its the mic. some mics are more sensitive to RF than others. I have a set of mics that are magnets in the MHZ range, anyone talking on a walkie talkie anywhere near me makes it intot he audio band loud and clear. Other mics in that exact same environment are totally bulletproof.

dave

[Zeppelin4Life]

badly shielded cables can do this too. Poor soldering jobs as well. bad grounding between the outlet.sometimes it's just the internal electronics getting 'birdies' from stations. if this is the case, you cant do much.this happens with really cheapo amps..It's really bad if the Tx is nearby. Commerical FM radio uses stations with as much as 100,000watts. Even small things like cell phones and walkie-talkies with less than 2 watts can screw things up. This stuff will go through anything. AM radio signals penetrate right into cables and things. HAM radio opps seem to go nuts with watts sometimes. My friends neighbor had some ridiculously powerful CB radio. probably illegal. well he turned that thing on and his lights would waver. His TV was all distorted. My friend made a qhetto solution by hooking a coathanger from the amps handle to the ground..and it solved everything. that was a grounding issue. YMMV