Audio & Electronics Geeks: gimme some help with interference

Factual Questions
1

Let me tell you about my radio.

It consists of a Roland electronic piano, the sound outputs of which contain cables that run into my amplifier’s CD jacks (my amp for some reason lacks a pair of “piano in” jacks and I don’t have a CD player). On the other side of the amp is where I hook up my PowerBook when I’m home, and hookup includes a miniplug that goes into the computer’s sound out port, and from the miniplug it divides into paired cables that go into the amplifier’s AUX jacks. (You were looking puzzled when I mentioned that I don’t have a CD player. I have a CDROM drive and I have a 60 gig drive full of MP3 files. Now you aren’t looking puzzled.) Finally, to the left of the PowerBook’s home base sits a 15" Sony Trin monitor on a stand, and the VGA cable goes into a CardBus card so that I have dual monitor.

I know this may not sound much like a radio, but if I turn off the piano but leave the cables plugged into the piano’s sound out ports, or if I shut down the PowerBook but leave the Sony monitor plugged into the computer, trust me, it sounds a whole hell of a lot like a radio. I haven’t taken notice of the call letters but I’ve got damn good reception on some channel. Even when the computer is booted, I get faint pickup of the signal, noticable when I’m not playing music.

• If the piano is hooked up, the faint radio reception gets quite solid, very loud.
• When I shut down, the faint radio reception gets quite solid and very loud also.
• When I pull the VGA cable out of the CardBus card, the sound goes away.

(Obviously if I turn off the amp the sound goes away. On second thought, all things considered, maybe that isn’t at all obvious. Such is the case, though. All radio reception reported here takes place with the amp turned on)

I’m guessing there’s some kind of deelybobber, a resistor or dampener or something, that I should put somewhere, and that it has a name that the salesthing at Radio Shack (or equiv) will recognize. What might that be? Or, if it ain’t that simple, how might I go about troubleshooting this arrangement?

2

Sheesh. You’ve got a veritable rat’s nest of ground loops and other problems there! Since RFI seems to be the main problem, you’ll want to try one or more of the following:
[ul]
[li] Try to isolate all the possible routs of entry (the VGA cable appears to be one), and put ferrite bead chokes on the wires the signal seems stongest on. Radio Shack has a snap-on ferrite choke that should work nicely.[/li][li] Replace any old, worn or damaged cables with new, good-quality ones. Bad cables are a common entry point for RFI.[/li][li] Break as many ground loops as possible using 1:1 ground loop isolation transformers. These go inline on various kinds of audio inputs or outputs. Ground loops make very nice antennas, and breaking them can fix the sort of problem you describe.[/li][li] Organize your interconnections. Wherever possible, use switchboxes instead of Y-adaptors. Be sure you have no unneccesary connections. Use the shortest possible length of cable for each connection, and do NOT coil excess cable into a loop.[/li][/ul]
More suggestions as I think of them, but these are definitely the biggies.