My amp is driving me crazy by picking up AM Radio. Any help appreciated!

Hi everyone!

Last weekend, I bought (used) a GK MB200 head and CX210 cab. I tried them out first and they sounded so great. I was staying with a friend at the time, so I set them up at his place and played bass all weekend and it sounded wonderful. However, now that I've brought them home to my own house, I'm having a really annoying and distracting problem with always hearing AM radio through the amp while I'm playing!

I've done some troubleshooting. I tried every combination of equipment I own and what I've noticed is this:
- the head & cab are completely silent on their own with nothing plugged in.
- as soon as I plug a cable in, I can faintly hear the radio. Some cables are better/worse than others.
- when I plug my bass in, that's when the radio gets really loud and distracting. It's worse when I touch the strings. Even with one of the "better" cables from the previous step, the noise gets extremely distracting at this point.
- putting any pedals in the chain definitely makes it worse.
- my other amp (my tiny Fender Rumble 15w) very occasionally also picked up AM radio, but it was always very faint - never at this annoying and distracting level.
- I tried moving all over the house with the amp to see if I could find a better spot, try different outlets, etc, but it was mostly even worse than the corner of my living room where I usually play.

So, I think I have to conclude that the GK is just more sensitive to this that the Rumble, but ultimately it seems most of the noise is coming from my bass. I did already (long before this) take it all apart and shield all cavities thoroughly with copper tape. It has DiMarzio Model P/J pickups, if that helps. I did not take apart the pickups and shield inside their plastic covers because it seemed they were fairly solidly in there, maybe glued? I'm not sure, but I didn't want to mess with them.

So, my question is this: what can I do about this? Would really expensive cables help, or more likely not since the noise seems to be mostly coming from my bass? Would shielding inside the pickup covers help (and has anyone done this with DiMarzio's - are they easy to get into?) I'm really feeling bummed that currently I can't really use my lovely new amp in my own house.

Thanks for any help!
JPOT

 

Hi Lovep! Yeah, probably should have mentioned that. The house is, I think, about 30 years old. I am renting, so I'm not at liberty to change anything about the wiring. It's just regular municipal power grid, nothing weird or special.

 

I have a multi-meter and checked that there is continuity from the ground on my bass through to the ground on the amp's power plug. That seemed fine. Is there anything else I can/should check on my own before involving an electrician?

 

I am the OP and there's no more to the story... yet. I am hoping I can resolve this somehow!

What does "strong attenuation at 1k" mean?

 

Yeah, I've only barely heard of Paul Harvey, but I did get the gist. It is definitely kinda funny hearing radio through the amp! Last night they had a comedian on. I did some googling and found out that the transmitter for this station is about 4.4km away from me, and it's a 50,000 W tower!

So, you're talking about the EQ settings? On the GK, there are 4: treble, hi-mid, low-mid, and bass. If I turn the hi-mid down to 0 it definitely cuts this radio noise, and if I tweek the treble a bit as well, I can pretty much get rid of it. I thought that might be a good enough solution, but when I started to play... nah. My bass sounded all dull and thumpy then, not the big round sound that I loved so much when I bought the amp. So that's a no-go as a permanent solution.

 

The bass is passive, and I hear the radio with both pickups on or either soloed, no difference.

 

4.4km away, 50,000 W.