I've got a set of Gretsch Filtertrons in an old Kent hollowbody and for some reason, the F'trons are not living up to their name. I've tried all sorts of wiring configurations, new wiring, new pots, tried different basses to see if maybe it's my amp, plugged the amp into a different outlet, played the bass at my friends house through his amp, and concluded that it must be the pickups. Oddly, though, they hum the most when they are facing up or down. Tilted to the side greatly reduces the hum (although it's still there). I've shielded the pickup covers with copper tape, but that had little to no effect. So... does anyone have any ideas as to what's causing these humbuckers to hum?
No. I had a P bass humming like hell. Fri night, I went thru the pain of shielding, no cigar. I then opened her back up, replaced the jack, reversed the wires and no cigar. Frustrated, I put her back together and cleaned up all the solder joints and the hum magically disappeared. I did end up reversing the wires. So I would suggest this if you have not done this yet. And also the shielding is connected to ground yeh? And you did not mention bridge ground and pot case grounding but assume you have done that.
I thought it was a grounding issue, at one point, so I took desoldered the pickup from the controls and got dead silence. If the hum were caused by the wiring, it would still be present even after removing the pickup.
I would argue that the pickup is in deed the noise source. By their very nature they will pickup up noise. Thus the importance of proper wiring / grounding. Just because the wiring does not buzz without the pickup present does not mean the wiring is good.
My jazz bass likes to hum when its angled in certain directions in my room. Some ways it can be silent even with all the controls at 10 and some ways it can be noisy as hell! I know my j bass has single coils but it sounds like a similar thing to what I expereince. I've always assumed it was interference from the lights in my room + other electrical equip.