Odd hum problem - advice needed

If noise goes away facing down, the shielding in the back is good. Noise coming in the front is getting picked up. Top shielding may have an issue, or one of the pickups is picking up noise.

When testing outside, leave your phone inside. Cell phones can be noisy.

Does the noise go away if switched to just the Zen Blade?

 

The Zen Blade is a hum bucking pickup. Hum bucking is designed to cut 60Hz hum, but will cut noise over a wide frequency range.

OPB pickup (I assume you mean original precision bass) is a single coil pickup. That can act like an antenna. If you really want that shape of pickup, but cut hum, Nordstrand makes a 51P4S. I have not heard what they sound like.

Rolling tone off a little bit can cut high frequency buzz a lot. I have a bass with an unshielded control cavity that picks up noise from my computer. Until I get around to shielding it, I just back off tone a tiny bit.

 

Did you check the bridge grounding?

 

I had a bass with hum that would not go away when I touched the strings. The ground wire from the bridge had snapped. Replaced it, and no more hum.

Is there any noise that goes away when you touch the strings? How about if you touch the outside of the output jack?

 

Is the pickup wired in series or parallel?

 

It’s the opposite. The 60 cycle hum will stop when you touch the strings if the bridge ground is connected. That shunts all the noise your body picks up to ground instead of it interfering with the pickups. You don’t need to disassemble anything to check. Use a multimeter and see if there’s continuity from the metal on the bridge or the string ball ends to the sleeve terminal on the output jack or the metal cover of a plug plugged into the output jack.

 

This sounds like RFI, which is another reason I would check the bridge ground.

 

Does the noise get better when you touch the output plug (on the cable)?

 

Do other basses do the same in the same place? if it cancels out the noise by changing the orientation, it's some nasty electromagnetic inteference. My last studio had a metal roof, and in the third floor suite, had a similar problem. There was a 25KV transmission line ten feet away from the roof! I started using a Lightwave (optical!) bass and a Line6 Variaxe up there because it was such a hassle having to sit at precisely the right angle and stay there the whole track... that building was the inspiration for my multiple-brand "humbucking jazz bass noise-resistance shootout test" (which I still havent gotten around to publishing)

 

Just as a thought, how bad is it? Could a filter capacitor be added to the output cct to attenuate that freq? Can't offer much more as I've no experience designing ccts, I can build 'em and read 'em, but that's about it.

 

Check bridge grounding, and also if your bass has a pickguard, the connection to cavity grounding.
Last, but not least, check your pickups screws and springs and input jack, perhaps something is not making full contact with the cavity grounding when the bass is in playing position but contacts well when stored facing down.

 

No. You just have to see whether touching the output plug behaves differently than touching the strings.

Or use an ohmmeter between plug and strings.