Puzzling electronics issue (grounding?)

Hello people,

I 've replaced the pickups electronics on a Brian Moore i5 bass I have and I am having a weird issue show up. I 've wired up more than a handful of basses in my life but it's the first time something like this occurs.



So this is our specimen. I have installed to it a couple of 4-wire humbuckers with one coil tap switch each. They are generic but seem good, meaning they sound good and seem to humcancel nicely, each pickup alone but also with each other. I have also installed a three band preamp (Bartolini MK1 from an Ibanez I used to have).

Each humbucker has 4 wires and a ground wrap. On both humbuckers the ground wrap is connected to the black wire.

The pickups seem to work correctly.

- With each pickup soloed, parallel humbucking mode is completely silent, series humbucking has very little noise, single coil mode has the typical significant single coil noise.

- In single coil mode, the front coil of the pickups is activated. When blend is at center, the pickups hum cancel each out nicely and the noise goes away. This is also the case when the pickups are in series mode (although the noise that is eliminated is much less).

Now for the problem:

When I do not touch the bass there is a slight noise. When I touch the strings this slight noise goes away completely.

The second problem is that if I move my fingers close to a pickup, say touch its plastic casing, the slight noise is dramatically increased. Again when I touch the strings it goes away completely. The situation is the exact same to the previous case where I don't touch the pickup casing. The bass is completely silent.

This is the core of the problem. I 've had this happen with the bass connected directly to my audio interface, and also to an Aguilar Tone Hammer plugged to a wall outlet (24v) and listening to it with my headphones.

BUT, because I suspected some issue with grounding, I also tried using THIS:



This is an EHX headphone amp, battery operated. When I plug the bass to this thingy, there is no noise whatsoever. The situation is the exact same as when I'm plugged to my audio interface or Tone Hammer but touching the strings. If I checked the bass with only this headphone amp I would reach the conclusion that everything is perfect.

Does anyone have a clue what is it I might be facing here?

Here's some facts that may be of help to you:

- The bridge is connected to ground.
- All pot casings are connected to ground.
- The pickup cavities and electronics cavity are shielded with conductive shielding paint and are connected with each other and to ground. The shielding paint actually helps a lot with pickup noise, especially in single coil mode.
- There is a preamp installed on the bass, but I checked for the problem with the preamp not installed as well, it is still there.

If you have any ideas or pointers to what I should check next please let me know. Also if you require more information don't hesitate to ask. Many thanks for any help whatsoever.

 

The power supply supplied (lol) with the Tone Hammer indicates 20-24V so I guess the pedal can handle this easily, even more headroom.

 

So I have pretty much simplified things trying to figure out what's going on.

I hooked up one of the pickups to a jack in order to test it isolated.

The situations are as follows:

Pickup -> Tone Hammer (2x 9V batteries) -> earphones
Pickup -> EHX headphone amp (1x 9V battery) -> earphones

With each of these setups the pickup is silent. Note there is no connection to a wall outlet or an audio interface.

But when I do one of the following two:

Pickup -> Tone Hammer (power supply) -> earphones
Pickup -> Tone Hammer (2x 9V batteries) -> audio interface

I get some noise. It is a 50Hz (Europe) hum, I checked with a tuner.

If I touch the cable's metal socket (pickup to Tone Hammer) the noise goes away.

If my fingers approach or touch the pickup casing the noise is increased (I am assuming my body acts like an antenna and picks up the magnetic field from the power lines in the room). Again, when I touch the cable's metal socket, all the noise goes away.

Could someone electronics savvy explain in simple terms why I am getting this noise when I am connected to the wall outlet (power supply) or to the obviously grounded audio interface? When I am not grounded (headphone amp or Tone Hammer with batteries) all is perfect. Why can't I have this perfect functioning when I am connected to something?

Thanks

 

No power conditioner available unfortunately... I checked with my neighbor's house power installation, got the same results...

 

A week later, I plug in the same bass expecting no difference, and it's fixed. It just works. Same cable and everything. I 'm starting to think there was indeed something wrong with our power that went away. Hope it stays this way. Thanks guys for the responses.