Horrible pickup noise

[d-basser]

And no, it isn't my playing.

 

Cross posting from my build diary since this has graduated to technical support.

 

Just fitted a pair of Gemini chrome thunderbird pickups into a modified Sire bass I've been working on. I hooked them up and plugged into an amp before stringing the bass, since any fixes would require removing the scratchplate and therefore strings. I am glad I did. I am getting this horrible cycling hum. I am trying to debug it but it seems to be the pickups themselves.

 

That is both pickups, in a fully shielded cavity, routed through a passive jazz style VVT loom. I have confirmed ground continuity for the shielding, bridge and pickup cases. I get the same noise off either pickup, with one or both soldered up. I even get it with one of them soldered straight to a mono 1/4" socket so it isn't the loom wiring. Pickups are connected with the white live wire to the live leg of the pots (or jack in the later case) and both the black wire and outer shielding braid (which connects to the chrome casing) routed to ground.

 

I've check the same amp and cable, in the same room, with another bass with similar pickups and there is no issue, so it isn't that.

 

Are there any suggestions of what may be wrong, or of what I could do further to diagnose it? I am a bit gutted tbh as I've spent the last three nights working on this bass. The whole project was centred around these pickups, and I haven't really pinched pennies so I really want to sort it.

 

Edited February 7 by d-basser

[PaulThePlug]

Not the amp, tried another bass

How about with a finger on a pup case?

I'd try removing the Pickup Case Ground / Braid...

Half reminds me of mains hum on a turntable to amp... with the extra ground wire v's turn table psu grounded (rather than 2 wire  and obvs the amp earthed)?

I'd share you findings with Gemini

Fingers Crossed.

[d-basser]

Not the amp, cable or room as I tried another bass. Other bass is also fitted with chrome thunderbird pickups so a good like for like.

 

I'll double check removing the ground braid but surely that just going to give crazy hum due to all the ungrounded metal.

 

Sent a message to Gemini so we'll see

Edited February 7 by d-basser

[d-basser]

You might be onto something Paul 

[d-basser]

Seems to have gone after removing the outer braid from the ground, which is counter intuitive.

 

Wonder if it's a grounding loop issue, if the casings are grounded via the braid and contact with the copper shielding 🤔

[d-basser]

Gemini weren't much help. Suggested I tried a few things I already had (swapping live and ground, checking I hadn't wired the jack backwards)

 

Got on to talking about how removing the braid connection fixed it, and suggested it could be a ground loop issue and he bowed out.

 

I do think that could have been the issue though. I half remember an conversation at work regarding this when we were working with shielded coax and grounded sensors. 

 

Quick Google backs up the hypothesis 

 

 

 

Thanks again @PaulThePlug