Weird high pitched electrical noise coming from amp(?)

[Maddlava]

Not sure whether to post this here or in the amps section, but I hope I'll still get help.

I have a very cheap bass (80-100$) that I got a year ago. The original electronics broke, probably due to bad wiring but I'm not sure. My dad replace the electronics in them today, and it sounded fine until about an hour ago when they started making a high pitched electrical noise. My dad mentioned something about the jack being unleveled or misaligned, but I can't remember what he said exactly. When rewiring it, he said he couldn't find a place for a grounding wire and he said the instructions for the new electronics didn't mention one so he cut it out, so I'm wondering if it could be that.

The noise gets louder and more aggressive when I turn the tone knob, but stops if I touch any of the knobs or the metal part of the cable. If I touch the metal parts of the pickup, the noise changes tone. Any ideas or fixes?

 

[Maddlava]

Forgot to mention that it's worse when the compression button is pushed in, but still happens when it isn't.

 

[Alex Masters]

Which preamp are you using? Is it active or passive?

You should be connecting the cavity screen to the signal ground - are you hearing noises from a nearby PC? does it change in intensity if you rotate the bass?. Other things to check - see if the pickups have a screen connection that is disconnected. Check that there is continuity between the bridge grounding wire and the signal jack.

I think you are hearing RF hash - it will certainly be better if everything is grounded - pickup cavities, pickup screen, bridge wire, preamp cavity etc. to a single 'star' earthing point, which also goes to the signal ground. If that's all good (check with a multimeter), then you've done all you can.

If you can identify the bass and preamp your Dad fitted, others can offer some more advice but do you know if it has single coil pickups, humbuckers, or a P-style split pickup?. If it's a Jazz-style bass, you only get hum cancellation if the pickup blend is in the middle.

P.S. compressor will boost low level signals - unfortunately that includes RF noise. If you have a multiFX, you may benefit from having a noise gate before any effect/amp/EQ blocks.

Good luck.

 

[dwizum]

Let's see some photos of the wiring. It sounds like we need to figure out the ground wire your Dad disconnected.

Ground wires can either be part of the signal path (ie, the ground side of the pickup) or part of the shielding/grounding of metal parts on the bass (ie, the ground wire(s) from shielding in the cavity). If you cut the former, the bass won't make noise. If you cut the latter, the bass will behave like you described - you'll hear a lot of interference in the signal, which will go away when you touch grounded metal on the bass.