buzz that I cant kill

[wellREDman]

   I have a project bass that has developed a buzz, its driving me mad,
Ive taken it all apart and checked all the connections and nothing is loose, Ive replaced  the volume pot with a new cts one (the only control currently on it) and swapped pickups and it's still there!
   If the buzz reduces by about half when I touch the bridge or control plate does that mean something is touching that shouldn't be , or something not connected that should?
 
Help!

[Pilgrim]

Sounds like you need a ground wire from under the bridge to the electronics, and perhaps shielding in the pickup cavity.

[wellREDman]

bridge ground present and checked, all cavities lined with copper tape

it used to be quiet so it is something that has changed, or moved or failed

could a bridge ground wire still be registering as a circuit when tested but be compromised enough to cause buzz?

would soldering the ground wire to the bottom of the bridge help?

[clankenstein]

does it get worse when you take your hand off the stings?

[Lightyear]

The title of this topic somehow bothers me   

Keep in mind that I'm sure my wife has been trying to kill me for years, has been unsuccessful and has probably uttered this phrase more than once to herself... 

Simple test for the ground wire thing - just clamp a jumper, short piece of wire with an alligator clip at each end (Radio Shack was good for something), between your cavity ground and the bridge - if you lose the buzz it's the wire itself or the solder joint or mechanical contact at the bridge.

[nofi]

i have a bass that plays quietly through one amp and  buzzes loudly through the other amp.

i use the quiet amp.

seriously, both amps work fine with another bass. i know its a grounding issue but i can't find it, but i suspect it may be a poor soldering point or the wire itself.

good luck!

[Granny Gremlin]

bridge ground present and checked, all cavities lined with copper tape

it used to be quiet so it is something that has changed, or moved or failed

could a bridge ground wire still be registering as a circuit when tested but be compromised enough to cause buzz?

would soldering the ground wire to the bottom of the bridge help?

So you checked continuity from bridge to ground with a multimeter - am I reading that right?

If there's continuity then that's all you need; soldering is a pain (might not work to chrome actually) and should not be required.

Check also that the shielding is connected to ground somehow; again, just contact, no soldering required per se.

Other than that, an actual circuit component could have gone bad on you suddenly or the environment you play in may have changed - EMI etc.... or it's your amp thast went noisey (try another instrument).

[wellREDman]

does it get worse when you take your hand off the stings?

Yes it lessens when I touch the strings or output jack, and almost completely goes when I touch the bridge or (Jazz type) control plate

Simple test for the ground wire thing - just clamp a jumper, short piece of wire with an alligator clip at each end (Radio Shack was good for something), between your cavity ground and the bridge - if you lose the buzz it's the wire itself or the solder joint or mechanical contact at the bridge.

Did that no difference with a test wire, only my hand, also definitely electrical/ground issue as same touching on the bridge with a piece of foam between gets no reduction in buzz

So you checked continuity from bridge to ground with a multimeter - am I reading that right?

Check also that the shielding is connected to ground somehow; again, just contact, no soldering required per se.

Other than that, an actual circuit component could have gone bad on you suddenly or the environment you play in may have changed - EMI etc.... or it's your amp thast went noisey (try another instrument).

Yes and shielding connected, and other basses work fine with Amp

This is why it's driving me crazy

I guess next step is replace all the wiring, but i thought I would avoid that by continuity testing every wire (they all checked out

[Granny Gremlin]

What's the electronic config (pup(s); controls)?

[Alanko]

I've spent ages chasing away loud buzz from bass projects on a couple of occasions. In each case I forgot that the temperature control on my soldering iron emits a lot of EMI. The buzz may be coming from something like that, so it might be worth finding out the source of the buzz, rather than trying to chase it out of your bass.

I've wrestled with copper tape in the past, and I think shielding of that sort is a bit unnecessary, and can introduce extra noise if not correctly installed. I see a lot of wrinkly, ungrounded copper shielding jobs on other forums. I saw some guy on Basschat using regular kitchen foil, no adhesive, and no obvious ground wires. It looked like was planning to bake a potato.

[Granny Gremlin]

Yes, with humbuckers on a bass I can't see shielding being required.  With single coils maybe.

That said, kitchen foils should work if done properly (its basically what Gibson used, glued on the back of their pickguards/control plates since the 60s).

[wellREDman]

     the shielding is adhesive backed copper foil strip (sold as slug deterrent for around plant pots) was a tip from a guitar tech.
     
    the pickup is a single coil so some noise is expected. I've ruled out soldering iron noise etc. as my other bass with the same type of shielding works silently in the my workshop with the same amp/cable etc.

  The thing is it was so quiet before that when I used it for college in a recording lesson when  we were learning about DI boxes,  my tutor told me he thought I had already turned on the ground lift switch, and complimented me on such silent, well shielded electronics

   interesting that badly done shielding can cause noise, when I strip it down again I'll check continuity between each cavity shielding, that may be where the break has come 

the ground wire from the bridge is soldered to the bottom of the Vol pot. on a strat I've just repaired I noticed that the bridge ground wire is wired straight to the output jack, might this make a difference ?

[Granny Gremlin]

No; ground is ground.... assuming the pot casings are grounded (that could totally be the issue, actually).  Are the pots mounted to a control plate (front opening cavity) or to the wood of the top (rear openning cavity).  If the former, ensure the control plate is lined with metal foil and that at least 1 pot casing or switch is connected to jack ground.  If the latter then make sure there is a wire (bare copper solid is fine and easy) daisy chaining all pot casings to ground.

Single pup means can't troubleshoot by isolating pickups.

[wellREDman]

What's the electronic config (pup(s); controls)?

single jazz type pickup, jazz control plate with 3 xtra dummy controls(it's going to be active one day when Ive saved up for the harness ) one CTS volume pot, boat type output jack

Ive just realised the shielding in the pickup cavity might not be connected to the shielding in the control or output cavities, ill strip it apart at the weekend and see if that makes a difference

[Alanko]

interesting that badly done shielding can cause noise, when I strip it down again I'll check continuity between each cavity shielding, that may be where the break has come.

Shielding is, to some degree, like building a big net to capture electrostatic interference. That interference is then sent to the ground side of the circuit. Single coil pickups are prone to capturing electromagnetic interference, which cannot be easily removed (enter the realm of dummy coils and other technology). You could use twisted-pair wiring to cut down on EMI, as well as shielding.

It might be worth checking continuity between all the strips of slug tape you used. Copper shielding tape is manufactured with a conductive adhesive, whereas this isn't necessary to keep slugs off your lettuce, so don't assume anything! I would solder a wee joint between each strip of copper tape if you don't get 100% emphatic electrical continuity across all sections of your shielding.

On the flip side, some people find that an extensive shielding job actually kills highs due to the capacitance of the shield interacting with the wiring in the guitar. I also believe there is a bit of a 'ghost in the machine' element, and simply taking time out to unscrew everything off your instrument then screwing it all back together will have a profound psychological effect outwith any sort of electronic improvements! I hold 'Guitarnutz' accountable for creating a lot of panic about the need for shielding and star-grounding guitars.

A final thought, Gibson shielded the back of their control cavity covers, but didn't ground this shielding or apply any additional shielding to the cavity itself? Why?!?