This is a Shielding Issue, Right? (Nordstrand Pickups / Preamp)

[Modern Growl]

^ yup, I got it. Alright - I give up now. Star ground didn't fix the issue... noise when not touching metal is still present.

Sigh.

[1958Bassman]

Originally Posted by Modern Growl

Hey there - no, none of the above.

All pots are connected with a common ground wire that ends at the jack (came pre-wired this way).

All pots are making good contact with shielding as well.

Bridge ground is connected to the jack ground. There is a wire connecting the jack ground directly to the shielding as well.

No lugs or wires from any of the pots are touching ground.

This is one of the cleanest jobs I've done... I'm stunned that I still have noise. Doesn't make sense....

There's what looks like a pot or rotary switch near the output jack- am I right? All I see in there is single wires that aren't shielded or twisted around another wire that's carrying the negative signal (i.e., a pickup that has only two wires would either need a shield for the negative or a second wire). At the upper left, I see twisted wires, which I would assume are from the pickups. This is a bad wiring scheme-there's no way to reject common-mode noise after the pickup wires.

A pair of wires that carry signal can be twisted to perform the only method of noise cancellation and that's why phone wire and Cat5/6/7 are this way. A wire will carry a certain amount of signal and along with that signal, comes some noise. The current creates a magnetic field and when the + wire's field meets the field from the - wire, they're basically equal but opposite, so they cancel. A foil or braided wire shield makes a connection at both ends, so it performs the dual role of being the negative conductor AND it carried the noise that hits it away, to ground.

However, if you turn off all electrical/electronic devices other than your amp, do you still have noise? Is the amp plugged into a grounded outlet, as another TB-er mentioned? Did you verify that the outlets are wired correctly? It's cheap, easy to check and it's a tool you should have in your case, anyway. Gardner Bender makes them and they have been linked to here and every other audio/video/instrument forum for years. The reason polarity is important when the amp is un-grounded or the outlet was wired wrong is that the chassis becomes an attractor for noise, not a ground plane or a shield.

BTW- "star ground" isn't a physical topology, it's an electrical characteristic. You can have everything grounded to one point and not have everything at equal electrical potential. This means your attempt will fail. Unfortunately, the amounts of resistance required to make noise a problem are too small to measure with a basic meter. It's also possible to have too many ground points- if the bridge, pickups, jack and control ground wires are daisy-chained (bridge ground wire to back of a pot, pots connected to the jack with one wire that also has the preamp ground connected to the back of the pots), make everything reach to a large star washer at the jack and make all of the ground wires equal in length. Solder joint quality is paramount. You may find that removing the pots eliminates the noise- if it does, remove enough foil from where they mount that they no longer touch foil anywhere. The way it is now, you have a ground at the control shafts, another at the back of the controls, switches, pickups and the jack. If you have a multi-meter (an oscilloscope is even better), set it to resistance and measure from the foil to each part that's grounded to the jack. If you see differences, you have current flowing on the ground wires. It's not a lot, but it doesn't need to be, in order to cause noise.


The cable, amplifier's jacks & internal connections, the outlet and any pedals all work as a group WRT having noise, or not. List the whole signal chain, please- don't leave anything out.

[SGD Lutherie]

You have the bass shielded, but the pickups are not shielded.

That high pitched buzz is electrical field noise. You can try removing the covers from the pickups, and wrap some masking tape around the coils to protect them, and then wrap some copper foil around the coil. Do not connect the two ends of the foil to each other. Use some masking or electrical tape to stop the ends from touching. Before putting the tape around the coils, solder a ground wire to the foil. Don't do that when it's wrapped around the coil.

Also star grounding in a bass is pointless. You have a single ground point at the output jack. Everything is at the same potential because the runs of wires are short, and you do not have the high voltages and high impedances like you find in a tube amp, where start grounding is important.

And this buzz you are hearing is not from some ground loop, which you can't get in a bass anyway, due to the single ground at the output jack.

You will note that no major guitar maker uses star grounding.

[Modern Growl]

^ Hi there - thanks for the input.

The bass has two pickups - a neck (fully shielded) and a MM style humbucker which has the cover glued on.

I think the one MM style pickup may be the issue... but I don't know what else to do other then try to shield the cavity its in... but thats not equal to a fully shielded pickup...

[Modern Growl]

Originally Posted by 1958Bassman

There's what looks like a pot or rotary switch near the output jack- am I right? All I see in there is single wires that aren't shielded or twisted around another wire that's carrying the negative signal (i.e., a pickup that has only two wires would either need a shield for the negative or a second wire). At the upper left, I see twisted wires, which I would assume are from the pickups. This is a bad wiring scheme-there's no way to reject common-mode noise after the pickup wires.

A pair of wires that carry signal can be twisted to perform the only method of noise cancellation and that's why phone wire and Cat5/6/7 are this way. A wire will carry a certain amount of signal and along with that signal, comes some noise. The current creates a magnetic field and when the + wire's field meets the field from the - wire, they're basically equal but opposite, so they cancel. A foil or braided wire shield makes a connection at both ends, so it performs the dual role of being the negative conductor AND it carried the noise that hits it away, to ground.

However, if you turn off all electrical/electronic devices other than your amp, do you still have noise? Is the amp plugged into a grounded outlet, as another TB-er mentioned? Did you verify that the outlets are wired correctly? It's cheap, easy to check and it's a tool you should have in your case, anyway. Gardner Bender makes them and they have been linked to here and every other audio/video/instrument forum for years. The reason polarity is important when the amp is un-grounded or the outlet was wired wrong is that the chassis becomes an attractor for noise, not a ground plane or a shield.

BTW- "star ground" isn't a physical topology, it's an electrical characteristic. You can have everything grounded to one point and not have everything at equal electrical potential. This means your attempt will fail. Unfortunately, the amounts of resistance required to make noise a problem are too small to measure with a basic meter. It's also possible to have too many ground points- if the bridge, pickups, jack and control ground wires are daisy-chained (bridge ground wire to back of a pot, pots connected to the jack with one wire that also has the preamp ground connected to the back of the pots), make everything reach to a large star washer at the jack and make all of the ground wires equal in length. Solder joint quality is paramount. You may find that removing the pots eliminates the noise- if it does, remove enough foil from where they mount that they no longer touch foil anywhere. The way it is now, you have a ground at the control shafts, another at the back of the controls, switches, pickups and the jack. If you have a multi-meter (an oscilloscope is even better), set it to resistance and measure from the foil to each part that's grounded to the jack. If you see differences, you have current flowing on the ground wires. It's not a lot, but it doesn't need to be, in order to cause noise.


The cable, amplifier's jacks & internal connections, the outlet and any pedals all work as a group WRT having noise, or not. List the whole signal chain, please- don't leave anything out.

Ground from outlets are fine - I had an electrician come and inspect my house a while back.

Again - all my other basses do not have this issue (same amp, outlets, etc...).

I'm not sure how much the braided wire is effecting the noise though... my gut feeling is that isn't the issue...

[James Judson]

Your body is the noise source. It gets focused into the pu's, wires, electronics etc. When you touch the ground (anything metal on your axe), the noise is shunted to ground eliminating it. Sounds like its working normal to me. Why doesn't other axes do this. Different configurations.

Look at a TV antennae. There is all those bars of different lengths usually bigger to smaller. Only one is the antennae. The others "focus" the signal to it. Same thing your body is doing.

I could be wrong but I think the other TBer"s here have covered pretty much everything else.

[TimBosby]

I had this EXACT same problem with my Wilkins bass. Literally the exact same. Same preamp, same pickups, also with shielding paint.

To be honest, I'm not 100% sure what solved it. But I had a "single string" bridge where there was no metal connection between all the strings. But when I touched the strings, the noise went away. I figured I was completing the ground loop. Not very safe. So I had Carey Nordstrand put a metal wire underneath the single string pieces so that they were all all connected. That helped, but there was still an odd buzzing. We put copper foil over the shielding paint in the cavity. Didn't help.

I did two more things and I'm not sure which of them solved the problem, but it's gone now. I had Pat Wilkins install a nickel nut. I could have used brass but it would have looked "off" on this bass (which was inca silver with all chrome hardware.) Then I e-mailed John East of East UK (maker of the J-Retro) and he has these little conical copper "knob springs." They go over your pots and ensure a secure connection when you turn your control knobs. I had metal knobs and noticed that a lot of the problem occurred when my finger touched or rotated certain knobs. Why it was only certain ones I'm not sure. But the knob springs did the trick. All buzzing gone. John will mail you some for the cost of shipping from the UK (a few bucks.)

To this day I'm not sure what the root of the problem was but I imagine it was something with the shielding paint. I should say the roots of the problems because the ground problem was resolved with the nickel nut/wire under the bridge. But it WAS still noisy after that, so I put in the knobs springs.

[TimBosby]

I forgot to mention, at one point in the ordeal I even tried ANOTHER Nordy preamp and even an Aggie preamp. I eventually settled on a Glockenklang but the preamp itself wasn't the problem.

[Modern Growl]

Originally Posted by TimBosby

I had this EXACT same problem with my Wilkins bass. Literally the exact same. Same preamp, same pickups, also with shielding paint.

To be honest, I'm not 100% sure what solved it. But I had a "single string" bridge where there was no metal connection between all the strings. But when I touched the strings, the noise went away. I figured I was completing the ground loop. Not very safe. So I had Carey Nordstrand put a metal wire underneath the single string pieces so that they were all all connected. That helped, but there was still an odd buzzing. We put copper foil over the shielding paint in the cavity. Didn't help.

I did two more things and I'm not sure which of them solved the problem, but it's gone now. I had Pat Wilkins install a nickel nut. I could have used brass but it would have looked "off" on this bass (which was inca silver with all chrome hardware.) Then I e-mailed John East of East UK (maker of the J-Retro) and he has these little conical copper "knob springs." They go over your pots and ensure a secure connection when you turn your control knobs. I had metal knobs and noticed that a lot of the problem occurred when my finger touched or rotated certain knobs. Why it was only certain ones I'm not sure. But the knob springs did the trick. All buzzing gone. John will mail you some for the cost of shipping from the UK (a few bucks.)

To this day I'm not sure what the root of the problem was but I imagine it was something with the shielding paint. I should say the roots of the problems because the ground problem was resolved with the nickel nut/wire under the bridge. But it WAS still noisy after that, so I put in the knobs springs.

I hear you on the knobs thing - I spoke to Max @ BBB.com and we discussed that a long time ago (before this issue).

The noise goes away when I touch the bridge or tuners or strings though... not just the knobs.

[1958Bassman]

Originally Posted by Modern Growl

Ground from outlets are fine - I had an electrician come and inspect my house a while back.

Again - all my other basses do not have this issue (same amp, outlets, etc...).

I'm not sure how much the braided wire is effecting the noise though... my gut feeling is that isn't the issue...

That's the thing about electricians- they're more interested if motors and lights work, not electronics that are sensitive to grounding issues and noise.

What braided wire?

[Modern Growl]

Opened the seal on the MM pickup and shielded that... it helped a bit and lowered the noise - but its still there.

[bassbenj]

Originally Posted by Modern Growl

Opened the seal on the MM pickup and shielded that... it helped a bit and lowered the noise - but its still there.

The theory of shielding is that you enclose EVERYTHING in a water-tight copper box and the hum can't get in! Copper box and all copper pieces MUST be grounded to jack ground. Your cavity job looks good to me. Of course "watertight" isn't practical (tops of pickups stick out, for example) but you get the theory.

I has a similar problem with my MIM Fender Jazz V. (which already had conductive paint)

Key word is "everything". I had to shield the cavity (solder all seams) Shield the pickup cavities. Copper tubes to shield wires in holes going from pickup cavities to control cavity. Shield the Battery cavity! Shield the route where side jack fitted into body. None of those things were shielded. Also had to put copper foil on the back of pickguard that made pressure contact with copper from cavity at mounting screw. Bottom line: only tops of pickups sticking out of "copper box".

But wait still not there! Next had to ground all the magnet poles in pickups (MM pups especially prone to this). Without that poles will inject hum right into the coils, especially if you touch them. (remember pickup cavities and wires (roll up copper tubes to fit wire holes, tube soldered to cavity foil at both ends) are already grounded...again all copper pieces connected by solder). I think there is an article at Audere website on grounding poles.

And if there is STILL hum, replace the output jack just for drill. They are just crimped and sometimes can develop corrosion that increases resistance.

And THAT is about all I know.

Good Luck!

[1958Bassman]

I haven't seen an answer from when I asked if everything else in the room has been turned off- lights, TV, computer(s), printer, radio, fan- everything, especially if the lights have dimmers.

I decided to make my Baja Tele's noise go away- it was really bad and, having worked with audio equipment for quite a while, I'm at the point where I consider noise to be a kind of failure on the part of the designer/builder (I mean, c'mon! Others avoid it, right?). I opened it up and saw unshielded/untwisted pickup wires laying in the grooves. Knowing that twisting wires helps them reject noise, I un-soldered the neck pickup and took care of that. IIRC, the neck P/U's copper backing plate had a ground wire but the bridge pickup had none so, after twisting its wires, I added one. Then, I changed the grounding so everything met at the jack, reassembled it and found......noise. Less, but still there. Not a hum, but a buzz (there's a difference).

What had I failed to notice in my quest for silence? I did everything by the book. I made sure all of my solder joints were nice and shiny, nothing was shorting or pinched. Oh. Let's try this- my laptop computer was on and not far away. DOH!

I think we need to determine the actual noise- it was called "noise" and I saw at least one post that referred to it as "high pitched buzz". I don't remember if it has been called "hum" but these have different causes. Hum is caused by ground loops or AC power wires in close proximity to signal-carrying wires or something that's sensitive to electro-magnetic interference (called EMI). Buzz comes in using the same mechanism, assuming it's not coming in through the power source- it's still EMI if it's coming through the air, even if it's a buzz. However, buzzing is caused by devices like motors, dimmers, computer/switching power supplies, TV screens and things like that. The solutions are very different- strong low frequency EMI is hard to block but RF noise is easier to remove. RF noise (may still be audible) is eliminated by using shielding that may include braided wire or metal screen (copper works best). EMI can be blocked using Mu-metal, which is a sheet made from a combination of copper and nickel. It's used (or was) on the metal cover that was mounted over tape recorder heads. The best method of reducing noise involves distance, as in, move farther from the source. It's the only 100% reliable way to decrease interference.

To the OP- what happens when you stand up and listen for noise? What happens when you walk around the room or turn to one side or the other? If this changes the sound of the noise, there's a source for it and it may not be a grounding problem although, as I posted before, every ground point from the breaker panel to your instrument matters. If you're not plugging the instrument into the amp with nothing else between them, do that now. Then, add one effect at a time. It could be caused by one short cable but the other instruments aren't susceptible to the same noise.

[guy n. cognito]

Originally Posted by Modern Growl

Alright - well that was frustrating... I just spend a good time shielding the entire cavity and connected to ground and I'm still getting the buzzing.

You need to connect the shielding to the common ground. Connect all cavity shield to each other, then connect them to ground. Search "star grounding" for some tips.

[megafiddle]

As James Judson said, you are the noise source.

Which means you can use your hand as a 60 Hz (hum) signal generator. Set the bass down, so you can move away from it.
Is it now quiter?

Place your hand flat against various spots on the body, especially where any wiring might be (without grounding yourself).
You should be able to locate the sensitive area that way.

On my jazz bass, I get some 60 Hz buzz if I touch the back under the neck pickup. It disappears if I touch the strings.

Originally Posted by James Judson

Your body is the noise source. It gets focused into the pu's, wires, electronics etc. When you touch the ground (anything metal on your axe), the noise is shunted to ground eliminating it. Sounds like its working normal to me. Why doesn't other axes do this. Different configurations.

Look at a TV antennae. There is all those bars of different lengths usually bigger to smaller. Only one is the antennae. The others "focus" the signal to it. Same thing your body is doing.

I could be wrong but I think the other TBer"s here have covered pretty much everything else.

[1958Bassman]

Originally Posted by megafiddle

As James Judson said, you are the noise source.

Which means you can use your hand as a 60 Hz (hum) signal generator. Set the bass down, so you can move away from it.
Is it now quiter?

Place your hand flat against various spots on the body, especially where any wiring might be (without grounding yourself).
You should be able to locate the sensitive area that way.

On my jazz bass, I get some 60 Hz buzz if I touch the back under the neck pickup. It disappears if I touch the strings.

The human body is not a noise source. It can, however, act as an antenna for available noise. If it hits a person's body, it can act as what's known as a 'secondary radiator' but your point about grounding it (the body) to make it stop is correct. This still doesn't eliminate the real source of the noise or the reason it's audible.

[SGD Lutherie]

Shield the pickups adequately, and you don't even need to ground the bridge. That's how EMG gets away with that (and the differential input to the op amp). But the shielding has to be in the pickup, and not in the cavity.

[megafiddle]

Originally Posted by 1958Bassman

The human body is not a noise source. It can, however, act as an antenna for available noise. If it hits a person's body, it can act as what's known as a 'secondary radiator' but your point about grounding it (the body) to make it stop is correct. This still doesn't eliminate the real source of the noise or the reason it's audible.

Well that's true, the body doesn't generate anything.

However, with a few volts of AC on ourselves, and because of our close proximity to the bass,
we could effectively be more of a "source" than the original or real source. On the other hand,
if the "real" source is dominant, it seems possible that we could actually be acting as a shield,
if grounded.

[1958Bassman]

Originally Posted by megafiddle

Well that's true, the body doesn't generate anything.

However, with a few volts of AC on ourselves, and because of our close proximity to the bass,
we could effectively be more of a "source" than the original or real source. On the other hand,
if the "real" source is dominant, it seems possible that we could actually be acting as a shield,
if grounded.

Grounded, yes- we act like a shield (given polarity concerns are favorable) but mass affects this, too. I used to do car audio and in the '80s, several cars had shielding/EFI/RFI/secondary radiator noise problems and, before the solutions were found, it was a royal PITA. Fortunately for me, I have a friend who worked for GM at the time and he used to send tech bulletins when I would ask about some of them. Everything from the air cleaner cover, radiator, heater B+ wire to the type of screws used to fasten the hood hinge where the bonding clip was installed were to blame. It was a matter of either finding a way to increase the separation distance or using the appropriate shielding material, when it would work. EMI is the hardest to shield against. Ironically, copper screen tends to work best against RFI, rather than copper sheet or foil.

As I posted before, the best way to approach this is to find the actual source and deal with that.