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Noisy P bass when not touching metal parts help needed!


Tjhooker
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Hi

Can anyone advise me on this .. I have a passive P bass that is dead quiet when you are touching strings bridge etc but makes a buzz/ hum when your not.

When plugged into my pedalboard any high gain pedals make this sound louder...

I can also stop the hum/ buzz when touching and metal casing on the pedalboard pedals too!?

😬

I have an active bass with EMGS that doesn't do this when plugged into the same rig.

 

Does this sound like a problem with the bass or the mains earth ..? Any suggestions welcome

 

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That or shielding (a lack thereof). Not uncommon but easy to fix or have a repairbloke sort for you. My G&Ls suffered from this (they're barely shielded at the factory, no idea why) and once everything was lined and shielded it's silent. 

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I always shield my Precision Scratchplates with copper shielding tape as a matter of course, only ever had one noisy Precision and doing this sorted it. But do agree with checking out the earth wire too.

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Nope, it's typical for Fender to buzz (not hum here as it's a Precision with a hum-bucker) as the shielding is poor to non existent.

 

And graphite paint is really a poor shielding.

 

I already explained it here :

 

 

 

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Thanks everyone for replys... 🤔 the shielding thing might be right as it does seem to get worse when moving the bass around like it is picking up interference.. it has been copper shielded inside but maybe something is loose or not connected?

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Mains hum of the kind described is often an electromagnetic field (low frequency radio) effect. If the strings are unconnected to the guitar earth, they act as a very inefficient antenna and the current that flows in them transmits hum to the pickups. One solution is to put the guitar in a faraday cage - this works for the pickup connections when you shield the cavities of the instrument, but this is a small effect. This shielding also stops capacitative noise. The practical solution is to ground the strings, bridge etc. to the signal reference point i.e. the ground connection of the instrument.

 

When the noise stops on touching the bass, this is because you're effectively helping ground the signal. Also, it frequently varies as you rotate the instrument - radio waves are directional.

 

Another source of interference is magnetic fields. These are weaker but are picked up by large loops (e.g. ground loops when both PA and amp are grounded AND have their grounds connected via the signal lead. This can be cured with a ground lift switch on the SIGNAL line only). Small multiple loops (e.g. pickups) pickup this sort of interference as well, hence humbuckers.

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With the way I copper shield instruments, strangely they become dead quiet...

 

And I've done this on hundreds if not thousands electric instruments, even if the theory you exposed is totally correct and I'm fully aware of it, it seems that there's a glitch somewhere in the science facts.

 

Otherwise, there's this solution for these recalcitrant instruments.

 

For U.K. :

https://www.bassdirect.co.uk/bass_guitar_specialists/Aero_DBuzz.html

 

For EEC :

https://bassmatters.nl/en/1703/Aero-dBuz-Cable

Edited by Hellzero
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3 hours ago, Hellzero said:

With the way I copper shield instruments, strangely they become dead quiet...

 

And I've done this on hundreds if not thousands electric instruments, even if the theory you exposed is totally correct and I'm fully aware of it, it seems that there's a glitch somewhere in the science facts.

 

I'm a believer in shielding, as I said I do it myself, there's a reel of conductive adhesive backed copper tape two metres away from me right now!

 

My experience is that shielding helps with things like interference from 'noisy' bulbs. Buzz unless you touch the strings always seems to come down to grounding issues in my experience.

 

I suspect that you are thorough in your work and make sure both grounding and shielding are done well, making it hard to prove which is solving the noise issue.

 

 

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3 hours ago, Stub Mandrel said:

 

When the noise stops on touching the bass, this is because you're effectively helping ground the signal. Also, it frequently varies as you rotate the instrument - radio waves are directional.

 

No. It's the other way round. The bass in question seems properly grounded given that touching the strings / bridge stops the buzz. That is because it is the player that is acting as an antennae and transmitting radiated interference to the bass electronics that are sensitive to it due to high impedance (normal passive bass). Until the player connects to ground via the bass Similarly as the OP observed, the player can ground themselves by contact with any other grounded metalwork.

Screening will help  as has been advised.

 

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Looks like the D-Buz is a supplementary ground wire (with a resistor in it, probably around 200K to 1M) as a supplementary ground to the player.

 

https://d-buz.com/

 

Quote

dBuz is a ground noise solution and will not cancel common mode, power supply, microphonic or other noise. It also works for bad bridge grounds, Aluminum bridges (notoriously hard to ground), plastic coated strings, acoustic instruments, upright bass, improper or over-shielded instruments, and will cure many ground loop problems.

 

I think you and I would probably agree that 'over shielded' instruments are unlikely to cause hum.

 

There doesn't seem to be a patent. £55 seems a lot for something a competent electrician could knock up in a few minutes.

 

 

This seems a bit of scare-mongering. Any properly wired supply would fail open circuit or trip if AC live is wired to ground. And for the lead to provide its putative protection, you would have to remove the 'death connection' bridge ground from all your instruments, conveniently ensuring that you need to use dBuz at all times to make your instrument playable...

 

Quote

2. The standard instrument bridge ground, when AC power hot is wired to ground, and the musician is gripping the neck, the electric current will flow through the bridge ground, into the metal strings, and cause the muscles of the hand to contract, what's known as a "death grip," because they won't be able to uncurl the fingers and let go. Current then flows through the arm, chest, heart (and all other major organs except the brain) towards the feet, and earth ground. dBuz CAN'T cause this problem! dBuz is designed to be worn on the hip, and fails open circuit. Even in the extremely unlikely event it fails short circuit, the sensor is located below all major organs, so there'd be a bad sting, but pulling the insulated sensor cable easily removes the sensor, and it WOULDN'T KILL YOU! Because the standard bridge ground is so dangerous, Aero recommends removing it entirely and using only dBuz. A standard bridge ground is 100's of times more dangerous than dBuz.

 

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My ‘77 Precision has the same problem of buzzing until the strings are touched. I initially suspected a grounding issue but when I checked it with a multimeter I was able to confirm continuity between the strings and the ground of the output socket.

 

In contrast, my recently completed bitsa build is completely silent. That too has continuity between the strings and the output ground but the main difference is that I shielded all of the cavities and ensured the shielding was also grounded. I suspect that shielding is the answer and when I get a moment I’ll do the same with the older bass. 

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6 hours ago, Stub Mandrel said:

As above, usually a poor connection for or missing ground wire to the back of the bridge. Pop the bridge off and see if it has pulled out.

You can use copper tape to hold it down 

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45 minutes ago, Geek99 said:

You can use copper tape to hold it down 

Yes. Copper tape is great. But make sure to use one with a conductive adhesive if relying on that - tales from the EMC lab 🙄.

But the OP's bass seems to be correctly grounded. The noise is coming from the player. When the player touches the strings/bridge or anything else that is grounded then the noise stops as the player is held at a fixed electrical potential (voltage).

Edited by rmorris
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1 minute ago, Geek99 said:

Pacemaker ?

Not in general. Anyone near the bass but not at a fixed potential - practically this means not touching 'Earthed' metal acts as a source of radiated noise due to the RFI soup we are generally immersed in. 

So if there were no one near the bass there wouldn't be the buzz. But it's difficult to play it from a distance !

By 'Earthing' to the player it stops the antennae effect.

Having said that I did once he ave a glitch at distinct one second intervals and I really should have realised it was my quartz movement watch causing it as it was synchronised with the movement of the seconds hand 🙄

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21 hours ago, Tjhooker said:

I have a passive P bass that is dead quiet when you are touching strings bridge etc but makes a buzz/ hum when your not.

When plugged into my pedalboard any high gain pedals make this sound louder...

I can also stop the hum/ buzz when touching and metal casing on the pedalboard pedals too!?

😬

I have an active bass with EMGS that doesn't do this when plugged into the same rig.

 

Does this sound like a problem with the bass or the mains earth ..? Any suggestions welcome

 

 

The EMG's will be less susceptible to noise, as they barely have any windings to pick up noise and rely on their internal preamp to get the output to the desired level, and are internally shielded so well that they don't even require a ground connection to the bridge. I would expect it's either the (lack of) shielding of the passive bass, the mains earth, or a loose ground wire to the bridge of the P-bass. I would start by checking whether the wall socket you're plugging into truly is grounded, and I'm surprised this hasn't been mentioned yet. I live in a home built in or around 1990 and the only place where I originally had grounded sockets was in the kitchen, in the shed (attached to the house) and in the attic, for the central heating boiler and the ventilation system, even though the sockets in some other rooms look like grounded sockets too :|

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34 minutes ago, LeftyJ said:

 

The EMG's will be less susceptible to noise, as they barely have any windings to pick up noise and rely on their internal preamp to get the output to the desired level, and are internally shielded so well that they don't even require a ground connection to the bridge. I would expect it's either the (lack of) shielding of the passive bass, the mains earth, or a loose ground wire to the bridge of the P-bass. I would start by checking whether the wall socket you're plugging into truly is grounded, and I'm surprised this hasn't been mentioned yet. I live in a home built in or around 1990 and the only place where I originally had grounded sockets was in the kitchen, in the shed (attached to the house) and in the attic, for the central heating boiler and the ventilation system, even though the sockets in some other rooms look like grounded sockets too :|

 

Yes - low impedance pickups like EMG are less susceptible to interference as you say. And the associated controls are then lower impedance themselves eg 25K pots vs 500K or 1M0.

But can we dispense with the idea that there is some problem with the earthing of the bridge in this particular case.

The noise 'goes away' if the OP touches the strings. That indicates that the 'Earth' path is intact.

When the player is near the bass but not touching any grounded metal - be it the bass strings / bridge or another piece of metal that is grounded eg a rack unit / chassis - the body acts as quite a good antennae for the 'emi soup' we are immersed in and causes this to be picked up by the (High Impedance) bass electrics.

Screening is advised as it will attenuate the amount of interference getting through to the electrics. I'm an advocate of screening the rear of any plastic pickguard. It also reduces the problem of them "going static" where touching them causes a "brushing / rustling" noise in the output.

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The basses I've shielded have really benefited - there is an extra silence to the background that lets them sound more clearly - even if you can't really hear it: the hum and interference is there - it's a bit like getting a new TV with a blacker black - the colours in contrast seem to pop a bit more.

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All instruments (mainly Fender's, go figure) that I've shielded were theoretically well grounded as I always first check the ground conductivity, but were buzzing.

 

After a full copper (aluminium is excellent too, but a pain in the a*s to solder) shielding including the entire back of the pickguard and all cavities, everything fully interconnected and grounded, the instrument becomes dead quiet.

 

What we're doing here is like all those useless meetings you have to attend at your job : there are obvious solutions, but nobody is willing to apply them, because we didn't come to a (scientific) concensus...

 

Strange how human beings need to talk for talking and need to be heard even if they have absolutely nothing to say.

 

And why never listen to experienced people with 100% of success even if science facts (which are too often wrong ... afterwards) are not really suggesting that it's correct.

 

Make that perfect shielding and forget the buzzing.

 

As I also said, you can use this cable too and it's clearly stated why it will work and how : https://d-buz.com/

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Wow.. I'm trying to keep up with all this, some truly knowledgeable individuals here.. thank you...... 🤯

 

a bit more info that might help pin point the problem but I'm not sure.

Had a practice last night at a local Venu.

I did have a tiny bit of the same hum when not touching the strings but to be honest if I wasnt listening out for it I would not have noticed.

AND this was at not maxed but pretty high volume, at home it would have been buzzing like crazy.

I live in a very old building so the wiring in here could be about as early as it gets 😬

I'm thinking my bass may not be perfectly shielded but I'm starting to think it may be a problem with the wiring of the house?

That or a bass hating poltergeist 👻

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