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Hum when no strings are touched


(@banre)
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Joined: 17 years ago
Posts: 417
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Hey all,

I picked up a new bass over the holidays and everything has been great. Yesterday I was playing with it at church before the service and noticed then when I was not touching any of the strings, a hum came through the PA. I touched any string, not played mind you just touched, the hum went away. And when I roll the volume all the way off on the guitar, it goes away as well. For the service it wasn't a huge deal, I just made sure I was touching something the whole time.

I've since tried i here at the house and noticed the same thing. I suppose it could have been doing it before yesterday and I just didn't notice it until I got some real volume on it.

Any idea what's up? It's not unbearable, just annoying the heck outta me.

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(@davidhodge)
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Joined: 14 years ago
Posts: 4485
 

I may be totally wrong here (you'll notice I rarely post in this area ) but that sounds like a grounding issue. Could be your bass but could also be the wiring in the church itself.

Wait for the better minds to chip in with other options, though!

Peace


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(@ricochet)
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Joined: 18 years ago
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There needs to be a wire in contact with the bridge (to ground the strings) grounded inside the guitar to the shell of a pot or to the sleeve of the jack.

A little hum like that is common enough that I'd consider it normal, but if it's bad, you need to check the grounding.

"A cheerful heart is good medicine."


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(@moonrider)
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Joined: 17 years ago
Posts: 1309
 

Hey all,

I picked up a new bass over the holidays and everything has been great. Yesterday I was playing with it at church before the service and noticed then when I was not touching any of the strings, a hum came through the PA. I touched any string, not played mind you just touched, the hum went away. And when I roll the volume all the way off on the guitar, it goes away as well. For the service it wasn't a huge deal, I just made sure I was touching something the whole time.

I've since tried i here at the house and noticed the same thing. I suppose it could have been doing it before yesterday and I just didn't notice it until I got some real volume on it.

Any idea what's up? It's not unbearable, just annoying the heck outta me.

I'm gonna ask the obvious question . . . what kinda bass is it? Does it have humbucking or single coil pickups?

Playing guitar and never playing for others is like studying medicine and never working in a clinic.

Moondawgs on Reverbnation


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(@gnease)
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Joined: 18 years ago
Posts: 5058
 

if touching the strings improves the situation, then it is usually an electric field issue. grounding and/or shielding is inadequate, and humbucker versus single coil is not nearly as relevant as whether the pups have grounded metal covers (good) versus plastic (unshielded).

Ric's identified the most likely cause: the bridge ground connection is probably broken or non-existent. use an ohm meter to measure the resistance between the strings or bridge to the jack nut to check for this connection. if the reading is any more than a few ohms, the connection is not there. long shot: it's also possible -- but very unusual -- this bass has a fuse between the bridge and the signal ground to prevent accidental electrocution. if so, the fuse probably needs to be replaced.

-=tension & release=-


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(@banre)
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Joined: 17 years ago
Posts: 417
Topic starter  

Thanks for all the info guys. It's not an unbearable hum, by any means. I'm going to get the ohm meter out after I get back from vacation and see what that says.

To the single coil question: yes, it's a jazz bass style Peavey and does have single coil pups. I don't think this hum is coming from that because when I have the volume up on only one pup, I get a different sort of hum and that hum gets less and less as I raise the volume on the second pup (and that makes them act more like a humbucker, right?).

It does look like the covers to the pickups are indeed plastic. The back of the guitar has a big cavity for all the pots and the input jack covered by a piece of plastic, but it has some shielding on it. Probably not enough, but there is some there. If I wanted to shield all that further, what sort of material should I use?

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(@kent_eh)
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Joined: 16 years ago
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It does look like the covers to the pickups are indeed plastic. The back of the guitar has a big cavity for all the pots and the input jack covered by a piece of plastic, but it has some shielding on it. Probably not enough, but there is some there. If I wanted to shield all that further, what sort of material should I use?

A shield with a hole in it is as effective as a bug screen with a hole in it.

Here's an article about shielding. He uses a Strat for an example, but it should translate fairly easily to your Peavey.

I wrapped a newspaper ’round my head
So I looked like I was deep


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(@gnease)
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Joined: 18 years ago
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A shield with a hole in it is as effective as a bug screen with a hole in it.

not true. depends upon wavelength of signal/interference one is trying to shield. ever notice that a bridge superstructure will kill AM radio reception, but not FM. all about relative dimensions of holes and wavelengths.

the insidious holes most people leave in shields are the slots where cover shielding or metalization does not contact the control cavity shielding often enough around the periphery -- maybe even only one place.

the Guitarnuts site is good, but does contain mistakes. examples are: the ground loops between the pots are fairly benign. doesn't hurt to remove them, but probably not necessary. and the shielding of a pup often does indeed change its tone -- didn't see that noted, but maybe I missed it.

-=tension & release=-


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(@ricochet)
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Joined: 18 years ago
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Yeah, on pickup makers' forums there's lots of discussion about pickup cover materials, thicknesses and effects on tone.

"A cheerful heart is good medicine."


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(@kent_eh)
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Joined: 16 years ago
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A shield with a hole in it is as effective as a bug screen with a hole in it.

not true. depends upon wavelength of signal/interference one is trying to shield.
Yup, that's a much better way of explaining it.
A shield with holes can work fine, as long as the holes aren't too huge or numerous.

To beat my metaphor to death: a holey screen can let in the mosquitos, and keep out the wasps.

I wrapped a newspaper ’round my head
So I looked like I was deep


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(@ricochet)
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Joined: 18 years ago
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Or at least keep out those crazy Luna moths I see on TV flying around biting people and giving them sleeping sickness!

"A cheerful heart is good medicine."


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(@kent_eh)
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Joined: 16 years ago
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Or at least keep out those crazy Luna moths I see on TV flying around biting people and giving them sleeping sickness!
it was the best face saving I could think of that late at night

I wrapped a newspaper ’round my head
So I looked like I was deep


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(@gnease)
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Joined: 18 years ago
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no reason to save face, Kent. all of us toss out glib comments about ... everything. unfortunately, noobs may take at face value.

(oh, if you really feel bad about it, use the short knife )

-=tension & release=-


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(@ricochet)
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Joined: 18 years ago
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Oh yeah, I was just being silly. My usual state.

"A cheerful heart is good medicine."


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