Hum Starts When I touch Bass

[shakerattleroll]

Ok, so I searched and could not find the answer for this.

In my garage i normally get some buzz, but with my new j bass, the hum starts when I touch it. What kind of issue is that?

And yes, I turned both pickups to full, but that did nothing. Normally when you touch a bass with poor grounding hum stops, and I don't have ground issues in other power sources (practice space) with this bass or my amp.

[slyjoe]

Could be the dreaded garage EMI.

[Bass Mule]

Do you have a ground-lift switch on your amp?

[shakerattleroll]

Originally Posted by Bass Mule

Do you have a ground-lift switch on your amp?

Yes, and flipping it did absolutely nothing.

[shakerattleroll]

Originally Posted by slyjoe

Could be the dreaded garage EMI.

But why would it start to hum like crazy only when I touch it. Isn't EMI interference constant and seperate from a grounding issue? There is some EMi going on, as any guitar I plug in out there buzzes independently of being ground...but this is different, like a buzzsaw as soon as I touch metal on the bass.

[slyjoe]

Well, you are a bigger antenna.

A reversed ground can cause this too - or it's a garage grounding problem. Have you tested for proper grounding in the garage?

Last but not least, shielding the bass may help also.

[shakerattleroll]

True, I am a bigger antenna.

Reversed ground??? What is that? I'm assuming you mean that when I touch the bass, instead of grounding it I remove the ground, but how does that work, and how can I fix it?

Also, how is shielding going to stop me from being an antenna? By that logic, wouldn't I need to shield myself?

[slyjoe]

I have read on other forums that touching strings causing hum is kind of backwards from what most people experience, where touching strings reduces hum. This is generally due to the strings not being grounded at the bridge properly. Reverse ground is when the output jack is wired backwards.

You mentioned that this only happens in the garage - if so, I would suggest a ground problem in the garage is to blame.

[shakerattleroll]

Originally Posted by slyjoe

I have read on other forums that touching strings causing hum is kind of backwards from what most people experience, where touching strings reduces hum. This is generally due to the strings not being grounded at the bridge properly. Reverse ground is when the output jack is wired backwards.

You mentioned that this only happens in the garage - if so, I would suggest a ground problem in the garage is to blame.

I'll pop the pickguard off and double check the output jack.

As far as the garage being wired improperly, it might be, but even if so, with other guitars I ground them and the hum stops as soon as I touch it.

So, I will possibly do some resoldering this evening and let you know how it turns out.

[slyjoe]

This is a NEW jazz bass? That sounds weird. I've never had a factory jazz with wiring problems.

[clinedt1]

In the cavity of your bass you probably have a wire that is sticking out of some random hole and connected to your ground. at least on the basses I've seen this wire is connected to the bridge which obviously touches the strings and is why you change the ground of you bass when you touch it. If this problem rises when you add your self to the circuit, take yourself out of it permanently by disconnecting that wire. The bass will still work just fine.
I had a grounding issue with the stage I usually play on. There was a potential difference (voltage) between the grounds of 2 different outlets. So every time i would accidentally touch the mic with my mouth I would get a shock! Not cool. So I just disconnected that grounding wire and the problem is solved.
As a senior physics major and a construction worker, I can't think of anything right off that would cause this problem. I'll think about it some more though.
Do you have the same problem when you play other places?

[slyjoe]

You can keep the bridge grounding and prevent the shock by adding a resistor and capacitor to the ground wire. I don't remember the exact wiring - series or parallel.

[shakerattleroll]

Originally Posted by clinedt1

In the cavity of your bass you probably have a wire that is sticking out of some random hole and connected to your ground. at least on the basses I've seen this wire is connected to the bridge which obviously touches the strings and is why you change the ground of you bass when you touch it. If this problem rises when you add your self to the circuit, take yourself out of it permanently by disconnecting that wire. The bass will still work just fine.
I had a grounding issue with the stage I usually play on. There was a potential difference (voltage) between the grounds of 2 different outlets. So every time i would accidentally touch the mic with my mouth I would get a shock! Not cool. So I just disconnected that grounding wire and the problem is solved.
As a senior physics major and a construction worker, I can't think of anything right off that would cause this problem. I'll think about it some more though.
Do you have the same problem when you play other places?

No, the bass has no noticable hum (even with the J neck p/u soloed) when I play at our practice space. In other words, it seems to be ground correctly.

I'm not so sure that removing the ground wire is a good thing, as my understanding of electronics tells me that then I will have grounding issues no matter what I do, or where I am playing. And having a potential difference is an entirely different problem unrelated to mine (as I'm only playing bass and not using a PA).

To be fair, I could just not play in the garage...I don't even play there that often, but occasionally friends will want to jam, and my parents place is much closer than my rehearsal spot.

As for the garage being ground improperly, maybe, but my dad is a general contractor, and our electrician has worked innumerable projects for my dad. He does a solid job and I doubt that would have slipped by them, but anything is possible. I'll check tonite.

I'm thinking that the input jack being reversed sounds most likely, as that would change the grounding so that I'm actually shorting the ground when I touch the strings.

[shakerattleroll]

Originally Posted by slyjoe

You can keep the bridge grounding and prevent the shock by adding a resistor and capacitor to the ground wire. I don't remember the exact wiring - series or parallel.

There's no shock, the bass just buzzes like crazy when I touch it.

[slyjoe]

Yea - I was responding to another post - should have quoted it.

[Jared92]

If its used, someone could have messed with it. I had a P that did this once. I re grounded it and everything was fine. So id shoot for grounding again

[shakerattleroll]

Originally Posted by slyjoe

Yea - I was responding to another post - should have quoted it.

I get it now...And yes, you're right, the way to fix problems with potential differences is to properly modify your circuit to prevent you from being shocked, not eliminate grounding; that is asking for trouble.