Grounding?

McCay · #1 05-16-2007, 09:23 PM

I'm having some noise issues.

I have a 2006 Peavey Grind 4string. Looks Great, Sound Great, but still:

When I crank both tone knobs all the way up, I start to get a harsh buzzing sound. This goes away if I only turn one tone knob up at a time, or if I touch the G string with my fingers. I have tried the instrument on several amps and it is always there, so it must be a problem with the bass.

So if it is a wiring thing, do I need to properly ground it? Shield it?

All help appreciated. Thanks!

stanger503 · #2 05-17-2007, 01:07 PM

well shielding should be included any way. its not a must, but youd probably want it. and it sounds like a normal thing, you turn your tone up....you get more noise. thats a fact, at least on passive basses, active im not sure.

middy · #3 05-18-2007, 02:05 PM

Even some high-end basses come with poor shielding and ground loops. It's a shame, really, that manufacturers can't do it right.

McCay · #4 05-19-2007, 01:03 PM

Thanks for the help.

Jo6Pak · #5 05-19-2007, 01:57 PM

'Generally', if the hum goes away when you touch the strings, it means the bridge is not grounded. Did you have the electronics cavity open and maybe yanked the wire loose? If not, pop it open amd make sure there is a wire going from ground (soldered to the back of one of the pots or going to the neg clip on the input jack) to the bridge (possibly thru a hole drilled from the cavity over to the bridge. If you have a multimeter, ohm it out between the bridge and ground. You should see a short (zero ohms)...

202dy · #6 05-19-2007, 04:12 PM

When the system is properly grounded there will be no hum when your fingers touch the strings. That is because you are the path to ground. All passive systems will produce hum when not grounded. You must be in contact with the strings for more or less noise free performance. It appears that grounding is not the problem with this instrument.

Turnaround · #7 05-20-2007, 04:15 PM

Quote:

Originally Posted by Jo6Pak

'Generally', if the hum goes away when you touch the strings, it means the bridge is not grounded.

Unfortunately, it's not true. If the hum goes away when you touch the strings it means YOU are not grounded. There is a common misconception that when you touch the strings, you ground them. What really happens is that when you touch the strings you ground yourself. You are a source of the noise.

Here's how you can prove it. Plug a lead cord into your amp and turn the amp on. Turn up the volume a bit and grab the tip of the free end of the lead cord. Be sure you are only touching the tip - don't touch any part of the sleeve. You will bear a nasty buzz. Now, without letting go of the tip, grab the sleeve of the lead with your other hand. The noise reduces. So what's going on?

When you grabbed the tip of the lead, you introduced all of the noise from your body to the amp. But when you then touched the sleeve, you grounded yourself and the noise dissipated.

Likewise, when you touch the strings of your bass, you ground yourself and dissipate the noise. In fact, if the noise dissipates when you touch the strings, it tells you the strings are grounded, which means the bridge is grounded.

middy · #8 05-20-2007, 08:23 PM

Quote:

Originally Posted by Turnaround

Unfortunately, it's not true. If the hum goes away when you touch the strings it means YOU are not grounded. There is a common misconception that when you touch the strings, you ground them. What really happens is that when you touch the strings you ground yourself...

+1

Poop-Loops · #9 05-20-2007, 08:39 PM

Quote:

Originally Posted by Turnaround

Likewise, when you touch the strings of your bass, you ground yourself and dissipate the noise. In fact, if the noise dissipates when you touch the strings, it tells you the strings are grounded, which means the bridge is grounded.

So if I want to get rid of the hum, I should make the wiring and bridge float?

theshadow2001 · #10 05-20-2007, 09:53 PM

Quote:

Originally Posted by Turnaround

Unfortunately, it's not true. If the hum goes away when you touch the strings it means YOU are not grounded. There is a common misconception that when you touch the strings, you ground them. What really happens is that when you touch the strings you ground yourself. You are a source of the noise.

Here's how you can prove it. Plug a lead cord into your amp and turn the amp on. Turn up the volume a bit and grab the tip of the free end of the lead cord. Be sure you are only touching the tip - don't touch any part of the sleeve. You will bear a nasty buzz. Now, without letting go of the tip, grab the sleeve of the lead with your other hand. The noise reduces. So what's going on?

When you grabbed the tip of the lead, you introduced all of the noise from your body to the amp. But when you then touched the sleeve, you grounded yourself and the noise dissipated.

Likewise, when you touch the strings of your bass, you ground yourself and dissipate the noise. In fact, if the noise dissipates when you touch the strings, it tells you the strings are grounded, which means the bridge is grounded.

Your explanation seems a little unusual to me and I have a hard time believing it.

I would be interested to see what happens if the original poster put his strings against something that was already grounded like a radiator or something.

Baleen · #11 05-20-2007, 10:05 PM

'Turnaround', in any given case, the person may or may not be grounded - that depends on what he/she is in contact with. Yes, you are being grounded when you touch the instrument ground (if it's good), but the instrument's buzzing doesn't diminish when you touch it because it is grounding you, rather it does because you are helping to eliminate the buzz. Furthermore, the person is not the source of the noise that's aggravating the instrument. If I solo one of my single-coil Jazz pickups, it'll buzz no matter my proximity to it. Actually it'll buzz because it is susceptible to interference from electrical fields, e.g. CRTs, light dimmers, motors, etc.. It'll act like an AM radio antenna**.

In the case of single coil pickups, the person can help reduce the noise, but can't always eliminate it. Though, with split-coil (hum canceling) pickups, a person can almost always provide enough help to overcome shielding inadequacies.

'Turnaround' is correct that we are not a clear path to ground. If we were, then touching the tip of the patch cord would make no noise as the input would would be shorted. This is also proven by how it is possible for a person (read: knowing electrician), with good rubber soled shoes, to touch only the hot leg of an electrical outlet and not get shocked.

I think the main problem with Jo6Pak's statement, "'Generally', if the hum goes away when you touch the strings, it means the bridge is not grounded." is that it is backwards. If the hum goes away when you touch the strings, it does in fact mean that the bridge is grounded. Otherwise, your touching it would've made no difference. Again, it's like, as 'Turnaround' points out, when a person touches the sleeve of a patch cord, it quiets the noise. The person helps by being added to the electrical equation because the bridge IS grounded.

Why people quiet the buzzing, I must confess, is not entirely clear to me. I'm guessing it's because we act as an extension of the shielding, which is what the noisy instrument is lacking. We do conduct electricity (if you touch the hot leg of the outlet and the ground, you will definitely get shocked), and we do have/can carry a charge of our own. Maybe we're more like capacitors. Or maybe we act as an extension of the shield because we are much larger than the pickup coil and we are basically spread out like a ground shield. I think this would also explain why touching the tip of the patch cord makes noise - because the person is exposing the hot signal over a large area without shielding. It would be like connecting your instrument to an amp with speaker wire (unshielded), the lack of shielding would allow the introduction of interference.

Last (finally) thought: I think people are commonly associated with being ground, because adding ourselves to the ground-side of an audio circuit often reduces noise. I admit I do the same thing.

** The orientation of single-coil pickups can eliminate the buzz, or nearly so because they act like AM radio antennae. Of course, in the case of the instrument, we are trying to find the worst reception. This happens when the coil of the pickup is in line with the disturbing field (often you can find the right direction and tilt to point the instrument to quiet the noise - note that it is also quiet 180 degrees from that orientation because the pickup coil is essentially oriented the same way). The buzz can't be quieted, though, when there are multiple fields coming from multiple directions, or when the interference is stronger than the positive benefit of a person's shielding help.

middy · #12 05-21-2007, 11:51 AM

Turnaround is right, even if you think it doesn't make sense.

Nice essay, though.

Poop-Loops · #13 05-21-2007, 11:57 AM

Okay, but nobody's answered how to get rid of that damn noise yet.

202dy · #14 05-21-2007, 12:17 PM

The answer to getting rid of the hum is the same as eliminating wolf tones. Keep the left hand in contact with the strings at all times.

Turnaround · #15 05-21-2007, 12:31 PM

Quote:

Originally Posted by Poop-Loops

Okay, but nobody's answered how to get rid of that damn noise yet.

Sorry about that - we got caught up in a discussion and missed the whole point. The answer is that you probably need to shield the instrument. That means lining the pickup and control cavities with copper or aluminum foil and making sure that the foil is grounded. Or paint the cavities with shielding paint. This will probably lessen the noise, but it may not get rid of it entirely. Be sure to included the inside of the control cavity cover.

No guarantees that this will cure your problem though. Some basses have inherently noisy pickups - others have noisy pre-amps. Generally shielding doesn't help with them.

Turnaround · #16 05-21-2007, 12:45 PM

Thanks Baleen for your insight. I have heard various explanations about the body being a source of noise, which doesn't explain why an instrument can be equally noisy when you are not near it. I have heard the argument that the body is like an antenna, picking up noise and inducing it in the instrument. And I have heard that when you ground yourself to the instrument/amp ground, you become part of the noise shield. No single explanation works for me. I tend to think of myself as a noise source because of the "grab the hot end of a lead" argument.

But I suppose the point of it all is that if you touch the strings and the noise disappears, then your strings are grounded. So too is your bridge (assuming electrical continuity between bridge and strings). This doesn't work so well though if your strings are coated (I have some DR Black Beauties on right now and there is no continuity from strings to bridge). THis bass is now noisy.

But it looks cool.

fishdds · #17 05-21-2007, 03:21 PM

Quote:

But I suppose the point of it all is that if you touch the strings and the noise disappears, then your strings are grounded.

This doesn't make sense to me, because I have an SX jazz copy, and if my hands weren't on the strings, it would make a lot of noise. I looked in the control cavity, and there was no wire coming from the bridge to a ground connection. No hole for that or anything. So, I backed out one of the bridge plate screws and ran a wire around that and re-inserted the screw. Next I ran the wire up and into the bridge pickup route and through the hole from there to the control cavity, and soldered it to a pot (with the ground wires from the pickups) Now it makes a lot less noise when I'm not touching the strings. (still some, but nothing like before) So, I know the strings weren't grounded before, and the noise was going away when I would touch the strings, and now I know that the bridge is grounded, and the noise is a lot less. I've seen wires routed through from the bridge to ground, and on some Jazz basses, I've seen a thin strip of metal coming up from the bridge to the bridge pickup route (presumably to ground) This is sort of what I did with a 22 gauge plastic coated wire, and hey, it works for me...

Baleen · #18 05-21-2007, 04:12 PM

Fishdds, there had to be some connection from the strings to the signal ground before you added the wires. Perhaps through the paint or the undercoat. But now you have a definitive connection.

Poop-Loops, sorry, I shouldn't've buried my answer in the, ahem, 5th paragraph: "I'm guessing it's because we act as an extension of the shielding, which is what the noisy instrument is lacking."

Turnaround, I'm still not convinced that a person is causing buzzing in the instrument. Consider this (using the patch cord connected to an amp on one and nothing on the other end): Touching the tip of the patch cord to a mic stand (that's not connected to anything), a metal music stand, a trombone (I have one sitting here), to a 2" screw in my bass stool, and even my area rug (laced with metallic strands?) produces buzzing. All to a different degree, depending on the object. Mic stand, music stand and trombone: lots; screw: some; rug: nearly nothing. I believe these objects simply extend the hot leg of the patch without the protection of any shielding.

I believe we are experiencing the same thing here that a long unbalanced cord experiences: susceptibility to interference. The greater distance/area with the least amount of adequate shielding produces the most noise.

Yes, I think humans probably do produce some noise, as we carry a small electric charge (but so does a potato), but I think this noise is negligible.

And I do agree with Turnaround, and as I alluded to earlier, that shielding the instrument will probably help reduce the noise (can't hurt), but may not be enough to eliminate it. Like the long unbalanced patch cord, no matter how well shielded it is, without the benefit of a second leg, i.e. balance cable (or in the case of a bass, a second reverse wound pickup, a humbucker, or a phantom coil), the noise can't always be eliminated.

Poop-Loops · #19 05-21-2007, 06:09 PM

I put some copper around the cavity (Not around the pickups, though, seperate cavity. So I'll have to do that.), but didn't know I should ground it.

By the way, I have 2 J pickups that have 2 magnet bars per string, so I thought that would act like a humbucker. Guess not.

Also, I have 2 soap bar pickups in my fretless and I still get a lot of hum when I switch to my bridge pickup and up the treble. =/

Baleen · #20 05-21-2007, 06:52 PM

Poop-Loops,
Typical single-coil J pickups cancel hum when they're both at the same volume because their windings are in the opposite direction of each other. This causes the interference in each of the pickups to be in the opposite phase, canceling itself out when the two pickup signals are combined. This is how a P-style split-coil pickup cancels hum - two coils, wound opposite of one another.

If there's still noise when the pickups are set at the same volume, then check the shielding in the control cavity, as the noise is being introduced elsewhere. Or if the pickups aren't matched, then they won't properly cancel.

As for the soap bar pickups, either they aren't actually humbuckers, or the noise is being introduced after the pickups, like in the control cavity. Sounds like they might be single coil if the noise starts when you solo one of them.

All of the shields have to be connected to ground to have any positive effect. Preferably at the output jack or at a star ground point. In passive systems it is less critical, but where there is a preamp, the shield should be connected after the preamp to ensure you are connecting it to the amp's (or whatever you're plugging into) ground. The pickup's ground going into the preamp isn't necessarily the final signal ground.

I had to throughly shield my P's, J and EB-3 to cut down noise, but the EB-3 and J still buzz like mad with one pickup soloed. And they all still buzz a little in particularly bad environments if I'm not holding the strings.

Turnaround, that's a drag about the coated strings. I've only ever used nylons on a MM Sterling that was quiet, so I never thought about the drawback.