Why do you need a string ground ?

[Paul P]

Why should guitar strings, and bridge, be grounded ? It seems to me
that the strings are only 'connected' to anything through the magnetic
field of the pickups so I don't see what purpose grounding them would
serve. I read that you can reduce noise by grounding the strings but
if so where does the noise come from and how does it get into the
amp ?

Also, if an amp's chassis were to become live through some malfunction
wouldn't grounded strings be a hazard ?

Paul P

[Paleo Pete]

I'm not sure exactly why, but if the strings are not grounded there's a very good chance the guitar will buzz or hum or hiss or pop when you touch the strings. Or all the time. My Harmony got lots of static that would quiet down when I touched the strings. I had to install a ground where none ever existed, which involved carefully drilling a long hole diagonally through the body to the tailpiece, but it stopped the hiss, hum and static completely once the strings were grounded.

Why is a multifaceted answer, and I can only repeat some of what I've read about it. Different ground paths can cause hum, wall warts can emit a magnetic field that causes hum if your guitar cord is too close, same for any magnetic field (which is why you get loads of noise if you play in front of a CRT monitor), neon and flourescent lights cause noise, a bad guitar cable can turn your guitar into a radio antenna, and 50 or 60 cycle hum can be a big problem that gets bigger the more equipment you plug in. Good grounding with no ground loops goes a long way toward diminishing or eliminating noise, static, hum and pops in the system. Extension cords lying parallel to the guitar cables can set up a magnetic field that causes hum too. On stage I have to run my extension cord for the wall wart on the other end of the pedalboard from the guitar cables, to stop the hum it causes. Or most of it. I use a splitter I built and one wall wart instead of 4. And I have to turn off any neon beer sign within 15 feet...

The first thing I do when I get a used amp is replace the plug with a grounded one, the ground pin is almost always broken off. If it never had a ground, I add one. with a new (to me) guitar I go through it and check all solder joints, and make sure it has a good solid ground, then if it makes noise I find out where the bad ground is, add a ground wire or figure out where the ground loop is. I also shield my guitars, at least the back side of the pickguard. It makes a huge difference, just shielding the pickguard.

Maybe some of the guys here who actually know something about electronics can give you more details about why, I just know a little that I've looked up and what experience has taught me. Grounding, shielding and placement always matter...

I can't even think about answering the amp question, I think it would be risky, but some older amps were built with live chassis', so it might only be an issue of watching the ground carefully. That may be why ground reverse switches were invented...

[David Schwab]

The strings (and other metal parts near the pickups) act as an antenna and picks up noise.

The pickups pick up more than just the strings. Humbuckers use two coils to cancel electrical interference, but magnetic interference still gets through.

Grounding the strings shunts that noise to ground.

[Paul P]

The strings (and other metal parts near the pickups) act as an antenna and picks up noise.

Grounding the strings shunts that noise to ground.

I can see that but what I don't get is if the strings are not connected to
anything how can the noise they pick up go anywhere ? Can picked-up
noise be transferred through the magnetic field to the pickup (or disturb
the magnetic interaction between the string and the pickup) ?

On a similar note, I understand humbuckers were created to reduce/cancel
60 cycle hum. Is this mainly a problem on a stage with many high power
electrical devices nearby or are pickups sensitive enough to pick up hum
in a home environment ?

Paul P (Happy Thanksgiving to all you turkey eaters :-)

[dai h.]

if the strings are not connected to
anything how can the noise they pick up go anywhere?

couldn't they capacitively (electrostatically) couple into the wiring? Looks most susceptible after the volume when it is turned down. Might have something to do with the analogy of a boat on water where you don't notice as much how high or low you are relative to a fixed position since the boat moves up/down with the water (no potential difference = no voltage difference = no separate voltage apart from the signal voltage).

something I was wondering about related to grounding is the truss rod. My understanding was that metal parts should not be left floating (not connected to anything) and it seems a truss rod is a big hunk of metal but doesn't seem to be grounded usually.

Also, on related note there was an old post (by Steve C.?) on how when you touch the strings your body acts as an electrostatic shield to help reduce buzz (I guess the higher harmonics of hum in the environment) or something like that. Sticking a cap in between the send (noise) and receive (gtr.) passes less of the noise through and as I understand layering shields is effective since Cs in series = less capacitance (ex. 500pF + 500pF in series = 250pF) = less gets through. (I'm not sure of what is conductive in your body though. Moisture? Iron particles in blood?)

[LeftyStrat]

I always thought that grounding the strings simply provided a little shielding to the pickups. My EMG-SA equipped strat doesn't have the strings grounded, because the pickups are internally shielded, and I have no problems with noise.

[David Schwab]

I can see that but what I don't get is if the strings are not connected to
anything how can the noise they pick up go anywhere ? Can picked-up
noise be transferred through the magnetic field to the pickup (or disturb
the magnetic interaction between the string and the pickup) ?

The pickups don't only sense disturbances to its own magnetic field. It's a coil of wire hooked up to your amp... it will pickup noise. The strings will pickup noise, and yes, the pickups will sense that noise too because the strings are close enough to the pickups and it gets induced into the coil.

On a similar note, I understand humbuckers were created to reduce/cancel 60 cycle hum. Is this mainly a problem on a stage with many high power electrical devices nearby or are pickups sensitive enough to pick up hum in a home environment ?

Any single coil pickup will pickup hum, doesn't matter where you are.

[David Schwab]

I always thought that grounding the strings simply provided a little shielding to the pickups. My EMG-SA equipped strat doesn't have the strings grounded, because the pickups are internally shielded, and I have no problems with noise.

EMG's use a very effective shield. The entire pickup is encased in a brass screen (like window screen, only finer), and that screen is grounded. That acts as a Faraday cage.

You can also use a metal cover, but that usually softens the top end of the pickup's tone a bit.

I fully shield my pickups, and I still need string grounding.

[Steve Conner]

I believe that string grounding has its effect mostly by grounding the player's body. If the guitar has a poorly shielded control cavity, then it will pick up capacitively coupled hum from your body, which in turn is picking it up from the mains wiring in the room. But once your body is grounded it turns from a big squishy antenna into a shield.

Pickups without metal covers can also pick up stuff capacitively, and the grounded strings help to shield them.

My latest "amp" design needs the best shielded guitar possible, not to mention a 30ft fibre optic guitar cord for personal safety.
http://www.youtube.com/watch?v=lSAExHBrfwU

[Joe Bee]

I agree with that, usually the hum decreases considerably once you touch the strings, and the only explanation for that is that you turn your body from a bag of noise into a grounded shield.

I had a rather shocking experience a couple of days ago though when I had my guitar in one hand and was fumbling around at the back of my amp with the other. I touched the plates supply at the OT and got the full 430V from hand to hand. Made me drop my guitar and rethink my safety procedures.
I also get shocked frequently from my microphone because it is connected to my computer via some USB thingie so it has no physical ground connection but is ground referenced through the Y-capacitors on the computer switch mode PSU. This brings the mike up to more than 100V through capacitive coupling.


thus I would argue that it is a lot safer to have the strings floating, at least if you can afford EMGs that is :-)

[Paul P]

My latest "amp" design needs the best shielded guitar possible, not to mention a 30ft fibre optic guitar cord for personal safety.

You crazy ! :-)

[David Schwab]

I agree with that, usually the hum decreases considerably once you touch the strings, and the only explanation for that is that you turn your body from a bag of noise into a grounded shield.

Well your body picks up noise too. Just touch the tip of your patch cord and listen! But the string grounding isn't just to ground you, because you can see that a guitar with no string ground will hum even when you aren't touching it.

I had a rather shocking experience a couple of days ago though when I had my guitar in one hand and was fumbling around at the back of my amp with the other. I touched the plates supply at the OT and got the full 430V from hand to hand. Made me drop my guitar and rethink my safety procedures.
I also get shocked frequently from my microphone because it is connected to my computer via some USB thingie so it has no physical ground connection but is ground referenced through the Y-capacitors on the computer switch mode PSU. This brings the mike up to more than 100V through capacitive coupling.

Ouch! There's a few things you can do. One is to install a capacitor between the string ground wire and ground. This will block DC current from flowing. Some people use a cap and resistor. I forget the values off hand.

Another smart thing is to bring a small neon bulb outlet tester with you. Touch one end on your strings, and the other on the mic, and see if it lights up.

A small VOM would also work. I measured 80 volts once!

thus I would argue that it is a lot safer to have the strings floating, at least if you can afford EMGs that is :-)

I have a '74 Ric that I had totally shielded with copper foil, and had a Hi-A (Bartolini) and Gibson sidewinder, and it had no string grounding. It was dead quiet except around light dimmers.

What EMG does is wrap the whole pickup in a brass screen.

[jack briggs]

Ouch! There's a few things you can do. One is to install a capacitor between the string ground wire and ground. This will block DC current from flowing. Some people use a cap and resistor. I forget the values off hand.

.001uf/220K. I use to wire them into all of my guitars. Cap should be rated for 500V. The only downside is that the network acts as a fuse, needing replacement if blown by a spike.

[Liam]

You crazy ! :-)

I think "unwell" describes Steve adequately. That Youtube video is absolutely awesome, I want one. Well done!

[Sir Cuitous]

You can shield pickups and cavities all you want, but the they will still receive emi from the same poles that receive the string vibration. Thus your single coils are always going to have hum. The metal parts and strings are an antenna, but it will also transmit. Grounding to the bridge/strings will transmit some noise straight into the air, but much more noise will be grounded through your body when you touch the strings.