Bridge Ground

disaster

Active member
Messages
45
Why is the bridge (& therefore the strings) grounded in an electric guitar?  Assuming you plug into a modern amp with a 3-prong AC cord in a building with compatible grounding & therefore a path to earth (mains ground) this shouldn't be too scary.  But if you plug into a "vintage" amp with a 2-prong AC cord or a building without compatible grounding & therefore no path to earth this could kill you.  "Vintage" amps are floating ground systems with significant power.  A modern amp in a "vintage" building becomes a floating ground as well.  If AC power ends up in the guitar "ground" which is directly connected to the strings the player goes poof.  Can anyone explain the purpose behind grounding the strings?

Thanks.
 

exalted

Senior member
Messages
723
I'm by no means an expert, but if I had to guess...it's so that when you touch the strings, the buzzing goes away.  :dontknow:
 

ByteFrenzy

Senior member
Messages
1,177
Ever touch the tip of a cable plugged into an amp with the volume turned up? The hum is your body being an antenna for the stray 50/60Hz electricity in the air. When you touch the strings your body is grounded and stops acting as an antenna.
 

disaster

Active member
Messages
45
from ByteFrenzy: "You may want to read up on http://www.guitarnuts.com/technical/electrical/safety/index.php".

Thanks, read it.  It seems to confirm that grounding for musical instruments is not a simple proposition.  Bummer.  I'll keep researching it and see if I can learn anything more definitive.  The downer about the article is it claims isolating the player from ground generates more noise (hum) in the circuit.  I'd like to eliminate the noise without eliminating the player as a side effect.

Thanks.
 

SkuttleFunk

Senior member
Messages
1,156
gounding on modern instruments comes down to this simple scenario: the overwhelming majority of players will not buy an instrument that 'buzzes' when they are not touching the strings. because of this, most companies ground the bridge so that they can more easily sell their instruments

I've had several clients who refused to allow me to leave the bridge ground disconnected in the control cavity, even after clearly noting the significant risk that a grounded bridge brought to them (they played a vintage amp in numerous venues with less than modern wiring standards - and they preferred not to use a wind filter over their SM58 microphone when singing) ... can anyone say potential disaster just waiting to happen?

the link provided earlier is something I considered installing on all of my instruments (has-sound.com even has this mod as a preassembled item you can purchase,) but I was informed that this actually would cause me a greater liability potential because I was grounding (industry standard) the bridge in a non-standard manner. if someone was ever to get zapped while playing one of my basses, I'd need a slew of lawyers and electrical experts to testify that my modification to the industry standard was indeed significantly safer. they recommended I pay fo the research before I release an instrument grounded like this so that I had clinical proof I was building in a safer manner in advance of turning it loose to the public.

ugh!  :sad: uncle!  :tard:

all the best,

R
 

mayfly

Senior member
Messages
8,307
Everyone above speaks the truth:  The reason to ground the bridge is to ground you so that your pickups don't pickup the 60Hz hum that you are picking up.  If you get me.  On the other hand, if you are playing in some skanky old bars (like the one I was playing in tonight), the electrics might not be in great condition.  There may be several volts difference between the michrophone windscreen and your grounded bridge.  This could give you a big ass shock when you caress your lips on the tip of that mic.

My solution - ground the bridge with a 10K-50K resistor.  works like a champ.
 

dbw

Senior member
Messages
4,531
If the strings are not grounded they pick up noise.  Touching the strings grounds them pretty well (a human body is hefty enough to ground such a small signal, and you might even be grounded to Earth by what you're standing on), but a better solution is to ground the strings to your bridge, which is grounded to Earth by any 3-prong amp.

With regard to the safety issue... just get an outlet tester, they cost like $2.
 

SkuttleFunk

Senior member
Messages
1,156
from personal experience: outlet testors are defeated by sound techs who mod things during the first break  :sign13:

all the best,

R
 

ByteFrenzy

Senior member
Messages
1,177
How about NOT grounding the bridge, but putting a ground terminal somewhere out of harms way (say the strap button), and then using one of those antistatic grounding straps as when working on computer equipment? Those do ground you but contain a hefty resistor (IIRC in the wheareabouts of 1MOhm) so a voltage differential won't fry you outright.
Would the grounding still be sufficient to eliminate hum?
 

disaster

Active member
Messages
45
Wow.  Talk about your hot button topic.

Thanks for all the advice & support.  I'm going to experiment for a while.  The legal issues I'm sure are formidable.  I have no intention of wading out into that mess.  I'm just trying to understand things.  I experimented with a static wrist strap.  Apparently it has a 1 Mega-ohm resistor (whatever a Mega-ohm is) to limit the "in-rush current" (again, whatever THAT is).  It didn't seem to impact the noise much.  Currently I'm thinking about a "Y" cable at the guitar input jack.  I can make a cable to ground that plugs into one of the "Y" inputs while the other input goes to the amp.  If I get noise I can try the ground cable.  If no noise, no ground required.  I can experiment with filters, etc on the ground cable without having to fool around inside the guitar.  I'll probably experiment w/ isolating the strings/bridge if I can figure out a way that doesn't require opening the guitar repeatedly.

Thanks again.
 

bpmorton777

Senior member
Messages
1,651
guitar nuts has some good info on this subject.

http://www.guitarnuts.com/technical/noisebucket.php

and

http://www.guitarnuts.com/technical/electrical/safety/index.php

Brian
 

markwayne

Active member
Messages
26
This is the primary reason I started using EMG pickups years ago. There were far too many venues with funky wiring to not use a string ground and far too many venues with funky wiring to have a string ground.

Wayne
 

dbw

Senior member
Messages
4,531
1 megaohm is a million ohms, usually written 1M.  You may be familiar with the kiloohm (= 1000 ohms = .1M) from 250K and and 500K pots.
 
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