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Is Grounding Strings/Bridge Necessary?

Discussion in 'Luthier's Corner' started by LajoieT, Oct 10, 2004.


  1. LajoieT

    LajoieT I won't let your shadow be my shade...

    Oct 7, 2003
    Western Massachusetts
    OK I've done a quick search and found a lot of threads mentioning the hums and such that you get from having problems with the bridge/string grounding or grounding in general, but here's the situation.

    We've got the Talkbass Wish Bass II making the rounds and the second person has mentioned noisy electronics like a bad ground, problem is, it doesn't look like the strings CAN be grounded. The strings are fed through the body without ferrules (just holes drilled through the body a little deeper in back than in front) and the nut is Corian, which i'm pretty sure is non-conductive (not sure but I think the nut is Corian also so you can't just ground one string and have the nut take care of the rest as if it were brass). The first person who had it didn't notice any hum and other Wish users (the satisfied ones :confused: ) have said that their instruments are dead quiet.

    So the question is, is the string grounding necessary, and if so why? I've heard that some active circuites don't need ground wiring but never been told why. The wish has a simple volume only passive circuit, so that shouldn't be the issue but it may be be nice to know why one circuit doesn't need one while another does.

    Mods, this seemed best here in Luthiers, but if it would be better in pickups feel free to move it.
     
  2. Groove Theory

    Groove Theory Grizzly Adams DID have a beard.

    Oct 3, 2004
    The Psychiatric Ward
    Hey, I'm by no means a master electrician or anything, but what I understand is that the string ground thru the bridge actually uses your own body to complete the ground, so you'll notice alot more hum and noise if some part of your body is not in contact with the strings. I have a MIM J bass that this is VERY noticable on.

    However, you are right, some pickups/circuitry that are out there recommend that you DO NOT ground them in this way. one that comes to mind is the EMG active bass pickups...I've got a custom axe I'm working on with the 35CS and 35DC pickups in it...they are some of the quietest pickups out there in terms of unwanted humming, and right in their setup instructions, it states :
    "When installing EMG pickups DO NOT reconnect the bridge ground wire. This wire is usually soldered to a volume or tone control casting and goes to the bridge.This wire grounds the strings and uses them against your body as a shield against buzz and hum. It also creates a shock hazard. EMG pickups are shielded internally and do not require string grounding. This greatly reduces the possibility of reverse polarity shock from microphones and other equipment."

    So, although this isnt a complete answer to your question. I hope it helps.
     
  3. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    I recently read an article online that supported EMG's statements, and also had more. It seemed to me to be correct in all points. (I think I have the URL at home, I'll post when I find it.) I was actually pretty excited to finally find a source that laid things out consistently and correctly.

    To summarize:
    - Your body does not act as a ground for the guitar. This is a fallacy. Unless you're standing barefoot in a puddle, or you're touching something grounded, such as a mic (safety issue!!), your resistance to ground is too high for you to act as a ground.
    - When your body is is not grounded, it actually acts as an antenna when in proximity to an unshielded pickup or electronics.
    - It is common practice to ground the strings through the bridge. In this case, when you touch the strings, you are then grounded, and you then act as a shield for the pickups. The noise does go down! But this creates a potential safety hazard. If there are any mains wiring problems, you can be electrocuted!
    - If your pickups and electronics are sheilded, and/or if your pickups are humbucking, then there is no need to ground the bridge and use your body as a shield. This is the idea with the EMGs.


    Here's a different site that has info on shock hazard, but not on the RF shielding. It is a good thing to read. http://www.guitarnuts.com/technical/electrical/safety/index.php
     
  4. Tim Barber

    Tim Barber Commercial User

    Apr 28, 2003
    Serenity Valley
    Owner: Barber Music
    I'd really like to read that.
     

  5. My take on this comes from a rather heated discussion on the Bottom Line Newlsetter a couple of years ago. The main proponent of string grounding was Bill Bolton - Fender historian and an electromechanical engineer working in the design of power tools and other hand held tools for 30+ years. I tend to agree with him and his opinion was that the bridge (strings) should ALWAYS be grounded to the output jack. His reasoning was very simple. While true that this MAY cause a potential hazard, that would only happen if the player's equipment were faulty. Keeping ones equipment in good working order is the best way to avoid this. The more likely source for a shock hazard is from coming in contact with another, out-of-phase circuit powering another piece of equipment. That could be a PA or another guitar. Strings touching a mike stand or another guitar will produce the deadly voltage. If the guitar is grounded, this voltage will be shunted to ground through the players amplifier and not through the body. A human body isn't the best path to ground when there is a nice hardwire connection for the stray current to get there. THAT's my reason for grounding all of my instruments and using a GFI on my own equipment.

    If my opinion needs further explanation, I'll research the Bottom Line Archives and get the discussion.
     
  6. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Hambone,

    That's kind of circular logic. If the strings aren't grounded, then it doesn't matter if you touch another instrument/mic/whatever that's connected to another electrical source with reverse polarity. There's no potential, since your strings aren't part of the circuit your amp's plugged into.

    But there is still the danger from a grounded control plate in the above scenario, like on a Tele or Jazz Bass, or the metal knobs on a P Bass. So I'm not totally discounting your argument, but for those with no metal parts on the bass other than the strings/bridge, there doesn't seem to be much risk in that scenario.
     
  7. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Allan

    I'm surprised that Bill B. said that - but while he has a world of knowledge, he's not infallible. I recently could have started a thing with him about a mechanical issue on which he was wrong, but I didn't pursue it when he proved both inflexible and insulting. (Enough of that.) I usually expect his electrical comments to be right, though.

    The two-different-phases problems is one of the main reasons you don't want your strings grounded. If there are two non-common mains systems, for example the PA and mics on one system, your amp and bass on another, then if the two "grounds" are allowed to connect, current will flow. If the connection is from your fingers, throug your arm and chest, then through your other hand or your lips to a mic, the current will flow through your heart in making the circuit. If your lucky enough to have your strings touch the mic or the other guitarists strings, the current will flow, and you'll only lose some fuses or maybe an amp, but not your life.

    As Lyle said, if your strings are not grounded, you're safe from completing the circuit unless you touch something like the shell of your cable plug.
     
  8. Eldermike

    Eldermike

    Jul 27, 2004
    NC
    If the idea of floating strings is based on limiting shock hazard, it fails. At some point you will still come in contact with the equipment that is actually at fault. You will have to turn it off/on, plug into it, move it. Also, the risk from a pa is small, if not impossible. If the pa input goes "hot" the pa will tell you, it will not like it at all, you will hear it. So, it's your amp that you have to worry about, and unless you never intend to touch it, then floating your strings only delays the brutal truth about your amp sending you high current/high freq. which is in fact dangerous stuff. Although it may protect you from a transient spike. All in my humble opinion. Although I am also an electromechanical design engineer. But this is not my specific field, and that matters.
     
  9. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    I carry an outlet tester and voltometer with me to gigs. I make sure that anything I plug into is wired correctly with a functional ground and I check for potential between my gear and the PA using the voltometer.

    I've had my lips scorched in the past from the stage electrical supply having the opposite polarity of the PA.

    The worst is old 2 prong amps with "ground" switches. You have a 50% chance of being right, and a 50% chance of being dead. Big fun!
     
  10. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    I think that what I had seen was the combination of two articles on the GuitarNuts site. Taken together, they convinced me of this guy's reasoning.

    Noise article
    Shock article
     
  11. Eldermike

    Eldermike

    Jul 27, 2004
    NC
    This is why I wear leather soled shoes when I play. Tanned leather is a fair conductor for static buildup, so in the winter it really helps keep down the noise. I know people that think that they were "hit" by some device when in reality they were the ones with the charge. Noise from static comes from people wearing tennis shoes while playing bass, especially in low humidity situations.

    Mike
     
  12. Squidfinger

    Squidfinger I wish I could sing like Rick Danko.

    Jan 7, 2004
    Shreveport LA
    VERY informative thread. My MIM P hums like crazy if I'm not touching the strings.
     
  13. Groove Theory

    Groove Theory Grizzly Adams DID have a beard.

    Oct 3, 2004
    The Psychiatric Ward
    It seems as though I was misinformed about the "completing the ground" thing. Your explaination makes total sense now that I think about it. Thanks for clearing that up.
     
  14. Suburban

    Suburban

    Jan 15, 2001
    lower mid Sweden
    There is a way out of this argument, namely to keep the best of the two worlds.

    To avoid the open capacitance hum, you need to ground the strings. At least when you use a cable.

    To avoid being fried by faulty gear, you do not want to be grounded.

    So what you do, is connect the bridge to grund via a quick and small fuse. E.g. a glass fuse of <100mA will blow immediately when there is a risk, and the current thru you will be disturbing but not harming (NB pacemaker or similar may be disturbed!).
     
  15. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Sounds like a good idea, and an alternative to the inline capacitor method. I guess you'd want to be sure that it blows quickly enough to protect, but it doesn't blow in a non-dangerous situation. It would be nice if a fuse could be installed right where the ground comes off the jack, so you also wouldn't have to worry about knobs and switches. This would require isolating the jack from the cavity shielding.
     
  16. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Another approach would be to always use wireless.
     
  17. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    No fuse in the world (discounting purely electrical ones) is fast enough to protect you, even fast blow types take a few milliseconds to break and 100ma for a few milliseconds through your heart can kill you. In my opinion you should either...

    A: Ground your strings through a small cap in parallel with a large resisitor.

    or

    B: Not ground them at all.

    And of course if your not familier with the venue, use an outlet tester.
     
  18. Suburban

    Suburban

    Jan 15, 2001
    lower mid Sweden
    +1 :oops:
     
  19. Showdown

    Showdown Supporting Member

    Jan 21, 2002
    Honolulu, Hawaii
    I think when equipment had two prong plugs electrocution was a serious possibility, but with modern equipment with three prong plugs it shouldn't be because all equipment should have the same polarity. If you have a vintage amp you need to be careful and check with a multimeter.

    Almost all instrument manufacturers ground the bridge, so there must be something to it.
     
  20. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Unfortunately, it's all too easy to come across a 2-prong outlet, which forces someone to use a 3-to-2 adapter, which can be reversed either way.
    *Especially* on those old amps which have an on-off-on power switch on the front, which is enabling you to reverse the polarity any time you feel.
    One thing to it is that it makes your body part of the RF shielding while you're playing, so they don't have to shield the cavities properly.