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Star Grounding - Output Jack Question

Discussion in 'Luthier's Corner' started by captainate, Feb 3, 2014.

  1. captainate


    Apr 30, 2012
    Hey guys,

    I did my due diligence performing a search on this topic, and I'm sure this information is out there but I couldn't find it.

    I've been reading up on star grounding and proper shielding technique, and everything makes sense to me except one element. If the body of the output jack is electrically connected with the grounding lug (which most, if not all of them seem to be), then wouldn't star grounding to the output jack create a ground loop in a shielded cavity?

    It seems one would have to isolate the output jack from the copper shielding in the control cavity, otherwise you have your star ground point on one side of the loop, and the pots/switches also grounding to the shielding in the cavity, which connects to the output jack on a separate path. The problem is, it doesn't seem like anyone's isolating their output jacks. So what do I have wrong? Thanks for the help!
  2. SamanthaCay


    Nov 16, 2008
    Denver, CO.
    There is no such thing as a ground loop in a low voltage application such as a bass.
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  4. captainate


    Apr 30, 2012
    If this is the case, then why is everyone so paranoid about properly star grounding the circuit? Just another example of mass hysteria about the perfect tone by a bunch of caffeine ravaged gear heads?
  5. JoeWPgh


    Dec 21, 2012
    From what I've read, star grounding a simple circuit like a bass or guitar is generally considered to be pointless.
  6. Hopkins

    Hopkins Supporting Member

    Nov 17, 2010
    Houston Tx
    I just ground everything to the closest point in the ground circuit. Star grounding is absolutely unnecessary, and IMHO just makes for an ugly, cluttered control cavity.
  7. mrbell321


    Mar 26, 2012
    N. Colorado
    Yes. people will find anything to obsess about, particularly on topics that aren't well understood by the average person. To the average person, electricity amounts to a magic. One of those people will do something they perceive as making a difference and there you have "black magic", but it gets dressed up in the guise of science...
  8. tjclem

    tjclem Supporting Member

    Jun 6, 2004
    Central Florida
    Owner and builder Clementbass
    There is an amazing amount of voodoo in instrument building. :rollno:
  9. Because you are reading into the opinions of the wrong people. Star grounding is a pointless waste of time and effort. Just get everything grounded in the easiest way possible, and don't worry about it.
  10. kohntarkosz

    kohntarkosz Banned

    Oct 29, 2013
    Edinburgh - Scotland
    We can all thank Guitarnuts.

    Before Guitarnuts came along, copper foil factories were shutting down at a rate of two a week. Now everybody is carefully applying copper foil to every internal cavity in their guitar....

    I think Guitarnuts saw guitar circuits with an electrical engineer's eye. At much higher voltages ground loops are a problem. At the tiny voltage levels in a guitar they are not a problem at all. I think too many newbie modders get hung up trying to implement star grounding when they have no real aptitude for solder dress. I'm speaking from experience here, and I've seen this problem crop up on different forums as well. Perhaps boutique luthiers can make a big deal of star grounding as the 'icing on the cake'; an unnecessary but 'belt 'n' braces' extra for people worried about problems that don't exist (but appear to not be being addressed by Fender et al). Those guys have the soldering skills to make a clean job of what is, basically, The Emperor's New Clothes.
  11. Wagz


    May 2, 2012
    Milwaukee, WI
    Leave STAR grounding to the guitards. Spend the time and money you would've spent on soldering on a tort pickguard instead :bag:
  12. 1958Bassman


    Oct 20, 2007
    While it's not technically a ground loop, resistance between the pots, any shielding and the signal ground will result in unacceptable noise levels.

    Also, someone needs to explain that 'star grounding" isn't a physical concept/topology, it's electrical.
  13. 1958Bassman


    Oct 20, 2007
    Higher voltages cause ground loops to be a problem? Ever heard "alternator whine" in a 12VDC car stereo? That's a classic ground loop- the power supply ground has too many paths and impinges on the audio ground because of resistance in the DC ground.
  14. Hopkins

    Hopkins Supporting Member

    Nov 17, 2010
    Houston Tx
    12 volts DC is high voltage compared to a guitar signal.
  15. Bassamatic

    Bassamatic keepin' the beat since the 60's Supporting Member

    Sorry - My genius engineer has tediously explained why star grounding works and is necessary if you want your instrument to be as quiet as possible under ALL conditions. Guitar voltages are tiny, so tiny ground currents can have an effect.

    Try to tell the techs that wire up recording and broadcast studios that it is not necessary because the audio voltages are tiny.

    The problem is that most people don't know how to do it RIGHT. There is a library of books available on grounding and shielding.

    IMHO - It's the people that don't want to bother that pooh-pooh it.

    Regarding the OP's question - it is only the BODY of the pots and switches that are connected the copper. The ground lugs should NOT be soldered to the body of the pot, but go instead to the star grounding point.
  16. kohntarkosz

    kohntarkosz Banned

    Oct 29, 2013
    Edinburgh - Scotland
    No. Thanks for blurting out the one random fact you know about ground loops though! (Is this unique to Talkbass?).

    12V is far higher than the voltages in a passive guitar circuit. Don't let simple facts get in the way of your chance to explain things and demonstrate your knowledge though!
  17. kohntarkosz

    kohntarkosz Banned

    Oct 29, 2013
    Edinburgh - Scotland
    Try to make a decent point without the smug hyperbole and pretzel logic.

    I can be obtuse too!

    "Try telling the techs wiring up the Cern reactor that it is not necessary to remove ground loops because the audio voltages are tiny".

    Your "genius engineer" clearly knows how to milk paranoid cork-sniffers, who didn't even know about star grounding prior to Guitarnuts, of their cash.
  18. Mahataru


    Apr 7, 2013
    It's amazing that a discussion about something as impersonal as wiring technique can become so heated.
  19. 1958Bassman


    Oct 20, 2007
    That's not the signal voltage, though. While 2V or 4V signal is definitely a lot higher, it's higher for a reason- to drive the signal from the head unit to the amp(s) and by setting the gain structure properly, to mask noise. Regardless of the signal level, ambient noise sources require that the grounding and shielding be great, not just good. People with guitar/amp noise problems often look only inside of the amp, cable and guitar, when the problem can lie in the building's wiring. An amp/cable/guitar can have the best ground connections in history but if the neutral wire(s) aren't continuous from that receptacle to the panel and/or the connection to the ground buss and grounded conductor have more resistance than is allowable, noise will be an ongoing problem.
  20. 1958Bassman


    Oct 20, 2007

    I was going to post a longer response but you're not worth it.
  21. Hopkins

    Hopkins Supporting Member

    Nov 17, 2010
    Houston Tx
    None of that explains how star grounding in a guitars ground circuit prevents noise.

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