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In defense of 'star' grounding

Discussion in 'Pickups & Electronics [BG]' started by frits51, Jan 29, 2013.


  1. frits51

    frits51 Supporting Member

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    Heath, Texas
    I posted this in reply to a reply to a question I put up in another thread. Thought the subject deserved its own post (not that this is the first one on the topic!)

    I'm an instrumentation and electrical tech by trade with minimal experience in guitar electronics. Nevertheless, electricity is subject to the same rules in my bass as it is in an instrumentation circuit.

    My reason for 'star' grounding is this - The voltage we use in guitars is low. Thus, that voltage's ability to push through a resistance without being diminished is also comparatively low.

    I do not want to make any signal, ground or otherwise, have to push its way through a steel pot case. I would rather have it zoom through a copper wire and back to the amp.

    That is why I personally have chosen to employ 'star' grounding which provides each component in the bass with its own 100% copper path back to the amp.

    That being said, my MIM P bass still has a buzz that goes away when I touch a knob, the bridge, the strings, the jack nut, etc.

    My MIJ Jazz, on the other hand, is 'star' grounded (and has a Bourns M/N blend pot) and is quiet.

    Interesting creatures, these basses...
     
  2. llldino

    llldino

    Joined:
    Dec 16, 2012
    When I rewired my bass, I didn't use star grounding and she's quiet. I think it's a matter of convenience more than anything. As long as everything goes to ground, the connections are solid, and there's no loops, right? Tested with a multimeter and it's 0 resistance across the board. Just sayin'.
     
  3. line6man

    line6man

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    Close to Los Angeles, CA
    Quoting myself from your other thread:

     
  4. Mad Tango

    Mad Tango

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    Apr 18, 2006
    Location:
    Pearland, Tx.
    Last night, I installed my new Bareknuckle 58' P-bass pup and it buzzed like crazy. I then (= took everthing back out) to shield w/aluminum tape my pickguard and cavity to ground (non star grnd.) and it is dead quite now. You might want to run the pup leads in a twisted pair as well. Make sure to Ohm out the overlapping tape passes and tuck over the ends to make a good connection back to ground. Because of the glue on the back of the tape I had to scratch the ends to make it get to 0 ohm readings. Its worth it!
     
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  6. 4Mal

    4Mal Supporting Member

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    Noisy mim bass ... Or any fender for that matter, first thing I do is check the bridge ground.
     
  7. Eight_Stringer

    Eight_Stringer

    Joined:
    Feb 22, 2009
    For a laugh, from the bass to the amplifier most use a "shielded" cable, ie one central conductor insulator material then, an enclosing braid or foil or combinations of same. Outer protective sheath synthetic insulation material, mechanical protection incorporated.

    Play bass, signal generated by pickup(s), arrives at the above connection cable. Premise one, the inner conductor has the wanted signal present and conveyed to the amp input, in electrical circuits we need a path for current to flow, by implication then the "return" current is through the outer conductive sheath, amp to bass. Hang on, this outer sheath is what we call a "shield"! Which is it, a signal carrying conductor or a shield, cannot be both can it? Conundrum one.

    It would be great if there was a "shield" that did not carry signal current, lets try a two core inner conductor with an outer conductive braid. Wonder why that is not used all the time? On everything? Now, lets see, where do we connect this "outer shield", in order to decouple the wanted from the unwanted signals present. The amp end of the chassis? The most "earthy" part of the bass? Why not just connect it to one end of the path only, that will stop shield ground loop ( the two core signal conductors in the cable has the wanted signal path covered, separated from the "shield" ). But wait, what is the voltage gradient at the amp end, mean how much is that removed from mother earth, all the stage equipment is inducing voltages into the other stage equipment, they all cannot be at equipotential left to right front to back of the stage.

    You make your best estimates of circuit success in decoupling wanted and unwanted signals, some will work with star, some will not, due to other aspects in play. Try this and try that if the process is simple enough to obtain the result you want, there is no one shot solution to all aspects and operational conditions when performing. We take a big bag of tricks 'guised as such. In reality it is the wealth of experience in that bag of what does not work, hope that makes sense. Maybe not. Grin.
     
  8. frits51

    frits51 Supporting Member

    Joined:
    Apr 30, 2011
    Location:
    Heath, Texas
    As always, I'm learning a LOT here. Thanks, everybody!

    4Mal... zero ohms, bridge to jack nut.

    I may try daisy chain grounding on the P.

    I keep running into recommedations for shielding. I have a Yamaha RBX250F fretless that may be a candidate for my first attempt.

    Thanks, again. This is a great community.

    Mark
     
  9. frits51

    frits51 Supporting Member

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    Heath, Texas
    Question to line6man - If star grounding adds extra wire to the point of possibly creating a problem, what about the 12' to 18' of extra wire (cable) that connects bass to amp? Just wondering.
     
  10. line6man

    line6man

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    Jun 20, 2008
    Location:
    Close to Los Angeles, CA
    I was using your logic. The reality of it is, you do not need to be worried about equivalent series resistance AT ALL in this application. Consider how much resistance your volume pot adds when you roll it down just a hair. Even several thousand Ohms don't significantly decrease volume for the average high impedance signal. Most pots don't even go down to 0 Ohms when you turn them all the way up. You could have a couple of Ohms of resistance in series with the signal path when your volume pot is on "10."
     
  11. 1958Bassman

    1958Bassman

    Joined:
    Oct 20, 2007
    The reading with the meter is great, if you're dealing only with DC. If you're dealing with RF or RMI, it's almost useless. EMI is exceptionally hard to reduce and eliminate, RF is somewhat easier.
     
  12. 1958Bassman

    1958Bassman

    Joined:
    Oct 20, 2007
    With instrumentation, star grounding means everything is equipotential, does it not? That means path lengths can be different, as long as there's no difference between pieces, right?

    Is your bass noisy? What devices cause this noise- amp transformers, a TV, lights/dimmers? Have you checked the supply voltage, to make sure it's clean and the noise isn't bleeding into the audio circuits?

    Do you have any copper screen? Solder a wire to it and ground it to your amp, then move it in air around your bass. Pass it over the front, the sides/end and back- does it have any effect on the noise level? Copper screen is used extensively in sensitive government facilities, for making specific areas 'black', wrt surveillance. If it works for that, it should work for a bass.
     
  13. frits51

    frits51 Supporting Member

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    line6man,

    It's starting to make sense. Instrument electronics is different than what I do for a living.
     
  14. SGD Lutherie

    SGD Lutherie Banned

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    So, star ground the bass, and then remove all that star grounding when it gets to the output jack and coaxial cable (and amp). ;) Yep. Do you see why I'm saying it doesn't do anything?

    If you really want to keep your signal from the shields, run a balanced line into a differential input at the amp.

    (BTW that's how EMG pickups are setup internally, which helps with noise reduction.)

    Will it make a noticeable difference? Very unlikely. Not unless you have fully shielded pickups. Then you will notice you probably don't need any of the above. ;) It certainly will NOT make a difference with something like a Jazz bass.
     
  15. 1958Bassman

    1958Bassman

    Joined:
    Oct 20, 2007
    If these were supposed to be totally noise-free (or, close to it), they would have been designed with low impedance pickups, made to be totally shielded with balanced line/connections but when they became available, they were quiet enough for all practical purposes. Audio equipment that was intended to be located in one place doesn't really need balanced/lowZ because, even with unbalanced lines, the chassis of all pieces is close enough to the same potential for, again, practical purposes. Low level, low gain doesn't need -156dB S/N ratio- the difference between that and -70dB S/N will never be heard once the signal is present but when someone is pounding the crap out of a rig at high SPL, connecting to an extremely sensitive preamp input or connecting one piece in one location (a preamp or mixer) and a power amp in another location, this becomes important. Les Paul used LowZ pickups for close to 60 years because he was extremely interested in sound quality but he would have never used a high gain/high SPL guitar rig because it wasn't necessary for getting "his sound", which was always very clean.

    Another thing that makes a huge difference between the RF/EMI levels we have vs 1940s-1960s is that the dimmers, lighting, switch mode power supplies, wireless phones and WiFi weren't in our homes and businesses and we never had these problems until high gain/high power rigs began to be used.

    For those who want/need less noise and use a high gain/high power rig- don't expect an unbalanced line to do this for you- it can't. A preamp with LowZ output in the instrument is a good start but it has to see the proper input impedance for that to do any good. Using a LowZ-HighZ converter to connect to a preamp/amp with HighZ input is asking for noise levels that aren't acceptable. Also, having a preamp in an instrument isn't only so the gain can be higher, it's so the gain stages can be set up correctly for the best S/N ratio. High level into low sensitivity means high S/N- anyone who has installed a large car audio system knows this- head units, equalizers & crossovers with the ability to send 4V audio signal to the amp will be stupidly loud and very quiet WRT noise level and musicians don't always understand this aspect of setting up a signal chain. They want everything to "go to eleven" but don't pay attention to the level going in vs sensitivity of the input stage and end up with a heavily distorted signal when they want more audio level and less noise.

    I suspect that if more people learned how to correctly set levels on their equipment, they'd hear less noise & distortion. They'd also kill far fewer speakers and amps. However, if all manufacturers told people how to do this so their equipment would last longer, they'd sell far less of whatever they make. Are they guilty in this? I think so.

    If anyone wants to find out how to set their controls to get the lowest noise & distortion levels, they should talk to someone who works with communications electronics- not all EEs concern themselves with this and not all need to know it.
     
  16. Cadfael

    Cadfael

    Joined:
    Jan 4, 2013
    Location:
    Germany, EU
    This is the reason why I don't use the star wiring:
    [​IMG]
    SdKfz 250, for control of motorized formations, equipped with FuG12 radio which used a 2 meter star aerial.

    They must have had a reason - and using an antenna form isn't the best shielding solution to me ...

    BUT I AM NO EXPERT! :rollno:
     
  17. 1958Bassman

    1958Bassman

    Joined:
    Oct 20, 2007
    Pretty sure that was used so it would broadcast omni-directionally.
     
  18. Bassamatic

    Bassamatic keepin' the beat since the 60's

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    Location:
    Studio City, SoCal, USA
    I can appreciate both sides of the argument. However, my genius audio engineer that knows everything about guitars and amps, tells me that star grounding is still effective due to the high impedances involved - that it is easy to induce currents in the wires.

    Now he was an instrumentation engineer, designed electronics for electron microscopes, etc. before moving into audio, and now does tweak amp and guitar mods and repairs in SFO, for whatever that is worth.

    I'll ask him again about this next time we talk.
     
  19. 1958Bassman

    1958Bassman

    Joined:
    Oct 20, 2007
    The difference is that SEMs and that kind of equipment is a lot less forgiving of eddy currents and EMI/RFI. Guitars and basses work with <1VAC going to the preamp input, in most cases and stacking gain stages is where the noise problems that aren't ground loops are worst.

    When I did car audio, we were (eventually) taught that star grounding should always be used because a car is a poor platform for putting a head unit in the dash and amps/crossovers/equalizers in the trunk. The problem is that many cars had LESS noise when the amp was grounded at the rear and the head unit was grounded to the firewall and that running a ground wire from one place to another ended up acting as a great antenna for noise. That's when I was taught that "star grounding" isn't a physical topology, it needs to be seen as an electrical characteristic- all parts need to be at equal electrical potential i.e., zero volts measured between any of them.

    WRT ground loops, the best info I have seen is in this link and the author is the same person who did the presentations about star grounding that I attended, twice-

    http://www.jensen-transformers.com/apps_wp.html

    IMO, this info should be read by anyone who connects any audio equipment, for any use.
     
  20. okcrum

    okcrum in your chest Supporting Member

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    That star antenna is probably multiband - one top piece + coil for each band like the current day Hustler ham radio antennas.
     
  21. khutch

    khutch Praise Harp Supporting Member

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    Star grounding is most useful when you need to isolate sensitive circuits from the effects of high current circuits. The reason this is necessary is that there is no such thing as an equipotential ground system. They are a textbook fairy tale that makes calculations easy and in many cases they are close enough to being real as to make no difference. But not in all cases. All ground systems have finite impedances between any two points and the amount of current flowing between those two points produces potential shifts. In a star ground you eliminate the ground paths between circuits and you tie them all to some common point. The potential differences between the circuits still exist, in fact they might increase. But the sensitive circuits no longer see a variation in their local ground potential induced by large currents generated in another circuit. Usually this significantly improves their performance. As to how large a current is "large", that depends entirely on how sensitive the sensitive circuits are. Sometimes microamp level currents are large enough.

    But bass guitar electronics are not particularly sensitive circuits. And bass guitars do not have circuits that need to be isolated from one another, they are all one circuit. The signal flows in a linear path from the pickups to the output jack much as in a radio receiver where the signal flows from the antenna to a speaker. You never see a star grounded radio receiver, as much as possible they are built on a continuous conductive "ground plane". Since bass electronics are not particularly sensitive the ground system you use is not particularly important but to the extent that it matters a ground plane is a better choice than a star ground. In a bass with a good low impedance metal shielding system you could just as well use the shield as a ground plane. The traditional pot-to-pot daisy chain ground connection is fine too and probably necessary if your bass uses conductive paint shields.

    Ken
     

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