Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Photos of Star Grounding?

Discussion in 'Pickups & Electronics [BG]' started by Peter Weil, Nov 8, 2004.


  1. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Hi all,

    I've been doing some rewiring work on my bass and would like to see some photos of people's control cavities - namely, those who have what you would consider to be superb star grounding schemes.

    I'm particularly interested in seeing the inside of a Sadowsky control cavity, if anyone would be kind enough to oblige me.....

    I have rewired a bass with star grounding similar to that seen at the www.guitarnuts.com website and would like to see what the major luthiers do.

    Please help!

    Thanks all.

    Pete
     
  2. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Sorry, no pics of star grounded control cavities.

    Here is another option for you to consider:

    Most manufacturers ground one end of the pickup coil. This is a bozo no-no if you're interested in minimizing hum. All the star grounding and shielding in the world isn't going to help if your circuit isn't wired correctly in the first place.

    Crusty old audio engineers (and guitar players, like Les Paul himself) have been advocating the use of "balanced lines" with guitars and basses for many years. This is the industry standard in the world of microphones, but for some reason the instrument manufacturers haven't found it cost effective to implement. Recognizing that most amps have single ended inputs, the trick is to convert the balanced signal from your pickup into a single-ended signal that can feed your amp.

    Lifting the pickup ground will solve your hum problems in 99% of all cases. However, additional electronics will be needed to provide a ground reference so you can run a single ended cable from your instrument to the amp. It's actually a fairly simple exercise in electronic construction, but some understanding of the theory behind this concept would be very helpful, before attempting to do this to your instrument.

    Here is a helpful link:

    http://www.tvhandbook.com/support/pdf_files/audio/Chapter10_6.pdf

    The relevant sections start at 10.6.3a :)
     
  3. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Thanks..... I think. ;)

    Lot of reading here.....I'll get through it. Understanding is a different matter.... :D

    Anyway - anyone else have any photos/suggestions?

    Pete
     
  4. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    C'mon everyone......this is a poor show so far. Anyone?

    Pete
     
  5. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Does this thread need to be moved to Setup?

    Hint, hint....

    Pete
     
  6. Nino Valenti

    Nino Valenti Commercial User

    Feb 2, 2001
    Staten Island NYC
    Builder: Valenti Basses
    [​IMG]

    Here is a Warmoth Koa Jazz I built a year or so ago with Sadowsky p/u's & preamp & I tried to match it to my Vintage 4 as close as possible.

    [​IMG]
     
  7. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Thanks Nino!

    Nice wiring work.

    Looks to me like the 'signal' ground, pickup casing grounds, and the pot casings grounds are wired to that terminal ring at the top, which then has a ground running to the ground lug of the output jack; the cavity shielding is wired directly from that lug at the right side of the photo to the ground lug of the jack. That about right, Nino? Or am I missing comething?

    The whole reason I'm asking about this subject is a problem I have with my current bass - hum. It shouldn't be there, either, as I have a fully shielded cavity and (Bill Lawrence) humbucking pickups. It's driving me nuts.

    I've hooked up 'signal grounds' from the pickups/tone control to a common 'signal ground' ring terminal, and then taken a wire from that to the ground lug on the output jack. There is a separate 'shield ground' ring terminal where the pot casings, copper shielding, pickup casings, and bridge are hooked up to -> this then has a wire sent out to the ground lug on the output jack.

    Theoretically, there should be NO ground loops using this technique. However, the strings still make a little 'pop' noise when I touch them (almost like a capacitor discharging) and there is hum over and above this, which especially worsens when I change between series/parallel switching. Very odd.

    I'll photo my control cavity and invite criticism (please try to hold back, my wiring skills aren't up to Nino's). Perhaps someone out there has a good photo of a passive Jazz wired with a series/parallel switch which has star grounding and cavity shielding? ;) I'd love to compare.....


    Thanks all.

    Pete
     
  8. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Is this a completely passive bass?

    Is one end of your pickup coils grounded in the conventional way? If so, there's no point separating the signal ground from the shield ground. In fact, doing so can even cause problems. Try connecting the wire from the shield ground to the signal ground ring terminal (instead of the output jack).

    Not odd at all. In fact, sounds like a very common situation.

    What kind of amp are you using, and how long is your instrument cable?

    Excellent. That'll help. :)
     
  9. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Yes.

    The pickups have three wires each. White (signal 'hot), black (signal 'ground'), and blue (presumably pickup coil ground?). I have already tried hooking 'signal' and 'shield' ground ring terminals to each other and then sending a wire from these to the ground lug of the output jack, but the problem remains the same.

    Amp: Peavey MaxBass Preamp -> Peavey DPC 1000 -> Flite custom 4x10 cabinet. (The same problem of noise/'pop' occurs if I plug into either one of two other amps I own also, one a generic keyboard amp and the other a Trace Elliot Boxer 30 watt practice amp).

    Cable: Either a 6' or 10' cable, generic. No noise when I use either of these with my other bass - but on the other hand the other bass is an active Peavey G-Bass.

    I've seen your previous posts about the benefits of a differential input preamp - I've actually been considering contacting you about the design.....

    Will post photos soon. Try not to laugh.....

    Pete
     
  10. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Perfect. You're in good shape for a differential preamp, if you choose to go that route.

    Have you verified which (black or blue) is the shield ground with an ohm meter?
     
  11. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    My ohm meter's battery has run out. Dammit. I'll get another one tomorrow.

    From the instructions provided with the Bill Lawrence pickups (which I have followed, obviously), the blue wire is meant to be soldered to 'shield ground', as I have done.

    I'm not sure if I have the time to build a differential preamp at the moment. However, I'd gladly pay someone else to make one for me......hint, hint..... ;)

    It's getting to the point where I'd seriously consider buying an active preamp to perform the function of a differential preamp and just not use the EQ! (John East makes a preamp which buffers many inputs, inlcuding a piezo input, but has no EQ....)

    Photo of my control cavity to follow.

    Pete
     
  12. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Warning: photo file >1 MB.

    See http://www.biscituk.biz/~pweil/bass wiring.htm

    Hmm......bit messy in there. It looks visually confusing. I'll try and provide an explanation.

    Yes, that is speaker wire (22-gauge). It's easy to use, is a good conductor, and solders nicely. Stop laughing :D

    White wire = signal hot.
    Black wire = signal ground.
    Blue wire = ?coil ground

    Overall wiring: volume, volume, tone/push switch for series/parallel

    'Shield ground': Pot casings (all three pots), bridge, copper shielding, and blue wires (coil grounds) -> terminal ring at farthest right of photo -> ground lug on output jack.

    'Signal ground': All signal grounds from pots, tone capacitor -> terminal ring at top of picture -> ground lug of output jack.

    Normally both terminal rings wrapped in insulation tape to prevent inadvertent short circuit connections.

    Yes, I know I need to shorten my wire lengths and plan runs a little better......I just need to have more time to do that in.....

    Pete
     
  13. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Peter,
    With the pots contacting the copper shielding, there should be no need for individual pot grounds, and it could introduce ground loops.
     
  14. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Yeh,

    I've thrown down a strip of shielding from pot to pot to eliminate pot to pot ground wires althogether. Simplifies things considerably: cuts down on the wiring maze, minimizes poor connections, facilitates trouble shooting, and eliminates potential damage to the pot from the heat required to solder a ground. You can also solder to the shielding if needed.
     
  15. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    I didn't originally have the pot casings wired directly to the 'shield ground' terminal until the day before yesterday; however, I wanted to be absolutely sure that they were grounded and so wired them up.

    However, you are right - I'm sure my meter will confirm that there is no difference in resistance readings whichever way I do it, and extra wires mean the possibility of ground loops. So, they'll go.....

    I'm still frustrated as to why the bass goes 'pop' when I touch anything metal and why noise is present with a well shielded cavity and humbucking pickups (although it disappears when I touch the strings.....)

    I hate noise problems like this. Perhaps the DIAP solution is the way to go.

    Pete
     
  16. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    To verify grounds are good I always run a meter from each pot to the shielding, pot to pot, and pot to jack (jack to bridge if the bridge is grounded). Also if the bridge is grounded and grounding is as it should be, touching the strings should decrease hum if it exists (as with singles). Increase hum indicates a bad ground.

    The only thing I've encountered that's anything I'd call like a pop is when I've had the pups to high and drove the strings into them, but not that occurred from a component/wiring malfunction.
     
  17. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    How do I go about doing this?

    My ohm-meter is up and running again and I have verified, as you have described, that all the various grounds are good.

    The 'pop' sound is odd - perhaps a capacitance being discharged when I touch a metal component?

    As the photo is difficult to interpret I have drawn a quick bitmap schematic of my wiring as it stands. (Warning, large file > 1 MB)

    Have a look at http://www.biscituk.biz/~pweil/bass wiring 2.

    If anyone sees anything glaringly wrong, I'd love to know. I'm really frustrated here.

    Pete
     
  18. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Well, I don't see anything "wrong", but I have a few suggestions:

    First, there is no difference between your signal ground point and your shield ground, as they connect. So you could eliminate the signal ground. I'd just have the one ground lug point, connected to the cavity shield. At that point, the ground wire going to the output jack would be unnecessary, though you might want to keep it just in case the jack came loose and didn't contact the copper shielding fully.

    Second, move the bridge ground from the volume pot to the ground lug.

    Third, go ahead and move the ground on the tone cap from the grounding lug to the tone pot case. This is just so it won't be prone to mechanical stress from wires moving.

    To be clear, there can be a benefit from separating the signal ground from the shield ground, but that's not what you've done here.
     
  19. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Hmm, maybe I've found the problem.

    The series/parallel switch. If the "top" of the switch has grounded metal contacting the copper shield or a grounded metal control plate, then the ground wire from the switch could be causing a loop. Sounds like a job for electrical tape.
     
  20. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    I orginally kept the two grounds - 'signal' and 'shield' - separate so that I could put a high-voltage rated capacitor between them, as per the shielding instructions on the www.guitarnuts.com website. Need to find a cap if I'm going to do it....

    ??...The bridge ground is connected to the 'shield ground' ring terminal, not to the volume pot. Or do you refer to the 'signal ground' lead of the bridge pickup?

    Presumably in order to do this I'd have to insert the capacitor I mentioned earlier between 'signal ground' and 'shield ground'.

    The series/parallel switch is not actually separate from the tone pot - it's Yamaha 300k pot with a push/push switch built into the bottom of it. So the top of the switch is in contact with the bottom of the tone pot, which itself is in contact with the cavity shielding. However, the effect is the same as what you describe above, so maybe isolating the tone pot/switch might prevent a ground loop from occurring. I'll try it. Thanks!

    Pete