G&L SB-1 Noise Problem

Discussion in 'Pickups & Electronics [BG]' started by Bassmick30, Aug 5, 2013.

  1. Bassmick30


    Aug 5, 2013
    As a long time reader and fan of Talkbass, I finally decided to chime in and ask you guys if you could help me with a problem I've been having lately:

    I've recently acquired a G&L SB-1 (1985). This is the one with the Schaller PBX pickups (pre-MFD pickups). I absolutely love the tone and playability of this bass. However didn't quite like the unwanted noise the PU picked up: There was a humming noise that disappeared when I touched the strings, but also a sort of high pitched whine.

    So, first thing I did was shield the bass (control and pickup cavity + pickguard) with copper foil to remove the unwanted noise. I also checked all the connections and solder joints; no problems there.

    So I closed the bass up and hooked her up: The bass was now free of hum (the one that disappeared when I touched the strings) but the high pitched whine was still there. Weird things is that when I positioned the bass facing a different direction in the room, the whine disappeared. Also when I roll off the tone on the bass the whine is gone or at least kind of muffled.

    I tried different cables, playing in different rooms (even the garden shed :meh:), switching off computers and wifi routers and using different amps. It all made no difference; that annoying whine is still there.

    What did make a difference was plugging in a different bass. This one has a brand new Delano PMVC 4 FE/M2 in it and is dead quiet (same amp, same settings). BTW I use a Sansamp RBI and a Markbass Little Mark 250 into a SWR Goliath JR III.

    At this point I think the problem has something to do with some sort of external interference or maybe a power supply problem in my house. I think it is definitely related to the Schaller PBX pickup as the Delano pickup is completely silent.

    I guess my question is: Do you guys have any idea what might be the source of the problem? And if so, is there something I can do about it? Would you recommend changing pickups? I'm thinking maybe changing to G&L MFD or Dimarzio Model P pups, but I'm not sure if this will fix the problem or change the tone (which I love).

    I apologize for this long post, it is WAY too long, and for my mediocre English (which is unfortunately not my native language and probably the reason this post is so long :)). Anyway, any input or similar experiences on this problem is greatly appreciated!
  2. bassbenj


    Aug 11, 2009
    You've done good so far eliminating the electrical hum pickup with shielding (hum that goes away when you touch strings).

    Clearly you are now getting single coil hum (and noise) pickup. Your pickups are P-bass type and hence humbuckers so this should NOT be happening!

    First try reversing the wires on ONE of the p-bass pickup coils (two coils should be wired in series). Unless the two coils are wired out of phase it will pickup single coil hum.

    If that doesn't solve the problem, then that means that one of the coils is partly shorted or out of balance. In that case a new set of P-bass pickups is in order (or having the old ones rewound to keep the tone).

    High pitched whine is probably from some high frequency switching type power supply (like a computer). The fact that it disappears on orientation but not when touching strings shows it's single coil type noise.

    Good luck.
  3. Bassmick30


    Aug 5, 2013
    Thank you bassbenj for your input! I've been away for a couple of days, hence the late reply. Yesterday I opened my bass up and it was wired like this:

    White to hot
    Yellow to ground
    Brown and Green soldered together

    My guess is that, as bassbenj suggested, this wiring is in single coil. I looked up the color codes on Stewmac ( www.stewmac.com/freeinfo/Electronics/Color_codes/i-schaller.html ) and wired the bass as a standard humbucker:

    Yellow to hot
    Green to ground
    Brown and white soldered together

    No more interference! I'm still wondering why it was wired like this. The bass sounds slightly different so I'm thinking of adding a switch for series / parallel mode or maybe series / parallel / single coil mode. Would you guys recommend this modification with this bass and pickup?
  4. sunbeast

    sunbeast Supporting Member

    Jul 19, 2006
    Denver, CO
    Your bass was wired in series to begin with, but you just reversed the orientation of the coils. It is possible that they were originally wired out of phase as mentioned (since the coils of a P pickup don't sense the same strings as each other out of phase doesn't really change the tone but it does affect the hum cancelling ability of the pickup). It is also possible that that pickup has some internal noise cancelling built in to it, but that it was wired backwards, causing the grounded shielding to actually be wired to the hot signal path.

    It would be possible to wire a switch for series/parallel modes with a split P pickup, but you can't get single coil operation because you need both coils functioning in order to hear all 4 strings! Single coil switches are for pickups that have side-by-side coils or coils on top of one another where both coils in the pickup sense all the strings. When the other poster mentioned "single coil noise", he was referencing the possibility that the two coils of your humbucking P pickup were out of balance with each other- in order for them to cancel hum they have to be wound within very close tolerances of each other (and wired correctly as you found!).
  5. Bassmick30


    Aug 5, 2013
    Well I'm learning as I go. I'm beginning to understand more of the whole single coil / humbucking thing. At first I was like: :confused: ! Thanks for the additional info.

    I'm glad all your answers have guided me into the right direction. Problem solved!

    BTW, I've decided not to put in a series/parallel switch. Right now I'm digging the tone as it is. Perhaps a nice project when I have a little bit more time.