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So my beloved '76 has developed an annoying hum

Discussion in 'Basses [BG]' started by 9mmMike, Oct 18, 2013.

  1. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Been giggin' the schniggies outta my '76 Fender P and I took it to church to play one Sunday AM and it made the most awful noise when I plugged it in.
    I swapped cabs and cables and I thought it got better when I switched the instrument cable but the noise was still there, just a little quieter...maybe.
    Now I notice it in every cab/head combo into which I plug it in.
    It used to be dead-silent.
    I pulled it apart and shielded it and it made no difference.
    I replaced the jack and there was no difference so I soldered the original back in.
    I have run out of skills to figure this out and have switched to a "plan B" bass which is nice but just not as awesome as the '76.
    Any idea of what might bring on a very sudden input hum (if that is the correct term)?
    It does not seem to be grounding or at least I can say that it does not change at all when I touch the strings.
    Plug it in and there is a hum. Rolling off the tone helps a little but the bass sounds muddy. Turning off the tweeter helps but the hum is still there if you listen for it.
    It is all original from pots to pups.
    I hated shielding it as it was working fine before but I was desperate to get it quieted-down.
    This is not "normal" as it was silent before and my other basses are also quiet. I am playing a '73 and '74 parts-bass now.
    I am a little reluctant (OK call it an irrational fear) to take it to a tech who will pronounce this as a "normal" P bass noise since I know it was quiet before.
  2. dropbass

    dropbass

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    Had you used it In that room before with no hum? Could be power. Or rf interference from florescent lighting..or wireless mic system...my 78 is dead quiet some times... uless I touch a pup pole but I just go with it. It is in essence a single coil which are noisier.. certain rooms do weird shizz. ..I had random grounding issues I just re did the wiring to be sure. . Bad parts and pots can do weird things too.. stuff does die
  3. two fingers

    two fingers Loud Mouth Know It All Blowhard Gold Supporting Member

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    Well, did you try plugging into a different circuit? Have you played the '76 somewhere OTHER than church? Did it still hum?
  4. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Yes. Sorry if this was not clear. Once it started this hum, it does it everywhere in every amp/cab combo.
    It is actually not such a big deal at gigs as you cannot hear the hum over everything else but at home for practice or church, it is very noticeable due to lack of other racket.
    Something "happened" to cause this but I've not a clue where to begin beyond what I already tried.
  5. cybersnyder

    cybersnyder Always groove.... Gold Supporting Member

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    Disclosures:
    Endorsing artist: Xsonics cabinets
    Any chance the ground wire on the bridge has pushed into the wood to the point where it's no longer making contact? I guess if that were the case, the noise would go away when you touch the volume or tone knob.
  6. 1960jbass

    1960jbass

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    How about the wiring?? Are the solder joints still solid?? I had a solder joint go bad in amp and it was 10 years old!! My only other suggestions would be some tuner cleaner in the pots and check to see if the tone capacitor is starting to go. Hope you solve your problem!!
  7. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

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    Does the hum remain constant even if you touch metal/strings/bridge? If it goes away when you touch metal your shielding needs to be completed. If it gets louder when you touch metal the ground wire under the bridge would be my guess. If it remains constant you have a deeper issue.
  8. sowilson

    sowilson

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    If you can, I would direct wire the pickups to the output jack and see if you have hum. Then I would remove the pickups from the circuit and see if thee circuit is hum free. I suspect either the bridge ground wire or the VT wiring.
  9. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Thanks for all the ideas guys. If the hum does not go away when I touch the strings, what does that mean? The hum/buzz gets louder when I turn up the volume on the bass. Could a bad cap do this?
    I have had plenty of non-shielded basses that buzz when I am not touching the strings or controls. This is something different. I know it is not the jack as I have already changed that out and back with no difference.
    Maybe a volume or tone pot? I hope it is not the pups.
  10. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Not sure if I can do that much work without mucking something up. If I cannot interweb diagnose it, I guess I will need to break out the soldering iron. I could make it worse though!
  11. jarheadbassman

    jarheadbassman

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    Have you tested or looked at all the circuitry? ...76? The potentiometers. ..(what the knobs control) maybe going bad...I noticed that you solder so not trying to insult intelligence.
  12. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Simple solder. How can I tell a pot is bad? I have had them go scratchy before and then fail altogether but never had one cause a steady hum. I do have a multimeter that I can fiddle about with.
  13. mjac28

    mjac28 50th Anniversary Ed Sullivan February 9, 1964 Gold Supporting Member

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    I'm pretty sure it's toast and I don't do this for everyone but I'll take it off your hands for a small disposal fee if it were anything but a 76' I would do it for free but those 76's are a pain. :)
  14. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Thanks. Hold your breath! Ha!

    I have another 76 that has a ground issue that sounds exactly like this one but it stops when I touch the strings or controls. However, it also has a shakey tone pot that will cause this sound as well if I give a wee jiggle. Hmmmm.

    This bass i am hoping to fix had just climbed to my number one and I am really bummed. I do not want to give it to a tech where it will vanish for months and probably come back the same anyway. Cynical, I know but I was sure hoping for an easy "I know what that is" solution from someone else's experience.
  15. jarheadbassman

    jarheadbassman

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    Take the multi meter and connect the leads to the tabs of the multi potentiometers, gona need help unlessbyou have grasping leads...than turn the knobs...set multimeter to ohms, I don't know if it would cause a hum but try to inspect the circuitry and see if anything looks discolored or the capacitors are ready to go...see if disfugured...I have a degree in electronics (not that good at it) and I am quite knew to playing bass let alone instruments.
  16. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

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    Your other '76 is grounded it has a shielding issue. That is why the noise goes away.

    In regards to this one, did you check the ground wire under the bridge? Ensure it makes good contact, I like to put a piece of copper foil under the bridge and press the wire into it. Does the shielding make contact with any of wiring? (aside from the ground wire connected to the shielding)
  17. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    I have not pulled the bridge. I will do that next. Thanks.
  18. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    I will try this after I check the bridge ground. My meter does not have grasping leads. My next one will though!
  19. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Good grief. I swapped a new harness (pots, cap, jack) into the bass and the volume is always on. The wiring looks identical. This is why I am not employed as a guitar tech!
  20. 9mmMike

    9mmMike Would you happen to have a cookie for me? Supporting Member

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    Ok. Swapped out the volume pot to another one and the volume is fine. The hum is now there when I crank up the tone control.
    To sum up:

    All pots and jack and cap are new. The bridge was pulled and I made sure that the ground was good. All I have left to swap are the pups. Very sad.

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