Epiphone Jack Cassady grounding issue

Discussion in 'Pickups & Electronics [BG]' started by mrmagoo, Oct 8, 2017.

  1. mrmagoo


    Feb 11, 2016
    Hi all,
    I just bought an Epi Jack Cassady, Korean made from 2003. In really good shape except for a grounding issue that I can't figure out. I get a lot of ground hum/noise as long as I don't touch any of the metal parts.

    I have run my multimeter across it, and the strange thing is that I have perfect continuity between all exposed metal parts (tuning pegs, bridge, pot pointers) and the output jack. I first thought that it was something simple such as the bridge ground connector being dislodged, but apparently not. (I also confirmed its not an issue with my guitar cable.)

    So - I am clueless as to how to pinpoint the problem. This bass does have a transformer inside it whose continuity I have not been able to check as there is no metal exposed from it. Perhaps that could be it?

    Thanks for any advice you can give.

  2. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism

    So the hum stops completely when you touch any metal/strings/bridge? If so, that is not a grounding issue. A grounding issue would get louder when you touched metal. Your bass is getting RF interference and a proper shielding job will resolve it. Normally this is a really easy job but I don't know about doing it on a semi-hollowbody. There are a lot of resources on TB that can help you along. Pretty much everything I know on the subject can be read in the link in my signature. If you want to confirm with a multimeter, check the resistance at your jack and a metal part. I would imagine it is a very high number, it should be 0.1~ ohms.

    I hope that helps.
  3. Lobster11

    Lobster11 Supporting Member Supporting Member

    Apr 22, 2006
    Williamsburg, VA
    I've heard about a variety of problems with the JC over the years but never this one. My understanding is that the low-impedence pickup is usually immune to this problem, unlike Fenders and many other basses that require shielding to eliminate it. (Someone please correct me if I'm wrong about this.) I'm no expert on electronics, but here are a few ideas:

    1. Is it possible that you have a strong source of interference nearby, such as a light on a dimmer switch? That will make the typical hum of a Fender much worse, so maybe could produce hum in the JC.

    2. Try plugging your amp into a different outlet. One night my Fender was humming much louder than usual, and I eventually discovered that (unbeknownst to me) my amp happened to be plugged into the same outlet as a window AC unit. Switching to another outlet solved the problem.

    3. What kind of strings are on your bass? In searching TB I came across a thread discussing how this problem is common when using tapewound nylon strings rather than metal strings. The OP wasn't talking about a JC, but someone posted in the thread to say that they had this problem with a JC after installing tapewound nylon strings.
  4. mrmagoo


    Feb 11, 2016
    Thanks Diabolus and Lobster. In fact, I do have nylon strings on it. I just read around about that and it seems indeed it may be the culprit. But: I do have continuity between the tuning pegs and the bridge, meaning that the metal core of the strings are providing ground. Could this still be the issue?
    Lobster11 likes this.
  5. Lobster11

    Lobster11 Supporting Member Supporting Member

    Apr 22, 2006
    Williamsburg, VA
    Sorry, this is above my pay grade. All I can say is that whether this is the problem or not, I wouldn't use nylons on the JC unless I was really trying to emulate an upright sound. Jack uses Blue Steels, which sound great on it, but I also love it with TI flats (but not other flats that I've tried). IMO the beauty of the JC's tone is in the richness of the mids, so using "thumpy" strings means missing out on the best it has to offer.
  6. mrmagoo


    Feb 11, 2016
    Lobster, yeah, I hear you. The bass came with the nylons as I bought it a few days ago. I will try something else in time.

    As for the hum: when I touch the bridge or output jack, the hum gets lower, but it doesn't disappear completely. I just compared it to my Fender P with GZR P+J pups, and that one is dead silent in comparison (regardless of whether I touch metal).

    Something is wrong with the Cassady, and I find it hard to believe its the fact that there's some non-conductive material wrapped around the otherwise well-grounded strings?
  7. mrmagoo


    Feb 11, 2016
    Diabolus, I measured resistance between the bridge and the output jack. With the multimeter set to 200 ohm, I get readings between 45 and 50. What exactly does this mean?
  8. bholder

    bholder Affable Sociopath Gold Supporting Member Supporting Member

    Sep 2, 2001
    Vestal, NY
    Received a gift from Sire* (see sig)
    It would seem to mean a bad ground. The bridge on the JC is grounded via the stud that is closest to the controls - I wonder if that pulled out and someone glued it back in (defeating the ground?) - could happen...
    mrmagoo and DiabolusInMusic like this.
  9. Primary

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    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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