SE Custom 24 35th Anniversary 1st - Hum issues

Discussion in 'PTC - PRS Tech Center' started by massimo, May 23, 2020.

  1. massimo

    massimo New Member

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    Hi guys,
    I got las week my first PRS, an SE C24 35th Anniversary.
    Overall, I am very happy with the guitar: good finishes, beautiful top, good mechanics and a sound with tons of personality. I love it.
    I am only concerned by one topic: noise.
    As I said this is my first PRS, I come from an SSS Stratocaster and I expected to have less noise on a HH guitar. Unfortunately it is not the case.
    In summary: when I plug the guitar in and use high gain I notice a strong hum that diminishes when I touch any metal part with my hands. When touching any metallic parts the noise is acceptable and lower than a single coil.
    This made me first doubt about circuitry: grounding issues or cold solding so I opened up the back covers and checked (I am electrical engineer so I have a decent experience doing so) with a multimeter (diode tester) and found that all metallic parts (bridge, pots back covers, all ground solding, jack ground plate, blade switch) are well connected between them, no weird impedance, just full conductivity.
    I also noticed that while the back, detachable covers are conductive, the inside wood cavity is not. just painted in black (which by the way is very well done) but no conductivity at all. This makes me think there is no Faraday shielding.

    I just want to make sure that such configuration (no shielding) is standard and having such noise is a common behaviour.
    Also, has anyone tried to shield pick ups and cavities with copper tape? does it reduce noise?

    I was about to send the guitar back to the shop for replacement, yet I doubt it is something that happens on all PRS SE.
    Can you help with some advise?
     
  2. AP515

    AP515 Mostly Normal

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    Sounds like a grounding issue to me. It may be the input plug instead of in the cavity. It could also just be a noisy environment. If you are next to a computer it will amplify the EM coming off the computer.
     
  3. massimo

    massimo New Member

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    thanks for your reply.
    I guess you mean 'wall plug grounding' issue. In that case, it might be.
    However, being in the same environment and plugged into the same plug, I have more noise from the PRS than the Strat, this is what I don't understand.
    It only explains itself being the PRS not shielded 'by factory' while the Strat is.

    I want to make sure that it is not 'this' PRS having issues, as in case it was I could send it back to the shop.

    thanks.
     
  4. AP515

    AP515 Mostly Normal

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    If you have 30 days, I'd say take it in and have them look at it. See if it hums on their rig. Take your Strat with you to compare.
     
  5. Ovibos

    Ovibos Naughty Wood Librarian

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    At the risk of asking a dumb question: are you running the pickups in split mode (noisy) or humbucker?
     
  6. massimo

    massimo New Member

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    @AP515 unfortunately I can't do that, I bought it online. I can only ship it back for another.
    @Ovibos it does almost the same on both positions, split and hum bucker

    my questions was:
    - is hum common on SE?
    - are any SE shielded from factory?
     
  7. massimo

    massimo New Member

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    a note for what it worth: the neck pick up is more noisy than the bridge one.
     
  8. massimo

    massimo New Member

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    Hi again, I have run some tests, here results:
    with the PRS connected to the amp head (Blackstar HT5RH)
    - I found 100ohms between guitar ground and house ground (picked on another wall plug)
    - I found 0ohms between guitar bridge and amp input ground/cable ground
    - I found 100ohms between amp ground at input jack and amp ground at power socket
    -> this make me think that guitar grounding is fine, but the impedance on the HT5RH is too high to ground the guitar

    with the PRS connected to a Scarlett 2i2 and to an iPad with no grounding at all (floating N and no ground)
    - I have the same problem, the noise decrease only when I touch strings/bridge i.e. I am the ground.


    I also tested house grounding and it looks fine.

    Conclusions: I believe it is a shielding issue. the guitar catches EM noise and is not able to discharge it to ground 1.because it is isolated when used with iPad or 2.because amp ground impedance is too high when plugged to the amp.
    In fact, The Strat is shielded so it does not catches EM noise at all.
    The problem should solve with a proper shielding.

    What do you think?
     
  9. Jorgen

    Jorgen New Member

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    I bought an SE Custom 24 last year and have been very pleased with it, but wiring seems to be its weak point: I found a cold solder joint on the blade switch when it suddenly went silent in the bridge position, and now the same blade switch has started becoming noisy and unstable. I just checked the cavity, and it seems that the very nicely done black paint job has nothing to do with shielding. But the guitar is not noisy and I plan to go on loving it after I have put in a new, better quality blade switch. summing up: Check the solder joints and prepare to upgrade some of the electrickery -- and enjoy your beautiful and extremely well-playing guitar!
     
  10. Ovibos

    Ovibos Naughty Wood Librarian

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    I would contact the dealer.
     
  11. massimo

    massimo New Member

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    thanks for your comments.
    I tend to believe it is a shielding issue indeed, and overall low quality on electronics, Which makes me think another piece would do the same....
    I will ring the dealer to see what they suggest.

    thanks!
     
  12. Ovibos

    Ovibos Naughty Wood Librarian

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    I have several SEs and they don’t do this. I wouldn’t impugn all of them.
     
    shimmilou likes this.
  13. PDC

    PDC I'll be right back...

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    I had noise problems on an SE Custom 22. I shielded the interior cavities with conductive paint. It did help.

    Another time I had a noise problem, and it turned out to be the guitar cable. I changed the cable and the buzz went away. But with the bad cable it was just as you describe. Noisy, and less noisy when touching metal parts. Try a couple of different cables.
     
  14. massimo

    massimo New Member

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    Thanks all for the suggestions.
    I’ll keep you posted :)
     
  15. Jorgen

    Jorgen New Member

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    I just rewired mine with a 5-position superswitch and found out that signal wiring -- also from the volume pot to the output jack -- is done with shielded wire which seems to explain why the cavity has not been shielded: it does not need to be. Actually it might explain your hum problem if one of the wires is not grounded properly -- my SE had a cold solder joint on the selector switch which eventually failed. So maybe you have got one too ...
     
    #15 Jorgen, May 30, 2020 at 11:06 PM
    Last edited: May 30, 2020 at 11:52 PM
    massimo likes this.
  16. massimo

    massimo New Member

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    Update: I contacted the seller and sent a video of what happens. They said it is defective and will replace.
    I am confident it was a one-off issue. I’ll share how the new one behaves.

    thanks all for the comments.
     

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