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Dupont Buzz/Checking for loose brace in petite bouche

CraigHensleyCraigHensley Maine New Dupont MD60

Hi, I recently purchased a preowned 2013 Dupont MD60 on reverb and immediately noticed it had fret buzz, or so I thought. So I brought it to my luthier and refretted the whole guitar only to discover the buzzing persisted. After consulting builders, dealers, and forum posts, I discovered it was sympathetic vibration and not a fret buzz.

The guitar buzzes on the C and C# notes only on the G and D strings. If I tune those strings down a half-step the buzz will follow the note. I've checked the tailpiece, bridge, truss rod, and tuners. I purchase an LED luthier mirror to look inside the guitar and can't see anything abnormal. If i strike the note softly it doesn't buzz, but when I play at regular volume it does.

Has anyone encountered this type of sympathetic vibration before, or have any further suggestions?

How do you check for a loose brace in a petite bouche when you can't physically fit your hand in to feel for it?

Thanks,

Craig

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Comments

  • mac63000mac63000 Tacoma, WANew Geronimo Mateos Jazz B
    edited March 28 Posts: 100

    I also thought I had noise caused by a lose brace about a year after I bought my guitar, but it turns out was sympathetic vibration in the truss rod. I took it to a really good technician who was able to fix it by properly setting the relief. He sets up tons of these guitars and said it's really uncommon to find one with a loose brace, which is hopefully reassuring! They are made to resonate a lot more than a flat top so unfortunately vibrations are common.

    It wasn't always noticeable due to playing at different volumes and it only occurred on certain notes, as you noted. Try tapping the back of the neck with your thumb to see if that creates the vibration. I can send you a video of what mine sounded like if you're curious. Otherwise, I think I've read other forum posts about buzzing caused by a zero fret being too low. Good luck!

    Matt

    MichaelHorowitzCraigHensley
  • TwangTwang New
    Posts: 89

    could it be a back buzz? The strings is vibrating between you fretting hand and the nut in sympathy with the other strings. Does it sound more like a rattle than a buzz. If so the problem is usually fixed by adjusting the zero fret/nut. Its too low or high I cant remember which.

    CraigHensley
  • TwangTwang New
    Posts: 89

    Oops sorry mac63000 I’ve just repeated what you said.

  • BonesBones Moderator
    Posts: 2,831

    Oh right, make sure the truss rod has at least a little tension on it but I'm sure your luthier did that on the refret.

    CraigHensley
  • CraigHensleyCraigHensley Maine New Dupont MD60
    edited March 29 Posts: 15

    Thanks for all the insight and suggestions, everyone! I managed to tighten the truss rod and then shimmed up the bridge to compensate the action for less neck relief. This quieted the buzz to where it's barely audible and much more enjoyable to play. I'll keep tweaking it as time sees fit. Super helpful!

    Craig

    mac63000
  • ChiefbigeasyChiefbigeasy New Orleans, LA✭✭✭ Alves de Puga DR670; Dupont MDC 50; The Loar LH600
    Posts: 267

    My Alves de Puga had the same problem. Finally figured out it was the truss loosening up over time. Tightening in either direction did the trick. Still happens over time, but now I know how to fix it.

    CraigHensley
  • mac63000mac63000 Tacoma, WANew Geronimo Mateos Jazz B
    edited March 29 Posts: 100

    A small piece of soft foam weather stripping is also great to mute unwanted symptathetic tailpiece and post-bridge vibration, which can be quite annoying and rather unharmonious. It's light enough that it slides in without dampening the top.

    Glad you got it under control!

  • BonesBones Moderator
    Posts: 2,831

    Oh yeah, what Mac said too. Although I have used a piece of Velcro just around the strings so nothing touches the top.

    mac63000
  • mac63000mac63000 Tacoma, WANew Geronimo Mateos Jazz B
    Posts: 100

    Ooh velcro is a great idea too!

  • ChiefbigeasyChiefbigeasy New Orleans, LA✭✭✭ Alves de Puga DR670; Dupont MDC 50; The Loar LH600
    Posts: 267

    A variation of the non-musical raspy vibration has returned and this time, it’s not the truss rod. Confirmed this because I had setup redone, frets leveled, truss rod set, and I’m still getting a rasping nonmusical resonance on one note in a couple of positions on the neck.

    Put on a set of loop Argentines and that helped, perhaps enough. Advice indicated that ball end and string tension could be playing a part. Now considering replacing tailpiece with something lighter and/or with a wood insert.

    Will report back with results.

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