argh! weird feedback problem!

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by spaceboy, Jan 26, 2005.

  1. spaceboy

    spaceboy Member

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    ok, took out my previous "main" guitar, a 60s RI MIM strat, to give it a bit of a setup so i can get it sold.

    now i haven't had it out in months and months, but it never did this before. It's got a Rio Grande pickup in the bridge, a Muy Grande i believe, and this pickup produces a very weird kind of feedback. It acts much like normal feedback that i get with the other two pickups, but it comes on very VERY easily and quickly, and can only be made to go away by very careful turning and tilting of the guitar. if I do make it go away i can induce it easily by placing my hand over the pickup. it changes pitch with tilting, like normal feedback, but the note is very definate and sustained (almost like an ebow), and very shrill and high-pitched. it goes away if i play a note, but only while the note is loud enough to cancel it out, and returns as soon as the note starts to fade.

    I wired it to the middle position on the switch (no need, i assume, to physically change the position of the pickup). no change.

    then i took it out and swapped it round with a stock pickup from my Mex Standard. in the Standard, with the Rio, the problem is gone. perfectly normal. in the RI, with the stock pickup, there is no problem.

    i swap them back, Rio in the 60s RI. problem recurs.

    ARGH! makes no sense at all, but is this a problem anyone has experienced, or has any ideas on?

    mightily annoying, as you can imagine. cheers
     
  2. alderbody

    alderbody Member

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    very strange...

    did you by any chance damage the coil of the pickup?
    (cutoff wire making contact?...)

    never experienced such a prob, just guessing...

    :confused: :confused: :confused:
     
  3. Jim Collins

    Jim Collins Member

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    It sounds as if the pickup is microphonic. I take it you haven't played the guitar in some time. How and where was it stored?
     
  4. spaceboy

    spaceboy Member

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    hey guys.

    i can't think how i would have damaged it, but i'll definately have a close inspection of the coils when i get back to the flat.

    I don't know much about microphonics, but if it is, does that mean it's just buggered and there's nothing I can do about it? it's been stored in a very basic soft case in my wardrobe back home, and then just stood in a corner while i've been at uni for the last few months. Is there any real way to "test" for microphonicism? (probly a word of my own invention there ^_^ oh well)

    cheers folks
     
  5. Jim Collins

    Jim Collins Member

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    Do I have this correct -- the Rio Grande in the MIM RI gets the feedback, but the same pickup in the Mexican Standard does not?

    What type of pickup routes do the two bodies have? I would assume that the MIM RI has something akin to vintage routing -- each pickup cavity is just big enough to hold the pickup. I don't know what the Mexican Standard has, but I wouldn't be surprised if it had different routing than the MIM RI has. It sounds like the pickup is somewhat microphonic, but its environment may be making things worse. Perhaps the route in the MIM RI is a little smaller and shallower than the route in the Mexican Standard -- or maybe the Mexican Standard has a swimming pool route. If the pickup just barely fits in the MIM RI's route, the vibrating air in the tiny space could be causing the pickup to move in such a way as to cause the squealing. When you put the same pickup in the other guitar, there may be enough extra room that the vibrating air has another place to go, meaning it won't cause the pickup to vibrate.

    A microphonic pickup is not shot. It can be repotted, but if it is too big for the route in the body, the real solution is to fix that problem.
     
  6. spaceboy

    spaceboy Member

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    yeh, you got it right. i don't think it could be the routing cos, although coincidentally i did just chisel out the cavity in the standard for a swimming pool route, i tried it in the RI a couple of times with the pickguard not even on the guitar.

    But, another coincidence - i ran across this http://www.guitarnuts.com/technical/electrical/index.php

    it all seems to point to microphonics, so I reckon i'll try repotting the bastard. thanks for the pointer! i'll let you know how it goes
     

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