A Note on Squealing Feedback and Some Ways to Avoid It

Discussion in 'Tonefreaks' started by freefrog, Aug 16, 2017.

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  1. freefrog

    freefrog Senior Member

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    The past week I had to deal three times with a set of pickups including a squealing transducer...

    The first was a pair of machine wound / unpotted P.A.F. replicas. The magnet of the bridge PU had been glued (!) to the baseplate by a previous owner but sadly, it didn't kill the high pitched feedback heard under overdrive.

    The second duet included two other unpotted P.A.F. replicas, hand guided. This time the squealing one was the neck transducer, probably because a bobbin holder screw had been broken in its hole: the loosened structure was the culprit (that's why I'd recommend to be cautious when swapping parts in a pickup: IME/IMHO, it's one of the best ways to create a squealing fedback initially absent).

    The third example involved two P90's. One of them had been literally drowned in some thick wax and was mounted upon a thick bit of foam but still squealed, without apparent reason, as soon as any overdrive was enabled, even at low volume...


    There's various well known solutions against such issues - going from silicon or paper tape between cover and slugs to cotton balls under the baseplate (!). There's other less known empirical tricks, efficient or not: I've already found a thin foil of foam glued under the bar magnet in some cheap Chinese HB and as a matter of fact, it didn't squeal. I've also seen a wide rubber elastic wrapped around the bobbin and squeezing it... but it did increase stray capacitance and altered the harmonics.

    Sadly, there's never any certitude that any of these tricks will kill high pitched feedback. In some cases, I've found myself swapping bar mags until the pickup stopped to squeal. That's what I had to do with the first HB aforementioned: some rough cast mags are so roughly molded that it creates unwanted gaps between components, opening the door to vibrations and related feedback.

    A trick that I've found a while back has helped me to solve such problems so let's share it:

    Teflon thread sealant tape... The kind used to secure moving whammy bars.

    It's thin, soft and auto adhesive. It can be wrapped around height setting screws and/or their springs, bobbin holder screws, around screw poles or around the pickup itself, filling the gaps between cover and bobbin(s).

    The most spectacular effect happened the last week with the P90: I've wrapped in teflon its screw poles and height setting screws then built a cushion between the bobbin and plastic cover (without allowing any pressure on the wire itself). Now, the transducer is dead silent (hum excepted), even in a cranked up tube amp with two overdrive pedals enabled.

    FWIW.

    FOOTNOTE - The theoretical "dielectric constant" of teflon is lower or not worse than with paraffin or silicon, BTW, so it won't increase stray capacitance in a significant way. but PTFE is much easier to use than wax potting to do...
     

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    Last edited: Aug 16, 2017
    moreles likes this.
  2. dmoss74

    dmoss74 Senior Member

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    if the teflon tape actually works, that's a great tip. and it's also a bonus in how economical a fix it is. you can even use colors. :)

    thanks for the research.
     
  3. moreles

    moreles Senior Member

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    Yow! I'm glad I've only once encountered squealing with a mechanical source -- the classic HB cover, loose, acting like a mic diaphragm. I like the Teflon tape idea for a bunch of uses. Never heard it, never thought of it - thanks!
     
  4. Kaicho8888

    Kaicho8888 Senior Member

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    Hey, that's worth trying PTFE... thanks for the tip!
     

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