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Thread: Microphonic Feedback After Wax Potting

  1. #1
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    Question Microphonic Feedback After Wax Potting

    Greetings All -

    tl;dr - I wax potted my Rickenbacker Toaster pickups but still have really bad microphonic feedback. What can I do now?

    I recently installed Rickenbacker Toasters into my 650D. At practice volume, the guitar sounds very nice. Just enough of the classic jangle of the toasters but the natural walnut balances the sound nicely. But then I brought the guitar to a sizable gig and cranked my 59 LTD Bassman to 6 and squeal city!! These toasters are terribly microphonic.

    I purchased these from a licensed dealer (Chicago Music Exchange) and they were brand new. But because I had soldered them, no refunds. I spoke to their techs and they recommended I get them wax potted which was consistent with the advice I've seen given to others on this forum.

    So now they are wax potted. Still sound beautiful at low volume/gain but still getting the high pitched squeal. I'd read that wax potting was the cure for microphonic feedback but apparently that's not the case. I also tried the ISP Decimator II which did not reduce the squealing. Finally, I tried tuning out the offending frequency on the amps but had to take treble to 0 - not viable.

    Before I start trying some of the other tricks I've read about on some of these forums, I wanted to check in with you knowledgable folks to see if there's anything I'm missing. I'm getting the feedback with 2 different amps and 2 different overdrive pedals. It's definitely microphonic (bad) feedback. I took it to a very good amp tech who confirmed both pickups were microphonic. Both produce the squeal at a reasonably loud volume or with gain.

    One thought is that when installing, I used the screws that came with the 650D instead of what shipped with the Toaster pups. I did this because the Toaster screws were a bit longer and I didn't want to have to drill into the 650D. Could the screws be vibrating or otherwise contributing to the problem?

    I've read that using poster putty between the pickup and the pickup cover can fix this problem. The cover on the toaster is not soldered on but is held on by bolts which I've heard can result in vibration causing squeal. Is this recommended? I've also heard that melting some wax between the cover and pup can help in the same way.

    I've also seen folks will put foam or some other insulating material in the pickup cavity. Some say it's to absorb some of the high frequencies in the cavity and others say it's to keep the pup from rattling around in there. I have rubber grommets between the pickup and the guitar wood so theoretically, the latter would not be a problem. Hoping the truth is the former. I have some high frequency sound absorbing foam (wall panel/foam wedge) but have also read that folks recommend something denser like a mouse pad. What's the recommended material?
    er idea I've seen is around adjusting the screws. I've seen recommendations to either loosen (so the pup doesnít pick up the body vibrations) or tighten (so the pup doesnít rattle around). Iíve also seen a recommendation to place a rubber washer between the screw and the pickup cover so it is less coupled to the guitar. Which (if any) of these are best?

    Finally, Iíve read mixed advice around potting. Some folks have said if the microphonic arenít fixed by one round of potting, to do it again with more wax (more time to soak, more to dry, etc.) But Iíve also read that over-waxing will kill the tone of a pickup, something I definitely donít want to do. Would it be worth waxing these Toasters a second time?

    Kind of crazy that such expensive electronics would have such trouble in high volume/gain situations. The tech that potted the pups said this is to be expected with some of the Ric pups. Anyone else have this experience?

  2. #2
    Supporting Member mozz's Avatar
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    Who or how did they wax pot them? 5 minutes? 30 minutes? Vacuum? Covers on or off?

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    Quote Originally Posted by mozz View Post
    Who or how did they wax pot them? 5 minutes? 30 minutes? Vacuum? Covers on or off?
    Who is easy - Chicago Music Exchange. I'll ask them for exact answers to the rest of the questions but they said that the whole process takes about a day and that they had to melt the wax so I would guess it was at least 30 minutes. I don't believe it was vacuum wax potted. They definitely took the front cover off.

  4. #4
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    Quote Originally Posted by dcmusic View Post
    They definitely took the front cover off.
    Unless the pickups are solidified in the covers, the cover will act like the diaphragm in a microphone and squeal uncontrollably if used with any gain or volume. You can check i f this is the cause of your problem by shouting at them - you'll probably hear yourself coming through the amp :-)
    big_teee likes this.

  5. #5
    ToneOholic! big_teee's Avatar
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    Pot them again fully assembled.
    Potting them a part, will pot the coil, which is good, but not take care of the metal parts.
    Had similar problems with metal covered humbuckeers.
    I now always pot them with the covers on.
    140 degrees, for 10-15 minutes should do the trick!
    T
    Justin Thomas likes this.
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    Terry

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    Yes the pups are definitely microphonic - I can talk into them and hear them in the amp clearly! Kind of surprising to me that Rickenbacker would manufacture pups that are this microphonic but I guess that's vintage (how did those 60s rock bands play huge venues?!)

    The tech clarified his approach. He potted them for about 15 minutes total. He put them in for 5 minutes, let the wax run off and put them in for another 10 or so. He called it double wax potting. He didn't vacuum pot because he hasn't experienced a ton of difference with that approach.

    He also advised against potting with the covers on. He said the cover should create a Faraday shield around the pickup to protect against RF interference and that when he's potted with the cover in the past, noise has gone way up.

  7. #7
    ToneOholic! big_teee's Avatar
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    Why not post it over there at the pickup forum?
    Think you would get more pickup winders to join in.
    Lots of pros there.
    Pickup Makers
    I make all kinds of regular humbuckers, and fender single coil stuff.
    But no Ric's or Gretsch stuff made here.
    T
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
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    Terry

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    Thanks for the advice big_teee!

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    Ask him to explain how a few microns of 80/20 paraffin/beeswax mixture affects the cover's ability to act as a Faraday cage! I've solidified literally hundreds of pickups in their covers over the last 40 years without affecting the noise level one whit. Covers affect the tone, negatively imho, but solidifying them onto the pickup is mandatory if they are to be useable at anything above bedroom volume.

  10. #10
    ToneOholic! big_teee's Avatar
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    If your pickup is made like the Single coil in this web-link?
    Curtis Novak Pickups www.CurtisNovak.com: Mod: Cheap aftermarket pickup to something useful
    Then I would have no problems with potting this pickup, fully assembled.
    There are too many metal parts touching things, to not be microphonic with high gain.
    This pickup was designed back in the day when guitars were played clean with small combo amps.

    If you want to experiment, try taking the top cover off and mount it without the cover and see if it is still microphonic.
    I build and pot pickups all the time, If I can help, let me know with a PM.
    T
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
    Keep Rockin! B_T
    Terry

  11. #11
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    Yes, big_tee, it looks just like the single coil (and the end result after repairs). I'll try taking the top cover off to see how it sounds. If that fixes the issue and there isn't a ton of noise then I'll have a better idea of what to do next.

    And TOA Bassman - what you're saying makes sense but this guy from CME does sound pretty knowledgable. I do worry about killing the tone of these pickups but you're right that they're not useable above bedroom volume which won't cut it for me.

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    An update here - I took the front cover off to test big_teee's idea out but found that unfortunately the top cover is required to keep the pickup in place.
    pickup.jpg

    While I had everything apart, I thought I would experiment with some of the approaches others have recommended. First, I added some poster putty to both sides of the pickup to adhere the covers a little better to it.
    putty.jpgputty2.jpg

    Then I filled the cavity with two different foams. One dense rubber to keep the pickup in place and the other, high frequency sound absorber to absorb the high frequencies and to fill the areas that would be difficult with the denser foam.

    Dense foam
    rubber.jpg

    Light foam
    audio.jpg

    Cavity filled
    stuffed.jpg

    And for reference, here are the rubber grommets that had kept the pup from rattling around prior to my work. They are still in there but not really doing anything because the denser foam is doing the work
    grommet.jpg


    The end result is definitely improved headroom before getting squeals. I can definitely get loud before that terribly howling. The neck pup is better than the bridge but I can work around the bridge feedback by dialing back the tone on it. It's a smaller room so I have to imagine it's worse than in a live setup and I can get pretty loud before getting the microphonic feedback.

    This MIGHT be workable. I'll have to get it into a full volume/stage situation to really test it but I think this might have gotten me close enough. I will say the one downside I've noticed with this is that the neck pickup lost some brightness. I wouldn't call it dull by any means but it sparkled a lot more before stuffing the cavity.

    We'll see how this thing does at full volume. If not well, I'll be PMing you, big_teee.

  13. #13
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    I forgot to say that if anything I did looks wrong, please let me know. I'd love to improve the headroom and brightness if at all possible.

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