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Full Circle resonances: Fit, or soundpost? (long and detailed)

Discussion in 'Setup & Repair [DB]' started by Chris Fitzgerald, Dec 16, 2018.

  1. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Am working with the new travel bass to get it ready for upcoming gigs that require flight, and am trying to work out the kinks. Before I begin the body of this post, I want to make sure it is taken in the right spirit, so I want to be clear about several things:

    1) I think the bass is really cool and I'll be reviewing it once I get everything set up to my liking. Please resist any impulse to denigrate the bass or its maker in any way.
    2) The shop where the pickup was installed is wonderful and the guys there are well known makers who have always treated me well and are a great boon to bass players for hundreds of miles in all directions. Please resist any impulse to denigrate the work of the shop.

    That said, here is the problem I'm trying to solve. I had a Full Circle fitted to the bridge this week. This necessitated filling the original adjuster holes and then re drilling for the 5/16" Full Circle installation. The bass sounds fine acoustically, but remember that it's a small body bass with new spiros on it that I'm still acclimating to. The bass sounded acoustically about the same after I left the shop with the new adjusters as when I arrived. They did move the bridge a little back toward the tailpiece from where I had it, but that was because I had apparently set it a little too far forward in relation to the notches. I noted after the installation that the back of the bridge post seemed to have a little space between it and the pickup top, and was told that the top of the pickup wasn't perfectly flat. I did not see the pickup when it came out of the box, so this is a possibility.

    When I got it home and plugged it in, it sounded basically OK with a different EQ paradigm than my regular basses sporting the same pickup; I had to cut a lot more low mids and lows, but I figured, "different bass, different EQ" and left it at that. The next day, when I plugged it in to experiment some more, there were two powerful resonances on Bb and F# on the G string, resonances that basically amounted to wolf tones that I would want to resolve before gigging with this bass. It also sounds way more bass-heavy than my other FC-equipped basses, and I am thinking that some adjustments might be in order.

    Last, I will mention that since it is a travel bass and the bridge is going to come on and off often, I kind of expect some of this. I noticed that the resonance moved and became different and even better when I wiggled the bridge foot around on the top. This may indicate that the issue could be soundpost related, or I may just be ignorant about how such things work. Feel free to denigrate my knowledge of luthierie!

    Here is a picture of the pickup fit on the travel bass:
    Busetto FC.JPG

    Here is a picture of the pickup fit on my main bass:
    LaScala FC.JPG

    I am probably "average" when it comes to fix-it type skills. I own files and even a belt sander kind of like this one, but I lack any actual woodworking skill and especially the patience that real wood workers have. I can fix basic stuff around the house and not much more, but am willing to give solving this issue a shot if there is some advice on how to approach it.

    Apologies for the length of this, and suggestions welcome!
  2. Don Kasper

    Don Kasper Supporting Member

    (Non-FC User commenting...just to get things started.)
    In the Travel Bass photo, does the "gap" extend around all 360 degrees between the top of the FC wheel and the bridge surface? If so, it appears that the blind-hole in the top part of the bridge is not deep enough and is limiting the contact between the wheel surface and the bridge.
    The top of the pickup wheel surface should be flush partially or (ideally) completely with that part of the bridge - as shown (beautifully) in the second photo.
    Just my $0.02
  3. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Thanks, Don... I had that thought as well. The "gap" is not all the way around that I can see, but rather seems to be weighted toward the back side of the bridge, even when the wheel is turned. Still, could it be just be a little shallow on that side? Wonder if this is something that I could fix with a hand drill or whether a drill press is required if the luthier contingent recommends trying that? The picture makes it look way more drastic than it is because it's a close up, but that idea makes sense.
  4. Don Kasper

    Don Kasper Supporting Member

    It appears that the blind hole is not (perfectly) perpendicular to the flat surface of the bridge. You may need to precisely remove material from the bridge surface to make full contact with the top of the wheel.
    Not sure how best to do this - a belt sander can be too aggressive and does not result in a perfectly "flat" surface - usually slightly curved, unless you are extremely careful.
    I'll let some Real Woodworkers/Luthiers chime in.
    Good Luck.
  5. jallenbass

    jallenbass Supporting Member Commercial User

    May 17, 2005
    Bend, Oregon
    If it's touching on one side of the bridge but not the other then the surface probably needs to be trued up so that it's parallel with the wheel. That's what I would look at along with determining if the hole is deep enough.
    Chris Fitzgerald likes this.
  6. I know I'm stating the obvious, and repeating what others have said, but I don't think the FC will perform properly unless the bridge leg is perfectly flush to the pickup/wheel. If it were me, I'd go back to the shop that did the install and ask them to fix it. Good people make mistakes sometimes too. :)
  7. Steven Ayres

    Steven Ayres Supporting Member

    Mar 11, 2007
    Northern Arizona
    It's not just the performance of the pickup; if the bridge face isn't flat to the pickup, the uneven pressure can damage the pickup (btdt). I don't think this is acceptable, and I'd ask the luthier to fix it. There'll be no way to accurately evaluate your setup with the pickup until that's right.

    You can see better than we can in the photo whether the bridge is aligned with its feet and not tilted on the screws. This can make a difference too.
  8. If the shop is correct and the top surface of the pickup is not perfectly flat, i.e. it suffers from a manufacturing defect, why not complain to Fishman?
    Dabndug, DoubleMIDI and RSBBass like this.
  9. tsheldon


    Jun 20, 2005
    Western New York
    It should be easy to prove whether the adjuster is faulty or the bridge needs work:

    Turn the adjuster 1/2 turn. If the gap stays on the same side the bridge needs adjustment. If the gap moves with the adjuster the pickup is faulty/bent.
    DoubleMIDI, robobass, RSBBass and 3 others like this.
  10. Don Kasper

    Don Kasper Supporting Member

    See Chris's reply in #3 above. This has been answered. The gap does not move.
  11. I’m not sure if it’s an ‘illusion’ but the top cap part of the full circle that screws onto the actual main body of the the wheel looks not to sit flush in it’s space?

    I’ve had this issue before where I very carefully took off a fraction of wood with a belt sander to get the pickup sitting flush . Have you tried rotating the adjuster slightly (1/4 turn or so) to see the impact on the sound?
    Chris Fitzgerald likes this.
  12. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    I appreciate all of the replies. Based on what can be seen here, is there anything I can do to get more info before trying to schedule another appointment out of town this close to Christmas and spending another 4 hours on the round trip?

    Does it seem worthwhile to take the bridge off and check the surface of the pickup and the depth of the blind hole? Also how tight does the blind hole need to be?
  13. Personally I’d take the bridge off and actually see exactly what’s going on in order to see if it’s a physical FC fault or hole depth etc .
    Not everyone would feel comfortable doing this if they’re not used to it. I’ve had sound posts fall before.
  14. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    New development - just for ****s and giggles, I rotated the pickup 180 degrees and plugged it in. The little gap stayed exactly where it was, but in this position the pickup sounds perfect - exactly as I thought/hoped it would when decided to install the FC on this bass in the first place. Curious, since I've never run one with the cable facing south out of the adjuster before, but good news for me! The pickup signal is also a good deal stronger than it was in the other position.


    @bassedsouth there is no worry about the post falling, as it's spring loaded in place on this instrument! Also (edit) I see what you see in the picture, but I think that may be a photo angle/shadow illusion since I can't see or feel the same in the actual physical real world. :)
  15. craigie


    Nov 11, 2015
    I don’t have anything practical to contribute but I’m curious and would like to learn about this so will chime in.

    You will be removing the bridge for travel? In that case why not do it once and see if the sound changes.

    Also, it sounds like the shop is aware of how it looks and so have done their best. They may prefer to do any adjustments themselves though. If you do any filing then that absolves them of any responsibility or warranty on the work.

    Perhaps another type of pickup would work better for this bass?

    Can you hear these wolf tones acoustically?

    Unrelated: does the neck come off to travel? I’m curious about how the sound post stays in place.

    Edit: seems all my questions were answered.
    Last edited: Dec 16, 2018
  16. .. if they are wolf tones, they may be more apparent playing arco - is this something you have tried? I had a wolf tone issue recently after changing strings, and it settled quite a bit as the strings lost their 'newness'. You didn't mention if the wolf tone changed or reduced after the 180 deg adjustment..
    good luck!, Steve
  17. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    There are no acoustic wolf tones; there is a resonant open D (which all of my basses have), and a couple of what I call "Spirocore G string notes" that will probably even out as those strings wear in. To answer the questions above, all of the weird quacky resonances are gone with the 180 degree turn and the pickup sounds just as I imagined/hoped it would with this pickup. In addition, I can now set my preamp and amp exactly the same as I do with my other basses (i.e. - basically flat with the exception of a high pass filter) and get the same basic amplified sound.

    Oh, and I won't be playing any arco on this bass. I'll save that for the full sized ones. :)
  18. rickwolff

    rickwolff Certified Gear Junkie, Amateur Adjunct Professor Supporting Member

    And now we are all looking forward (wink, wink) to hearing a recording of this incredible new bass through the Abox II.
  19. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    That, too. :)
    rickwolff likes this.
  20. unbrokenchain

    unbrokenchain Supporting Member

    Jun 8, 2011
    Asheville, NC
    If you run into more issues, you might be able to make a very thin wedge of wood to make up the difference in contact?
    Chris Fitzgerald likes this.

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