Hey gents -

I'm just finishing up my second build and spent a good part of the day messing about with a disc piezo. The wires that came off of them are extremely thin and today had me:

1) Installing one between 3M tape and then to the inside of the box under the low string, right below the bridge only to find I crushed the ceramic disc after pressing it between the foam tape. I read of this method on a blog...

2) Installing it in a bottle cap (looks very cool), but the solder joints on the thin piezo wire failed. Followed a YouTube video for this one (filled the cap with hot glue, etc.)

3) Tried the bottle cap method again because I liked the look of it so much, got my wiring sorted out (finally) and plugged her in, but...

Is it normal to have to really crank up the volume to get any decent sound from these pickups? I have mine mounted in the cap, surrounded with hot glue, no voids and then glued tight to the inside of the box, right below the bridge on the lowest string.

I know setups are subjective, but for comparison, my first build has a mini-humbucker and I can turn my little Fender tube amp to about 2 in the living room, v/c on the guitar full on, and she throws some good sound.

With the disc piezo, v/c full-on, I had the amp to 4 and it sounded 'ok' but kind of anemic... definitely not fired up about the sound. Also, at '4', theres noticeable hum.

Am I missing something? Expecting too much?

I'm tempted to scrap the piezo and put a mini-humbucker in there; the unfortunate part is that I put a sound hole / screen near the top front corner, so the new pickup could only go dead-centre where box art is - shame to cut that away.

If I am expecting too much from this round piezo, how does a bridge piezo compare? Can this setup be saved?



P.S. I'm running CBG 4-string Acoustic .034 - .013 with a wood bridge with bone.




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  • Hi, my first thought re the problem is this. A piezo pickup needs to have vibrations or pressure for it to work. The reason it is placed on the soundboard is that is the greatest source of strong vibrations. This is due to the bridge location on the top being at the sweet spot to make the top plate vibrate.

    In your CBG it looks like the bridge is not on the sound producing part of the top but on the very edge, and under that is structural timber. So maybe limited vibrations equals limited output. Just thought.
    Cheers Taff
    • Thanks Taff - 

      What you're suggesting makes perfect sense.

      The photos I posted originally were without a bridge as my bridge took a trip through my jointer (don't ask).

      I've since created a new bridge (see attached) and put a thin smear of hot glue to the back side of the piezo and mounted it beneath the bridge under the lid - that made a world of difference.

      Again, I'm puzzled as to how some cats are getting the 'glue in the bottle-cap' method to work. The only thing I can think of is to fill the cap with hot glue and then rest the pickup in the 'pool' of glue while making sure the back side is flush to the edges of the cap. This way, when placed against the box the disc makes contact.

      If this is a feasible solution, I can't really see what purpose the cap would serve aside from aesthetic.

      Anyway, I did get it sorted. Here's a quick test drive with my second build to show the sound... not bad considering it's a little 9V, 4" speaker.


      Cheers -


  • Here's an update of her plugged in... my thoughts on the piezo have changed now that I've pulled it out of the glue / bottle cap. Still curious how guys are getting decent sound from that setup.

    • probably gluing the piezo side of the cap instead of the thick glue side of the cap to the soundboard, just a guess...

  • 306641828?profile=RESIZE_1024x1024306642478?profile=RESIZE_1024x1024You do know that the piezo disc`s can be cut. I use the cut ones in my bone carved saddle bridges. I embed the disc in hot glue.

    • Hey Randy - awesome work man - the detail is incredible! No - I didn't know they could be cut. Can you shoot me a link to your site?

  • I invested in a benchtop belt & disk sanding station, and do a whole lot of my work on it, including shaping bridges, tail pieces, nuts, pegs, sanding down the sharp ends of frets and the sides of the fingerboard and neck, I've even made some drum sticks using the disk sander.

    • Hey JL - Good call. I was actually looking at one of those shaping setups from StewMac and wondered how good it was: http://www.stewmac.com/Luthier_Tools/Types_of_Tools/Jigs_and_Fixtur...

      Do you have any tricks for sanding things evenly / level? I find it hard to get things perfectly level  / square when doing things like reducing bridge height.


    • I started with using my electric hand held belt sander upsidedown in the bench vice, then I got something like this: http://www.homedepot.com/p/Ryobi-120-Volt-Bench-Sander-Green-BD4601...

      tips for even and level, sure.  Pressing hard will cause the leading edge to grind down faster, go easy with the pressure, do a little at a time,  flip ends/direction of the workpiece often, use the metal table and miter gauge if you need things square.


    Before I glue this disc down, given the recent issues, would it be better to put a few dabs of glue around the perimeter of the disc to attach it to the box vs a thin smear of hot glue between the disc and the lid?

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