Dual piezo wiring: in series or in parallel?

I'm working on a license plate resonator guitar with two piezo pick-ups. The piezos are super glued to the back side of the plate, either side of the bridge.

This guitar also has a CB Gitty 3 pole, prewired, dual humbucker pick-up installed. I plan to use a 3-way switch to switch between the piezos, the humbucker or both. I'll have a volume knob for each pick-up and a tone knob for the humbucker only.

I would like the volume output from the piezos to be approximately the same as the humbucker volume output. So my question is: should I wire the two piezos in parallel as normal or in series for more voltage?

I can add more piezos in series for more voltage or in series-parallel for more oomph. What has been your experience?

Replies

Cause the Blue rat December 23, 2018 at 3:46am

Think of it this way. Series doubles the impedance. Parallel divides it in half. Unfortunately you may not get the same output between the pickup and the piezos. Could turn the pickup volume down a bit to make up for the difference. Let your amp work harder to get the over all volume level you need.
- Bryan Pieper > Cause the Blue rat January 14, 2019 at 3:19am
  
  Very cool that you did that experiment. I would love to do more of that sort of thing, mixing and matching 100 combos of pickups to see what happens, but I already have too little time for building without venturing too far off the beaten path.
  - Martin Simpson > Bryan Pieper January 17, 2019 at 8:27am
    
    Now that the build is finished, I have the answer to my own question.
    
    The dual piezos wired in parallel are actually louder than the humbucker! If I run the humbucker at full volume, the piezos have to be set at about 2/3 to 3/4 volume to match.
    
    Ill get picures up ASAP.
    
    By the way they sound great. Thanks for all the advice.
    - Paul Craig > Martin Simpson January 17, 2019 at 2:36pm
      
      Always remember that sound/tone results vary according to the user. We all have different ideas of what is good or bad. So you get ideas about things, but you have to try them to find out if you like it or not and you may get different results in different guitars.
      - Martin Simpson > Paul Craig February 12, 2019 at 12:40am
        
        Here's the pictures that I promised. As you can see, it is just quick and dirty construction.
        
        The disks marked P are in parallel and the ones marked S are in series. The toggle switch selects one or the other, or both.
        
        When the box is closed and plugged into an amp, it makes a good pickup for acoustic instruments. I put the but end of my canjo on it and played it like a stand-up bass. Sounded pretty good. It also sounded good when I layed a ukulele on it and played do-bro style. But the best sound was when I put a kalimba on top.
        
        I'm betting it would work well with a lap harp too.
        
        Paul Craig > Martin Simpson February 12, 2019 at 1:16pm
        
        That's cool and a good idea.
- Martin Simpson > Cause the Blue rat December 26, 2018 at 9:50am
  
  After thinking about this alot and reading the generous advice above, I decided to build a simple test jig.
  
  I hot glued four jumbo piezo disks to the inside lid of a cigar box. I put them in a square configuration right in the center of the lid. I took two of the piezos that were diagonally across from each other and wired them in series. Then I took the other two piezos that were also diagonally across from each other and wired them in parallel.
  
  Next I put an output jack and a SPDT switch in the side of the box so that I could swap instantly between series and parallel.
  
  Then I plugged it into an amp and started tapping on the box.
  
  As with most things in life, the sound output was a compromise...
  
  The series setting does give more output volume. Maybe 10 or 15 percent more, but it also picks up more hum from flourescent lamps. The sound in the series setting is also fuller compared to the parallel setting. In the parallel setting some of the lower frequency sound rolls off, but the hum is noticeably less.
  
  Since this is going into a resophonic style guitar, I think I'll go with the parallel wiring in order to get a sharper, more jangly tone.
  
  I'll let you all know how it comes out.
  - Rob Todd > Martin Simpson February 11, 2019 at 12:57pm
    
    I am just about to put two piezos in my latest build and found your research invaluable. Many thanks.
  - Tom T > Martin Simpson January 14, 2019 at 7:13am
    
    An excellent approach to a common question. Your experiment should be helpful to a lot of folks.
  - Paul Craig > Martin Simpson December 26, 2018 at 4:08pm
    
    The series wiring could be a good thing to have with low output volume amps as long as you use a lot of box shielding and enough insulators between the piezo's and box. Solid body gits might work better with that type of wiring.

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