Piezo pickup problems

[David Cadenhead]

Like the alliteration in the title? So do I. So I'm building a semi hollow bass using only acoustic pickups, right? Now, I had the bridge pickup in and everything was fine, but today when I put pickups in the chambers the volume output dropped significantly and I started having issues with feedback. I'm running everything straight to the output because I'm fine doing volume and eq off board for this one, so I thought wiring it up would be almost impossible to mess up, but somehow I was wrong. Any ideas on what's up? Also I should mention that the plastic cover thing on the bridge pickup fell off, but I don't know if that messes with the pickups functionality at all

 

[line6man]

It isn't a good idea to run piezo elements straight to the jack. You need to buffer them before they reach the instrument cable.

If you noticed a volume drop when adding piezo elements, then you may have a problem with the piezos loading each other down.

 

[RobbieK]

Yeah those two disks in parallel will have a very different impedence than an undersaddle bridge type piezo. But more importantly, they will also have a very different output due to their positioning. Actually they may also be out of phase. Try reversing the leads from the disks or even just flipping them over. Because piezos are capacitive, you could also try running them in series instead of parallel. But realistically, they need buffering individually or at least using a preamp with a very high input Z.

If you have to keep everything off-board, then I would recommend using a stereo jack. This way you can run the bridge pickup separately and use a twin buffer type preamp.

Also you should use good shielded wire for the piezo discs. These will hum terribly otherwise.

Oh, and don't leave un-insulated solder joins and loose uninsulated wire floating around like this. Not only will they vibrate and cause noise, but they will potentially cause shorts.