I've spent the last few weeks attempting to build better piezo film pickups since the limited success with the prototype discussed in my last post. Unfortunately, the two I've built so far make noise mostly.Using the template above, I cut out two 5" by 1 1/2" rectangles of .003" thick PVDF film. Then, on the hatched out area on each side I put electrodes. For one of the pickups I painted each side with Amazing Wire Glue as the electrode. According to the label, Amazing Wire Glue is non-toxic adhesive and carbon. On alternate sides of the film, I also painted into either the (+) or (-) rectangle to provide a place for a contact to the cable. For the pickup made with Amazing Wire Glue, I stapled on the cable ends and then glued them, following the advice of Trout Cove Lutherie.
For the other pickup, I taped on copper tape with conductive adhesive as the electrode. On this pickup I soldered the cable ends directly to the tape on each side of the film. Here is what both pickups looked like before I had them laminated:
Then, my lovely wife laminated each using some self-sealing lamination. I soldered the ends of the cables to some 1/4" phono jacks which I covered in shielding foil and heat-shrink and then I was done.
I recorded with both and both work, but produce a lot more hum than signal. The foil pickup seemed to produce a little more signal (and hum). The hum isn't apparent until pressure is applied to the film (e.g by taping it to a guitar), but then it's overwhelming. I tried the following to no avail:
- I checked that to make sure that the positive and negative sides were not shorted (they weren't);
- I covered each temporarily with some EMI shield, which made the hum worse;
- I reversed the polarity;
- I tried a commercial film through the same preamp (and heard no hum).
