Can Piezo Films be Trimmed (revisited)?

by Bart on October 4, 2011

YES! (contrary to previous post)

 Some time ago, I posted some notes here on the question of whether the piezo films we sell will still work if you cut them to a smaller size.  What I said was, it can be done in some limited ways, but it’s not recommended because it will destroy the pickup if you snip in the wrong place.  It turns out that I was incorrect in some of my information, and trimming of the films is not so problematic after all, though there still are some caveats. This is good news for a lot of our customers, because there are many situations in which a slightly resized piezo is just what the doctor ordered. My thanks go to Joe Patrick in Michigan for recognizing the possibilities, investigating further, and getting back to me with better information. Here are the details:

In the earlier post I said that the end of the film opposite the lead wires should never be snipped off because, I incorrectly thought, this would break the electrical continuity between the two terminals.  It turns out that this isn’t true; you can snip the film any which way and it will still function. The important caveat is this: the films we sell consist of two layers of piezo material layered over with a protective plastic laminate, and process of snipping frequently creates a short between the two layers of piezo material.  When this happens, the piezo will not function.  To avoid this problem when trimming piezo films, snip cleanly with good, sharp scissors. Then gently smooth the newly cut edge with emery cloth or very fine sand paper.

Next, check the pickup to make sure it’s working. The easiest way to do this is to make a temporary hook-up using two hook-up wires with alligator clips on the ends (these alligator clip wires are available in electronics stores).  Clip one end of each hook-up wire to either the lead wires or the terminals on the piezo film. Clip the other ends to the tip and sleeve of the plug at one end of a standard musical instrument lead cable. Plug the other end of the cable into an amplifier input. Turn up the amp and flick the piezo with a finger verify that the sound is coming through. (If you don’t have alligator leads conveniently on hand, you can try other ways to make the temporary connection between the piezo and the lead cable plug, such as contrivances involving binder clips or clothes pins.)  

If the pickup is not working, turn off the amp, gently re-sand the newly exposed edge, and try again.   

When you’ve got the pickup working dependably, go over the newly cut edge with a clean cloth to remove any possible remaining particles there. Then tape over the edge with cellophane tape, creating layer or two of protection similar to the clear plastic laminate that covers the rest of the film.

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