Inexpensive piezo discs have a short life

Discussion in 'Pickups, Electronics & General Tech' started by jack_cat, Dec 5, 2019.

  1. jack_cat

    jack_cat SS.org Regular

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    Since my 9-string fanned fret classical needs some kind of custom pickup arrangement, I can't buy something off the shelf. I had piezo discs installed inside, but I disconnected that system and removed all but the discs because of some rattles I couldn't solve, and moved to external piezo discs.

    My current rig consists of three (cheap $5) discs wired in parallel and one
    .022uF capacitor at the jack, this is pretty sweet. I have the jack velcro'd to the lower bout, and the wires occasionally hit the top and buzz, but I can deal with it. The three discs allow me to adjust the relative strength of the signals from the bass, treble, and midrange strings merely by moving the discs around on the top.

    The last pickup was similar but lacked the capacitor and was not as sweet and focused sounding. I have been using cheap $5 chinese piezo discs in a red and black plastic housing. When that pickup failed during a gig a couple of weeks ago, I ran in a panic down to my local electronics guy, who had it repaired in a half-hour flat (I had made the thing myself, but I'm slow, and it would have taken ME all day to repair, plus having to run all the way home, so I was grateful and made it to my next gig only ten minutes late.) But the details of how the piezo discs failed are interesting and informative.

    All three discs had failed after using the pickup about two years, maybe less. In one, the soldered connection to the ceramic disc had broken entirely; this is the connection that was making thumping staticky noises, probably. On the second disc, the same connection had frayed and was ready to break. On the third disc, a piece of the ceramic disc had broken off and fragmented, and was lying in pieces inside the housing. I conclude that that 10-million-ohm vibration going on in the ceramic disk actually generates a mechanical stress on the solder connection and that the wire must break from metal fatigue. It was not the solder joint that had failed, but the wire itself where it entered the glob of solder.

    Once the wires on the two discs were re-soldered, the PU was working fine again, and the broken disc didnt' seem to be having a negative effect. All the same, since my repair guy had the capacitor I hadn't been able to find locally, I had him wire me up a new one (eh, it's awfully hard for me to solder those little tiny wires) with the capacitor, which yields a much more focused sound, but I am now aware that I will need another one within two years.

    I would like to know what other piezo solutions for acoustic ERGs people have come up with, and what better-quality piezos are available.
     
  2. Lemonbaby

    Lemonbaby SS.org Regular

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    If you absolutely need a PU in your classical guitar for gigs where mics don't work, I'd always prefer magnetic systems to Piezo. Give Schertler a go, their PUs might suit your needs and are actually quite cheap.
     
  3. jack_cat

    jack_cat SS.org Regular

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    I would be very interested to find a magnetic pickup that works on nylon strings, on the face of it, it appears to be technically impossible, doesn't it? Do you have a model number for a PU by Schertler that you think would work? In the meantime I will go to their web site and see what I can find.

    thanks!
    jack
     
    Last edited: Dec 12, 2019

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