Using Piezos in Cigar Box Guitars: Part 1 – Piezo Basics

Piezo ElementsA lot of new Cigar Box Guitar (CBG) builders (and more than a few veterans) tend to get a bit uneasy when the topic of piezo pickups comes up. Everyone seems to have a different idea of how to use them. Some folks say that they should be built into the bridge, others attach them to the exterior of the bridge; some mount them inside the box lid, others attach them to the outside of the lid. Add in concepts such as insulation methods, multiple piezos, volume potentiometers and wiring schematics, and the waters tend to get pretty muddy pretty fast.

This two-part article is meant to be a basic “here’s what you need to get started” approach to helping people install a piezo pickup into their Cigar Box Guitar build. We will cover the basics of what piezo to use, where you can put it, how to mount it, and how to wire it to a jack. We will also briefly discuss the topic of wiring in a otentiometer.

Be sure to check out our web store for a nice selection of piezos, jacks and other components at great prices!

What is a Piezo?

A standard piezo consists of a thin metal disk (usually brass, sometimes stainless steel), with a very thin wafer of ceramic glued to it. Wire leads are soldered to these disks (one to the metal part, one to the ceramic part). When excited with an appropriate electric current, the interaction between the metal and the ceramic can cause sound to be produced. Using piezos to create sound, rather than detect sound, is the most common usage of them in manufacturing. Many devices, from smoke alarms to alarm clocks to children’s toys, use piezos as a sort of miniature speaker to produce sound.

Fortunately for CBG builders, the piezo can also be used in a different way: to pick up sound vibrations, which can then be amplified by other circuits such as those in a guitar amplifier. Basically, the amplifier sends a small current through the piezo element (though not enough current to cause the piezo to MAKE sound). When the piezo is affected by vibration (such as the vibrations of a guitar sound board when strummed), those vibrations cause the metal and ceramic to interact in such a way that the current is modified. These fluctuations in the current through the piezo are picked up by an amplifier, increased and reproduced on a larger speaker. The end result is that we hear our instrument in an amplified form.

There are other types of piezos beyond the metal/ceramic disk we have described, but since that is the most common kind available (and the kind we carry in our shop), it is what we will be discussing here.

It is worth pointing out here the difference between a magnetic pickup (like those in electric guitars) and piezos. Magnetic pickups pick up sound when their magnetic fields are caused to fluctuate by the vibration of steel strings near them. These fluctuations are increased by an amplifier and reproduced as the familiar electric guitar sound. A piezo, on the other hand, has nothing to do with magnets: it picks up vibrations only. In this sense, a guitar with a piezo pickup is really still an acoustic instrument – the acoustic vibrations are just being amplified, in a similar manner to playing into a microphone.

Choosing a Piezo

Piezoelectric elements (piezos) come in various shapes and sizes: encased vs. unencased, wired vs. unwired, brass vs. stainless steel disks, disk form vs. strip form, etc. Sizes can range from quite small varieties around 10mm in diameter to very large 50mm disks. We will discuss each of the key factors below to give you some groundwork to build from when considering what to use on your build.

Size

There tends to be a lot of discussion about what size of piezo element is best. We sell piezos from 20mm to 41mm in our shop, and builders are always asking us which is best. Opinion on the matter tends to be pretty evenly divided. Some builders claim that the larger piezos are better at picking up bass tones from an instrument, which would therefore give you a deeper tone and less of the higher treble tones. Other builders, including Ted Crocker who has worked extensively with piezos and done a great deal of testing, believe that there is no perceivable difference between different sizes of piezos when it comes to using them as instrument pickups. Our advice is: use what makes you happy. If a bigger piezo strikes your fancy, you feel it sounds better or works better in your build, then go for it. If you want to be more economical, go with the smaller piezos.

Encased vs. Unencased

All of of the piezos we sell are the plain unencased disks, which is how you want them for use in a cigar box guitar. Radio Shack and other retailers sell piezos (for outrageous prices) which come encased in a plastic housing. These piezos are manufactured this way because they are intended to be used as sound producing devices, instead of sound detecting devices. While you can certainly glue or screw the encased piezo – housing and all – right to your build, this is really not recommended. You will always get much better sound if you mount the unencased piezo in your build, perhaps sandwiching it between some other material (such as leather or thin wood) first. Cutting the piezo disk out of the plastic encasement can be tricky to do without ruining the element itself, so our advice is to avoid the encased piezos and always buy the plain disks.

Brass disks vs. Stainless Steel

You don’t see the stainless steel disk piezos as much as the brass piezos, but they are out there. There isn’t all that much difference in how the metal affects their behavior as a pickup, but what the stainless steel DOES do is make it a LOT harder to solder wires to them. In our opinion, trying to solder to stainless is simply not worth the time and effort. Stick with brass disks and you will be much happier. All of the piezos we carry in our web shop have brass disks.

Wired vs. Unwired Disks

In our web shop we offer most sizes of piezos we carry in both pre-wired and unwired form. The only difference is that the pre-wired piezos have 2-inch leads soldered to them already, while the unwired ones are just the plain disks. While soldering leads to piezos is not hard, it can be a pain for people without much soldering experience, or without a good solder station setup. As such many folks prefer to get the pre-wired ones. It should be noted however that the 2-inch wires are really not long enough for attaching the piezo directly to a jack, so you usually have to attach extender wires anyway, whether with solder (preferred) or tape.

HOW TO SOLDER A PIEZO

To solder lead wires to a piezo, choose a generous length of thin-gauge insulated copper wire and start off by stripping off about 1/8″ of insulation. Then twist the strands of each wire together firmly (assuming a multi-strand copper wire). Now heat the wire and apply a small amount of a good electrical solder to it. This is called “tinning” the wire, and is always recommended to make the later soldering process much easier. Now apply two small beads of solder to the piezo disk: one to the metal portion, and one to the ceramic portion. Be sure that you don’t connect the brass and ceramic with solder, as this will short out your piezo. The size of the beads should be as small as you can make them, but big enough that there will be enough to surround your wire lead.

Now take the stripped, tinned end of one of your leads and place it against one of the solder beads. Touch the soldering iron tip to it, and hold it just until the solder melts and the wire sinks into the bead. Immediately remove the heat and hold the wire steady for a few seconds while the solder hardens. Resist the urge to blow on it – it will form a stronger bond if it cools at its own pace. Repeat this process for the second lead, and you should be all set.

Disks vs. Strip Piezos

Specialty piezos are now available that come in strip form rather than the traditional round disk form. Rod-shaped piezos are also available. Some companies that make professional-grade pickups for stringed instruments have begun using these strip piezos in their pickups. However, it can be hard to find these piezos on the market, and we have not yet been able to find a wholesale supplier of them for our web shop. They can provide an interesting alternative, but are beyond the scope of this article.

Conclusion

This ends Part 1 of this article. In Part 2 we will get more of the nitty gritty “need-to-know” information regarding WHERE to mount a piezo in your build, as well as HOW to mount it. Click here to go to Part 2 of this article . Also, be sure to check out our web store for the various electronics components we offer, including various sizes of piezos, jacks and also potentiometers!

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