Here is a quick and easy construction plan for pick-ups made from piezo buzzers or disks.
Piezo disks can be optained as single disks in various shapes and sizes or can be taken out of buzzers for example. Both piezo elements can either be acquired at electronic stores or possibly stripped out of older electronics such as old, sound producing toys or door buzzers. (The following construction plan includes cutting disks out of buzzers.)
Parts
In order to build a pick-up consiting of piezo disks, following parts are needed:
- Microphone cable
- Male XLR plug or a 6.5mm jack plug (also know as 1/4″ or TRS jack connector; in this example an angled jack plug has been used)
- Piezo disk
Preparation-A: Some Theory
XLR Connectors
XLR connectors are widely used as audio connectors and mainly come with three pins; XLR connectors with more pins are only used with specialist microphones.
A five pin cable is mostly used for stereo microphones (as can be used in boom poles for example).
It is important to distinguish the front and the back of the XLR connectors:
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On the male XLR connector, the wires of the cable are soldered to following pins:
| pin 1 | pin 2 | pin 3 |
|---|---|---|
| shield (ground) | hot (+) | cold (-) |
| mostly a bare wire | mostly a red cable | mostly a blue cable |
6.5mm Jack Connectors
6.5mm jack connectors (or TRS connectors) are also widely used in audio, but instead of connecting audio devices with each other, these connectors are rather used to connect instruments to audio equipment. Hence, also the use of the name ‘instrument cable’ among musicians.
6.5mm Jack connectors can be wired as balanced or unbalanced mono or as stereo connectors:
| Unbalanced Mono Jack | Balanced Mono Jack and Stereo Jack |
|---|---|
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| Unbalanced Mono Jack | Balanced Mono Jack | Stereo Jack | |
|---|---|---|---|
| Tip | hot (+) mostly red wire |
hot (+) mostly red wire |
hot (+) mostly red wire left channel |
| Ring | not connected | cold (-) mostly a blue wire |
cold (-) mostly a blue wire right channel |
| Sleeve | shield/ground | shield/ground | shield/ground |
The piezo disk has only two contact points: the white part (electret material) and the brass part:
The electret should be connected to the hot wire leading to the connector. There are two options for the brass part of the piezo. Either it is handled separately by the wire for the negative signal (cold wire connects to the cold inlet of the connector; ground wires are cut off on either end before touching either connector or piezo) or the shielding of the cable can be combined with the cold wire on the end connecting to the piezo, while on the connector side the negative wire connects to the cold inlet and the shield to the ground inlet.
Preparation-B: Freeing the disk from its casing
Depending on the way the piezo disk is obtained, it might need to be cut out of the buzzer.
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After the disk has been freed, strip the wires of their protective isulation on both ends of the cable.
Soldering the Parts
Depending on the type of the connector…
- Male XLR connector: connect the wire carrying the plus (+), hot or positive signal (red wire) to pin two, the negative (-) signal or cold wire (blue) to pin three and the earth or ground to pin one.
- 6.5mm jack plug (TRS): connect the wire carrying the plus (+), hot or positive signal (red wire) to the ring (centre ‘nose’), the negative (-) signal or cold wire (blue) to the tip (top ‘nose’) and the earth or ground to the sleeve.
- Piezo disk: connect the white part to the wire carrying the positive signal and the brass part to the wire carrying the negative signal.
Alternatively the wire connecting to the brass part (cold signal) can also be soldered together with the shield on the end of the piezo disk and split up into cold signal and ground in the connector.
These pick-ups can be used to record an audio signal traveling through material, opposite to audio waves which normally travel through air. Examples are DIY guitar pick-ups, triggers for self-made ‘electronic drums’, DIY hydrophones or directly recording the material of an object.
More recording examples (objects of different kinds of material and especially hydrophones) will follow in later blogs.
Listen to some examples right here:
