DIY Pick-ups from Piezo Disks

DIY—Audio Series

Here is a quick and easy construction plan for pick-ups made from piezo buzzers or disks.

Piezo disks can be obtained 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 sound producing toys or door buzzers.
(The following construction plan includes cutting disks out of buzzers.)

Parts

In order to build a pick-up from piezo disks, following parts are needed:

Microphone cable Male XLR plug or a 6.35mm jack plug (also know as 1/4″ or jack connector; in this example an angled jack plug has been used) Piezo disk (not in picture)

Preparation

The connector plugging into the audio interface or (field) recorder can either be a TRS (balanced), a TS (unbalanced) or a balanced or unbalanced XLR connector. Balancing the cable has the advantage of preventing hums.

XLR cables are considered to be more stable when connected to an audio or (field) recorder and therefore introduce less handling noise. However, either connector will be fine.

XLR Connectors

XLR connectors are widely used audio connectors and mainly come with three pins. XLR connectors with more pins (e.g. five or seven) are either for stereo or valve/tube microphones. The latter plug into a pre-amp provided specifically for the microphone, though.

For the correct wiring it is important to distinguish the pinout of the male XLR connector as seen from the front:

Connections

TRS Connectors

TS or TRS connectors (or 6.35mm jack connectors) are widely used as instrument cables—carrying line level or high-Z signals. The mini version—3.5mm mini-jack—is known for consumer products such as headphone buds, tablets and computer outputs for example.

Regardless of being  a jack or mini jack plug, the connectors are wired balanced (or stereo) or unbalanced (or mono):

Balanced or stereo jack connector	TS versus TRS
	TS = unbalanced jack, TRS = balanced jack

Connections

Piezo Disc

The piezo disk itself has only two contact points: the  electret material (white) and brass.

Piezo disc

The electret material is the one translating the audio wave into current and therefore should be connected to the hot wire of the connector. The brass is to be grounded.

Preparation

Depending on the way the piezo disk is obtained, it might need to be cut out of its housing. However, individual piezo discs can easily be bought nowadays in many different sizes.

In case it comes with a housing, carefully break it open. Avoid any scratches or damage to the electret material!

Piezo disc freeing from housing	Piezo opened
If necessary:a small set of pliers can help break the plastic around the piezo

Then proceed to strip the cable and wires of their protective insulation.

Soldering

Depending on the type of the connector…

• • • Male XLR connector:
      connect the wire carrying the positive (+) signal to pin two, the negative (-) signal to pin three and the earth or ground to pin one.
    • 6.35mm jack plug (TRS):
      connect the wire carrying the positive (+) signal to the ring (centre ‘nose’), the negative (-) signal to the tip (top ‘nose’) and the earth or ground to the sleeve.
    • 6.35mm jack plug (TS):
      connect the wire carrying the positive (+) signal to the ring (centre ‘nose’), and the earth or ground to the sleeve. If the cable carrying the signal has two wires and a protective shield around the cable, combine the wire of the negative signal (i.e. tip) with the ground at the end which connects to the brass of the piezo.
    • Piezo disk: connect the electret (white part) to the wire carrying the positive signal and connect the brass to the wire carrying the negative signal.
      If the cable also has a shield around the two wires, the wire carrying the negative signal and the shield (ground) can either be combined or the shield around the cable can be stripped.

Practical Use

Piezos can be used as pick-up microphones, recording an audio signal traveling through material instead of air. Examples are DIY guitar pick-ups, triggers for self-made ‘electronic drums’, DIY hydrophones and simply microphones for audio waves travelling through other media than air.

Listen to some examples right here (water bubbles 44/24)

Finished cable