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Piezo Transducer

Contact microphone assembly

There are too many posts on alt.noise concerning how to build contact microphones, and to my knowledge, nobody ever posted a page like this in response. Plenty of bad advice out there… Hopefully this page is a little more useful than some of the responses I have seen over the years. If you actually follow these directions.

This is one way to put together a contact microphone. It is not the best way, but the end result is pretty satisfying. And it doesn’t cost much (once you have a soldering iron).

Here are a couple of interesting ideas on improving this design that were sent to me.

Radio Schlock parts list: Piezo Transducer 273-073A Two conductor inline 1/4″ Phone Jack 274-340A 24AWG “audio cable” 2 conductors plus shield part no. 278-514 Heat shrink tubing.

The functional element – a piezo electric transducer is commonly used as the speaker. For most, this will be the best home theater speakers.

Different models come in different plastic packaging, each more annoying to excise than the other. Do not buy the 12VDC versions – they cost more, and you’ll end up throwing away the drive electronics anyway.

Start by breaking off the two plastic tabs on the sides of the casing with a pair of pliers.  Next, take pliers and ‘crunch’ the back panel around the circumference. Do not ‘crunch’ the input leads. Do not ‘crunch’ hard enough to mash the PZT.

Use a thin edge (screw driver, xacto blade etc.) to gently pry the back plate off of the packaging. Careful not to bend the visible brass PZT disc.

The back is off. Now, take the pliers and grip the 1/8″ top edge of the plastic cylinder. Bend radially outwards. Repeat all the way around the housing cylinder. This should free up the PZT. Gently pry it out of the casing.

There it is, your very own $1.50 contact microphone. It needs to be connected to something…

Cut off about a 3 foot length of wire and strip the ends.

The ground wire needs to be twisted together (far left of the three).

Twist one of the wires together with the ground wire, and tin the ends of the wire with solder. Do this on one end only. On the other end of the cable, cut off the ground wire so that only the two insulated wires are exposed.

Your cable ends should look something like this:

Unscrew the housing from a 1/4″ jack. Solder the ground wire to the large contact, and the ‘signal’ wire (white) to the contact point (see below). Careful not to melt the cheapo connector. Also, be careful to make sure your solder wycks on the surface of the contacts, meaning that you have a good solder joint.

Clip off any excess wire that protrudes from the contact points (the white wire goes through the a hole, cut off the excess once it is soldered into place).

Tin both wires on the other end of the cable. Put two short pieces of heat-shrink tubing on the PZT leads. Solder wires together. I prefer to do this by lining up two tinned leads side by side.

Some people prefer to twist the wires together before tinning and soldering.

Pull the heat shrink tubing back over the solder joints. Use a hair dryer to shrink the tubing over the joints. You’re done. Go stick your contact mic on something, and call it art.

Mounting the microphone is easy – I use double sided tape to affix the element to whatever I wish to probe. It is a VERY good idea to tape the grey cable down to the object for strain relief. If you don’t do this then one good tug and you’ll be e-mailing me asking about soldering to the element itself. This is a pain in the ass, but can be done – usually with some minor damage to the element.