Step 1: Materials
To Turn Nearly Anything into a Speaker you will need:
(x1) Audio output transformer
(x1) Small Amplifier*
(x1) Small project enclosure
(x2) 1/8" mono jacks
(x1) Piezo disc element
(x1) One-sided 1/8" male mono cable***
(x2) 1/8" male-to-male mono (or stereo) cable
(x1) Double-sided tape
* It has been brought to my attention that the Radioshack test amp I used is no longer available since they went out of business. You might still be able to find it on Ebay. This one that is linked should work as replacement.
To connect the amp's output to the piezo I recommend just buying a female jack adapter, and connecting wires between the adapter and one of the red and black pairs of speaker output ports in the back (black-to-ground, and red-to-left). Then plug the piezo cable into the female adapter.
*** This type of cable has a plug on one end and a signal and ground wire on the other end. If you can't find one, then just buy any old male-to-male mono cable and cut off one end, and strip away the insulation to expose the wire.
Step 2: Holes
Make a mark centered upon each of the 1" x 2" sides of the project enclosure.
Drill both of these marks with a 1/4" drill bit.
Step 3: Wire the Jacks
Attach 3" black wires to the center barrel pin of each, and 3" red wires to the pin connected to the outer signal tab.
Step 4: Wire the Transformer
Since the transformer is basically two coils in proportion to one another, the only thing to be mindful of is aligning the wires when they are soldered.
Solder one set to the outer pins on one side of the transformer, and the other set mirrored on the opposite side. The colors of the wire should be aligned.
Trim the center pins on the transformer. We are not using these.
In a schematic, a transformer is represented by a double-line core surrounded by two coils.
Step 5: Insert the Jacks
Insert the jacks into the mounting holes in the enclosure.
Make note of which jack is connected to the side of the transformer labeled "P". This stands for primary.
Typically the primary is the input side, but we are actually driving the transformer backwards, so the primary side is our output to the piezo.
The reason the input is the output is because of impedance, a concept we are not really covering in this class, but one particularly important when dealing with transformers and AC electronics. Long story short, impedance is kind of like resistance in AC electronics (but not exactly the same). Typically, audio sources have a high impedance of a few thousand ohms, and speakers have a low impedance around 8 ohms.
The audio output transformer is designed to take a high impedance source and make it low impedance. However, we have the opposite problem we need to solve. The piezo is typically a high impedance device, and the audio amplifier is always providing a low impedance signal to drive a speaker. In order to drive the piezo using the amplifier, we need to take the low impedance output from the amplifier and make it high impedance. To do this, we simply send the low impedance signal from the amplifier into the low impedance coil, and this will produce a high impedance signal to drive the piezo. Simple as that.
Step 6: Glue (optional)
Hot glue the transformer to the base of the enclosure. This is not entirely necessary, but will ensure it does not accidentally get damaged.
Step 7: Close It Up
Close the case with its mounting screws.
I recommend that you use tape, a sticker, nail polish or a marker to indicate the output on your enclosure to eliminate guesswork. In my case - or should I say on my case? - I cut a piece of white tape into a little arrow.
Step 8: Wire the Piezo
A piezo disc is basically a metal disc with a special piezoelectric ceramic coating. This is a special type of material that expands and contracts when electricity is applied, and can also produce electricity when expanded and contracted.
It is different than a speaker in that it does not use any coils or magnets, but has some similarities. Like a speaker, it can work as a transducer to both turn sound into a voltage and voltage into a sound.
To be able to drive the piezo disc, we first need to attach it to an 1/8" mono cable.
Solder the center signal wire from the cable to the solder blob on the center of the piezo disc.
Solder the outer shielding wire to the solder blob on the golden outer ring of the disc.
Trim away all of the excess wire leads.
Step 9: Connect Cables
Plug the piezo disc wire into the output side of the enclosure (connected to the primary), and connect a male-to-male mono (or stereo) cable into the input side of the enclosure.
Step 10: Amp
Connect the input from the transformer enclosure into the output from the amplifier. This connection enables the amplifier to drive the transformer.
Connect any audio player into the input using a mono (or stereo) cable.
Step 11: Tape
Step 12: Stick the Piezo Onto Something
Once everything is wired up, stick the piezo onto a surface that you want to make music.
Don't forget to turn the amp on, and the volume up.