Step 1: Materials and Tools
2 – Piezo Transducers - Radio Shack 273-0073
1 – 1/4” Phone Jack - Radio Shack 274-0340
1 – 10 nF Capacitor
1 – Straight mute
1 – Trumpet
Wire stripper or knife
Electrical and ScotchTape
Safety glasses or solder shield
The piezo transducers are often marked as buzzers or elements. These will be used as pickups to convert the sound to electrical signals. In short, mechanical vibrations of piezoelectric crystals creates a voltage with respect to the vibrations. More detail on how these work can be found at wikipedia.
The phone jack can be replaced with any type of connector you need. This is set up to be plugged into an electric guitar or bass amp. A 1/8th” jack could be used to connect to a microphone input on a computer for recording.
For the mute, I used a Stone Lined straight mute because it is inexpensive and has good mounting locations for the pickups.
My total cost for this was $3.99 for the phone jacks, and $1.99 for each piezo transducer. The rest of the items are relatively cheap except for the trumpet.
Step 2: Disassembling the Piezo Transducer
The first step towards assembly is to remove the piezo elements from their case. These are the metallic disks inside the buzzer that are shown in the picture. Depending on what exact parts you have, they will have to be unscrewed, pried, or cut out of their case. For these, wire cutters were able to break the plastic from around the elements. Some of these have PCB's planted in the case to drive the buzzers. These will be unnecessary for this application. There should be two wires attached to each piezo element. These are your positive and negative terminals of the element.
Be extra careful in this step to not damage the piezo crystals. They can be cracked and will not function.
Step 3: Mounting the Pickups
I found that simply taping the elements directly on the end of the straight mute was the easiest and cleanest way to mount them. I tried adding various fabrics and placement for dampening valve noise, but they did little to help this and decreased the volume of the output. Mounting the pickup over hanging the edge of the mute is not advisable as it will pick up less of the lower (fundamental) frequencies of each note. Epoxy or super glue could be used for permanent mounting, but tape worked well for this purpose.
Step 4: Wiring the Pickups
1. Cut the 2 wires to appropriate length, approximately 3/4ths of and inch.
2. Strip the ends of the end of each wire to expose about 1/8th of an inch of bare wire.
3. Wrap the two bare ends together to form a mechanical connection.
4. Solder this junction together.
Solder a 10 nF capacitor in series with the pickups as a high-pass filter to help reduce valve noise with minimal effect on the trumpet's tone. This step is optional but with a little experimenting, you can find your own personal preference. The pickups will still work fine without the filter. Just solder the red wire directly to the inner terminal.
1. Cut about 1/2” off the remaining red wire.
2. Unscrew and remove the strain relief from the ¼” phone jack.
3. Feed the wires through the strain relief. Don't forget to do this unless you really like to de-solder
4. Solder the shorter wire to the capacitor, making sure that it will be able to fit in the strain relief.
5. Solder the other end of the capacitor to the inner terminal of the jack
6. Solder the black wire to the larger outer terminal.
7. Electrical tape and surfaces or wires that could contact something of the other polarity.
8. Screw the strain relief back on to the jack.
Be careful to not let any of the wires, especially around the capacitor, to short or become shorted when sheathed in the strain relief. Electrical tape can be used to help with this.
Step 5: Using the Mute
These pickups do pick up extraneous noises like valves and other impacts. The capacitor helps get rid of some of this, but much of this noise is the same frequency range as the trumpet making it difficult to suppress. Its still a fun project to experiment around with and even record a bit of music.
I've attached a sample clip that I made by attaching the pickups to the microphone jack of the computer.
This is my first instructable, so thanks for reading!