I made two videos showing how to solder the teensy headers and the piezo amplifier and cable.
Note that the transistor "2N5457" we are using this semester has a slighlty different pinout. Therefore the connections are slighlty different as shown in the photos below. We also need a resistor for draining spurious voltages on the piezo to ground. Without this resistor the amplifier could drift into clipping, outputting no sound at all. The smaller the resistor the lower the gain of the amplifier. Try with a 100kOhm resistor first (yellow band). If you need more gain, you can get some more with the integrated analog amplifier built into the teensy microphone input electronics (as you will see from the teensy audio library examples).