Each pad requires a 10-inch tunable practice pad. Tunable pads allow you to adjust the tension of the pad so that you can adjust the action to your playing style. Each pad requires a piezo element (model # 273-073), a piece of poly foam rubber cut to the circumferences of the pad (usually about 10 inches in diameter) and a thin, circular piece of 28-gauge galvanized steel with a circumference that is about 2 inches smaller than the practice pad's circumference. Some 20-gauge speaker wire, glue (such as Gorilla glue) and a panel mount RCA phono jack also are needed.
To begin making the PC drum, take the practice pad apart. You may discard the foam inside, but save the Mylar disc. The Mylar disc makes a great stencil, and you can reuse it as a skin for your new electronic drum if you like. Use your Mylar stencil to cut two circles from the foam rubber and one slightly smaller circle from the steel. The steel sheet will act as large contact microphone once everything is reassembled, and the foam rubber will protect it from damage. Cutting a hole in the middle of one of the foam rubber pieces allows you to pass the RCA jack and wires through it when you reassemble the pad. To turn the steel into the contact microphone, attach a piezo element to its center. The piezo element is housed in a plastic casing and can be difficult to remove; you can crack it open with pliers, but be very careful not to damage the element. Use glue to stick the copper side of the element to the steel plate. Scoring the area before gluing make a better connection surface.
The next task is to wire everything together, which is fairly straightforward. Use shielded copper wire to connect the piezo element to the RCA jack. Because this is a percussion instrument and inevitably will take a beating, it is a good idea to reinforce your solder points with glue.
Now that you have your giant contact microphone and protective foam, the practice pad needs to be reassembled. This has to be done in a certain order. First, pass the RCA jack and excess wire through the hole in the bottom foam rubber disc. After drilling a couple holes opposite each other through the bottom plastic part of the pad's casing, install the RCA jack in one of the holes. The other hole's function is to relieve pressure. Finally, reassemble the pad with the bottom foam first, followed by the steel disc, the second piece of foam, the Mylar disc and then the top plastic cover.