Fire up your soldering iron and get ready to build the circuit.

To charge the 500mAh battery more quickly, you can set the LiPoly backpack to charge at a higher rate. Solder a small blob on the charger rating pad set on the bottom of the board that bridges the connection.

Cut the trace on the LiPoly backpack that connects the two switch holes, then solder the leads of the tactile switch to these holes. Orientation does not matter, so either wire in either hole will work.

The LiPoly backpack will be connected directly to the Audio FX board (this is not how it is shown in the circuit diagram for visual clarity).

Break off a section of three header pins that came with the backpack, place them on the top of the Vin, Gnd, and BUS pins of the Audio FX board and solder them in place from the underside. The longer end of the pins should be pointed up from the Audo FX board. Fit the LiPoly backpack on top of the Audio FX board so BAT corresponds to Vin, G to Gnd, and 5V to BUS, then solder the pins to the backpack.

Solder a 2” length of red wire to the header pin that's protruding from the LiPoly backpack's BAT header pin, this will be used to power the amplifier. Loop the wire around the pin before soldering for a stronger connection.

Prepare to connect the class D amplifier to the Audio FX board by twisting together one end each of two 2" lengths of black wire. Solder this twisted end of the pair of wires to GND on the Audio FX board, as seen in the circuit diagram. Connect the other end of one of these wires to the GND of the amplifier as indicated on the circuit diagram.  

Now, solder the red wire connected to the LiPoly backpack to the VIN of the amplifier.

Next, you'll attach the amplifier to the Audio FX board. Solder two header pins into the Audio FX board’s L and GND pins. Then, fit the amplifier’s  A+ to L and A- to Gnd respectively and solder them in place.

You’ll reuse one of the mask's the momentary switches and wiring to trigger the sound files. Either will work, I chose the red wire. This red wire will be connected to the rotary switch so that different sound banks can be selected by turning the knob.

Based on knob placement, you may need to extend the length of the momentary switch wire by grafting on an additional length of wire and then soldering and heat shrinking the joint. 

After extending it, strip a 1/2” piece of insulation from the free end of the red wire, then wrap it around the common center post of the rotary selector switch, then solder it in place.

Prepare the wires that will connect the rotary switch positions to the triggers on the Audio FX board. These should be about 8” in length to route through the mask to a knob position in the upper left of the mask back. Prepare as many wires as you want to use sound banks, up to eight, by trimming a small bit of insulation from their ends.
Next, solder a wire to each of the rotary switch lugs you want to use, then insulate each of the connections with heat shrink tubing.

Fit a piece of tubing around the bundle of wires to keep them together more neatly, no need to heat shrink it.

Solder each wire to its corresponding position on the Audio FX board, then trim the excess from the other side.

Strip a bit of insulation off of the free end of the black wire you previously clipped from the original circuit board, slip a piece of heat shrink tubing over it, and solder it to the other black ground wire you soldered (as a twisted pair) to G on the Audio FX board, as seen in the circuit diagram. Cover the joint with the tubing and heat shrink it.

Strip the ends of the mask's two yellow speaker wires and solder them to + and - on the amplifier. Orientation does not matter, so connect either wire to either hole.

Plug the battery JST connector into the JST connector on the LiPoly backpack. Click the tactile switch on and off to make sure you’re getting power to the board — the LEDs should light up. Now, carefully open Chewbacca’s jaw (he won’t mind) and you’ll hear the test sound file that is factory programmed onto the Audio FX board.

Next, you’ll prepare your own audio files for use.