Power Amplifier IC

The power amplifier IC (U4) is a module containing an integrated circuit amplifier and supporting components that are always needed with it. A description of it is given here for those interested:
 * (+) - power from batteries
 * (-) - power return to batteries
 * FIL - filtered power from batteries
 * INP - input connection
 * OUT - output connection
 * See Project #242 for example of connections.