Public Address

So often, one arrives to speak somewhere, and the power is down, or the system is down, or there is no system at all. Recently, the power was down at my mother's funeral. I therefore designed and built a public address system, of which I completed all the electronics today (just the housing still required). It uses inexpensive PC speakers for the amplifier, and a stereo microphone amp -- the only challenge with the microphone amp being matching the gain with PC speakers (with a TL072 op-amp, two times 22K feedback does it). This can all be run off a netbook computer, or off a small power bank.