An audio amplifier is powered by a switch mode power supply optimized for audio applications. The light-emitting structure includes a first doped structural layer, a second doped structural layer, an active layer between the two doped structural layers, a first electrode, and a second electrode. The improved ball setting and tightening rack uses horizontal compression to create a compact formation of playing balls, thus reducing wear on the playing surface. In one variation, the optical devices are formed on a silicon-oxide layer that is formed on a substrate, such as a silicon substrate. The compounds of the present invention are inhibitors of \u03b2-secretase, also known as \u03b2-site amyloid cleaving enzyme, BACE, BACE1, Asp2, or memapsin2.