A common problem in audio systems is the speaker "thump" that occurs if all of the equipment is switched on at the same time. One way to eliminate this thump is by turning on the audio sources that feed the amplifiers (such as the sound board, etc.) before turning on the amplifiers. The power sequencer described here has two outputs that are turned on and off in a sequence that prevents speaker thump.
When the switch is turned on, sound board outlet is turned on first, and then the amplifier outlet is turned on a few seconds later. When the switch is turned off, the amplifier outlet is switched off first, and then the sound board outlet is turned off a few seconds later. See the timing diagram below.
A schematic of the power sequencer is shown below. The timing sequence is generated with a PIC10F202 microcontroller running a very simple program. The PIC outputs control two solid state relays that I found at All Electronics for about $10 each. They are each capable of switching up to 18A, which is more than enough that I need.
Part Description All Electronics Part #