For my subwoofer amplifier, I got a couple of free samples of the National Semiconducter LM3886 high power audio amplifier. From a scrap pile at work I was able to find power transformers, large electrolytic caps, and a case with power input filter, fuse, and switch. I was able to buy a very large heat sink at a good price on Ebay.
The National LM3886 chipamp is designed for use as a high power, low distortion, audio amplifier. With the right power supply and heat sink, it can deliver over 75 watts into an 8 ohm load. Since the Shiva driver I used in my subwoofer has dual voice coils, I used two LM3886 amplifier chips, each driving one voice coil. Each LM3886 is built onto an amplifier module. The module is made from a piece of fiberglass PC board material. Holes were drilled to mount the amp chip and components. A screw terminal strip is used for the input and output connections on each module. Both of the amp modules are mounted to a single large heatsink. Note that the mounting tab on the LM3886 is connected to the -40V supply inside the chip. I used plastic insulators to mount the heat sink to the chassis to prevent shorting the supply to chassis ground.
The design is based on the National Semiconductor application in the LM3886 spec sheet.