I have an old RCA SA-155 in the garage that drives four speakers removed from a Ford Explorer. It has worked well enough, but at 1.8w per channel, it doesn’t really get too loud. And lately, it has been less than that, I think it’s slowly failing.
There are a couple reasons I like this amp, and first is the size. Since it’s inside a cabinet that is only 12″ deep, there is enough room behind it for the cables. The second benefit is that it barely generates any heat, also important since it is inside a cabinet (even though the door is open when in use).
Instead of finding another amplifier to replace it, I thought it would be fun to build one from scratch. There are a lot of online resources to do this, as long as you have a basic understanding of electronics, it’s a reasonable project to accomplish.
The one I’ve settled on is the 25 Watt MosFet Audio Amplifier located here. There is a great schematic, detailed explanation and a parts list.
I’ve also decided to harvest as many parts as possible from other electronics to keep the cost of this project low. The donor circuit board come from an Integra amplifier that had the left channel not working.