I'm so happy I finally decided to add an amp to power my Polk db series speakers in my truck; it makes a world of difference in the sound quality, especially in the amount of bass added to my front stage. I went with this amp because I needed a small amp in the 50-75w rms range that would fit under my seat. This amp does not disappoint! I knew it would be small, but I wasn't prepared for how compact this little thing would be. Even with this amps small size, heat is not a problem. This amp is Class D, so it runs very efficiently, and therefore very cool. It just gets warm to the touch and has plenty of power for pretty much any system. The amp sounds great, although there is slight distortion at zero volume, but once music is playing this sound is inaudible (this distortion is probably more noticeable because I have 2v preouts and have to turn the gains a little higher than if I had 4v ones). Build quality is extremely solid and I expect this amp to last forever, my only gripe is that controls on top are a little flimsy, but this isn't a big deal at all. Overall this is a great little amp. If you're in the market for a small and powerful amp look no further than the R400-4D.