I know, those of us whom have been around in the music business and live sound scratch our heads at this. Fifteen years ago an amp putting out that much power was typically 40-50lbs on average. Take a look at the New Crown, Peavey, Behringer and QSC power amplifiers, you will look almost in disbelief. -10 lbs, some a bit more some a bit less. Sound men will spend less time at the chiropractor!
The trick is in the Class D amplifier technology. Class D amplifiers convert power with a practical efficiency of 90%, with only 10% being lost to heat. Theoretically these amps could run at 100% efficiency but in the real world, components which make it happen create heat. However, the weight savings is in the fact that these amps do not need large heat sinks to dissipate heat. Simply put the produce power much more efficiently as less energy is converted to heat. Older technology amps using AB-class technology are rated with a 78% maximum efficiency and often in the real world doing less than that. So figure if an average class AB amp runs at 60% efficiency then 40% goes to making heat.
The problem with that is heat is an enemy to components as it ultimately causes electronics to fail. So older technology was as good at making power for speakers as it was at making heat. However, unless you want to also heat the room you are using the power amp in, it is wasted energy.
Because of the need for far fewer heat sinks, these amps can be produced much lighter, and with less compact circuitry. I am no engineer and I know these amps had major technological hurdles to jump. It seems though that in the past year or so it has become a common manufactured product as many companies are producing high powered low cost and very light power amplifiers.
I would say that any of us stuck with a rig of heavy amps will soon want to upgrade once the confidence of the reliability is found to be good. Heat is still an enemy to the new breed of amplifier, so hopefully light has not gone too light and what heat is generated is not burning up the amps.
Jay Schultz, Pro Audio, Birdlandmusic.net