POWER AMPLIFIER
It takes a while for audio-related technologies to mature. Tubed amplifiers were invented by Lee de Forest in the nineteen-teens, but while there are still some adherents of early high-distortion triode designs, the age of mainstream high-fidelity amplification dawned with higher-power/lower-distortion amplifiers developed by Williamson and McIntosh followed by the Ultralinear take on the Williamson concept. That was 30+ years down the technology-evolution timeline after de Forest.
And when it comes to solid state amplifiers—the usual kind—does anyone prefer the state of the (germanium) art circa early 1960s to modern silicon class-AB designs? I doubt it.
Now, decades into its own development, class-D amplification seems to have sea legs, even in the audiophile world. Interesting fact: The class-D amplifier was invented and named in the 1950s by the man who had already invented pulsecode modulation for signal transmission, Englishman Alec Reeves. The first commercial class-D amp was a 2.5W kit from Sinclair Radionics of England, introduced in 1965 and followed the next year with a 20W second-generation model. Sinclair was eventually better known for pocket calculators.
The modern class-D amplifier, built into an integrated circuit, debuted in 1996 with the Tripath “Class-T” chips. Since then, there has been a steady march forward. Today, most “civilian” amplifiers in things like TV soundbars, “smart speakers,” Bluetooth-connected portable speakers, nonfancy automobile sound systems, flatscreen TVs, and the like are commodity-priced class-D “amplifier bricks.” They are small, efficient, cool-running, and cheap.
Class-D amplifiers started to appear in audiophile-grade components about 10 years ago, although there were earlier, outlier examples. In the pro-audio world, they have been around a bit longer, often but not always inside powered monitor speakers. Class-D amplification is ubiquitous in the modern sound-reinforcement world, that is, for live-concert sound.
I have observed this evolution, and in fact have used a cheapo Tripath-based amplifier for 10+ years in a little garage sound system fed by my phone or iPod when I’m out there doing work. If I pried open the cases of the various TVs, Bluetooth speakers, and soundbars around the house, I’m sure I’d find class-D amp chips
