SET amplifiers generally deliver very low power, sometimes just a few watts per channel.
You heard right: Large numbers of audiophiles are flocking to replace their modern power amplifiers with amplifiers based on 100-year-old technology.
I’ll explain how Class A/B amplifiers work later in this excerpt, but first I’d like to introduce you to some alternatives to the classic Class A/B amplifier.
These include the single-ended triode amplifier, the single-ended solid-state amplifier, the switching power amplifier, and the digital amplifier.
The movement back to SET amplifiers began in Japan in the 1970s, specifically with designer Nobu Shishido, who combined SET amplifiers with high-sensitivity horn-loaded loudspeakers.
Many who heard SET amplifiers were startled by their goosebump-raising musical immediacy and ability to make the music “jump” out of the loudspeakers.
Most power amplifiers, and the amplifier sections within integrated amplifiers, are strikingly similar in operation.
These so-called “Class A/B, push-pull” amplifiers have been around for decades and are the staple technology of nearly every amplifier manufacturer.
One SET designer told a reviewer, in all seriousness, “If you liked my 9W amplifier, wait until you hear my 3W model.”In addition to low output power and high distortion, SET amplifiers have a very high output impedance as amplifiers go: on the order of 1.5–3 ohms.
This is contrasted with the 0.1 ohm output impedance (or less) of most solid-state amplifiers, and the 0.8 ohms of many push-pull tube designs.
Although most SET amplifiers use a single triode output tube, additional triodes can be combined to produce more output power. In fact, there’s a kind of cult around SET amplifiers that strives for lower and lower output power.
These SET enthusiasts believe that the lower the output power, the better the sound.
(A single-ended triode power amplifier using the 300B output tube is shown in Fig.1 The 300B is the bulbous tube in the middle.)The triode is the simplest of all vacuum tubes; its glass envelope encloses just three electrical elements rather than the five elements in the more common (and modern) pentode tube.