High-fidelity. The one overriding advantage of class-A is high-fidelity, ie sonic performance.
Class-A amplifiers deliver the smoothest, most euphonic sonic performance and the lowest objectionable distortion. That’s what class-A is designed for, and that’s why ALL the very best amplifiers are class-A, where cost is no object.
But Mike, I heard a cheap Chinese class-A tube amplifier and it sounded like sh%t!Typical enquirer
Note: I said class-A is the best where cost is no option. I’m not including cheap gear that will just sound bad, no matter whether it’s class-A, B or Z!
There are no free lunches though and, as per my discussions on class-AB, class-B and class-D, each mode has its advantages and drawbacks. With class-A, the amplifier draws full power whether playing music or idling. Like a car engine running at its redline, things run hot and wear out faster at full power, there is no avoiding this.
This is all well and good where the required power output is very small, such as a headphone amplifier or preamplifiers like my Accuphase C-202 and Cayin Phono 1, which operate in full class-A at very low power. Big amplifiers running in class-A have to be very substantially built to cope.
As a result, class-A amplifiers are big, heavy and need excellent ventilation to deal with the constant high power dissipation. This also means that some environments won’t be well suited to class-A amplifiers. My power amplifier is about 30 Watts per channel of class-A and the Liquid Audio listening room gets a bit warm in summer, let me tell you! Good A/C is essential when running class-A amplification.
With these overbuilt designs come advantages though, like massive power supplies and premium, heavy-duty parts that can cope with the load. These build factors also deliver sonic advantages of their own, so class-A amplifiers tend to just be better all around.
So, the disadvantages of class-A amplifiers such as high cost, constant high power dissipation, electricity bills, carbon footprint, size and weight must also be taken into account. Class-A amplifiers have the highest cost per Watt, so cheap consumer designs avoid the use of class-A.
For the best sound, whether it be using tubes or transistors, class-A is the gold standard.