The one key advantage of class A topology is high fidelity, ie the best sonic performance.

Basics

Class A amplifiers deliver the smoothest, most euphonic sonic performance and the lowest objectionable distortion. That’s why class A is used in high-end designs despite its shortcomings and why the very best amplifiers are class A, where cost is no object. The best class A amplifiers are MOSFET or tube-based designs in my experience.

But Mike, I heard a cheap Chinese class-A tube amplifier and it sounded like sh%t!

Typical enquirer

I’m naturally excluding the myriad of cheap, low-quality designs flooding the market from brands like Vincent and various others. These sound bad, are hard to repair and service and should be avoided.

Compromises

There are no free lunches though and, as per my FAQs on class AB, class B and class D, each design has advantages and drawbacks. Class A amplifiers draw and dissipate their maximum rated power at all times, whether playing music or idling. They run hot and the only way to combat this is to use the very best parts and generous thermal design. Best parts and generous thermal design for class A means m-o-n-e-y!

Now, if the required power output is very small, such as a headphone amplifier or preamplifier like my Accuphase C-280V, class A is no problem and not that expensive to implement. Dissipating such low power is relatively easy. Big amplifiers running in class A have to be large and very substantially built to cope with this constant high power demand, 100% duty cycle and high heat dissipation, however.

Such class A power amplifiers are big, heavy and need excellent ventilation. Some environments/use cases won’t be well suited to class A amplifiers. My new Accuphase A-75 class A power amplifier weighs 45kg and delivers 60 Watts per channel of class A power. Good A/C is essential when running class A amplification like this beast, no sitting in a cabinet for this baby!

Bottom Line

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. The best sounding ones are the MOSFET types, like the A-75.

The disadvantages of class A design such as high cost, constant high power dissipation, increased electricity bills, size and weight must also be taken into account. Class A amplifiers have the highest cost per Watt, and therefore are not found at the lower consumer end of the spectrum. Proper class A cannot be implemented cheaply, so if you are looking for a cheap Chinese solution, know that there isn’t one.

For the best sound, whether tube or solid-state, class A is the gold standard.