Class A amplifiers deliver the smoothest, most euphonic sonic performance.

That’s why class A is always used in high-end designs where cost is no object. The best class A amplifiers are MOSFET or tube-based designs, for a variety of engineering reasons, but good BJT device class A designs also exist, like my old Krell KSA-150, for example.

But Mike, I listened to a cheap Chinese class A amplifier and it sounded like sh#t!

Indeed, and that’s why I exclude the myriad of cheap, low-quality Chinese and Indian designs from Vincent, Willsenton and various other junk brands from this discussion. This equipment sounds ordinary, is cheaply made, short-lived and should be avoided.

But Mike, I listened to a cheap Chinese class A amplifier and it sounded great!

This will simply be because it sounds better than anything you’ve owned or listened to, not because it’s inherently good. The frame of reference is important here.

Compromises

There are no free lunches, though, and class A amplifiers must obey the laws of physics just like the rest of us. Like class AB, class B, and class D amplifiers, class A amplifiers have pros and cons.

Class A amplifiers dissipate their maximum rated power at all times, meaning they dissipate a lot of thermal energy and run hot at all times. The way to deal with this heat is to use the best parts and engineering, big chassis and heatsinks, etc. The best parts and engineering always mean one thing: m-o-n-e-y baby!

Now, if the required power output is very small, such as a headphone amplifier or preamplifier like my Accuphase C-290, class A is not particularly expensive to implement. Power amplifiers running in class A are different, though, due to their large power outputs and have to be correspondingly large and heavily built to cope with this high power demand, 100% duty cycle and high heat dissipation.

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 Accuphase A-75 class A power amplifier weighs 45kg and delivers a very conservatively rated 60 Watts per channel into 8 Ohms (measures over 120 Watts/ch). Good A/C is essential when running class A amplification like this!

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, high power dissipation, increased electricity bills, and large size and weight must be taken into account. Class A amplifiers have the highest $/Watt ratio and are therefore not found at the lower end of the consumer spectrum.

Because powerful class A designs cannot be implemented cheaply, cheap Chinese solutions, like the ridiculous Mumysys/Musymys/Mumsymys (LOL) Chinese designs that look a little like an Accuphase something A-75 are literal garbage and should be avoided.

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