Class H amps?

Just came across 'Class D' (after years of A, AB, not really B). 

So what is Class H? How does it differ from Class D?



The output transformers are valves between 2 voltage rails. Say, + and - 10 V.

In A, B and A/B those rails are fixed values. Classes G and H vary those rail voltages. Carver and NAD got famous on G. The idea is that minimizing the difference between the rails and raising them only when needed minimizes heat of the output transistors.

NAD continues to dabble with their hybrid Class D amps today.

Wikipedia is your friend:


As an aside, an audio buddy is using a pair of Benchmark AHB2 Power Amplifiers to drive his SoundLab electrostatic speakers to great effect.

Benchmark's specs state it: “combines class-AB, and class-H topologies, using a feed-forward error correction system” (  My buddy is using two AHB-2’s that are in bridged mode to output enough power for his SoundLabs.

H is good.


D is a muddy mess.


My Sunfire sig 600 is class H, and smokes much if not most of the newer amps at lo local shop. They are sick of me showing up with it, and besting much of their high class amps. Im thinking's soon they will ban people from bringing in their stuff for speaker auditioning.


It’s all in the implementation. Making a generalization about amps by class is . . . well . . . unfounded. It’s like saying all blond(e)s are dumb. Every one I’ve met is different.

I’ve heard the AHB2 (class H) in my own system (with Janszen electrostats), and it sounded great.

I’ve heard Apollon amps made with PuriFi 1ET400A modules (Class D) in the same system, and the sound was great also.

It’s true that some early Class D didn’t sound so good. Development has been intense, and it’s paid off. The good ones are more than competitive with Class A and AB. Choice then becomes a matter of individual taste.