Class H describes the main power supply for the amp board. It is a dual-rail design. It will supply +/-35V voltage to the amp board as normal/idle supply. If the audio signal raises to a certain power wattage point (probably around 200-250 watts), the input power circuit will automatically switch to higher power +/-70V power rails.
The Class AB describes how the output transistors are biased/loaded. It has nothing to do with the voltage/rail of the power supply. Class AB says that the output transistors are constantly power with a set amount of watts (probably around 5-8 watts in the case of this Emotiva amp). This means that 5-8 watts are flowing through the transistors at all time, even if there is no audio signal.
The XPA-DR amps are fully balanced/differential amp boards and require two amp boards per channel.
The Class AB describes how the output transistors are biased/loaded. It has nothing to do with the voltage/rail of the power supply. Class AB says that the output transistors are constantly power with a set amount of watts (probably around 5-8 watts in the case of this Emotiva amp). This means that 5-8 watts are flowing through the transistors at all time, even if there is no audio signal.
The XPA-DR amps are fully balanced/differential amp boards and require two amp boards per channel.