Esun is pretty correct.
A very important aspect of the operational Class of an amp is:
1 - How much current the amp draws at any given moment
2 - How hot the amp is at any given moment
3 - How efficient an amp is from converting AC wattage to output watts
Amps running in Pure Class A operation suck A LOT of wattage at any given second (even idle) from the wall. They tend to use a constant wattage from AC no matter if they are idle or playing music. They can consume upwards of 10 (most amps less than 10 times) TIMES the amount of wattage idle compared to the wattage they put out at full power. Thus, a 100wpc Class A amp can theoretically suck 1000 watts idle. This means the amp is about 10% efficient. This massive intake of power has to go somewhere and is converted into heat. This is what makes amps that run in Pure Class A HOT even while idle.
Class AB amps run in Class A up to a power level while the rest of their power is drawn as needed from the AC. So lets say the amp is Class A to 10 watts while AB to 100 watts. This amp might draw 100 watts idle. If the amp needs to output more than 10 watts of power this power is taken from the AC as needed. Class AB amps stay a lot cooler than Class A amps because they generally do not draw nearly as much current on a continual basis. This makes Class AB amps much more efficient than pure Class A amps.
Digital amps or Switched amps are a bit different. I am not 100% certain about how to describe these amps operation; however, I do know that these amps are A LOT more efficient than either Class A or Class AB amps. Switched amps (most people call them digital amps, but I have heard that a more correct term is calling them Switched) are about 80% to 90% or so efficient. They can also be amazingly powerful. I have a friend who has had the Bel Canto amps (monoblocked), and he told me they were the most powerful amps that he has ever had.
KF
A very important aspect of the operational Class of an amp is:
1 - How much current the amp draws at any given moment
2 - How hot the amp is at any given moment
3 - How efficient an amp is from converting AC wattage to output watts
Amps running in Pure Class A operation suck A LOT of wattage at any given second (even idle) from the wall. They tend to use a constant wattage from AC no matter if they are idle or playing music. They can consume upwards of 10 (most amps less than 10 times) TIMES the amount of wattage idle compared to the wattage they put out at full power. Thus, a 100wpc Class A amp can theoretically suck 1000 watts idle. This means the amp is about 10% efficient. This massive intake of power has to go somewhere and is converted into heat. This is what makes amps that run in Pure Class A HOT even while idle.
Class AB amps run in Class A up to a power level while the rest of their power is drawn as needed from the AC. So lets say the amp is Class A to 10 watts while AB to 100 watts. This amp might draw 100 watts idle. If the amp needs to output more than 10 watts of power this power is taken from the AC as needed. Class AB amps stay a lot cooler than Class A amps because they generally do not draw nearly as much current on a continual basis. This makes Class AB amps much more efficient than pure Class A amps.
Digital amps or Switched amps are a bit different. I am not 100% certain about how to describe these amps operation; however, I do know that these amps are A LOT more efficient than either Class A or Class AB amps. Switched amps (most people call them digital amps, but I have heard that a more correct term is calling them Switched) are about 80% to 90% or so efficient. They can also be amazingly powerful. I have a friend who has had the Bel Canto amps (monoblocked), and he told me they were the most powerful amps that he has ever had.
KF