Thanks much Ralph
I was hoping you'd be the one to answer
CLASS A POWER RATINGS
In well designed SS class A power amps I was told that although power could increase to double in class AB mode from speaker demands of 8 ohms to 4 ohms, class A suffered to be cut in half.
For example a class A denominated amp rated at 50 watts class A into 8 ohms would double to 100 watts class AB into a 4 ohm load but only have 25 watts of class A power before switching to class AB.
But I've noticed of late claims of manufacturers stating their amps double their class A power as impedance demands are halved.
So is the explanation that technology has advanced ?
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Real Class A or not, this is the Class A amp I wanted to get (never say never). I had 2 lower powered amps in the same lineup, and they were great. Krell KSA-i400 40th-Anniversary Reference Stereo Power Amplifier (hifiheaven.net) Read the specs on it and how it operates in 'Class A'. |
While I do not understand their magic, this guy does all class A only, I believe his theory is, "if the first watt sucks, why continue". His go up and down from 8ohm to 4ohm, in either direction. All I know is, the stuff sounds pretty awesome. While I don't go to magic shows, their stuff is pretty magical. |
The only amps that you can be sure are always class A are single ended amps because their topology makes them always class A; they cannot go into class B since the output devices must be on all the time. Push/pull amps are different and what you read is true. Most 'class A' push/pull amps go into class B at some point, especially into lower impedance loads. Look at the Pass class A push/pull amps. They are rated at 30 watts and they are class A at 30 watts but all the tests show they actually develop about 70 watts but by then they are class B They are rich AB amps and Pass is honest since he only calls them 30 watts where they are class A. It's hard, expensive and difficult to make a push/pull amp of any power that stays class A essentially all the time. The only one I can think of was the Mark Levinson ML2 amp of decades ago It was huge and yet only rated at 25 watts 8 ohms. But it had huge bias that kept it class A all the time even doubling into low impedance loads. It was 50 watts 4 ohms and even 100 watts 2 ohms and I believe it still stayed class A. But stop and think even an 85 dB speakers only needs 1 watt to play that loud and 10 watts for 95 dB. So the Pass 30 watt class A amp is still class A when it's so loud you shhould not be in the room. It's only split second peaks like banging a piano where the amp goes out of class A and then for such short times the amp is in class A probably over 98% of the time and you don't notice the spit seconds it's class B. Most of us were super happy when we got test scores in school over 95. |
+1 This makes absolute sense. Either it’s a legitimate true class A designed and built circuit or it isn’t. Amplifiers that claim generous class A power and are barely warm to the touch are suspect to me. Perhaps some degree of class A biasing but not genuine full “A” circuit. Charles |
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