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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 ?

rost

Showing 4 responses by charles1dad

charles1dad's avatar
charles1dad
10,234 posts
 

@sngreen 

No. Class “B” and push-pull aren’t synonymous. @atmasphere has given a clear (At least to me) example/explanation. His OTL amplifiers and the Mark Levinson mentioned earlier are examples of pure class A push-pull topologies. There’re others as well.

Charles

charles1dad's avatar
charles1dad
10,234 posts
 

@sngreen 

By default SET/SEP  is 100% pure class A operation. But as has been pointed out above,  you can have pure class A push pull amplifiers that do not utilize any class B operation.

Charles

charles1dad's avatar
charles1dad
10,234 posts
 

@dynamiclinearity

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.

 

An excellent example of a pure class A push-pull amplifier. It was/is a beast.

charles1dad's avatar
charles1dad
10,234 posts
 

@atmasphere

The technology hasn’t advanced in this regard. When a class A amp can double its power into half the load impedance, its simply because its built to be able to do that. The technology to do that has been around for decades

+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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