Opamp Power Amp - Will it Work?

[jnmar]

Originally posted by AndrewT
Hi Jn,
just kidding, you're allowed.

The current in the turned off devices, is it zero or just very small?

I recall an earlier discussion on Leach's interpretation of ClassA for drivers and he stated that because the drivers never turned off (not zero current) they were always in ClassA.
Some of the forum (including I) disagreed with his statement.

I wonder if the same argument (discussion) would apply to output devices? is that a yes or no or in private?

The current in the off devices is about 1uA so is very low they are not completely off but they not are not driving the current they are supposed to drive to keep class A operation.

About the English classes i think that a few more posts (maybe 1000)will improve my skills. Thanks anyway.

Posso também começar a escrever em Portugês mas assim ninguém ia perceber.

Translation- I can start to write in Portuguese but no one will understand.

[GK]

Originally posted by AndrewT
was accepting the traditional way to specify ClassB, but I think most of us know that that definition does not hold up, partly due to the 180degrees being nearly impossible to maintain. If you can't build it then why define it?
and D.Self also modifies the definition of ClassB to be exclusive to bias optimised push-pull to minimise crossover distortion rather than 50% duty cycle.

But we are getting too far from the point we started from and for the sake of this argument I accept that the traditional definition of ClassB is 180degree conduction.

ClassA does not suffer from crossover distortion.

All the other classes (AB, B, & overdriven ClassA) no matter how you define them, all suffer from crossover distortion.

We have been playing with this for four decades and no-one has solved the problem, irrespective of all the clever topologies that have been invented to reduce it's effect.

ps. I thought about not posting this reply, but what the heck, I took the time to think & write.

The traditional way of specifying class B is that each output half conducts for 180 degrees, +/- only a small amount. There is a slight leeway given with regards to bias current. Practical Class B designs for audio either draw no bias current al all, or only very slight bias current.

Getting back to the simple point I made in my first post; an over driven class A amplifier, by traditional definition, will never enter class B, as each output half will still be conducting for well over 180 deg.