Simple Amplifier

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A couple of questions about the circuit....
I agree with your criticisms. There's something else too: the circuit is limited to about half a volt output by clipping of T1 and T2. Aside from the fact that the circuit doesn't work, I don't see why anybody would want to drive a class A output stage from a class B driver stage anyway - it gives you the worst of everything.
 
The circuit works in push pull mode with the two sets of transistors. When the upper transistors are open the lower are closed.

At what voltage the output is stopped ( "clipped" ) depends on the zener voltage.

The common emitters common collectors arrangement is pointless under normal circumstances but is great when double voltage is applied because the operational amplifier is limited to 36V power supply. Thus, one can put anything at the operational amplifier and anything high at the transistors. Thus, this circuit combines the advantages of the feedback around all involved components in this stage with the huge power which may be required.

Without any protection, the circuit works as an operational amplifier which swings 0.7 to - 0.7 and drives the first set of transistors connected in common emitter without the unnecessary components which are unnecessary in this case because the feedback will take care of correct adjustment of the signal, temperature compensation, etcetera.

The first set of transistors is used to ensure the whole range is covered ( to amplify ) as well as to provide a common point of the amplified signal against which the second set is controlled.

The second set of transistors are in common collectors. They can work with and without the feedback of the operational amplifier.

When protection is used, the operational amplifier goes out of balance and to one of the rails ( saturation ). Due to the lack of feedback, the common emitters are not controlled and work as switching transistors: one of them will open, the other one will close. The open transistor will display a very tiny voltage at the collector ( 0.3V ) and may not be able to open the coresponding common collector. Even in case the voltage is higher than 0.7V or whatever the right hand side transistors take to open, this tiny voltage will be displayed at the output because the open common collector works without the operational amplifier's feedback too.

Even in case the whole zener couple voltage is displayed at the common collector and the output, there is still no problem. This is where the output is desirable to be at maximal work.

I agree with your criticisms. There's something else too: the circuit is limited to about half a volt output by clipping of T1 and T2. Aside from the fact that the circuit doesn't work, I don't see why anybody would want to drive a class A output stage from a class B driver stage anyway - it gives you the worst of everything.
 
Just browsed at the schematics: T1 and T2 are the common emitters and the left hand side transistors. T3 and T4 are the common collectors and the right hand side transistors.

The output of the operational amplifier would swing higher than - 0.7V to 0.7V because of Rb. Without the Rb, yes.

The circuit works in push pull mode with the two sets of transistors. When the upper transistors are open the lower are closed.

At what voltage the output is stopped ( "clipped" ) depends on the zener voltage.

The common emitters common collectors arrangement is pointless under normal circumstances but is great when double voltage is applied because the operational amplifier is limited to 36V power supply. Thus, one can put anything at the operational amplifier and anything high at the transistors. Thus, this circuit combines the advantages of the feedback around all involved components in this stage with the huge power which may be required.

Without any protection, the circuit works as an operational amplifier which swings 0.7 to - 0.7 and drives the first set of transistors connected in common emitter without the unnecessary components which are unnecessary in this case because the feedback will take care of correct adjustment of the signal, temperature compensation, etcetera.

The first set of transistors is used to ensure the whole range is covered ( to amplify ) as well as to provide a common point of the amplified signal against which the second set is controlled.

The second set of transistors are in common collectors. They can work with and without the feedback of the operational amplifier.

When protection is used, the operational amplifier goes out of balance and to one of the rails ( saturation ). Due to the lack of feedback, the common emitters are not controlled and work as switching transistors: one of them will open, the other one will close. The open transistor will display a very tiny voltage at the collector ( 0.3V ) and may not be able to open the coresponding common collector. Even in case the voltage is higher than 0.7V or whatever the right hand side transistors take to open, this tiny voltage will be displayed at the output because the open common collector works without the operational amplifier's feedback too.

Even in case the whole zener couple voltage is displayed at the common collector and the output, there is still no problem. This is where the output is desirable to be at maximal work.
 
The circuit works in push pull mode with the two sets of transistors. When the upper transistors are open the lower are closed.
Huh? :confused:
When T1 is switched off, the current through Rc1 will switch T3 on. When T1 is switched on, it will switch T3 off. When one is "open", the other is "closed". Same story for the bottom two transistors.
 

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Huh? :confused:
When T1 is switched off, the current through Rc1 will switch T3 on. When T1 is switched on, it will switch T3 off. When one is "open", the other is "closed". Same story for the bottom two transistors.

I have ( conveniently, sorry : ) ) forgotten the discussion and I cannot clearly view your picture.

Seems you show two common emitters to ground which run the two common collectors. I have already discussed this schematics.

What you say seems to be OK and I should have said this. In case I have made a mistake or forgotten, sorry.

Anyway, I am in a process of making a similar schematics and will report the device once made or in stages.
 
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