ABSTRACT
Audio amplifiers use the conventional architecture. There are three stages, the first being a transconductance stage, that is differential voltage in/current out, the second is a transimpedance stage that is current in/voltage out and lastly a unity-gain output stage. The second stage provides all the voltage gain and is therefore formally named the voltage amplifier stage (VAS). This architecture has several advantages. A main benefit is that it is straightforward to arrange things so that the interaction between stages is negligible. In contrast, the architecture presented by Bengt Olsson is a two stage amplifier. The first stage is once more a transconductance stage. The second combines voltage amplifier stage and output stage in one block. The output stage configuration is totally different in operation from the conventional Class-B stages. It is a hybrid common-drain/common-source configuration, or, in bipolar speak, a common-collector/common-emitter (cc-ce) stage. In this sort of output, the upper emitter-follower has a common-emitter active-load.
