The basic idea behind a diamond buffer is using two emitter follower stages to shift the signal up and then down again (and vice versa), so that it ultimately ends up at about the same DC level but with much higher current delivering abilities. You could also do this in single ended, but here it's extended to a fully complementary topology for better performance.
BTW, in my headphone amp simulation adventures a while back I tried both complementary emitter follower and diamond buffer outputs. While the diamond buffer generally had lower distortion when run open-loop, within a feedback loop things looked quite different. The DB's additional pole (remember it's a two-stage buffer) meant that I had to reduce open-loop gain considerably in order to get things unconditionally stable, so in the end it actually performed worse than the simple EF output at similar or higher quiescent current levels. That was a bit disappointing.
I did eventually manage to reduce output stage distortion even further with a nested feedback approach (using two opamps). Getting that thing stable wasn't terribly easy though.
BTW, in my headphone amp simulation adventures a while back I tried both complementary emitter follower and diamond buffer outputs. While the diamond buffer generally had lower distortion when run open-loop, within a feedback loop things looked quite different. The DB's additional pole (remember it's a two-stage buffer) meant that I had to reduce open-loop gain considerably in order to get things unconditionally stable, so in the end it actually performed worse than the simple EF output at similar or higher quiescent current levels. That was a bit disappointing.
I did eventually manage to reduce output stage distortion even further with a nested feedback approach (using two opamps). Getting that thing stable wasn't terribly easy though.
Thank you for the information and clarification. The Diamond is a more complex circuit than a simple EF. It clearly goes against the design doctrine of Mr. Nelson Pass which is to keep the circuit simple. Your results do reflect the impact of this complexity.
Please goto the thread " A headphone Transconductance amp for a change!" for more discussion details.
I have simplified the headphone transconductance amp above which is built on an Experimenter's Proto Board. The amp started as a diamond buffer configuration; but now uses only two complemetary transistors working in the common emitter configuration. Fortunately, it still can be simplified futher!.
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