Finally got this little rarity fixed. Couldn't find a schematic so I traced it by myself. I bet this is the only one in the internet.

There are lot of claims that simpler power amplifier circuits sound better than complex modern ones. Could this really be so?

We all know that simplism has some non-arguable benefits:
- The devices are more likely closely matched since there is a smaller amount of them.
- The layout is simpler which can have some benefits: ie. shorter tracks, less interference. (Assuming everything is done right of course).

...As well as drawbacks:
- Simple design is more likely much more unstabile.
- Simple design is more likely much more unlinear.
- Bad layout will more likely cause more problems.



I simulated two circuits in ltspice. (See the thumbnail link). They are almost "identical", meaning the signal path is almost identical. Both circuits use long tailed pair input with the same amount of feedback so the gain is same, at least on 1 kHz. (There's soon more about this). The output topologies are a bit different: The simple, "old-fashioned" circuit has a quasi-complementary output, which was very common until high power complementary transistors became available. The topology has an advantage of closer matching between the output devices, while the "modern" one uses a fully complementary output. Besides output topology and replacing constant resistances or bootstraps with constant current sources these two circuits are identical.

Their performance however is not:
- The "modern" circuit has a more constant gain throughout bandwidth. The gain of the simple circuit drops heavily on higher frequencies.
- "Modern" circuit can swing closer to rails.
- Simple one suffers from higher DC offset.
- Simple one has worse distortion figures, especially on 2nd harmonic. An exception occures when the circuits are hardly overdriven: In the simpler circuit the 2nd harmonic drops 10dB in relation to "modern".

Every aspect of the simulation shows that the modern circuit is far more better. It shouldn't be more sterile or colder sounding, nor does it clip harsher in relation to simpler one. As a matter of fact, the the simpler one clips harsher than the modern! Undoubtedly the real-life indifferencies between devices will add something to the game. Is it enough to make a simple circuit perform better - i don't think so. Could this preferance over simplism be explained by "psychoacoustics": One knows that he is listening to a simpler circuit and regards the distortion as "pleasentness"? I will soon do some listening tests between these two simulated circuits and get back to this.

Meanwhile, be free to comment and present your ideas.