Still, the second design suggested appears to have a
Sziklai (complementary feedback) output stage, which is
a point in its favor. Either design is about as simple
as an amplifier built with bipolar transistors can get,
without being too simple and compromising performance.
Just some quick thoughts.
Please realise that the layout of the tracks on the PCB can make or break even a good amps performance. Often, getting the schematic right is only half the problem.
The first amp has some ouput protection, the ESP amp only hase fuses. Some output protection circuits are blamed for nasty sounds.
Elegant, yes. Linear, yes. But not easy to set up a stable bias point, and inclined to ultrasonic instability, particularly on the negative rail. The remedy is to throw it in manacles, which destroys the sound.
I have tested both Sziklai and Emitter follower output stages sonically, and can tell you the second type is easily the better.
Your initial instincts were correct-avoid the simplistic 'simpler is better' option, and construct the example you first considered, as it has a rather good dual slope vi-limiter. the 'sound.westhost.com' example will self-destruct at the slightest hint of a short-circuit, or indeed 'difficult' 'speaker load.
One of the reasons I chose the ESP amp was its robustness. Rod based on an amp design he has used for years. He's built dozens and had very few failures.
Yes, it's possible he's making it all up. But I doubt it.
Sorry, I disagree. Simpler is better. Witness the success of the Zen stuff here. The sophisticated protection schemes employed by some amps have a bad rep here.
I would recommend Rod's schematic because this one is simpler. When you want to protect the output stage against short circuits, you can add a protection like in the first schematic. In this case R4, R23, R28, D7 and D8 aren't necessary. The resistors R16 and R2 in the first schematic are replaced by R13 and R14 of Rod's one. The right values of R3, R10, R15 and R17 are:
R3, R17: 220 ohm
R10, R15: 47 ohm
With this values the base current of Q5 and Q6 will be cut off when the current through R13 and R14 is about 6A or more.
Some will say that such a protection isn't necessary because two fuses of 5A are used. In some cases fuses might be too slow to protect the transistors successfully.