Ok, I'll take a bite...
The PE magazine design undoubtedly works to some degree. To some that might be enough and they may be the same people who appreciate the seeming simplicity.
But then there are inherent issues...
Bias. Well, the bias string probably tracks thermal changes to some degree if diodes are thermally coupled to output devices. But it probably has to be somewhat "cold" bias, though, because... well... in all its simplicity it's a sub-optimal design and more susceptible to thermal overruns. This issue is enhanced by the lack of emitter resistors in the output stage. So we can expect more crossover distortion and compromised reliability.
Gain. As is, the stage is configured as inverting amplifier. Very similarly to opamps (this is a generic NFB circuit after all), gain is determined by feedback impedance and total input impedance. So, consistent performance will require an additional buffering stage to keep source impedance to power amp stage constant. Added complexity.
Reliability. Obviously this amplifier is not protected against exessive load currents in any efficient manner. A momentary short circuit or a complex load may destroy the entire amplifier in less than an eyeblink.
Overload performance. If this was a small signal stage, operating at low currents, similar circuit might provide rather musical, though somewhat hard and asymmetric, clipping. Being a high current stage it's much more susceptible to transistor "deep saturation", which leads to much less musical momentary "rail sticking", which will sound nasty. In worst cases rail sticking may become permanent and destroy the amplifier instanteniously.
Stability. As is, it looks poor and is highly affected by layout and overall design. A practical circuit may require local high frequency negative feedback in VAS (and possibly drivers), and the output probably should have a Zobel filter (remember those complex loads?). Added complexity.
I agree with the opinion that addressing these issues will require a complete redesign of the amplifier (I built a similar circuit myself and vouch for that). In the end, picking a more adequate design as a starting point may prove more effective. Unless you want to use this as a learning experience of course.
Anyway, as I said, to some degree it works. It's a moderately powerful power amp, makes noise and all. I would just be constantly worried about its reliability. No thanks.
The PE magazine design undoubtedly works to some degree. To some that might be enough and they may be the same people who appreciate the seeming simplicity.
But then there are inherent issues...
Bias. Well, the bias string probably tracks thermal changes to some degree if diodes are thermally coupled to output devices. But it probably has to be somewhat "cold" bias, though, because... well... in all its simplicity it's a sub-optimal design and more susceptible to thermal overruns. This issue is enhanced by the lack of emitter resistors in the output stage. So we can expect more crossover distortion and compromised reliability.
Gain. As is, the stage is configured as inverting amplifier. Very similarly to opamps (this is a generic NFB circuit after all), gain is determined by feedback impedance and total input impedance. So, consistent performance will require an additional buffering stage to keep source impedance to power amp stage constant. Added complexity.
Reliability. Obviously this amplifier is not protected against exessive load currents in any efficient manner. A momentary short circuit or a complex load may destroy the entire amplifier in less than an eyeblink.
Overload performance. If this was a small signal stage, operating at low currents, similar circuit might provide rather musical, though somewhat hard and asymmetric, clipping. Being a high current stage it's much more susceptible to transistor "deep saturation", which leads to much less musical momentary "rail sticking", which will sound nasty. In worst cases rail sticking may become permanent and destroy the amplifier instanteniously.
Stability. As is, it looks poor and is highly affected by layout and overall design. A practical circuit may require local high frequency negative feedback in VAS (and possibly drivers), and the output probably should have a Zobel filter (remember those complex loads?). Added complexity.
I agree with the opinion that addressing these issues will require a complete redesign of the amplifier (I built a similar circuit myself and vouch for that). In the end, picking a more adequate design as a starting point may prove more effective. Unless you want to use this as a learning experience of course.
Anyway, as I said, to some degree it works. It's a moderately powerful power amp, makes noise and all. I would just be constantly worried about its reliability. No thanks.