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This version includes a better output transistor protection circuit. It takes into account the reactive load curvatures, and is devised for MJW1302A and MJW3281A output transistors at up to 150 degrees Celsius operation. Of course, if you can cool the pairs to lower degrees, that's always better.
In the two figures you can see the limitations of the protection circuit (red) and the 4ohm load at 45 degrees phase shift. The upward knee after around 18V helps with greater phase shifts, such as the 60 degrees example (close switch), which is around the worst case scenario you can expect from speakers.
Note: In reality, a Zobel network is needed on the output to ensure Amplfiier stability if it approaches the threshold curvature. With highly inductive loads, such as speakers, if the protection is triggered, voltage spikes are generated, which are dampened by the two output diodes in anti-parallel to the transistors, but the deformed waveform may cause amplifier instabilities without the Zobel Network.
THD+N is 0.02% with emulated 4ohm load, and 0.007% with purely active 4ohm load at 110W@1kHz.
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