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This version is partially inspired by the non-switching bias methods that were used in amplifiers back in the 90s. The idea of the bias mechanism is to never let the transistors's current fall below a certain threshold, as power transistors don't have a very linear current characteristic at low current levels, so the crossover distortion is the main struggle for the negative feedback. By biasing the transistors slightly at any output level, you basically eliminate the transistors from completely shutting down and going through the non-linear low current region at crossover. The current is set at around 120mA.
P.S. Here's a new method I'm using to measure distortion here in EC. Just close the switch. The notch filter method is slow and a bit inaccurate, as it suppresses harmonics to some degree if you don't underdampen the filter, which in turn takes forever to stabilize. This simple cancelation method leaves only the differences in the shared point, which is the distortion. In this case, distortion waveform is around 400uV for the whole 60V cycle, which is 0.00066% distortion at 1kHz@110W.
Decreasing the differential amplfiier gain, by increasing the 10ohm emitter degeneration resistors to 330ohm or 560ohm will improve stability, but the distortion increases. At 560ohm resistors, the distortion increases to 0.02%, which is also a great value.
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