I must say: part of the credits go to Rod Elliott from ESP, I took his schematics of his Sziklai amp and modified it. Away with that old-fashioned bootstrap circuit, in with a current source. This way, the amp will have the correct bias everywhere in the circuit over a wide range of power supply voltages. Then: choosing better transistors than the standard types he suggested. A BD139/BD140 pair for the VGS? YIKES! WAAYYY to much collector-base capacitance... so I opted for the 2SA1406/2SC3600 pair. And so on... Then I designed a PCB for it, and sent the files to JLCPCB.com (I cannot recommend them enough!) and opted for the 70µm copper traces (AKA "2 oz. copper"). Te PCBs came in just 6 days after I ordered them and... building it could begin. Seemingly I did everything right from the start, as I could effortlessly adjust bias, connect a speaker and heard.... nothing at all. That's OK without a signal on the input! Started playing and drove the level up to insane levels with that highly demanding Dynaudio 4 Ohms loudspeaker connected to it, right until clipping level, which can be seen from the red LED of the clipping-indicator I incorporated in the design. With a hefty 2X 35V / 500VA transformer, this baby of just 55X88mm made a LOT of power! I intended to use a pair of 2SA1095Y/2SC2565Y but used the pair Rod suggested in the end. 230W high speed ON Semi devices. It's great this all works stable with 0.1 Ohms output resistors, and that you will only have to mount the output devices to the heat sink! The bias servo has to be thermally coupled to the DRIVERS, and NOT to the output devices or overcompenation (and thus cross-over distortion) will occur. Unfortunately, adding pictures is STILL a hassle here, so you'll have to do without them...
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