This is by far the most complex amplifier I have ever designed.
It includes the following features:
- Output transistor short circuit protection
- Advanced biasing for the power stage. Unlike standard Class AB amplifiers, where the push and pull cycles always force the transistors to shut down completely, and to start conducting earlier than 180 degrees, here the transistors never shut down completely and have a constant bias current (both during idle and dynamic) at around 100mA. This way, the highly non-linear region of most transistors between 0mA and 100mA is skipped.
- Symmetrical input stage with current mirroring and constant current source for improved stability and linearity.
- Automatic output voltage offset correction.
What's not included in the circuit:
- Thermal stability networks. Both the pre-bias formed by the Vbe Multipler and the bias for the class AA mode need to be temperature compensated for stable operation.
- Zobel Network and output LR filter.
The transistors used are as follows:
KSC1845 / KSA992 - For the whole differential amplifier, including current mirrors and constant current sources.
KSA1381 / KSC3503 - For the Voltage Amplifier Stage (VAS).
KSC2690 / KSA1220 - For the driver transistors of the output stage (the front-end transistors of the Sziklai pair).
MJW3281A / MJW1302A - For the output power transistors.
