Fully discrete Class AB power amplifier

I recommend using ±48V, with one 12V protection circuit. Both share a common ground.
The overall architecture uses a three-stage structure:
the first stage is a constant current source + common-base differential input + mirror current source;
the second stage is a constant current source + single-EF dual-VAS voltage amplifier with a Vbe multiplier circuit;
the third stage is the pre-drive, drive, and power stage.
The feedback capacitor, which has a significant impact on low frequencies, has been removed. The Vbe multiplier circuit has temperature negative feedback to prevent high-temperature thermal runaway.
Theoretically, the transistors do not need to be paired, as I used integrated dual transistors. Pairing the output power transistors depends on individual budget.
The circuit board has two output zero-adjustment potentiometers and
four 470uF potentiometers for Vbe multiplier adjustment. The F80V capacitor is placed to fill space; an external power board is actually needed, along with a minimum 10MF capacitor
for protection. The circuit uses a UPC1237.
Power is supplied via a single 12V heatsink. The power amplifier uses a heatsink with a 280mm hole
drilled in the top and bottom XH2.54 connectors. Two 10k thermistors are then screwed onto the heatsink.
Two hollow inductors are simply wound ten times with a pen.
The relay model is written on the PCB.
The power input uses 6.3mm cold-pressed terminals. Square wave testing on July 12
 
, 2024
, yielded unsatisfactory results due to the use of a large Miller capacitor and insufficient first-stage current.
Voltage: Dual 12V. Input: 5V square wave. Output: 3-ohm cement resistor
. For conservative reasons, I only applied 3V to the 6 PN junctions. Miller capacitor: 470pF. On
 
July 17, 2024,
I changed R1 and R53 to 150 ohms, R6, R7, R57, and R58 to 120 ohms, and R8, R9, R59, and R60 to 51 ohms. After changing C8 and C15 to 100pF, the slew rate significantly improved.
The differential input stage current is around 4mA, and the voltage amplification stage current is around 10mA.