The feedback is the resistor from the output of the amp to the -ve input of the opamp. This with the input resistor sets the amp gain. The series RC network around the opamp is for stability purposes. You don't need the OPA551 as the opamp, it doesn't need much of a supply voltage as the output only has to drive +/-10v . If you put clamping diodes on the -ve input you will prevent the output injecting overvoltage. Stability is a real issue. You need small ferrites between the gate of the FETs and the driver to prevent VHF oscillations of the output stage.
Nice explanation indeed.
In my case, bothside biasing is being well protected for DC smoothing. Feedback op-amp works at + and -24 volt. At 551 output, parallel combinaton of 2 ohm and 2k has been made for voltage divider, that was fed to C1815 and A1015 to complete 3 stage AB class.
Two 1N4148 is also connected oppositly on 551 output thus bothside signal can easily conduct.
Actually I have a control board, made from STM32.
15 VAC and 8 VAC stepdown transformer has fed to the system, may be regulated ADC/ DAC has been converted, scalled to a level. So, if you press decimal numbers on the key pad, certain signal will be produce for linear amp input.
Since its a power application, I was testing my CT and PTs, those are connected to this linear Amp output. In this case a power transformer ( having center taps for diffirent volatge ) is also used!
CT gives maximum 6A( if you press larger number on keypad) while PT gives maximum 360 Vac.
At this time TIP147, TIP142 shows steady state.
It succeed the aging test. But, at higher level of feedback amplifiers input, it shows high heat!
I think, there is swithing loss, heat loss. For the seek of high efficiency, I need to think Class D.
Still this design makes money, but need to me more advanced and smart on duty.