Power supply from power amplifier question.

First the PSU diagram form audio power amplifier



The upper part (A1 and A3) is used to power front end (65V).
The lower part (A5, A7) is used to power the output stage (55V).

I would like to know what's the purpose of this circuit D911/D913; C909/C911; R901/R903?

Maybe they are here to make sure that power-up and power down voltages change in the same rate for the front end and the output stage?

Jony130 said:

Maybe they are here to make sure that power-up and power down voltages change in the same rate for the front end and the output stage?

Click to expand...

To discharge both rails at a similar rate during power down.

I can think of other reasons too:

1) It's a good idea to discharge large high voltage caps.

2) The diode may have another purpose and that is somewhere in the circuit, it may be possible for the 65 V supply to backfeed the 55 V supply. The diode may prevent that. Look at the suggested protection diodes for the LM317. It does provide a reverse voltage 0.6V clamp, bit I don't think that's the purpose.

KeepItSimpleStupid said:

I can think of other reasons too:

1) It's a good idea to discharge large high voltage caps.

Click to expand...

That's the reason already suggested