Power amp PSU sag emulation for rack preamps?

[roberto]

You can't drive the power supply voltage regulator directly with the envelope follower's output. ...or you can but then the circuit is nothing but a high power buffer and your power supply voltage will be identical to envelope follower output. Not nice.

I agree, that's why I talked about scale and modulate the power regulator through a buffered version, not directly drive.

And why don't you want to emulate the power amp?

It's way simpler to directly do it through a power attenuator, or making the screen supplies weaker.

[roberto]

Think so ? Try running your preamp from a regulated bench power supply. Your amp will FEEL different.

Yep, I've never done measurements, but doing this exact test years ago I felt the preamp supply derived from the power amp sounded more... "articulate" gives the idea?
Like a modulation of the sound through the PSU. Use a dedicated PSU, or change the way the PSU is managed, and it will sound different.

Here the idea is to have a fixed voltage supply (independent from the wall voltage), and then modulate it as if it was supplied by the PSU of a pushed power amp.

[Reeltarded]

I have a '57 Gretsch catus and cowboys amp. Any volume over 5 and every degree to 10 the sag goes from subtle to amp flattening. It sounds like a microsynth and it feels AWESOME!

I know what you need. Find the node you want to do the sag and run parallel B+ to that node. Throw 8u and too much resistance there.