Zen Variations 3 - Questions

[vpharris]

Questions on Zen Variations- Part 3

I plan to build this, and am awaiting some parts. However, I would like to understand the operation and performance better before I assemble it. I really plan to build an Aleph, but I thought that this would be worthwhile as a learning exercise to do first.

Questions on the Modulated Regulator: See: http://www.passdiy.com/projects/zenv3-4.htm

1) I understand the basic idea of ‘bending’ the gate voltage of Q5 upward with a positive swing of the output signal. Initially I thought if the regulator nominally puts out 40v and the zener stack provides a 44v reference, then the amplifier output must rise above 44v before the connection through R25 pulls the gate reference up, which seemed impossible.

Looking again, I think I get it. The amp output is AC coupled to the regulator reference, allowing a portion of the output signal to ride on top of the DC reference. Right?

If so, how do I evaluate how much signal will be there? It’s got to do with R23 / 24 /25 and V=IR but I can’t quite get my hands around it.

2) NP mentions that with the modulated regulator the DC at the output of the amp rises to 23 volts from 20V. I haven’t seen any other components in the current source or gain stage change. How does the voltage rise? I’m guessing that re-adjusting potentiometer P1 does this. Correct?

Thanks!