stumped with this amp problem

[Ang3lus]

the audio probe actually helped, i noticed low signal right between the output of fx send and input of return

[Ang3lus]

any chance any of you could give me hints on how to mod the NFB circuit ?

I think the 22uf cap is giving a really small range to play with the nfb resistor, I hooked up a Pot with the NFB resistor and getting really small change (pot is 1M), only getting some difference in the between 900k-1M.

any hints/tips on how to mod the NFB part ?

[JazzGuitarGimp]

The nfb circuit is not correct: there is an error in the schematic. Both sides of the OT secondary need a connection to the nfb circuit for it to work. Typically, one side is grounded right at the OT, then the long wire that goes back to the input of the PI carries the signal to the nfb network (but it is grounded at the PI input in your schematic). You might try removing the ground connection at the minus end of the 22uF cap at the PI input, and then grounding the bottom lead of the OT secondary. If you hear a loud squeal/oscillation when the amp warms up, you need to reverse the phase of the nfb by either swapping the OT primary leads, or its secondary leads.

[Ang3lus]

or i could build the NFB circuit by taking a tap from the 8 ohm and connecting it to a 4.7nf/1M depth ? and presence with a 10k tail resistor and 100nf cap ? and ground the 4.7k resistor from the PI ?

do you think that will work ?