roger-k said:
Any opinion about this preamp?

I don't know so much about preamps and electronics but
I think the response curves looks good.

Is it worth a try?

Graham Maynard is a good designer, and his power amp is also recommended in this forum.

Why don't you write to him and ask about that design?

I personally think the feedback cap is a bit large and would prefer some kind of servo to control DC offset or an output cap. But that's me.

In any case you should always use a good film cap at the input of any power amp.