NFB101 Crisis Averted

I finally cracked it - or rather found the text with an explanation I 
could understand. Basically, with shunt applied feedback it is currents 
that are summed/subtracted at the input. As the output is a voltage the 
stage is a transconductance amplifier so the closed loop gain is in the 
form of Vo/Ii which does turn out to be Ao/(1+ß.Ao) and ß is simply 1/Rf 
where Rf is the feedback resistor

The input resistor effectively inputs a current equal to Vi/Ri from 
which you can work out the voltage gain as Rf/Ri since the closed loop 
transconductance is Rf. I'll include this in NFB101.

Cheers

Ian