# Why is the gain of feedback amplifier Vo/Vs?

Amplification = Output/Input

Then the amplification of the feedback amplifier should be Vo/(Vs +- Vf)

Here,

Vf = feedback signal

Vo = Output signal

Vi = Input Signal and Vi = Vs +- Vf

Vs = Source signal

I have used V instead of phi

• Without explaining your symbols you cannot expect a substantial answer. – LvW Nov 20 '18 at 10:12
• Define Vf by drawing a schematic and using words. Not much to ask. – Andy aka Nov 20 '18 at 10:33

Think of the whole block diagram as an amplifier wherein $$\\Phi_\mathrm{s}\$$ is the input and $$\\Phi_\mathrm{o}\$$ is the output. This is similar to a multi-stage amplifier. The total gain is the output of the second amplifier divided by the input of the first amplifier, which is equal to the product of the gains.