Electronics Handbook/Components/Amplifier

Transformer

${\frac {V_{o}}{V_{i}}}={\frac {N_{2}}{N_{1}}}$

When $N_{2}>N_{1}V_{o}>V_{i}$ Transformer acts as Voltage Amplifier

Transistor

${\frac {V_{o}}{V_{i}}}={\frac {R_{2}}{R_{1}}}$

When $R_{2}>R_{1}V_{o}>V_{i}$ Transistor acts as Voltage Amplifier

Op Amp

${\frac {V_{o}}{V_{i}}}=1+{\frac {R_{2}}{R_{1}}}$

When $R_{2}>R_{1}V_{o}>V_{i}$ Transistor acts as Voltage Amplifier