**Differential Amplifier with two Op Amps:**

The gain as well as input resistance of the differential amplifier can be increased by using two op-amps. The characteristics of such an amplifier are identical to those of a noninverting amplifier. A practical circuit using differential amplifier with two op amp is given in Fig. 34.46.

The circuit is composed of a two stage amplifier, the first stage being of a noninverting amplifier and the second being of a differential amplifier, both having gains of different values.

**Equations of First Stage and Second Stage:**

The output of first stage,

Output from second stage,

Since R_{3} = R_{1} and R_{f} = R_{2}, we have

Voltage gain,

Input Resistance: Input resistance of first stage,

where R_{in} is the open-loop resistance of op-amp, as first stage is noninverting amplifier

With v_{in2} grounded i.e. v_{in2 }= 0, the second stage also becomes a noninverting amplifier whose input resistance may be given as

where R_{in} is open-loop resistance of op-amp

**Drawbacks:**

The output signal may be of smaller magnitude than expected. This is a drawback of such an amplifier.