Non-Inverting Op-Amp: High-Impedance Gain Stage

Feed the signal to the positive input and return feedback to the negative. Gain = 1 + Rf ÷ Rin, output in phase, input impedance set almost entirely by the op-amp itself gigohms on FET-input parts. This is the default choice for buffering and amplifying weak sources.
> At a glance: 7 minute guide · part 2 of 10 in the amplifiers complete guide track · includes a worked example and a quick-reference table.

## Why designers reach for it

The huge, predictable input impedance makes non-inverting stages ideal for sensor chains, piezo pickups and any source that loading would distort. Gain is always ≥ 1; the unity case (Rf = 0) is the voltage follower.

| Parameter | Formula/Value | Note |
| — | — | — |
| Gain | 1 + Rf ÷ Rin | Always ≥ +1 |
| Input impedance | Op-amp defined | GΩ on FET inputs |
| Phase | Non-inverted | 0° |
| Unity gain | Rf=0, Rin=∞ | Voltage follower |
| Bandwidth | GBW ÷ noise gain | Noise gain = signal gain |

## The trade-offs

What this means at the bench. Input common-mode range must accommodate the signal the stage amplifies the difference, not the common mode, but rails still clip. Feedback network loading, noise gain and, on precision DC paths, the input offset voltage amplify identically with the signal.

## Applying it well

Set Rf + Rin high enough to spare the output but low enough to keep noise down (typically 1–100 kΩ total). For gains above ~100, consider two cascaded stages for bandwidth. Bypass the rail pins and keep the feedback divider near the inverting pin.

## How to apply this in your build

Work through the sequence below each step assumes the previous one passed. For numbers that need calculating, the linked tools at the end of this guide do the arithmetic instantly.
1. Confirm the signal fits the input common-mode range
2. Pick the gain with standard resistor values
3. Check bandwidth at the chosen noise gain
4. Place the feedback divider adjacent to the inverting pin

### Worked example

A thermistor divider with ~10 kΩ output impedance feeding a non-inverting stage of gain 11 (Rin 10 k, Rf 100 k) preserves the reading. An inverting stage’s 10 kΩ Rin would have halved its sensitivity. Run the numbers yourself with the opamp-gain and the result should agree to within rounding.

> Practical note from the bench. Sensor chains on our bench default to non-inverting first stages measurement begins by not loading the thing you measure.

## Field mistakes we see again and again

– Trying to build gain below unity (impossible here use a divider)
– Starving single-supply stages without a proper mid-rail bias
– Long feedback traces picking up switching rubbish

## Key takeaways

– Why designers reach for it the foundation of this guide; revisit it if any measurement here surprises you.
– The trade-offs the foundation of this guide; revisit it if any measurement here surprises you.
– Applying it well the foundation of this guide; revisit it if any measurement here surprises you.

## Prerequisites and preparation

Before starting. Confirm the signal fits the input common-mode range and pick the gain with standard resistor values. Keep the [opamp-gain](/tools/opamp-gain) open every number in the worked example is reproducible. Total time including the bench steps: about 6–7 minutes.

## Who benefits most

Hobbyists meeting this topic for the first time, students who want the version with real numbers instead of abstract symbols. Returning engineers refreshing a corner of the craft. The mistake list alone justifies the visit every entry in it was learned the expensive way.

### Quick reference card

| Aspect | Where to find it in this guide |
| — | — |
| Core theory | Why designers reach for it |
| Application steps | How to apply this in your build |
| Worked numbers | Worked example |
| Failure modes | Field mistakes we see again and again |

## How this fits the amplifiers complete guide track

This guide is one stop in the structured learning path. Start from the [amplifiers complete guide](/tutorial/amplifiers-complete-guide) pillar page for the full map, or continue with [inverting stage maths](/tutorial/inverting-op-amp-configuration) and [buffering with followers](/tutorial/op-amp-voltage-follower). For the arithmetic, open the [opamp-gain](/tools/opamp-gain).

## Frequently asked questions

Which input impedance do I really get?
The datasheet’s differential figure, degraded slightly by bias-current paths still enormous on FET parts.

Non-inverting or inverting for audio?
Non-inverting where source impedance matters; inverting for summing and phase gymnastics.

Is there a calculator for this?
Yes the [opamp-gain](/tools/opamp-gain) tool runs the formulas from this guide instantly, client-side, with no signup.

## Where to go next

– The complete amplifiers & audio guide: [Amplifiers & Audio complete guide](/tutorial/amplifiers-complete-guide)
– Read next: [inverting op-amp: gain, virtual ground and design](/tutorial/inverting-op-amp-configuration)
– Also in this track: [the op-amp voltage follower: small circuit, big leverage](/tutorial/op-amp-voltage-follower)
– Continue with: [transistor biasing: fixed, divider and q-point stability](/tutorial/transistor-biasing-methods)
– Calculate as you go: [op-amp gain calculator](/tools/op-amp-gain) · [power dissipation tool](/tools/electrical-power) · [gain to dB converter](/tools/opamp-gain)
– Bookmark this page against the day a measurement surprises you. Most readers return to the table and the mistake list first, and that is the correct order.

## Bench verification habits

When a result here disagrees with your expectation, write down both numbers before changing anything. The gap between predicted and measured is where the real engineering lives. It is usually a tolerance, a parasitic or an assumption that was never checked.

Keep a lab notebook entry for every build in this track. The measured values, the deviations from the guide and the reason for each. Six months from now, those notes are worth more than any tutorial. They describe your bench and your components rather than a general case.
## Formulas and checks from this guide

Verification checklist for this track: measure bias at idle before signal testing, check heatsink temperature under load. Confirm gain across frequency rather than at 1 kHz alone. Amplifiers forgive nothing at their edges.

Bookmark this page against your next build in the track. The checklist above is the same one used across 19 guides in this series.

## From our lab notebook

Across the emitter resistors at idle, no signal. Compare each output device.

Thermal drift in bias. Check the bias tracker is bolted to the heatsink and re-set per the service values.

## Final note from the author

A note on thermal reality, which ends most arguments in this track: dissipation is set at idle, verified under load, and never forgiven by a bigger heatsink alone.

Working through Why designers reach for itand The trade-offs with that habit in mind takes minutes, and it is the difference between reading about this topic and owning it.