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Project Notes

#159 ML741/InvertingAmplifier

Test an inverting amplifier circuit using the ML741 discrete component opamp


This is a demonstration of an inverting amplifier circuit using the ML741 discrete component opamp.

The inverting amplifier is a generalised case of the basic Inverter circuit, but with an arbitrary gain determined by the input and feedback resistor selection:

Vout = - Rf/Rin * Vin


How it works

Fundamentally, an op-amp strives to keep its inverting an non-inverting inputs equal by modulating the output.

In the inverter/inverting amplifier configuration, the inverting input is at the inflexion point of the Rin:Rf voltage divider. Hence the op amp achieves inverting/non-inverting input equilibrium when Vout = - Rf/Rin * Vin.


In this circuit, I am using a single rail supply (V- = GND) instead of the “conventional” dual rail supply (V+/V-).

For this reason, the non-inverting input is pegged to V+/2 with a voltage divider. In a dual rail configuration, V+/2 is usually “ground”.

The breadboard build has a fixed gain of -2 but of course the feedback resistor can be replaced with a pot for manual variable gain.


The Schematic

The Build

ML741 v “real” 741 Test

Here are some results comparing the behaviour of a standard UA741CN chip with the ML741 (protoboard version).


  • power is 5V single rail, i.e. V- = GND
  • non-inverting input is fed a sine wave 200mVpp with 2.5V DC offset
  • the function generator sine wave input replaces the manual 10kΩ input pot in the schematic above (at node FG)
  • CH1 and CH2 signals are DC coupled and vertical shifted by -2.5V in the screenshots that follow

Scope connections

  • CH1: non-inverting input
  • CH2: output

At 10kHz

  • very slight phase shift for both opamps
  • UA741CN is delivering almost exactly -2x gain
  • ML741 is also generating -2x gain, but the output is DC shifted up by ~20mV





At 100kHz

  • phase shift has increased for both opamps
  • output has started to attenuate. By 150kHz or so, already hitting unit gain
  • ML741 output remains pulled higher by ~20mV





Measurements in action…


Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.