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Project Notes

#459 Twin-Tee OpAmp Oscillator

A twin-tee sine wave oscillator using an TL072 Op-Amp, running in the audio spectrum.



A twin-tee filter in the feedback loop of an op-amp can be used to generate a sine wave.

  • one tee comprises an R-C-R low-pass filter
  • the other is a C-R-C high-pass filter.

Together, these circuits form a notch filter which is tuned at the desired frequency of oscillation.

Design Guidelines

For oscillations to be sustained, x>=2, where:

x = C2/C1 = R1/R2

And the frequency is then given as:

frequency = 1/(2πRC)

Breadboard Construction

I’m using a TL072:

  • one op-amp unit is used to establish a buffered AC ground at VCC/2
  • the other is for the oscillator

R2 is a pot so that it can be adjusted to be ~ R1/2 and thus allow the circuit to oscillate depending on the R1 values used.




Breadboard Results

With a 9V supply and R1 = 4.7kΩ, I get oscillation at about 3.238kHz:


Protoboard Construction

For some more reliable measurements with various resistor values, I put the circuit on some protoboard. Here’s the basic layout I used. It includes:

  • connections for substituting R1 values
  • pins for output and capacitively coupled output (via 100nF capacitor)
  • pins for ground and AC ground
  • some capacitors for power supply smoothing (100nF and 100µF across the power supply)


With a 5V supply and R1 = 4.7kΩ, I get oscillation at about 3.084kHz. The wave is not a perfect sine wave, with two main distortions present:

  • noticable cross-over distortion in both directions
  • clipping at the top of the wave if R2 not adjusted correctly


Some measurements with a selection of R1 values:

R1 Expected Frequency Actual Frequency
3.3kΩ 4.823kHz 4.503kHz
4.7kΩ 3.386kHz 3.084kHz
10kΩ 1.592kHz 1.445kHz


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.