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Project Notes

#459 OpAmp/TwinTeeOscillator

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

About LEAP#459 OpAmpOscillators
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LEAP is my personal collection of electronics projects, 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 (IMHO!).

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