Analysis of a Distortion Circuit

Building on my post about distortion, I built a distortion circuit with the help of Jon Bretan. The circuit takes in audio signal and uses transistors to distort the signal. Instead of outputting the distorted signal to a speaker, I recorded it using voltage probes. The final setup looked like this:

I recorded the voltage input (red) and the distorted signal (blue) in several different scenarios. First, I recorded the data for sawtooth, square, and triangle waves to look at how distortion uniquely effects each waveform. The data are pictured below:

100.87 Hertz Sawtooth:



100.87 Hertz Square:



100.87 Hertz Triangle:


Interestingly, the distorted waveform has a unique shape for the different input waves. The distortion is clear in the jagged and flattened parts of the blue wave, and it makes sense to see the amplitude of the distorted waveform match the general shape of the initial waveforms.  The type of distortion occurring here is called clipping, and I will be dedicating a brief blog post to this in the future. Normally, clipping results in a louder seeming wave because the top of the initial wave is "flattened" as it reaches peak intensity. However, in this circuit, the distorted sound is not amplified to a level that would make this apparent as its magnitude is significantly lower than the initial signal.

After looking at these different waveforms, I took a basic sine wave signal and recorded it at a range of frequencies to see how the frequency impacted the distortion occurring in the circuit. The following data represent the frequency range I was able to record:

59.44 Hertz Sine:

100.87 Hertz Sine:


200 Hertz Sine:



302.27 Hertz Sine:



403.48 Hertz Sine:


493.88 Hertz Sine:


I initially did not think that the effect of the distortion would not be significantly affected by the frequency of the input signal. However, looking at the data in order of increasing frequency reveals a really fascinating trend. The input signal for all the frequencies seem to be perfectly uniform, but the distorted signal at higher frequencies appears to follow a sinusoidal pattern. The peaks and troughs of the distorted signal that follow the shape of the clean signal seem to be superimposed over a sine wave. It is likely that this added oscillation is caused by the electronic components of the circuit as electric current flows through. It is interesting to see how this effect is only very clear for the higher frequency sine waves.

Works Cited:

Platt, Charles. Make: Electronics: Learning by Discovery. Sebastopol, CA: O'Reilly, 2009. Print.