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How To Make A Guitar Overdrive Pedal From Scratch
We’ll see how to use an op-amp and clipping diodes to distort the signal from an electric guitar.
When it comes to distortion, almost every electric guitar player has faced the dilemma of whether to use a transistor-based pedal or to turn all the way up the gain of a valve amplifier. It is common lore that while the latter sounds better, the former is usually cheaper and harder to break physically. Yes, there are also amp simulations that run on DSP chips, but that’s another story. In this article, we’ll see how to make an overdrive / distortion / fuzz pedal with a few pieces of electronics.
To begin with, what does a distortion pedal does is mainly two things: amplify the input signal, and cut some frequencies, hence generating so-called harmonics, that to our ears sound like a sort of metallic buzz. In the theory of Fourier analysis of signal processing, one can represent any signal as a wave or arbitrary shape, which is made by a sum of sine waves, each representing the propagation of a single frequency. In the image above, if we imagine that the signal is just a single sine wave (A), the amplification stage increases the amplitude (B) (i.e. the voltage), and the distortion stage clips the peaks. Since the resulting wave (C) is not a sine wave anymore, this means that the original signal has been turned into a new sum of sine waves, which are the harmonics we’re trying to generate.
How do we accomplish the procedure above with an electric circuit? As you can imagine, there is not a single answer, and each method results in different sounds. And that’s why there are so many overdrive pedals on the market! However, the two main pathways are either to use transistors in a configuration that creates the distortion, or to use an integrated circuit (IC) called op-amp to amplify the input, and at least two diodes to do the clipping. As a matter of fact, an op-amp is basically a pre-packaged circuit made of transistors and other components, but you don’t have to worry about the internal connections. In this article, we’ll focus on the op-amp approach, which is how many popular pedals have been designed (Electro Harmonix Big Muff Pi, Marshall Blues Breaker, Boss OD1 and SD1 overdrive, Ibanez Tube Screamer just to name a few).
