Who doesn't love the rumble of a distorted electric guitar? It is a key part of many important music genres, especially in blues and rock music genres, and is also often used in hard rock, metal or punk music genres. In this project we will build a basic distortion pedal for the guitar using a simple circuit.
guitar distortion pedal
The distortion pedal produces a distorted sound on the notes. Typically, a distortion pedal circuit is used between the guitar sound source and the power amp. A simple block diagram of a guitar with a distortion circuit is shown below.
Distortion pedals use at least two of the most important things, the preamp section and the diode limiting circuit. The audio preamp section adds gain to the input signal, and the diode clip section cuts or clips the positive and negative peaks of the audio signal. Often, distortion pedals are also called overdrive or fuzz pedals.
In this article, we will build a transistor-based distortion circuit. The components required to build a basic distortion pedal circuit are −
.1 uF Capacitors – 2
UF4007 – 2
2 audio input sockets
12v adapter (9V also works)
Guitar distortion pedal circuit diagram
In the image below, a schematic of a basic distortion pedal using transistors is shown. A transistor is like a basic preamp. The 100K resistor is used as the collector resistor, and the two capacitors are used for audio input and audio output related purposes. Capacitors will block any DC current and only pass AC signals. The value of the capacitor can be selected from 0.1 microfarad to 10 microfarad.
The choice of transistor is critical to this project. In the above circuit, we used a BC337-25 transistor. This transistor provides good gain to the input signal. Other transistors can also be used.
Two diodes D1 and D2 form a diode clipping circuit. This is where the distorted sound is produced. Assume that the input signal is an AC sinusoidal signal, as shown in the figure below.
This is a perfect sine wave. Now, similar to the diode clipping circuit used in the schematic, the sine wave is cut or clipped depending on the forward voltage of the diode. The truncated sine wave will look like the image below −
Diode D1 will be reverse biased with respect to the output and limit the negative peaks of the output signal. Similarly, diode D2 will be forward biased relative to the output clip and clip the positive peaks of the output signal. So if we compare these input and output signals, it will look like the image below
But how does this affect the distorted sound? That's due to the speaker's response to a sine wave. When the sine wave is positive, the speaker diaphragm moves forward, and when it is negative, the speaker diaphragm moves backward. But due to the proper sine wave response, the forward and backward movement of the speaker goes smoothly. Whenever the signal is clipped or chopped, the speaker diaphragm produces a chattering sound and the output tone is distorted.
How much distortion is required depends on the diode configuration. Different forward voltages and even different gauge diodes in D1 and D2 will produce different kinds of distorted sounds.
Possible combinations include 1N4148 in D1 and green LED in D2, or orange and green LED in D1 and D2, or a germanium diode configuration can also be used. Different distortion pedal manufacturers use different combinations in a single package and provide users with selectable switches. The user can choose which one to use based on the tone. Other diode configurations can be tried and create interesting distorted sound outputs.
Testing Guitar Distortion Circuits
The circuit we explained above was built on a breadboard and tested with a real guitar. The breadboard setup after the circuit is complete is shown below.
The pins of the BC337-25 are shown in the figure below –
To test the circuit, I used two jumper wires, a power amp, and a guitar. Jumpers connect to the two connectors (black) to take the audio input from the guitar and pass it through to the amp. However, distortion pedals are often used with electric guitars, but since they were not available during the testing phase, acoustic guitars were used here for testing.