Ever wondered how those crunchy sounds come from the guitars of modern rock gods. Well, the answer to that is electronics. So let’s go through the history of this “rock” sound. When electric guitars were invented, amplifiers at that time were tube amplifiers which, unlike today's amplifiers, used triodes or tube tubes instead of transistors to amplify the signal. Amplifiers back then were big and bulky. And when played at maximum volume, they produce a “distorted” sound because the guitar signal is greatly amplified and therefore cut off. The great guitarist Jimi Hendrix was the first guitarist to recognize that the guitar and amplifier together can be used as an instrument and began using this distorted sound to produce music. This is how rock music was invented.
But tube amplifiers were unreliable, consumed a lot of power and were expensive. So electronics engineers began to develop circuits that produced the same effect as a fully driven tube amplifier, but were much smaller, effective, and reliable. This gave rise to distortion pedals with transistors.
Ever wondered how those crunchy sounds come from the guitars of modern rock gods? Well, the answer to that is electronics . So let’s go through the history of this “rock” sound. When electric guitars were invented, amplifiers at that time were tube amplifiers which, unlike today's amplifiers, used triodes or tube tubes instead of transistors to amplify the signal. Amplifiers back then were big and bulky. And when played at maximum volume, they produce a “distorted” sound because the guitar signal is greatly amplified and therefore cut off. The great guitarist Jimi Hendrix was the first guitarist to recognize that the guitar and amplifier together can be used as an instrument and began using this distorted sound to produce music. This is how rock music was invented.
But tube amplifiers were unreliable, consumed a lot of power and were expensive. So electronics engineers began to develop circuits that produced the same effect as a fully driven tube amplifier, but were much smaller, effective, and reliable. This gave birth to distortion pedals with transistors .
Fig. 1: Distortion Pedal Prototype
Distortion pedals generally have three steps. The first stage is a buffer stage , which prevent signal loss due to impedance mismatch between the previous stage and the pedal. This can be a simple common collector transistor. The next stage is the amplification stage where the guitar signal is amplified. This is usually done using common source transistors or operational amplifiers. The third stage is the clipping stage which emulates the clipping of a fully driven tube amplifier. Clipping is done using diodes or mosfets. The final step of the course is tone control and output buffer stage which controls the frequencies of the output signal and helps prevent signal loss.
Depending on the type of electronic circuit used inside a pedal, distortion pedals can be of several types. For example, a distortion pedal for a bass and an electric guitar will have different tone control circuits, as the bass will operate at lower frequencies compared to an electric guitar. Additionally, different diodes will give different cuts and therefore different tones to the guitar signal.
Circuit Description
The schematic of a simple guitar distortion pedal is given in the circuit diagram tab. This circuit uses an operational amplifier instead of a transistor for amplification. Since operational amplifiers have very high input impedance, there is no need for a dedicated input buffer. Capacitor C2 is used as a low-pass filter to divert high frequencies to ground and therefore cut high-frequency noise. C3 is used for low frequency reduction. R5 in conjunction with C4 allows the gain and roll point to be adjusted and together with diodes etc. determine the “Character” of the pedal. C4 is very important for defining the “Character” of the distortion. Reducing it by half increases the roll point to 1440 Hz, decreases the gain and makes it more distorted IMHO. Doubling it reduces the roll off point to 360 Hz, increases gain and increases fuzz. Hence, it decides the tone of the pedal. R5 – defines the maximum gain when the Drive is at minimum resistance/maximum gain. In conjunction with C4, it sets the low-frequency cutoff point for the op-amp gain. This acts as two-stage distortion. At first the diodes will clip and when the drive is high enough the op amp will also start clipping.
R1, R2 and R3 are used to bias the input signal and R3 helps to improve the input impedance. R6 is a reverse log potentiometer. This changes the gain of the op amp and therefore makes the output signal more confusing. R8 is a log potentiometer that controls the volume of the pedal. It acts as a voltage divider, the further away the cleaner is, the greater the volume.
It is advisable to keep the circuit inside a metal container as this will reduce interference from the environment. Capacitor values can be adjusted to change the rotation of circuit frequencies and therefore change the tone of the pedal. Some popular distortion pedals include the Boss DD-1, Ibanez Tube Screamer, and Big Pi Muff. Furthermore, a bypass circuit must be used, otherwise the signal chain will be interrupted if the pedal is turned off.
Analog pedals are very expensive and are therefore being replaced by digital equivalents that use digital signal processing to produce the same effect. These digital units have a Digital Signal Processor that runs DSP algorithms to emulate analog effects. They are cheaper and can act as replacements for various pedals and are therefore popular.
Building it with your hands will cost less than $10, while buying it will cost more than $150.
So, if you are interested in DIY projects, do this and keep rocking!!.
Circuit diagrams
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