Electric Guitar Distortion: Vacuum Tubes Sound Better than Transistors by Julia Janczak

Distortion is an intentional modification of the sound produced by an electric guitar. It is used by musicians in many genres of music: pop, rock, heavy metal, punk, jazz... A popular tune played on the electric guitar without distortion sounds like this: The same tune played with distortion sounds like this: Distortion is produced by an amplifier, which may use tubes or transistors. Many musicians prefer the sound of tube distortion to transistor distortion.

Distortion Flattens Waves to Create Harmonics t A Sound waves from guitars are composed of many higher frequency waves called harmonics. Flattening the wave creates more harmonics. For Example: The Fourier series for a pure sine wave has just one term. The Fourier series for a flattened sine wave has higher order terms. higher order terms = more harmonics many harmonics = distortion sound Example guitar wave Sine wave versus flattened sine wave

Tube Amplification 1. Sound waves from the guitar are translated into an electronic signal. 2. The heated cathode releases electrons into the vacuum. 3. A charged grid controls the flow of electrons to the anode. 4. The charge on the grid is determined by the signal from the guitar. The signal can only be amplified up to the maximum voltage supplied to the tube. glass envelope anode grid cathode

Transistor Amplification 1. N-type and P-type semiconductors are stacked together. 2. Excess electrons move into the base semiconductor. 3. The semiconductors become insulators. 4. Signals from the guitar produce a voltage at the base. 5. Electrons are sucked out of the base, restoring conductivity. 6. Current flows through the transistor. The signal can only be amplified to the maximum voltage supplied to the transistor speaker guitar base emitter collector

Overdriven Tubes Produce Gradual Distortion Overdrive occurs when the tube is asked to amplify a signal beyond the maximum voltage. The top of the wave will be flattened, producing distortion. The transfer function shows that flattening occurs gradually. The tops of waves are compressed Transfer Function for Tubes Ouput Amp. Input Amp. Sine WaveTube-distorted Sine Wave Distortion Starts

Overdriven Transistors Produce Abrupt Distortion A transistor also flattens the top of a wave when overdriven. The transfer function shows that the flattening happens abruptly. The tops of waves are clipped The distorted wave has corners. Transfer Function for Transistors Sine Wave Output Amp. Input Amp. Transistor-distorted Sine Wave Distortion occurs

Tube Distorted Waves Sound Better Waves with corners contain more harmonics than rounder waves. Most listeners think too many harmonics sound unmusical. Clipping the tops off waves removes some small oscillations. This discards information about the natural sound of the guitar. Tube distortion compresses wave peaks without discarding any information.

Sample guitar chord Transistor-like Distortion Tube-like Distortion

Transistors and tubes produce distortion when they are forced to amplify a signal beyond their limits. Transistor distortion clips waves off sharply, producing more harmonics and discarding small oscillations in the peaks. Tubes compress the tops of distorted waves smoothly, preserving details in the peaks. Many electric guitarist prefer distortion produced by tubes to distortion produced by transistors.