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Guitar Tone and Distortion


The Electric Guitar is characterised by long thin steel strings attached to an almost completely non-resonant body, with a transducer system that has minimal effect on the string vibration and is used to provide an electrical facsimile of the string vibration. Such a system when played through a high performance low distortion amplifier produces a delicate sound with a large initial transient and considerable high harmonics. Plucking a string more heavily tends to produce more volume but with little change in harmonic structure. It has much in common with the Harpsichord, also a plucked instrument with thin steel strings, and like the Harpsichord struggles when used up against other instruments. The Harpsichord was superceded by the Piano which among other things is characterised by having thick strings under high tension on a heavy frame. This type of development is not available to the electric guitar. It must remain within the capabilities of the human hand for its operation, where if anything the demands of modern playing have meant that strings have got thinner.


The inspiration for the modern electric guitar tone is more in line with the characteristic of the Saxophone. Here we have an instrument with considerable power in the lower harmonics and very little in the way of initial transient. In addition when blown heavily the Saxophone is capable of considerable thickening of the middle harmonics due to distortion added by non linear movement of the reed. The electric guitar does not naturally produce a noticeable thickening of harmonics when plucked with more force, but there are two ways of achieving this, by saturation or clipping of the signal in the Pickup or in the Amplifier. This process also has the desirable effect of reducing the initial transient. Amplifier clipping initially came about because of normal short comings rather than intentional design, but was eventually recognised as an integral and desirable characteristic of an amplifier intended for guitar amplification.


The aim of the GP4 Guitar Amplifier distortion generation is to reduce but not eliminate the initial transient, to thicken the lower harmonics and increase the sustain. By carefully controlling the onset of distortion new capabilities of expressiveness become possible. Unlike traditional amplifiers the distortion is available at all operating levels. Due to the peculiarities of human hearing our ability to hear extreme bass and treble frequencies at low listening levels is less than at high levels. Thus an amplifier set up for moderate room levels will be perceived as having too much treble and bass when operated at higher levels for a larger environment. This means that the treble, mid and bass controls cannot be used to control the distortion and are placed after distortion generation. The guitar source signal has considerable effect on the distortion tone. In general we want moderate upper middle harmonics and not too much bass. This means that it is necessary to have control of the bass and treble response in front of the distortion generation to cope with the wide range of signals from humbucker to single coil pickups from bridge position to neck position.


The GP4 Guitar Amplifier has the following controls operating in front of the distortion generation. These give a wide choice of distortion characteristic as well as a very useful way of dealing with the wide tonal characteristics of single coil and humbucker pickups.


1. Treble and Bass cut filters.

2. Presence Control that can be set to operate over a wide range of frequencies from 100 Hz up to 4 KHz.

3. Compressor to control the depth of distortion. Set a 2:1 compression with a Threshold at or just above the point at which distortion commences and then adjust the Gain for the overall level of distortion. The general characteristic of compression in front of distortion is to give a very fluid sound with a singing quality, together with a reduction in inter-modulation distortion that works well with chords.