Loudspeaker Efficiency and Amplifier Loudness

Guitar Tone and Distortion

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Dealing with Hum and Noise

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Removing guitar control knobs

Hardman Guitar Amplifiers

Dealing with hum and noise

Hum and noise can be a problem for the electric guitar player. It doesn’t help that the guitar itself is quite a good antenna for a number of sources of interference. There are two forms of radiation that the guitar easily picks up. 1) Magnetic - the most common source here is mains transformers, 2) Electrostatic - a common source here is fluorescent lamps. The solution to (1) is simply keep well away from equipment with mains transformers and to use equipment fitted with high quality components. The  GP4 Amplifier uses a toroid transformer that produces a low external field. The solution to (2) is to ensure that the guitar internal screening is intact and to use a high quality guitar lead. Not all leads are equal. The best quality leads have superior screening as well as reduced capacitance, this will give reduced background noise as well as improved tone.
The next most common problem is hum loops. These occur when two pieces of mains powered equipment are connected causing a mains hum to appear superimposed on the signal. The most likely cause is that one of the pieces of equipment is letting current spikes from its power supply circuits get into the audio signal path. With good design practise this should not happen. What can be done? The first is to always use first class designed equipment. The GP4 Amplifier has the grounds of all inputs and outputs connected directly to its’ substantial 2 mm thick aluminium chassis. This minimises the influence of external currents associated with mains grounding. This technique together with advanced circuitry internally prevents power supply noise getting into external signal paths. The next thing is to use balanced inputs and outputs where possible, the GP4 Amplifier has an XLR output for this purpose. Finally, an in-line audio isolation transformer could be used so that there is no direct conduction between units.