A valve amplifier at high volume begins to distort in a typical way: the sound becomes rich and warm thanks to the preponderance of harmony. It's a pleasant sounding distorsion.
Transistor amplifiers, on the other hand tend to produce distorsion in mostly uneven harmonies, which causes an unpleasant sound, that is contrasted by the surrender of high fidelity that these amplifiers have at lower volume. Most electric guitarists prefer the harmonic wealth of the valve amplifier.
The request for valve type sounds is always present, plus the solid-state instruments are manageable, robust and generally easier to transport. Many manufacturers have therefore began combining the qualities of both types of circuits. Some hybrids use both valve and transistor stages, furnishing a certain variety of sounds. However, modern technology has brought some truly amazing results, where some forms of valve simulation of certain models are so impressive, it is difficult to differentiate.
Valve amplifiers require a few minutes to warm up before reaching a temperature suitable for operation. The valve, in fact, is not able to function until the filament has overheated the cathode to the point that the electrons are emitted from the surface under applied tension.
The stand-by button, found on almost all valve amplifiers, interrupts the high voltage of the valve, but leaves the mechanism of heating at low voltage. This allows the amplifier to stay warm, ready for immediate use.
Transistor amplifiers respond immediately and don't require any warm-up. The initial extra-current, produced by the circuit that loads the condensors and establishes the operating voltage, however causes a sudden noise in the speakers. Its not only annoying, but can also be dangerous for the cones, especially in high power amplifiers. But now in many amplifiers there is an automatic circuit that interupts the power to the loudspeakers for a few seconds.
The proper loudspeakers for the amplifier
Valve amplifiers must perfectly fit the resistance of the loudspeakers, which can be 4, 8 or 16 ohm. They must never be turned on if they are not connected to the loudspeakers. This can cause serious damage to the transformer or the valves.
Transistor amplifiers are in this sense more robust; most models of a certain level are practically immune to short circuiting.
In general, the lower the resistance of the loudspeakers, the higher the maximum exit volume. Speakers with higher resistance have a lower exit volume, but perhaps also a lower distorsion level. If there is no stand-by button on the amplifier, as a precaution it is best to set the volume to zero before turning it on. Do the same for transistor amplifiers.
The sound quality and the volume of a diffuser depends on three factors: its efficiency, the size and its use in combination with other diffusers. The efficiency, the amount of energy produced by the amplifier turned into sound, determines the volume that can be obtained from the amplifier. Very efficient diffusers (i.e. trumpet) can produce more volume from a 50 watt amplifier than from a 100 watts using less efficient diffusers. The size of the diffuser, and above all the cones, is closely related to the reproduction of the sound: the larger they are, the better they reproduce the low frequencies, which requires the displacement of large volumes of air. Similar loudspeakers can be used in multiple combinations to obtain a better overall volume.
The pick-up and the microphone convert the electric signal into acoustic energy; The loudspeaker (or electrical acoustic transducer) then converts this energy into sound. A signal coming from the amplifier is sent to a '' mobile spool '' wound around the neck of the cone and sent to the middle of the poles of a fixed magnet on the loudspeaker. When a signal crosses the spool, a varying magnetic flow is produced that interacts with the magnetic field.
When the mobile spool increases, the signal is "pushed" by the magnet, moving the diaphragm forward. When it decreases, the opposite happens. The forward and backward movement of the diaphragm vibrates the cone. The amount of movement is limited, and if the loudspeaker exceeds that limit, the cone could get damaged and detach itself from the suspension. Since the sound expands immediately from the source (the high frequencies are more directional than the low ones), you will discover that the mounting of the speaker on the front of the panel will give considerably different results than that on the back of the panel.
The speaker cabinet has an important role in the reproduction of the sound.
When the air is compressed in front of the cone it moves forward.
The opposite happens when the cone moves backward. If the air in front of the cone quickly reaches the back, the pressure difference is cancelled and there is a loss of volume. The pressures between the front and back are therefore out of phase.
The function of the speaker and its cabinet is to prevent or reduce this phase cancellation.
The cabinet "loads" the cone in order to optimize it with the surrounding air. Ideally, the sound should have no additional resonance from the speaker cabinet.
The construction of the cabinet must be of thick and heavy material in order to reduce the vibrations of the walls. Absorbent materials, such as the heavy felt, are often used to cover the inside surfaces to reflect any sound and return it to the diaphragm or cause "stationary waves". Sometimes absorbent material is added to the cabinet to dampen this return.
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