The preamplifier

Besides the microphone, the preamplifier is another fundamental element in the pick-up chain.

Preamplifier selection

We have already considered above what concerns the choice of a pre (or microphone) type valvular compared to one at solid state.

A high-quality preamplifier, while not having the same impact as the microphone, is also an important element in determining the sound quality of a vocal recording, in terms of:

impedance matching

each microphone requires a specific load impedance from the preamplifier, these values can be found in the data sheet of the microphone and the preamplifier itself; perfect coupling ensures that the performance of the microphone is very close to that desired by the designer; deviating from the right values changes the sound, creating the preponderance or deficiency of the middle register; to manage versatility in coupling, some preamplifiers are equipped with a load impedance selector

alchemical coupling

Unfortunately, there are no rules in this respect, but it is necessary to experiment. For example, I could mention the coupling between the Neumann U87 and the UAD tube preamplifier, or between the same microphone and the Neve preamplifiers, or between the latter preamplifier and the Rode K2 tube microphone.

tonal coherence and dynamics

a good preamplifier should guarantee constant tonal and dynamic performance at the various gain levels; lower-level preamplifiers, on the other hand, offer a relatively narrow range of quality in which they can express the best of their characteristics with good consistency

background noise

By now, all modern preamplifiers, with the exception of some very inexpensive models or some of the valve type, guarantee a very good signal-to-noise ratio, which is excellent for using high gain levels without creating too high an incidence of background noise

transient speed

the rapid and precise transient response is an element that distinguishes a high-level preamplifier from a more modest one; in particular, should a transient peak rise be very large and fast (especially if localised in low frequencies), it would put the preamplifier to the test; fortunately, voice does not have extremely rapid transients, nor particularly low frequencies; it follows that this characteristic is not basic for a preamplifier intended for vocal use; however, a good transient response is necessary in this case as well

loyalty

fidelity of a preamplifier is defined as the ability to amplify the signal coming from the microphone without substantially altering its tonal and dynamic balance and without inserting any harmonic distortion

transparency

there are actually preamplifiers defined transparent distinguished from others defined colourfuland all the ways in between; what is the difference? Here it is:

• a particularly transparent preamplifier will tend to express maximum fidelity up to values very close to those of clipping; harmonic saturation will tend to be expressed only in the last few db close to clipping - it is particularly suitable for acoustic sources in "purist" musical genres, such as classical music and in any case in which extreme fidelity and cleanness are required; it is also always preferable for crystal-clear sources such as drum cymbals, the triangle, wind instruments of high extension with a sound close to sinusoidal (such as the flute and piccolo)
• a particularly colourful preamplifier will tend to express a little harmonic saturation even at gain values relatively far from clipping; it will also tend to give the sound a slightly different colour from that generated by the microphone, both tonally and dynamically; this type of preamplifier is often preferred in modern, gritty genres such as rock, pop, funky, dance, especially with regard to drums, bass, electric guitars and synthesisers

for vocals, the preamplifier should be chosen according to the characteristics and character of the voice and musical genre, taking into account the fact that, at medium gain levels, even a coloured preamplifier is almost free of harmonic saturation

harmonic richness

by harmonic richness of a preamplifier is meant:

1. the ability to retain the original one sent by the microphone (in this case better defined by the concept of 'fidelity')
2. the ability to create new quality harmonics by means of harmonic saturation

harmonic saturation

means the ability of a preamplifier to generate, at high gain values (typically in the high end of headroom), good quality harmonic saturation, which can result in timbral enrichment rather than unpleasant distortion; saturation is not always well accepted, especially in purist genres such as classical music and others where extreme clarity of the audio programme is required; in other musical genres, however, it can often be very pleasant, capable as it is of warming and enriching an otherwise thin and cold sound

clipping resistance

Finally, a high-quality preamplifier will be able to deliver a very powerful signal before clipping, causing the latter to assume values of 22 db or more (up to 26 db, in certain cases) above the 0db reference

Two examples of preamplifiers: above, a modern, inexpensive model from Behringer; below, the stereo preamplifier version from Neve, a legendary brand, manufacturer of top-quality preamplifiers.