Microphone preamplifiers

Usually, all microphones are active - i.e. come with a preamplifier built-in. The only exception is ribbon microphones, which require a specific external preamplifier stage.
As a rule of thumb, when we choose a microphone, we should always evaluate which technology is used in the preamplifier stage. This is because we need a high quality input before the signal is digitalized. If we work with a faulty input, there is little left to do, to improve it later on.
There are three main technologies used in microphone preamplifiers: Transistors, JFETs, and valves (tubes). The first two are solid state, while the third is analogical.
As the microphone itself is analogical, it has little sense to use a non analogical stage before the signal is digitalized. The main reason is that solid state solutions tend to amplify only the dissonant harmonics - especially when the microphone is saturated. This causes the recording to become rich in highs, metallic, squeaky, distorted. Conversely, analogical solutions amplify only the consonant harmonics, making the recording round, smooth, creamy. Even when the signal is saturated, it comes out nice.
Transistors are current controlled and can easily distort the signal. JFETs tend to imitate valves, as they are voltage controlled. However, they are always solid state. Valves also have a high resistance. In order to pass as a flow of electrons in a vacuum tube, the signal has to win a lot of resistance and only the good and strong frequencies can go through. Therefore, valves somewhat clean the signal, make it focused, and confer to it their distinct valve sound.
If we choose a condenser microphone, it is a very good idea to select one with a tube preamplifier, as it will be the best sounding.
Preamplifiers for ribbon microphones are usually made with JFETs. Differently from all other types of microphones, which have a very low inductance and can be directly connected to any subsequent stage, they have a high impedance and a very low signal. Thus, not only the signal must be amplified, but also the impedance must be converted from high to low. Therefore, it becomes easier to do this conversion with JFET technology, with the result of having an exceptionally silent preamplifier stage.
The following schematic compares a JFET versus a triode generic preamplifier.
JFET vs Triode Preamplifier
Copyright © 2017-2022 musicsecrets.euniversity.pub. All Rights Reserved.