【 Weak current College 】 microphone amplifier

In the microphone and preamplifier application areas, the "impedance matching (ImpedanceMatching)" is a widely misunderstood topic exists. Due to the fact that most of the microphone and the vast majority of preamplifiers, each other to form a relatively satisfactory, no need for the so-called "true" for the impedance matching. As for the "impedance matching" problem, only in the pursuit of a specific try sound, tone, color (coloration) and features will only be meaningful.

In explaining the problem, we'll explain what is impedance. We know that any microphone inevitable have output impedance, while any preceding words are inevitable zone has input impedance. The "impedance" referring to the signal current in the circuit, from microphone preamplifier circuit flow of the "resistance".

Due to impedance generally use the "Z" to indicate, therefore, produces specifically designed to describe input and output interface terminology — "Hi-Z (high impedance)" (guitarist should be more familiar with this terminology). In practice, preceding words input impedance on the input signal sound effects have a significant impact. This is mainly because the microphone's output impedance and preceding words input impedance to the interaction between the relationship of mutual influence, will give a sound signal major changes brought about by the final effect, such as different sound Equalizer effect, different features, and more on impulse. Further stresses that different front words input impedance with a different microphone input impedance interaction in the manner and extent is not the same.

Next, we will use the garden watering with piping and pipes with nozzle in front to an analogy. Microphone like pipes, belong to the low impedance source, that is, the resistance of the water flow along; but a smaller predecessor words you like nozzle, the impedance is high. First of all, if we switch off the nozzles of the valve, input resistance (preceding wordsinput impedance) will increase dramatically, water pressure (voltage) also gave rise to the maximum, then the flow of traffic in the nozzle (current) becomes 0.

Next, if we give a little bit of the valve open, input resistance and water flow pressure correspondingly smaller (although still very big), water began to appear, however, at this point the nozzle will issue "hissing" sound (high frequency). Later, as the nozzle valve continues to turn up, enter the starting resistance and water pressure, declining water flow also began increasing, this time, "hissing" sound starts to fade away. In this example, we can see that the impedance of the preceding words, sound signal lower-frequency part becomes less obvious.

Actual operation, the microphone and predecessor words of impedance setting on the same level of practice is totally wrong, because this will sound signal level and signal to noise ratio while reducing 6dB. In General, for dynamic microphone and capacitor microphone, the preceding words best input impedance should microphone output impedance of 10 times. But for now the market emerging input impedance can be adjusted by the preceding words (such as FocusriteISA428, Summit2BA-221, etc.), these standards can be modified. Because the preceding words of transformer voltage and its interaction with the microphone impedance level can be adjusted to the front I mentioned balance effect, produce all kinds of microphones/front words "stain" effect.

The preceding words maximum advantage is that, in the sound recording, no need to add in the signal path, you can achieve the equalizer frequency content freely and adjustment, so as to avoid signal path in device too much and may cause noise increase, signal attenuation. In addition, when using this amplifier, except in accordance with the above mentioned 10: 1 to adjust the input impedance, you can not damage the equipment, as needed, set the input impedance of the test several times until you find themselves satisfied with the sound effects.