Amplification - The amplification chain

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An electric signal that is generated by an acoustic source, such as a signal issuing from a microphone, must be correctly amplified before it reaches the diffusers. The route the signal takes is called amplification chain and is illustrated in the following diagram:

Amplification - An amplification chain

An amplification chain

In this case a microphone transforms an acoustic signal into a very weak electric signal (a concept we will look at shortly), which enters a preamplifier. The latter's role is to bring the signal to a level which will allow it to be used and manipulated within a series of circuits, for example, the circuits present within a channel strip of a mixer (equalizers, compressors etc).

The electric signal coming from the microphone has a very low amplitude, which makes it difficult to handle. The preamplifier's role is to increase the signal's amplitude, in other words, increase its voltage [Electricity ] .

Amplification is calculated as the gain in dB resulting from the relationship between output and input voltage:

Equation 14.1. Voltage gain of an amplifier 

Voltage gain of an amplifier

For example, the average amplitude of a signal generated by an electrodynamic microphone is around 0.2 mV. After having passed through the preamplification stage, the amplitude goes up to 200 mV (these are indicative values to help us understand the action of the preamplifier on the signal). Once the signal has been manipulated, it is sent to the actual amplification stage. In this particular case, the amplitude already has the value we need, and all that's missing to the signal is the power to pilot the loudspeaker. That's why the final amplifier is a power amplifier, in that it increases the signal's power; this increase is measured as the gain in dB resulting from the relationship between output and input power:

Equation 14.2. Power gain of an amplifier 

Power gain of an amplifier

At this stage the signal has all the necessary features for controlling a loudspeaker.


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