What is the Difference between an Amplifier and Pre-amplifier?

What is the Difference between an Amplifier and Pre-amplifier?


DPA-90B Mixer Amplifier

DPA-90B Mixer Amplifier

Audio amplifiers are found in home stereos and hifi systems as well as in commercial audio systems like PA systems, recording studios and club DJ sound systems. Television also makes use of different types of amplifiers which are integrated with the antenna. Signal boosters are also available for cellphone networks for both home use and commercial installations. In audio systems, the amplifier is used to boost the input audio signal from different sources such as studio recordings (instrument, equalizer, mixer, sound effects, tone and vocal inputs), microphone, turntables, record, CD, cassette and digital audio players.

The audio amplifier increases the amplitude of the input sound waves, thereby giving the signals enough strength to energize or activate the speakers. Amplified sound waves have more life and intensity in them which allows them to be perceptible, heard clearly and enjoyed by the listener. Think of amplified signals as food with seasoning or bread with butter spread. Seasoning and spread enhances the taste, otherwise you wouldn’t enjoy the food.

Input signals are weak due to distortion, dispersion and relatively low energy levels. In Physics, the energy of a wave (K) depends on its amplitude and frequency according to the formula K=1/4(µA²w²λ), where A=amplitude, w=angular frequency, λ=wavelength and µ=constant linear density.

The proportional relationship between the Energy (K) and Amplitude (A) is shown below:

K ~ A²

The proportional relationship between the Energy (K) and Angular Frequency (w) is shown below:

K ~ w²

Amplifiers make use of this relationship to increase the energy of a sound wave. That is increasing its amplitude.

The wave energy can also be expressed in terms of power (P), which is the rate of transfer of energy:

P = ½*µ*w²*A²*v, where µ = constant linear density, w = angular frequency, A = amplitude, and v= wave propagation velocity.

Basically, a low-energy wave has a smaller amplitude, whereas a high-energy wave has a higher amplitude. The former is weaker and quieter whereas the later is stronger and louder.

So what is the difference between a Preamp and Amplifier?

Think of a preamp as a weak signal booster and the amp as an enhancer, refiner and producer of high quality sound.

A lot of audio amplifiers in the market have a two-stage signal processing system consisting of pre-amplifier and amplifier. These two components are inbuilt within the device, so you won’t need a separate pre-amplifier. The pre-amplifier is highly sensitive, designed to pick up weak audio signals from a microphone. It amplifies the microphone audio input by as much as 1000 times, bringing the audio to line-levels which can then be transmitted to the final or end amplifier which boosts the signals further, enhancing them for speaker reception and activation as well as audio appeal for listeners.

In recording studios, PA systems and other high level commercial systems, pre-amplifiers are rarely used because mixers can perform the pre-amplification role quite well. Standalone preamplifiers are another option if your amplifier doesn’t have one integrated, but it’s very to find these in use or being sold in the market. The advantage of a separate preamplifier is that it is free from the amplifier, therefore it is not affected by internal noise caused by the power amplifier. However, the disadvantage of a separate device is the matching difficulties and compatibility issues between the two connections, making it difficult to achieve the required synergy for optimum performance.

Some home stereo and hi-fi systems including TV have inbuilt amplifiers which power the speakers. However, standalone amplifiers can be purchased and connected to the speakers. It’s very important to know that a weak signal from a microphone and other inputs (e.g. turntable, record, CD, cassette or digital player) will be amplified by a different amount depending on the type of amplifier. Class A amplifiers are the best and commercial systems will produce more powerful outputs than home systems. There is a huge different between a club and home stereo amp. The former is more powerful.

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