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Amplifier Buying Guide |
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Every discerning music lover knows the difference between good and bad quality sound. When it comes to expectations from our listening experience with regards to music, we like it to be memorable and of crystal clear quality. An amplifier is one such device that enhances the listening experience by helping to provide crystal clear music. So, how does an amplifier provide for enhanced listening experience? An amplifier changes the amplitude of an audio signal. Simply put, it has the job of taking a waveform (an audio signal) and increasing the amplitude of the signal without changing (distorting) the waveform in any other way. What this means is that the amplifier receives a weak signal and boosts it to a required level to drive a speaker. This lets you hear the weak notes of your music more clearly. |
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Type | Power | Impedance | Input - Output | Amplifier Response Bandwidth | Crossover | Signal to Noise | Distortion
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1 - Introduction:
So an amplifier is acts as an interface between your audio system and speakers. It is not a device that can make a bad speaker give good quality output; on the other hand it requires speakers that are capable of handling the sound levels that it amplifies!
So if you intend to buy an amplifier, what are the key aspects that you should be observant of?
1.2 - How it works:
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The term amplitude indicates the loudness of the sound. Amplifiers increase the amplitude of the input signal without distorting it. Any form of distortion (e.g. Clipping) of the input signal would result in deterioration of sound quality.
The amplifier takes Alternating Current (AC), and stores this in large amounts as Direct Current (DC) in capacitors (charge storing devices). It then uses the input signal (the musical signal output from the preamp) to modulate (control) the release of the electrical energy stored in the capacitors. |
This energy released from the capacitors is passed though the output stage, from where the speakers receive the amplified form of the input signal.
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2 - Factors to consider when buying amplifiers
2.1 - Type
There are two types of amplifiers; Stereo Amplifiers and Surround Amplifiers. A Stereo Amplifier is a two channel (Left and Right) amplifier. Surround Amplifiers generally process 6 channels (Left, Right, Left surround, Right Surround, Center and Subwoofer). Surround amplifiers use decoders to decode surround sound formats. Dolby Digital Ô and DTS Ô are the most common surround sound formats. The amplifier should have the decoders for the format of the surround sound signal being amplified.
2.2 - Power
The volume output of the amplifiers is correlated to power output. So does this mean that an increase in power output translates into a proportionate increase in volume? Not exactly! Though one can get an idea of the volume output from the power output, they do not have a linear relationship. The volume and power output bears a logarithmic relationship. To put things in perspective, to get double the volume one needs to increase the power output up to ten times. This information can be used to compare the power outputs from amplifiers and gauge the difference it would make in the volume of the output. Power output in the range of 125 to 250 watts is considered sufficient to meet the volume requirements of most home users. In this range you can get big bass sound; enough to rock the house!
2.3 - Impedance
Impedance as mentioned in the specifications of the amplifier refers to output impedance. What is output impedance? What bearing does it have on the performance of the amplifier? In simple terms, impedance is the resistance to the flow of current. A speaker with low impedance draws more current making it difficult for the amplifier to drive it. When impedance for an amplifier is specified as 8 ohms (the impedance of most home speakers) it means that the amplifier is made to perform at that level of output impedance. Automotive speaker amplifiers have output impedance in the range of 4 to 6 ohms. If your speaker has lower impedance than the one specified for the amplifier, flow of large amount of current from the amplifier could damage the amplifier.
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The number of inputs and outputs determine the number of speakers that can connect to your amplifier.
2.5 - Amplifier response bandwidth
The amplifier response bandwidth is a measure of how "wide" a set of frequencies an amplifier will pass. It is indicated, as a range of frequencies. e.g. 20 Hz to 20,000 Hz. This means that the system amplifies all frequencies within this range. 'Good frequency response' therefore does not guarantee a specific fidelity, but only indicates that a piece of equipment meets the basic frequency response requirements.
2.6 - Crossovers
In-built crossovers are often used to keep high-frequencies from reaching a subwoofer. A low-pass crossover allows only frequencies below the crossover point to be amplified. A high-pass crossover allows only frequencies above the crossover point to be amplified. This proves useful in keeping low bass away from small speakers, enabling them to play more efficiently. Crossovers can be active or passive. Active crossovers detect and filter the frequency bands in the low level signal before they reach the amplifiers. This saves your amps from doing unnecessary work, making your system more efficient. Passive crossovers on the other hand, block certain frequencies from reaching the speaker after amplification. Though relatively inexpensive and easy to install, they are not as efficient as active crossovers.
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2.7 - Signal to noise ratio
This measurement compares the strength of the desired signal (music) to the level of background noise. A higher value indicates lesser background noise. An amplifier with signal to noise ratio of 90 dB is considered to be of good quality.
2.8 - Distortion
Output from an amplifier must be free from distortion. Distorted output from an amplifier can ruin your listening experience. An amplifier that distorts sound at high volume can be un-listenable. Distortion is expressed in terms of THD (Total Harmonic Distortion). It is generally accepted that 1 percent THD is the maximum acceptable distortion for high-fidelity sound reproduction. However, there are users who consider even a THD level of 0.5% to be unacceptable.
Though the aspects discussed above can help you in selecting a “good” quality amplifier, the ideal way to select an amplifier would be to try out the amplifier at your place and listen to a wide range of music to gauge if the amplifier measures up to your performance expectations.
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