It is easy to be baffled by the language which amplifier suppliers utilize in order to describe the performance of their products. I will clarify the meaning of a frequently utilized amp spec: "signal-to-noise ratio" to help you make an informed choice when getting a brand new amplifier.
When you have narrowed down your search by taking a look at a few basic criteria, such as the level of output wattage, the dimensions of the amp as well as the cost, you are going to still have quite a few models to choose from. Now it is time to take a look at a couple of the technical specifications in more detail. The signal-to-noise ratio is a fairly key specification and explains how much noise or hiss the amp makes.
You can do a simple comparison of the amp noise by short circuiting the amplifier input, setting the gain to maximum and listening to a speaker connected to the amp. You will hear some amount of hissing and/or hum coming from the loudspeaker. This noise is produced by the amp itself. After that compare several amps according to the next rule: the smaller the level of static, the better the noise performance of the amplifier. However, keep in mind that you must put all amplifiers to amplify by the same level in order to evaluate different amplifiers. To help you evaluate the noise performance, amplifier manufacturers show the signal-to-noise ratio in their amplifier specification sheets. Simply put, the larger the signal-to-noise ratio, the smaller the amount of noise the amp produces. There are a number of reasons why power amps will add some form of noise or other unwanted signal. Transistors and resistors that are part of every modern amplifier by nature create noise. The overall noise depends on how much hiss each component creates. Yet, the position of these components is also essential. Components which are part of the amplifier input stage are going to in general contribute most of the noise.
Many of modern amps are based on a digital switching architecture. They are referred to as "class-D" or "class-T" amplifiers. Switching amplifiers include a power stage which is constantly switched at a frequency of approximately 400 kHz. In consequence, the output signal of switching amplifiers exhibit a rather large amount of switching noise. This noise component, though, is generally inaudible as it is well above 20 kHz. Yet, it can still contribute to speaker distortion. Signal-to-noise ratio is typically only shown within the range of 20 Hz to 20 kHz. Thus, a lowpass filter is used while measuring switching amps in order to remove the switching noise.
Most recent power amps incorporate a power switching stage that switches at a frequency around 500 kHz. This switching frequency is also hiss that is part of the amplified signal. Yet, modern amp specifications typically only consider the noise between 20 Hz and 20 kHz. The signal-to-noise ratio is measured by feeding a 1 kHz test signal 60 dB underneath the full scale and measuring the noise floor of the amplifier. The gain of the amplifier is set such that the full output wattage of the amplifier can be realized. After that, the noise floor between 20 Hz and 20 kHz is calculated and the ratio to the full-scale signal calculated. The noise signal at other frequencies is eliminated via a bandpass filter during this measurement.
Time and again you will discover the expression "dBA" or "a-weighted" in your amplifier parameter sheet. A weighting is a technique of expressing the noise floor in a more subjective manner. In other words, this technique attempts to express how the noise is perceived by a person. Human hearing is most perceptive to signals around 1 kHz whereas signals under 50 Hz and above 14 kHz are hardly heard. Consequently an A-weighting filter is going to amplify the noise floor for frequencies which are easily perceived and suppress the noise floor at frequencies that are hardly heard. A lot of amplifiers are going to show a higher A-weighted signal-to-noise ratio than the un-weighted ratio.
When you have narrowed down your search by taking a look at a few basic criteria, such as the level of output wattage, the dimensions of the amp as well as the cost, you are going to still have quite a few models to choose from. Now it is time to take a look at a couple of the technical specifications in more detail. The signal-to-noise ratio is a fairly key specification and explains how much noise or hiss the amp makes.
You can do a simple comparison of the amp noise by short circuiting the amplifier input, setting the gain to maximum and listening to a speaker connected to the amp. You will hear some amount of hissing and/or hum coming from the loudspeaker. This noise is produced by the amp itself. After that compare several amps according to the next rule: the smaller the level of static, the better the noise performance of the amplifier. However, keep in mind that you must put all amplifiers to amplify by the same level in order to evaluate different amplifiers. To help you evaluate the noise performance, amplifier manufacturers show the signal-to-noise ratio in their amplifier specification sheets. Simply put, the larger the signal-to-noise ratio, the smaller the amount of noise the amp produces. There are a number of reasons why power amps will add some form of noise or other unwanted signal. Transistors and resistors that are part of every modern amplifier by nature create noise. The overall noise depends on how much hiss each component creates. Yet, the position of these components is also essential. Components which are part of the amplifier input stage are going to in general contribute most of the noise.
Many of modern amps are based on a digital switching architecture. They are referred to as "class-D" or "class-T" amplifiers. Switching amplifiers include a power stage which is constantly switched at a frequency of approximately 400 kHz. In consequence, the output signal of switching amplifiers exhibit a rather large amount of switching noise. This noise component, though, is generally inaudible as it is well above 20 kHz. Yet, it can still contribute to speaker distortion. Signal-to-noise ratio is typically only shown within the range of 20 Hz to 20 kHz. Thus, a lowpass filter is used while measuring switching amps in order to remove the switching noise.
Most recent power amps incorporate a power switching stage that switches at a frequency around 500 kHz. This switching frequency is also hiss that is part of the amplified signal. Yet, modern amp specifications typically only consider the noise between 20 Hz and 20 kHz. The signal-to-noise ratio is measured by feeding a 1 kHz test signal 60 dB underneath the full scale and measuring the noise floor of the amplifier. The gain of the amplifier is set such that the full output wattage of the amplifier can be realized. After that, the noise floor between 20 Hz and 20 kHz is calculated and the ratio to the full-scale signal calculated. The noise signal at other frequencies is eliminated via a bandpass filter during this measurement.
Time and again you will discover the expression "dBA" or "a-weighted" in your amplifier parameter sheet. A weighting is a technique of expressing the noise floor in a more subjective manner. In other words, this technique attempts to express how the noise is perceived by a person. Human hearing is most perceptive to signals around 1 kHz whereas signals under 50 Hz and above 14 kHz are hardly heard. Consequently an A-weighting filter is going to amplify the noise floor for frequencies which are easily perceived and suppress the noise floor at frequencies that are hardly heard. A lot of amplifiers are going to show a higher A-weighted signal-to-noise ratio than the un-weighted ratio.
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