It is easy to be puzzled by the terminology that amplifier producers utilize in order to explain the performance of their models. I am going to explain the meaning of one regularly used amp spec: "signal-to-noise ratio" in order to help you make an informed decision when buying a brand new amp.
After you have narrowed down your search by glancing at several basic criteria, like the level of output wattage, the size of the amp plus the price, you are going to still have quite a few products to choose from. Now it is time to take a look at some of the technical specs in more detail. One important parameter of power amps is the signal-to-noise ratio. To put it simply, the signal-to-noise ratio explains how much hum or hiss the amplifier will add to the audio signal. This ratio is typically shown in decibel or "db" for short.
Comparing the noise level of different amplifiers can be done rather easily. Simply collect a number of types which you want to compare and short circuit the inputs. Then put the amplifier volume to maximum and check the level of noise by listening to the loudspeaker. The noise that you hear is generated by the amp itself. Ensure that the volume of the amplifiers is set to the same amount. Otherwise you will not be able to objectively compare the amount of noise between different amplifiers. The general rule is: the smaller the amount of hiss that you hear the higher the noise performance.
If you prefer an amplifier with a small level of hissing, you can look at the signal-to-noise ratio number of the data sheet. The majority of producers will publish this number. Amps with a high signal-to-noise ratio are going to output a small level of noise. There are a number of reasons why power amps will add some form of hiss or other unwanted signal. Transistors and resistors which are part of every modern amplifier by nature generate noise. Since the amplifier overall noise performance is mostly determined by the performance of components situated at the amp input, producers will try to select low-noise elements while designing the amplifier input stage.
A lot of modern power amps incorporate a wattage switching stage which switches at a frequency around 500 kHz. This switching noise may cause some level of loudspeaker distortion but is typically not included in the the signal-to-noise ratio which merely considers noise in the range of 20 Hz and 20 kHz. Manufacturers measure the signal-to-noise ratio by setting the amp such that the full output swing can be achieved and by feeding a test tone to the amp that is usually 60 dB underneath the full scale of the amplifier. Then the noise-floor energy is measured in the frequency range between 20 Hz and 20 kHz and compared with the full scale signal energy.
Often the signal-to-noise ratio is shown in a more subjective manner as "dbA" or "A weighted". This technique tries to examine in how far the amplifier noise is perceived by human hearing which is most sensitive to signals at frequencies at 1 kHz. For that reason an A-weighting filter will amplify the noise floor for frequencies that are easily perceived and suppress the noise floor at frequencies which are barely perceived. The majority of amplifiers will show a higher A-weighted signal-to-noise ratio than the un-weighted ratio.
After you have narrowed down your search by glancing at several basic criteria, like the level of output wattage, the size of the amp plus the price, you are going to still have quite a few products to choose from. Now it is time to take a look at some of the technical specs in more detail. One important parameter of power amps is the signal-to-noise ratio. To put it simply, the signal-to-noise ratio explains how much hum or hiss the amplifier will add to the audio signal. This ratio is typically shown in decibel or "db" for short.
Comparing the noise level of different amplifiers can be done rather easily. Simply collect a number of types which you want to compare and short circuit the inputs. Then put the amplifier volume to maximum and check the level of noise by listening to the loudspeaker. The noise that you hear is generated by the amp itself. Ensure that the volume of the amplifiers is set to the same amount. Otherwise you will not be able to objectively compare the amount of noise between different amplifiers. The general rule is: the smaller the amount of hiss that you hear the higher the noise performance.
If you prefer an amplifier with a small level of hissing, you can look at the signal-to-noise ratio number of the data sheet. The majority of producers will publish this number. Amps with a high signal-to-noise ratio are going to output a small level of noise. There are a number of reasons why power amps will add some form of hiss or other unwanted signal. Transistors and resistors which are part of every modern amplifier by nature generate noise. Since the amplifier overall noise performance is mostly determined by the performance of components situated at the amp input, producers will try to select low-noise elements while designing the amplifier input stage.
A lot of modern power amps incorporate a wattage switching stage which switches at a frequency around 500 kHz. This switching noise may cause some level of loudspeaker distortion but is typically not included in the the signal-to-noise ratio which merely considers noise in the range of 20 Hz and 20 kHz. Manufacturers measure the signal-to-noise ratio by setting the amp such that the full output swing can be achieved and by feeding a test tone to the amp that is usually 60 dB underneath the full scale of the amplifier. Then the noise-floor energy is measured in the frequency range between 20 Hz and 20 kHz and compared with the full scale signal energy.
Often the signal-to-noise ratio is shown in a more subjective manner as "dbA" or "A weighted". This technique tries to examine in how far the amplifier noise is perceived by human hearing which is most sensitive to signals at frequencies at 1 kHz. For that reason an A-weighting filter will amplify the noise floor for frequencies that are easily perceived and suppress the noise floor at frequencies which are barely perceived. The majority of amplifiers will show a higher A-weighted signal-to-noise ratio than the un-weighted ratio.
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