5 Power amplifiers
There's much more to a power amplifier than its power rating. On top of that, even a simple, basic specification such as power can be measured in many ways. Not every company will specify the maximum output power of their amps the same way. There are no laws that dictate how power should be measured. Some will specify max power at 1% THD, some at 10% THD (true for most car amps), some will measure short-term power, others will specify long-term burst power, etc. etc. There's no right or wrong, they're just ways to measure. Often companies that offer low budget equipment choose a method that boosts their figures. Reputable manufacturers will often tell the blunt truth, even if it makes their figures look less appealing than their cheaper competitors.
Below is a table with the most common specifications on power amplifiers, what they mean roughly and "good" and "bad" values.
|Sensitivity||dB||Input voltage needed to achieve full output power. Useful for level matching.||-||-|
|Noise||dB||Noise produced by the amplifier itself with master volume set to 0||-80dB||-50dB|
|SN ratio||dB||Signal to Noise ratio||100dB||60dB|
|THD||%||Total Harmonic Distortion; describes how much the output signal resembles the input signal||0.05%||0.25%|
|IMD||%||InterModulation Distortion; describes how large signals (low frequencies) influence smaller signals (higher frequencies)||0.05%||0.25%|
|Slewrate||V / μs||The maximum rate at which the output voltage is able to change||50 V / μs||20 V / μs|
|Channel separation||dB||Crosstalk between channels of a stereo amplifier||60 dB||30 dB|
|Voltage gain||dB||Input-to-output voltage gain with master volume at maximum||-||-|
|Power consumption||W||Mains power consumption. Typically an amplifier requires twice its output power from the mains when operating at full power.||1.5x output power||3x output power|
© Joris van den Heuvel 2001-2009