5 Power amplifiers
5.8 Volume control
It's a common misconception to believe the master volume control of the power section directly controls the output power from 0-100% when it is turned from minimum to maximum level. The volume control of a power amplifier really is an attenuator and thereby attenuates an obviously too high input signal. It gives you the possibility to turn down from maximum power. If the input level (from the preamp/signal processor) is too low, maximum power will not be achieved with the volume dial at maximum. This may give the impression of the amp not performing well. If the input level is very high, maximum output power is reached long before the master volume control is set to its maximum position. Turning up will then simply overload the amplifier, or trip its limiter, if it has one.
The volume dial controls output volume, but the scale on which it does this is dependent on the input signal level, not the scale marked on the dial. Many amplifiers have a scale in decibels, which is a relative scale 
, marked -∞ (minus infinity), which signifies "maximum attenuation", to 0 dB, which signifies "no attenuation". This is much more on par with how the volume dial really works.
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© Joris van den Heuvel 2001-2009