Slew Rate

The “slew rate” is an interesting factor that is sometimes listed on the specification sheet. It is stated in Volts per microsecond or V/microsec., and refers to how fast the voltage rises from 0 to maximum power. The slew rate is measured by using a square wave and calculating the number of volts that the square wave rises vertically on the Y axis, over the amount of time it takes for this voltage rise to occur, on the X axis. If the slew rate is high, the sound will tend to be “crisp” with a bit of “edge” to it, while a low slew rate gives a sound that has less of these characteristics to it. Tube amplifiers usually have low slew rates (except for the Class A single ended triode amplifier, which is very fast). This may be one of the reasons tube amplifiers have a characteristic soft edged quality about them. Solid state amplifiers, on the other hand, often have very high slew rates, and this may contribute to the sharp edged sound that they can have. However, the precise effects of the slew rate on sound quality are difficult to define. The term just seems to be one of those things that appear on specification sheets, and makes an interesting topic for discussion.