9
What does the Clipping Indicator Do?
Next is the clipping indicator, a frosted red LED that lights up every time the amp clips.
“Clipping” is what happens when the signal tries to get bigger than the power supply
voltage, which it can’t, and the peaks in the signal get “clipped” off. The result is a
miserable crackling sound.
But in the case of the AirHead, the clipping indicator not only tells you when you’ve got
a hot signal, it also tells you when your batteries are low. Because we’re using multi-
voltage “rail-to-rail” interated circuit chips, the AirHead will run on a wide range of
voltages. And because “normal listening level” will vary widely due to the varying im-
pedances of headphones on the market, we can’t really estimate how long the AirHead
“should” run on a set of batteries. (The battery voltage may lower to clipping after 20
hours of use with a difficult-to-drive pair of AKGs, but you might get 60 or more hours
of use at a comfortable listening level when driving a pair of efficient Grados.) We
realized that a clipping indicator on the ever-diminishing voltage of a set of batteries
would be the best low battery indicator of all. For a given volume level at your head-
phones, the battery voltage will eventually get lower than the signal, and the clipping
indicator will start to blink with the louder bits of the music. If the clipping indicator
starts blinking more and more at your normal listening volume, it’s a sign that your
batteries are on their way out and need to be changed soon.
An example of the input signal, and the output signal clipping.
