19
Chapter 6
Protection Features
Each Brüel& Kjær amplifier has many advanced protection features, protecting both the
amplifier and the speakers connected to it should a fault condition arise. Under normal use,
these features are inaudible. All protection circuits are independent.
6.1 Clip Limiter
The clip limiter is included to prevent dangerous, clipped signals reaching the speaker and
damaging it. When an amplifier is severely overdriven, its output waveform is clipped (its
peaks are squared off) – reducing the crest factor. In extreme cases, the waveform can
approach that of a square wave. An amplifier is normally capable of producing far more
power under these conditions than its normal, undistorted, rated-output power.
The limiter works by monitoring the output and comparing the distortion produced between
the input and output of the amplifier. If the distortion exceeds 1%THD for any reason
(voltage or current clipping), the limiter reduces the input signal proportionally. Note that, if
the signal is distorted or clipped before it reaches the amplifier, the clip limiter cannot detect
it and will not be activated.
Under normal operation the clip limiting is inaudible. The limiter can be turned ‘On’ or
‘Off’ by depressing or pressing the relevant clip-limit switch.
Some manufacturers of loudspeaker controllers do not recommend the use of clip limiters in
amplifiers as they tend to upset the tracking of the controller’s limiters.
Apart from this one exception, we recommend leaving the clip limiters switched ‘On’ (button
depressed).
(As a side-effect, once the amplifier comes out of a protect condition, the output level has a
slow rise time – the effect is like turning the gain up slowly.)
BE169212.book Page 19 Tuesday, January 23, 2007 9:00 AM
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