Martin Audio M3 User Manual page 9

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CONTENTS
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The system-specific plug-in top cards provide the necessary channel gain
or attenuation to provide approximate system balance when the level
control is in the 0dB position. This assumes the use of amplifiers with
identical gains. Plus and minus 3dB's of gain or attenuation is available on
outputs 1 and 3 to adjust the balance of the system with respect to
channels 2 and 4 which have a nominal output level of 0dB.
Please note the M3 controller will always be shipped with the level control
set in the 0dB position. The screwdriver 'slot' in the end of the spindle is
un-calibrated and does not correspond to the front panel markings.
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Each M3 output has an associated limiter, which provides momentary gain
reduction when the output signal level exceeds a pre-set threshold value.
A red LED indicates the onset of limiting. Threshold settings for the limiters
may be adjusted by first disconnecting the power to the M3, then
removing the top cover (two screws on each side). The plug-in top card
must then be un-clipped from the four locating pillars and swung up on it's
ribbon cable to reveal the four banks of selector pins J11, J12 J13, and
J14. Threshold values corresponding to the jumper link positions are
printed on the lid of the controller and duplicated in Section 6.
Each output channel limiter sets a maximum voltage level from the M3,
which in turn sets the maximum continuous voltage that the amplifier can
present to the loudspeaker.
The limiters in the M3 may be used to control the average continuous
power applied to the loudspeakers, if power amplifiers with a higher
maximum power rating than that recommended are used. (See Amplifier
section). Alternatively, if the loudspeakers selected will handle the full rated
power, or if maximum system headroom is required, the limiters may be set
to prevent the amplifiers being driven into hard clipping.
WARNING. Care should be taken to avoid amplifier clipping. It is important
to understand that a low power amplifier driven into clipping is more likely
to damage a loudspeaker than a higher power amplifier used within its
ratings. This is because music signals have a high peak to average "crest"
factor. 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 power output. Correct setting of the limiters will
automatically avoid amplifier clipping and prevent damage occurring to the
loudspeakers.
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LEVELS
LIMITERS
Martin Audio – M3 System Controller
9
GUIDES