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CONTENTS
Front Indicators
The Clip/limit indicator tells when the amplifier output is clipping or limiting. It has two different indication statuses:
If the clip limiter is engaged it has a short time constant and it illuminates briefly.
If the clip limiter is not engaged it has an increased time constant and illuminates for a longer period.
The remaining yellow LEDs indicate if any protection circuits are activated. These are described on page 15.
9
PROTECTION FEATURES
Each Martin Audio amplifier has many advanced protection features, protecting both the amplifier and the
loudspeakers connected to it, should a fault condition arise. Under normal use these features are inaudible. All
protection circuits operate independently.
9.1
An output limiter is included to avoid amplifier clipping. 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 will not be activated.
Under normal operation the clip limiter is inaudible. The limiter can be turned "ON" or "OFF" by pressing the
relevant clip limit switch. See page 5
Some manufacturers of loudspeaker processors do not recommend the use of clip limiters in amplifiers, as it can
affect the tracking of the processor's limiters.
If the amplifier is being used without any external limiting, Martin Audio recommend leaving the clip limiters
switched "ON" (button depressed).
9.2
Thermal protection
When the amplifier is driven very hard into a low impedance load, the cooling fans will run at high speed. If these
operating conditions continue, the Protect indicator(s) will illuminate indicating that the amplifier is about to go into
thermal shutdown.
After five seconds the amplifier will go into thermal protect by muting the input signal. After 15-20 seconds the
amplifier will have cooled down enough for the amplifier to come out of shutdown and operate as normal. If the load
conditions remain unchanged the thermal protection will be re - initiated. Thermal protection occurs when the heat
sink temperature reaches 90
9.3
VHF protection
If a signal of more than 12kHz, at full power is detected for more than five seconds, the VHF protection mutes the
input signal. (This is indicated on the front panel (4) by the LED labeled Protect). After five seconds the outputs will
un-mute and return to normal operation, unless the output signal has remained unchanged, in which case the VHF
protection will re-initiate.
All material © 2007. Martin Audio Ltd. Subject to change without notice.
PRINT
PROTECT
CLIP
-40dB
ON
MA1.3s
PROTECT
CLIP
-40dB
ON
Output Limiter
0
C.
Martin Audio – MA1.3s Amplifier
13
GUIDES
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