Dynacord System Power Amp Xa 4000 - Manual (Page 6)

FRONT PANEL
This indicator lights when the power amplifier has been switched on. Causes for the
POWER-indicator not lighting are: the appliance is not connected to the mains
network or a defective primary fuse
The PROTECT LED lights indicating that one of the internal protection circuits
against thermal overload, short-circuit, Back-EMF, HF-occurrence at the output,
etc., has been activated. The output relays interrupt the connected load from the
power amps while input signals are interrupted as well, preventing the connected
loudspeaker systems and the power amplifier itself from being damaged.
Whatever caused the fault – e.g. a short-circuited speaker cable – needs to be
remedied. In case of thermal overload you have to wait until the power amplifier
automatically regains normal operation.
The SIGNAL LED lights as soon as an audio signal of approximately 30dB below full
modulation is present at the output. The LED is dimmed when speaker cables are
short-circuited or a protection circuit has been activated
The 0dB LED lights whenever the power amplifier is driven at its limits. Higher input
voltage does not result in higher peak output voltage. In addition, the 0dB indicator
comes in handy when adjusting external limiters.
This indicator lights as soon as one of the integrated dynamic audio signal limiters is
being activated and the power amplifier is driven at the clipping limit or generally at its
maximum capacity. Short-term blinking is not a problem, because the internal limiter
trims input levels of up to +21dBu down to a S/N-ratio of approximately 1%. If, on the
other hand, this LED lights constantly, reducing the volume is recommended to prevent
the loudspeaker systems connected from being damaged by probable overload.
Detent potentiometers scaled in dB for adjusting amplification
levels of SUB and TOP channels. To prevent distortion in
mixing consoles connected to the amp, setting these controls
to a value between 0dB and +6dB is generally recommended.
The dB-scale provides direct indication of the control
attenuation applied to the fixed internal amplification.
Use the POWER switch located on the front panel to power-on the appliance. The soft-start function
protects against current inrush peaks on the mains, which in addition prevents the mains line protection
switch from activating during power-on. The loudspeaker outputs are activated via relay switching with
a delay of approximately 3 seconds to efficiently attenuate eventual power-on noise. The PROTECT
LED lights during the delay time and the fans run at maximum speed. This is normal, confirming the
protection circuitry’s immaculate operation.
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