Adcom GFA-555MS - Manual (Page 16)

INSTANTANEOUS DISTORTION ALERT LEDs
The INSTANTANEOUS DISTORTION ALERT circuit is a unique ADCOM
distortion-detection system which reads all forms of non-linear distortion such as THD, 1M,
slew-induced, "clipping", etc. The INSTANTANEOUS DISTORTION ALERT LEDs will light
when distortion reaches 1% regardless of the impedance or the phase angle of the current
voltage and the reactance of the loudspeakers which the amplifier is driving. Sometimes,
when the amplifier is in use, the LEDs may occasionally flicker under high-volume listening,
particularly if you are driving low impedances. This flickering is no cause for concern. The
LEDs are simply warning you that the amplifier is approaching its maximum power output
into the specific loudspeakers which you are using. If, however, the INSTANTANEOUS
DISTORTION ALERT LEDs glow brightly or are on most of the time during playback, you
are overdriving the amplifier and should lower the volume control to reduce the
listening-level demands, or you may blow the DC RAIL FUSES, cause the THERMAL
PROTECTION to be activated or, in extreme cases, damage your loudspeakers.
THERMAL PROTECTION LED
The GFA-555ms is provided with a thermal protection circuit which will shut down the
amplifier if the temperature of either heatsinks reaches 85°C. The THERMAL PROTECTION
LED will light whenever the thermal protection circuit on either channel, or both channels,
has been triggered and the amplifier is inoperative. The thermal protection circuitry will
typically be triggered by very high-power demands into impedances much lower than the
amplifier is capable of driving at those levels. If the output of either channel of the amplifier
ceases abruptly, and the THERMAL PROTECTION LED glows, you will know that its
heatsinks temperature has become unacceptably high and the circuitry is protecting the
amplification devices. Please note that the POWER LED will remain on and the amplifier will
still be energized.
Once the temperature of the heatsinks drops to a safe operating level, the amplifier will
automatically return to operation.
If the amplifier ceases to operate and both the POWER LED and the THERMAL
PROTECTION LED are off, the condition may indicate that the AC LINE FUSE has blown.
Please refer to the section AC LINE FUSE e for instructions on replacing this fuse.