Adcom GFA-5500 - Manual (Page 8)

POWER LED (D
This LED will glow whenever the AC ON/OFF switch is turned on and the GFA-5500 is energized. If the AC LINE FUSE
blows the POWER LED will cease to glow.
The POWER LED indicates that there is AC voltage being fed to the amplifier, but it does not signify that all the
amplifier's circuits are in operation. If, for example, you have blown one or more of the EXTERNAL PROTECTION
FUSES, the amplifier will not operate. That is, the amplifier will not produce any audio signal even though the POWER
LED is glowing. Similarly, if the THERMAL PROTECTION LED glows, the amplifier will not produce sound even though
the POWER LED may still glow.
Additionally, the internal power transformer is provided with a thermostat which will interrupt power into the transformer if
its temperature exceeds 125°C. This high temperature will seldom, if ever, be encountered unless the amplifier is
subjected to abnormal conditions, such as operation into loads of less than 3 ohms at very high listening levels, etc. If
the AC POWER FUSE is not blown, the POWER LED is out, the THERMAL PROTECTION LED is out and the
EXTERNAL PROTECTION FUSES are intact, this would indicate that the thermostat within the transformer has opened.
Once the temperature within the transformer decreases to a normal level, the thermostat will reset itself automatically and
normal operation will resume. If you are to avoid continually tripping the thermostat in the transformer, you must reduce
the sound level demands, correct the load impedance of the loudspeakers, or both.
INSTANTANEOUS DISTORTION ALERT LEDs CU
The INSTANTANEOUS DISTORTION ALERT circuit is a unique ADCOM distortion detection system which reads all
forms of non-linear distortion such as THD, IM, slew-induced, “clipping”, etc. The INSTANTANEOUS DISTORTION
ALERT LEDs will light when distortion reaches 1% regardless of impedance, voltage/current phase angle or the
reactance of the loudspeakers which the amplifier is driving. Sometimes, when the amplifier is in use, the LEDs may
occasionally flicker during 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
particular loudspeakers you are using. If, however, the INSTANTANEOUS DISTORTION ALERT LEDs glow brightly or
are illuminated most of the time during playback, you are overdriving the amplifier and should turn down your volume
control to reduce the listening level or you may blow one or more of the EXTERNAL PROTECTION FUSES, cause the
THERMAL PROTECTION to be activated or, in extreme cases, damage your loudspeakers.
GFA-5500 Front Panel Diagram