Adcom GFA7807 - Manual (Page 9)

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automatically and normal operation will resume. If you
are to avoid tripping the thermostat in the transformer
continually, you must reduce the sound level demands,
correct the load impedance of the loudspeakers, or both.
(8) Thermal Protection LEDs
The GFA-7805/7807 are provided with a thermal protection
circuit which will shut down the individual amplifiers
if its heatsink temperature reaches 85°C. The Thermal
Protection LEDs will light whenever the thermal protection
circuit in its respective channel 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 any amplifier channel’s
output through the loudspeaker(s) ceases abruptly, and
its Thermal Protection LED glows, you will know that its
heatsink temperature has become unacceptably high
and the circuitry is protecting the amplification devices.
Please note that the Power LED (7) will remain on and the
amplifier will still be energized. Once the temperature
of the heatsink(s) drops to a safe operating level, that
amplifier will automatically resume operation.
Activation of the Thermal Protection circuitry in any
of the amplifiers in the GFA-7805/7807 is an indication
that the amplifier has been over-driven or that the
load the loudspeakers are presenting to the amplifier
is unreasonably low. If you wish to prevent recurrent
activation of the thermal protection circuitry, you must
reduce the volume-level demands or correct the load
impedance condition which may be causing activation of
this circuitry.
(9) Distortion Alert LEDs
The 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 Distortion Alert LEDs will light when distortion reaches
approximately 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 Distortion
Alert LEDs glow brightly or are illuminated most of the
time during playback, you are over driving the amplifier
and should turn down your volume control to reduce
the listening level, otherwise it may cause the Thermal
Protection to be activated or, in extreme cases, damage
your loudspeakers.