Adcom GFA-7700 - Manual (Page 8)

8
Distortion Alert LEDs (8)
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.
Thermal Protection LEDs (9)
The GFA-7700 is provided with both a thermal protection circuit and a current overload circuit which
will shut down the individual amplifier’s channels if its heatsink temperature reaches 85°C or the
amplifier’s outputs are shorted. The Thermal Protection LEDs will light when either of these protection
circuits are on 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. If the output of any channel of the amplifier becomes shorted
the protection circuit will trip and the Thermal Protection LED for that channel will light. After
approximately 5 seconds the unit will attempt to reset, if the short has been corrected the amplifier
will resume proper operation. If the short is still present the channel will cycle off again. The cycling of
the protection circuit will continue until the short is corrected or the amplifier power is switched off.
Activation of the Thermal Protection circuitry in any of the amplifiers in the GFA-7700 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.