Adcom GFA 7705 - Manual (Page 8)

8
Distortion Alert LEDs (7)
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 amplifi er is driving. Sometimes, when the amplifi er is in use, the
LEDs may occasionally fl icker during high volume listening, particularly if you are driving low impedances.
This fl ickering is no cause for concern. The LEDs are simply warning you that the amplifi er 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 amplifi er 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 damage your
loudspeakers. loudspeakers.
Thermal Protection LEDs (8a)
The GFA-7705/07 is provided with both a thermal protection circuit and a current overload circuit
which will shut down the individual amplifi er’s channels if its heatsink temperature reaches 85°C or the
amplifi er’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 amplifi er is inoperative. The thermal
protection circuitry will typically be triggered by very high power demands into impedances much
lower than the amplifi er is capable of driving at those levels.
If any amplifi er 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 amplifi cation devices. Please note that the Power LED (7) will remain on and the
amplifi er will still be energized. Once the temperature of the heatsink(s) drops to a safe operating
level, that amplifi er will automatically resume operation.
Activation of the Thermal Protection circuitry in any of the amplifi ers in the GFA-7705/07 is an
indication that the amplifi er has been over driven or that the load the loudspeakers are presenting to
the amplifi er 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.
S.A.F.E.® Protection Circuit (8b) ® ®
Self-Annealing Fuse Equipped: Instead of blowing internal protection rail fuses in the event of a dead-
short to either a loudspeaker or speaker cable leads, the GFA-7705/07 will enter into a self-protect
SAFE mode. SAFE SAFE
If the output of any channel of the amplifi er becomes shorted the protection circuit will trip and
the individual Thermal Protection LED for that channel will light. The Protection LED will blink
approximately every 5 seconds as the circuit will attempt to reset; if the short has been corrected the
amplifi er 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 amplifi er power is
switched off.