(6) Mode Switches
For normal stereophonic mode of operation, the STEREO/BRIDGED input switch should be set to STEREO. Otherwise, the amplifier will operate in the bridged mono input mode by which you will amplify only the left channel through both outputs of the amplifier. The BALANCED/UNBALANCED selector switches should be set to accommodate the type of input connectors that you are using. The upper connectors (RCA-jacks) are used for unbalanced input signals and the lower connectors (XLR- jacks) are used for balanced input signals.
DESCRIPTION OF UNIT: FRONT PANEL
(7) On/Off Switch
The On/Off Switch controls AC power to the power transformer and circuits of the GFA-555se. Whenever the GFA-555se is energized the Power LED (8) will glow red. To turn the GFA-555se on, press the button up. It will remain in the “engaged” position while the unit is energized. To turn the GFA-555se off, press the button down and it will move to the “disengaged” position.
(8) Power LED
This LED will glow whenever the On/Off Switch (7) is turned on and the GFA-555se is energized. 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, the Thermal Protection LED (9) glows, that amplifier will not produce sound even though the Power LED may still glow. When the GFA-555se is turned off, the Power LED will take some time to fade out completely. It may take up to 30 seconds to fully extinguish.
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 Fuse (4) has not failed, the Power LED (8) is out, and the Thermal Protection LED (9) does not glow, 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 tripping the thermostat in the transformer continually, you must reduce the sound level demands, correct the load impedance of the loudspeakers, or both.
(9) Thermal Protection LED
The GFA-555se is provided with a thermal protection circuit which will shut down the amplifier if its heatsink temperature reaches 75°C. The Thermal Protection LED will light whenever the thermal protection circuit 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 (8) 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.
(10) 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.
