Description of Unit Front Panel | Adcom GFA-555se instruction

(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.

GFA-555se specifications

The Adcom GFA-555se is a high-performance audio power amplifier that stands out for its robust design and exceptional sound quality. Renowned among audiophiles, it offers a blend of remarkable power output and fidelity, making it suitable for a wide range of audio systems.

One of the main features of the GFA-555se is its impressive power output, rated at 200 watts per channel into 8 ohms and 330 watts per channel into 4 ohms. This ample power allows it to drive a variety of speakers efficiently, delivering dynamic and impactful sound reproduction. The amplifier is designed to handle both high and low frequencies with precision, ensuring a balanced audio experience.

In terms of technology, the GFA-555se employs a classic Class AB design, which is known for its ability to combine the efficiency of Class B operation with the linearity of Class A. This results in lower distortion and better thermal management, contributing to a cleaner sound, particularly at high volumes. The amplifier also incorporates a high-speed output stage, which enhances transient response and enables the reproduction of fast-paced musical passages without degradation.

Another notable characteristic of the GFA-555se is its build quality. The chassis is constructed from heavy-duty aluminum, which not only results in durability but also helps to dissipate heat effectively. This is crucial in maintaining performance and longevity, as overheating can lead to shortened component life. Additionally, the amplifier features a massive power supply with a large transformer, providing stable voltage and current to the output stage, which further enhances audio performance.

The GFA-555se is equipped with unbalanced RCA inputs and can be easily integrated into existing audio setups, making it a versatile choice for both home theater and stereo systems. With its impressive parasitic rejection and low noise floor, it ensures that the audio signal remains clean and unaffected by external interference.

In conclusion, the Adcom GFA-555se is a powerful and reliable amplifier that combines advanced technologies with robust construction. Its ability to deliver high-quality sound across a broad range of frequencies, along with its impressive power output and efficient design, makes it a popular choice among music enthusiasts and professionals alike. Whether used as part of a high-end audio system or in a home theater setup, the GFA-555se continues to be a respected component for achieving an immersive listening experience.

Adcom GFA-555se owner manual Description of Unit Front Panel

Models: GFA-555se