Adcom Stereo Amplifier GFA 555se User Manual

GFA-555se  
OWNER’S MANUAL  
High-Current Power Amplifier  
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TABLE OF CONTENTS  
LETTER FROM THE ADCOM TEAM................. 2  
SAFETY INFORMATION ............................ 4  
DESCRIPTION OF UNIT  
GFA-555se FEATURES ............................. 5  
WARRANTY INFORMATION .........................5  
INSTALLATION & HOOKUP  
UNPACKING THE GFA-555se ........................6  
INSTALLING THE GFA-555se ........................6  
CONNECTING THE GFA-555se ......................7  
STEREO/BRIDGED MONO INPUT/OUTPUT.............7-8  
OPERATION  
FRONT AND REAR PANEL DIAGRAMS ................9  
DESCRIPTION OF UNIT: REAR PANEL ............10-11  
DESCRIPTION OF UNIT: FRONT PANEL .............11  
TROUBLESHOOTING  
RESOLVING PROBLEMS ...........................12  
CARING FOR YOUR GFA-555se ................... 13  
SERVICE INFORMATION .......................... 13  
GFA-555se SPECIFICATIONS ................... 14-15  
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THE FOLLOWING PRECAUTIONS AND SAFETY INSTRUCTIONS  
ARE REQUIREMENTS OF ETL AND ETLC SAFETY REGULATIONS  
Read all the safety and operating instructions before con-  
necting or using this unit.  
Retain this notice and the owner’s manual for future refer-  
ence.  
All warnings on the unit and in its operating instructions  
should be adhered to.  
All operating and use instructions should be followed.  
Do not use this unit near water. For example, near a bathtub,  
washbowl, kitchen sink, laundry tub, in a wet basement, or  
near a swimming pool.  
The unit should be installed so that its location or position  
does not interfere with its proper ventilation. For example,  
it should not be situated on a bed, sofa, rug, or similar sur-  
face that may block the ventilation openings; or placed in a  
built-in installation, such as bookcase or cabinet, that may  
impede the ow of air around its heatsinks or through its  
ventilation openings.  
CAUTION POWER LINES  
Any outdoor antenna must be located away from all power lines.  
OUTDOOR ANTENNA GROUNDING  
If an outside antenna is connected to your tuner or tuner/pre-  
amplier, be sure the antenna system is grounded so as to pro-  
vide some protection against voltage surges and built-up static  
charges. Section 810 of the National Electrical Code, ANSI/NFPA  
No. 701984, provides information with respect to proper ground-  
ing of the mast and supporting structure, grounding of the lead-in  
wire to an antenna discharge unit, size of grounding conductors,  
location of antenna discharge unit, connection to grounding elec-  
trodes, and requirements for the grounding electrode.  
a. Use No.10 AWG (5.3 mm2) copper, No.8 AWG (8.4 mm2) alu-  
minum, No.17 AWG (1.0 mm2) copper clad steel or bronze  
wire, or larger, as a ground wire.  
The unit should be situated away from heat sources such as  
radiators, heat registers, stoves, or other devices (including  
other ampliers) that produce heat.  
The unit should be connected to a power supply outlet only  
of the voltage and frequency marked on its rear panel.  
The power supply cord should be routed so that it is not  
likely to be walked on or pinched, especially near the plug,  
convenience receptacles, or where the cord exits from the  
unit.  
Clean unit only as recommended in its instruction manual.  
The power supply cord of the unit should be unplugged from  
the wall outlet when it is to be unused for a long period of  
time and during electrical storms.  
b. Secure antenna lead-in and ground wires to house with  
stand-off insulators spaced from 46 feet (1.221.83 m) apart.  
c. Mount antenna discharge unit as close as possible to where  
lead-in enters house.  
d. Use jumper wire not smaller than No.6 AWG (13.3 mm2) cop-  
per, or the equivalent, when a separate antenna grounding  
electrode is used. See NEC Section 810-21 (j).  
EXAMPLE OF ANTENNA GROUNDING AS PER NATIONAL ELEC-  
TRICAL CODE INSTRUCTIONS CONTAINED IN ARTICLE 810. RA-  
DIO AND TELEVISION EQUIPMENT.  
Care should be taken so that objects do not fall, and liquids  
are not spilled, into the enclosure through any openings.  
This unit should be serviced by qualied service personnel  
when:  
a. The power cord or the plug has been damaged; or  
b. Objects have fallen, or liquid has been spilled, into the  
unit; or  
c. The unit has been exposed to rain, or liquids of any  
kind; or  
d. The unit does not appear to operate normally, or exhib-  
its a marked change in performance; or  
e. The device has been dropped, or the enclosure dam-  
aged.  
WARNING  
TO REDUCE THE RISK OF FIRE OR ELECTRIC SHOCK, DO NOT  
EXPOSE THIS UNIT TO RAIN OR MOISTURE.  
AVERTISSEMENT  
AFIND’ÉVITERTOUTRISQUED’INCENDIEOUD’ÉLECTROCUTION,  
NE PAS EXPOSER CET APPAREIL À LA PLUIE NI À LHUMIDITÉ.  
NOTE TO CATV SYSTEM INSTALLER  
This reminder is provided to call the CATV system installer’s at-  
tention to Article 82022 of the National Electrical Code that pro-  
vides guidelines for proper grounding and, in particular, species  
that the cable ground shall be connected to the grounding system  
of the building, as close to the point of cable entry as practical.  
CAUTION  
TO PREVENT ELECTRIC SHOCK DO NOT USE THIS POLARIZED  
PLUG WITH AN EXTENSION CORD, RECEPTACLE OR OTHER  
OUTLET UNLESS THE BLADES CAN BE FULLY INSERTED TO PRE-  
VENT BLADE EXPOSURE.  
NOTE TO AUDIO SYSTEM INSTALLER  
ATTENTION  
WHENEVER CONNECTIONS TO OR FROM THE GFA-555SE ARE BEING  
MADE, BE CERTAIN THAT THE AC ON/OFF SWITCH OF THE AMPLI-  
FIER IS IN THE OFF POSITION, THE AC CORD OF THE AMPLIFIER IS  
DISCONNECTED FROM THE AC WALL OUTLET AND THAT ALL AS-  
SOCIATED COMPONENTS ARE OFF. Always make certain that the  
amplier is disconnected from the AC outlet for at least ve min-  
utes to ensure its lter capacitors are discharged before mak-  
ing connections to and from the amplier. Failure to heed this  
precaution may result in damage to the loudspeaker(s) and/or the  
amplier which is not covered by the Warranty.  
POUR PRÉVENIR LES CHOCS ÉLECTRIQUES NE PAS UTILISER  
CETTE FICHE POLARISÉE AVEC UN PROLONGATEUR, UNE PRISE  
DE COURANT OU UNE AUTRE SORTIE DE COURANT, SAUF SI LES  
LAMES PEUVENT ÊTRE INSÉRÉES À FOND SANS EN LAISSER  
AUCUNE PARTIE À DÉCOUVERT.  
THERE ARE NO USER SERVICEABLE PARTS IN THIS PRODUCT.  
DO NOT ATTEMPT SERVICING OF THIS UNIT YOURSELF. REFER  
SERVICING TO QUALIFIED SERVICE PERSONNEL.  
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GFA-555se FEATURES  
• Precision-matched devices used throughout the signal path.  
• 60,000 μF of power supply-lter capacitance for greater reserve capacity.  
• Independent power supplies for each channel.  
• Fewer gain stages improve signal reproduction accuracy.  
• Custom toroidal power transformer provides better regulation and greater peak current  
capability.  
• Independent distortion LED for each channel.  
• High quality, gold-plated 5-way binding posts.  
• High quality, gold-plated RCA jacks.  
• High quality, balanced XLR jacks.  
• Large independent heatsinks for greater cooling capability of output devices.  
• Heavy gauge, anodized aluminum front panel.  
• Powder-coated, baked chassis and top cover for greater durability.  
• Cooling vents for greater efciency and cooler operation while driving low impedance  
loads.  
ADCOM Protection Plan (USA Only)  
ADCOM offers the enclosed valuable Limited Warranty. Please read the details on the Warranty Card carefully to  
understand the extent of the protection offered by the Warranty, its reasonable limitations, and what you should  
do in order to obtain its benets. Be sure to verify that the serial number printed on the rear panel matches the  
serial number on the outer carton. If any number is altered or missing, or if the ADCOM Warranty Card is not  
included in the carton, you should notify us immediately in order to ensure that you have received a genuine  
ADCOM product which has not been opened, mishandled, or tampered with in any way. Always retain your  
original sales receipt as a proof of purchase. A proof of purchase is required for all warranty service.  
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INTRODUCTION  
Congratulations on your decision to purchase the GFA-555se power amplier. By use of updated components in the classic  
ADCOM GFA-555 design, we have reestablished our heritage of high performance and audiophile quality at the greatest  
possible value. You have made a wise choice that will reward you for years to come with exceptionally accurate and  
musical sound reproduction. To realize the full potential of your new amplier, and before making any connections to it,  
please read these operating and installation instructions thoroughly.  
UNPACKING THE GFA-555se  
Before your new ADCOM amplier left our factory, it was carefully inspected for physical imperfections and tested for  
all electrical parameters as a routine part of ADCOM’s systematic quality control. This, along with full operational and  
mechanical testing, should ensure a product awless in both appearance and performance. After you have unpacked the  
GFA-555se, inspect it for physical damage. Save the shipping carton and all packing material as they are intended to  
reduce the possibility of transportation damage, should the amplier ever need to be shipped again. In the unlikely event  
damage has occurred, notify your dealer immediately and request the name of the carrier so a written claim to cover  
shipping damages can be initiated. THE RIGHT TO A CLAIM AGAINST A PUBLIC CARRIER CAN BE FORFEITED IF THE CARRIER  
IS NOT NOTIFIED PROMPTLY IN WRITING AND IF THE SHIPPING CARTON AND PACKING MATERIALS ARE NOT AVAILABLE FOR  
INSPECTION BY THE CARRIER. SAVE ALL PACKING MATERIALS UNTIL THE CLAIM HAS BEEN SETTLED.  
INSTALLING THE GFA-555se  
During normal home operation the internal heatsinks of the GFA-555se may become warm. However, there are instances  
during high-level playback into low impedances when the heatsinks will become much warmer than usual. To ensure the  
amplier’s long-term, trouble-free operation it is necessary to provide adequate ventilation for the heatsinks. Therefore,  
the GFA-555se should be kept away from external sources of heat such as radiators and hot-air ducts. The GFA-555se  
should never be placed with other heat-producing components in a cabinet or enclosure lacking free air ow. The top  
and bottom panel of the amplier’s chassis have been provided with vents to allow the necessary cooling of the internal  
components. It is imperative that these vents are not obstructed in any way.  
We recommend that you do not stack other components on top of the GFA-555se. This is particularly important if your  
system includes low-impedance loudspeakers which are difcult to drive, or if you will consistently demand high volume  
levels from the amplier and speaker system. Not only will heat generated by the amplier affect the performance of  
equipment stacked on top of the GFA-555se, but the free ow of air through the ventilating slots in the amplier may be  
partially obstructed.  
If you observe these recommendations, the GFA-555se will perform reliably in any reasonable environment. You should  
also pay attention to such normal considerations as protection from excessive dust and moisture. Occasional vacuuming  
of accumulated dust on the chassis, panels and around the ventilating slots should be all that is required. The optimal  
performance of your new GFA-555se will ultimately depend on the care with which you make the connections between  
the amplier, preamplier and the loudspeakers. All input and output signal connections should be made only with high  
quality, low-loss, low capacitance cables following the recommendations in the Inputs and Outputs section of CONNECTING  
THE GFA-555se.  
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CONNECTING THE GFA-555se  
When connecting the amplier to the loudspeaker, it is vital to maintain proper polarity (positive to positive, negative to  
negative). On the GFA-555se , the positive terminal is color coded RED and labeled “+”, and the negative is color coded  
BLACK and labeled “-”. The positive terminal on the speaker will be color coded RED, or will be labeled “+”, “pos”,  
“positive”, “8 ohms” or “4 ohms”. The negative terminal on the speaker will be color coded BLACK, or will be labeled  
“-”, “neg”, “negative”, “C”, “Common”, “G”, or “ground”.  
It is recommended that your speaker cables be terminated with “U” type spade connectors. These will give the most  
contact area insuring long-term reliability. The spade connector should have a maximum width of 0.57 inches and an  
opening width of no less than 0.25”.  
To properly connect the speaker cable to the binding posts, turn the insulated head of the binding post clockwise until the  
wire or connector is rmly secured. Finger pressure is sufcient and you should not use pliers or other tools which could  
damage or over-tighten the binding-post assembly. The binding posts have been designed in such a way that nger pressure  
is all that is required to cause a “pinching” action among the different metal surfaces to ensure proper connection.  
It is very important to use the correct size of wire in order to avoid unnecessary loss of amplier power in the cable,  
reduction of amplier damping factor and other undesirable conditions. Sound audio engineering practice suggests the  
use of at least AWG16, stranded, copper cable. Recommended capacitance of the speaker wire should not exceed 5OpF  
per foot. This insures high frequencies will not be rolled-off.  
All loudspeakers having a nominal impedance down to 4 ohms can be connected to and driven by the GFA-555se. The  
amplier can drive these low-impedance speakers at more than adequate power levels with no difculty. It should be  
noted that many loudspeaker systems which are nominally rated at 4 ohms drop in impedance, in some parts of their  
frequency range, to as low as 2 ohms (and sometimes less). You will not experience difculties even with these very low  
impedance loads unless you demand excessively high volumes levels from your system.  
It is suggested to follow this chart for speaker lengths and wire gauges. If longer runs are needed, it is best to consult  
with your ADCOM Dealer to maximize the performance of your system with your exact conditions.  
up to 24 feet AWGI6  
up to 36 feet AWGI4  
up to 58 feet AWGI2  
STEREO/BRIDGED MONO INPUT/OUTPUT  
The GFA-555se can be used as a very powerful mono amplier to drive 8-ohm impedance loudspeakers when in its  
“bridged” mode. No modication to the amplier is necessary for operation in the bridged mode, nor are any additional  
accessories required. However, you will need two GFA-555ses for stereophonic reproduction, if you are using them in  
the bridged mono mode.  
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To set the amplier in bridged mono operation, ip the STEREO/BRIDGED input switch into the BRIDGED position. When  
in the bridged mono mode, input to the amplier is made only through the LEFT input jack. The connection to the RIGHT  
input jack should be removed since the right-channel input portion of the amplier is inoperative.  
Only a single loudspeaker is to be connected to the GFA-555se when in the bridged mono mode. Please note that  
connections made to the loudspeaker from the GFA-555se, when used in the bridged mono mode, are different from  
those made when the amplier is used in the stereo mode. The LEFT RED output binding-post terminal (labeled  
BRIDGED MONO OUTPUT “+”) should be connected to the loudspeaker input terminal color-coded RED (or labeled  
POSITIVE, “+”, POS, 8 OHMS or 4 OHMS). The RIGHT RED output binding post terminal on the amplier (labeled BRIDGED  
MONO OUTPUT “-”) should be connected to the BLACK loudspeaker terminal (or labeled NEG, “-”, C, COM, COMMON,  
G, or GROUND). Please note that if you want to insure correct stereo phasing with optimal bass response, you must  
observe these connections precisely.  
Although the GFA-555se can generate a substantially greater amount of power in the bridged mono mode than when it  
is in its normal stereo mode, it requires the use of loudspeakers whose nominal impedance does not drop below 4 ohms.  
It is not recommended that the GFA-555se be used in the bridged mono mode into loudspeakers, or multiple loudspeaker  
loads, which drop in value substantially below 4 ohms. Otherwise, you may trigger the THERMAL PROTECTION or blow  
one of the DC RAIL FUSES. A little known fact is that when any amplier is operated in the bridged mode, the load is  
“split” between the two ampliers in the bridged conguration. Therefore, an 8-ohm loudspeaker will be seen by the  
amplier as if it were a 4-ohm load; a 4-ohm loudspeaker load will be seen by the amplier as a 2-ohm load.  
NOTES:  
a) If the connections described above are followed exactly, the GFA-555se will be polarity correct, that is, it will not  
invert “phase”. Any positive-going signal at its input will appear as a positive-going signal at the loudspeaker.  
b) For use in professional installations, the GFA-555se may be mounted in a standard 19-inch rack using the optional  
RM-7 rack-mount adaptors available through ADCOM dealers. If the GFA-555se is to be mounted on a rack, along with  
other components which are interconnected to the GFA-555se, the amplier’s chassis must be insulated from the  
metal-rack rails to prevent ground loops, especially if the rack is grounded to “earth”, and to avoid defeating the audio  
grounding scheme of the power amplier (the audio-input grounds are isolated from and above the chassis ground).  
Please consult the instruction sheet packed with the optional rack-mount adaptors for more information.  
c) The DC RAIL FUSES provide protection for the output stages and power supply in the event of excessive current  
demands from the amplier, either long-term or short-term. If the amplier ceases to operate, either on one or both  
channels, particularly during high-level passages, or long-term high-volume playback, and the POWER LED glows while  
the THERMAL PROTECTION LED is out, the chances are that one or both of the DC RAIL FUSES on that channel, or both  
channels, are blown. In the event that the DC RAIL FUSES need to be replaced, refer servicing to qualied service  
personel. DO NOT USE ANY SUBSTITUTE FUSES WITH DIFFERENT RATINGS, TIME-CURRENT CURVES OR VALUES. Failure to  
observe this precaution may cause serious damage to the amplier circuits, MAY CREATE A FIRE HAZARD, AND MAY VOID  
YOUR WARRANTY.  
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REAR PANEL  
( )  
1
( )  
1
( )  
2
( )  
2
( )  
6
( )  
3
( )  
4
( )  
5
FRONT PANEL  
model GFA-555se  
power  
high current power amplifier  
instantaneous distortion alert  
thermal protection  
R
L
channel  
( ) ( )  
( )  
9
( )  
10  
7
8
(1) Inputs (unbalanced)  
(2) Inputs (balanced)  
(3) Output Binding Posts  
(4) AC Fuse  
(6) Mode Switches  
(7) On/Off Switch  
(8) Power LED  
(9) Thermal Protection LED  
(10) Distortion Alert LEDs  
(5) AC Power Cord  
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low-impedance loudspeakers. In either case, BE SURE TO  
REPLACE THE AC Fuse ONLY WITH AN EXACT REPLACEMENT  
FUSE. The proper fuse values are:  
DESCRIPTION OF UNIT: REAR PANEL  
(1) Inputs (unbalanced)  
The audio inputs for the GFA-555se are through  
high-quality, gold-plated RCA jacks to minimize  
high-frequency losses, noise, etc. They will accept  
standard RCA-type plugs, one for each channel; Left and  
Right. To insure that the performance designed into the  
amp is preserved, you should use the highest quality  
audio cables possible. There are many cables which are  
color-coded and specically designed for this application.  
Your ADCOM dealer can help select the best cable for  
your needs. (See CONNECTING THE GFA-555se for more  
information).  
GFA-555se for 115 volt operation  
Fuse Rating  
BUSS®  
Littelfuse®  
12 Amp 250 Volt ... AGC-12/250V .... (3AB) 314012/250V  
GFA-555se for 230 volt operation  
Fuse Rating  
BUSS®  
Littelfuse®  
6 Amp 250 Volt .... AGC-6/250V ..... (3AG) 314006/250V  
Before attempting to replace a failed fuse, be certain  
to unplug the AC Power Cord from the AC wall outlet to  
prevent possible electrical shock. Replace the AC Fuse  
only with one identical in type and rating as printed on  
the rear panel. DO NOT USE ANY SUBSTITUTE FUSES WITH  
DIFFERENT RATINGS OR VALUES. Failure to observe this  
precaution may cause serious damage to the amplier  
circuits, may create a hazard re, and may void the warranty.  
If the Power LED (8) does not glow, it may be an indication  
that the AC fuse has blown. If you are not sure, or the  
amplier displays other symptoms, please consult the  
RESOLVING PROBLEMS section on page 12.  
(2) Inputs (balanced)  
The audio inputs for the GFA-555se are through  
high-quality, Balanced XLR jacks to minimize  
high-frequency losses, noise, etc. They will accept  
standard XLR-type plugs, one for each channel; Left and  
Right. To insure that the performance designed into the  
amp is preserved, you should use the highest quality  
audio cables possible. There are many cables specically  
designed for this application. Your ADCOM dealer can help  
select the best cable for your needs. (See CONNECTING  
THE GFA-555se for more information).  
Fuse replacement  
To remove the fuse-holder cap, you will need a #2 standard  
Phillips screwdriver. Place the screwdriver in the recessed  
“crosshead” in the cap. Turn the cap counter-clockwise,  
until the cap releases out towards you. Grasp the cap with  
your ngers and pull it completely out. The fuse is inserted  
in the back of the cap; gently pull it free.  
(3) Outputs  
The GFA-555se connections to the loudspeakers are made  
through high-grade, 5-way, gold-plated binding post  
terminals. There are two terminals for each speaker,  
which are colored RED for the positive (+) output and  
BLACK for the negative (-) output.  
Since the fuse has a ceramic body, you cannot visually  
examine the fuse element, it is therefore suggested that  
you replace it with an identical substitute or bring the fuse  
to your ADCOM dealer so they may check its integrity. To  
replace the fuse, insert it in the back of the fuse-holder  
cap. Place the cap into the fuse-holder. Place the  
screwdriver in the recessed slot, gently press in and turn  
1/8-turn clockwise.  
The binding posts will accept a variety of connector types;  
the most secure and prevalent of these is the “U”-type  
spade connectors (at least 0.25wide and maximum  
width of 0.57”),. The terminal will also accept bare wire  
(up to AWG1O) and “banana” type plugs (single or dual).  
(Refer to your User Manual for your speakers for additional  
information).  
(5) AC Power Cord  
(4) AC Fuse  
The AC cord provides power to operate all the GFA-555se’s  
circuits. Its plug can be connected to a standard wall  
outlet provided the outlet supplies a voltage compatible  
with the power requirements printed on the rear panel of  
the GFA-555se.  
The AC Fuse protects the electronic circuits of the GFA-  
555se. This fuse, normally, will fail only if there is an  
overload within the GFA-555se. It may, however, fail if the  
amplier attempts to deliver very high power into very  
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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.  
(6) Mode Switches  
For normal stereophonic mode of operation, the  
STEREO/BRIDGED input switch should be set to STEREO.  
Otherwise, the amplier will operate in the bridged  
mono input mode by which you will amplify only the  
left channel through both outputs of the amplier. 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.  
(9) Thermal Protection LED  
The GFA-555se is provided with a thermal protection  
circuit which will shut down the amplier if its heatsink  
temperature reaches 75°C. The Thermal Protection LED  
will light whenever the thermal protection circuit has been  
triggered and the amplier is inoperative. The thermal  
protection circuitry will typically be triggered by very  
high power demands into impedances much lower than  
the amplier is capable of driving at those levels. If any  
amplier 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  
amplication devices. Please note that the Power LED (8)  
will remain on and the amplier will still be energized.  
Once the temperature of the heatsink(s) drops to a safe  
operating level, that amplier will automatically resume  
operation.  
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  
amplier, but it does not signify that all the amplier’s  
circuits are in operation. If, for example, the Thermal  
Protection LED (9) glows, that amplier 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.  
(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 amplier is driving. Sometimes, when the  
amplier is in use, the LEDs may occasionally icker  
during high volume listening, particularly if you are driving  
low impedances. This ickering is no cause for concern.  
The LEDs are simply warning you that the amplier 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 amplier  
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.  
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 amplier 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  
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RESOLVING PROBLEMS  
Use the chart below to solve common situations that don’t require professional attention. If the steps stated in  
POSSIBLE SOLUTION do not resolve your problem, then please contact your ADCOM Dealer or call the ADCOM Customer  
Service Department. Any problems not covered here should be brought to the attention of your ADCOM Dealer or ADCOM  
Customer Service Department.  
SYMPTOM  
Power LED does not  
glow.  
POSSIBLE REASON  
AC Power Cord(s) not plugged in.  
POSSIBLE SOLUTION  
Plug in AC Power Cord(s).  
Press the Power switch.  
Power switch not (pressed) on.  
No sound.  
AC Fuse(s) failed.  
Replace AC Fuse(s).  
Transformer thermal protection engaged.  
Preamp or source unit is not on.  
Connections in rear of amp are loose.  
INPUT(s) or OUTPUT(s) connector  
disconnected or loose.  
Wait until unit cools down. It will reset.  
Make sure whole system is on.  
Power LED glows,  
but no sound.  
Verify all connections on rear of amp.  
Verify both connections on that channel.  
One channel not  
producing sound.  
Speaker disconnected.  
Verify connection at speaker.  
Internal protection engaged.  
Bring to Dealer or Service Center.  
Hum from all speakers  
at any volume.  
Ground loop (difference in ground voltages  
between components).  
If Cable TV is present (see Note 1).  
If Cable TV is not present (see Note 2).  
Try different source (tuner, tape, etc.)  
and/or different RCA cable.  
Hum from all speakers  
(hum goes up or  
Problem with source unit (CD, tape, etc.),  
or RCA cable connecting that source unit  
to the preamp.  
down with volume).  
Hum from the amplier  
itself.  
Some major appliance, dimmer, halogen or  
uorescent light is creating interference.  
Make sure all appliances, dimmers and  
suspect lights are off.  
A special note on “hum” When there is a low-volume “hum” audible throughout your speakers, even with the main  
volume turned all the way down, you have a common phenomenon known as a “ground loop”. A ground loop is basically  
a difference in ground voltages between two or more components which are connected electrically and which creates  
multiple current paths where there must only be one. This difference in potentials creates a 60Hz low-level sound  
(approximately a low A#), that seems to “hum”, hence the name.  
It can be caused by adding new components to your system, but that does not imply there is anything electrically  
wrong with any new component. With the advent of audio/video and home theater systems, the problem has  
become commonplace. Generally, the cause is the Cable-TV incoming signal line. This new incoming line may add an  
additional ground at a different potential to the AC line ground of your other equipment (refer to Note I and 2 below to  
troubleshoot a hum problem).  
Note 1 Cable TV systems can sometimes contribute to ground loop problems which cause “hum”. To determine if your  
cable system is the contributing factor, disconnect the Cable-TV incoming signal line (round coax, 75Ω) at the wall, or  
the rst component the cable is connected to (i.e. the cable box, or VCR). If the hum is no longer present, you must  
insert a “75Ω Ground Loop Isolator” before reconnecting the line. You should check with your ADCOM Dealer to obtain  
one. If the “75Ω Ground Loop Isolator” works only partially or not at all, then please read Note 2 to complete the  
troubleshooting procedure.  
Note 2 Make sure that the power amplier is at least 6” from the Preamp and/or Processor. Usually putting another  
component between them is sufcient to minimize the hum. If this does not reduce the hum, turn the system off and  
disconnect all Inputs from the amplier. Turn the amplier on, if the hum still persists, then your Dealer or Service  
Center must examine the amplier. If the hum disappears, try a different set of RCA cables. Connect one RCA cable  
at a time to see if one specic cable is responsible. If any or all cables cause the hum to appear, then the preamp or  
processor should be evaluated for proper operation by your Dealer or Authorized Service Center.  
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CARING FOR YOUR GFA-555se  
Great care has been taken by ADCOM to ensure that your amplier is as awless in appearance as it is electronically.  
The front panel is a heavy-gauge, high-grade aluminum extrusion carefully nished and anodized for durability. The  
chassis, top cover and rear panel are heavy-gauge steel that has been powder coated and baked to ensure a lasting  
nish. If the front panel, top or sides become dusty or ngerprinted, they can be cleaned with a soft lint-free cloth,  
slightly dampened with a very mild detergent solution or glass cleaner.  
Do not spray or pour liquids of any kind directly onto the GFA-555se.  
SERVICING  
ADCOM has a Technical Service Department to answer questions pertinent to the installation and operation of your  
unit. In the event of difculty, please contact us for prompt advice. If your problem cannot be resolved through our  
combined efforts, we may refer you to an authorized repair agency, or authorize return of the unit to our warehouse.  
To aid us in directing you to a convenient service center, it would be helpful if you indicate which major city is accessible  
to your home.  
Please address mail inquires to:  
Phone, Fax or e-mail inquires to:  
ADCOM Service  
8541 East Anderson Drive, Suite 101  
Scottsdale, Arizona 85255 USA  
Voice: (480) 607-2277  
Fax: (480) 348-9876  
Monday through Friday  
9:00 AM to 5:00 PM MST  
For Fax inquires, please include a return Fax number for the reply.  
When calling or writing about your GFA-555se, be sure to note and refer to its serial number as well as the date of  
purchase and the dealer from whom it was purchased. In any communications to us, please include a daytime phone  
number where we may reach you. In the event the unit must be returned to our factory for service, you will be instructed  
on the proper procedure when you call or write for a Return Authorization. UNDER NO CIRCUMSTANCES SHOULD YOUR  
UNIT BE SHIPPED TO OUR FACTORY WITHOUT PRIOR AUTHORIZATION, OR PACKED IN OTHER THAN ITS ORIGINAL CARTON  
AND FILLERS.  
If the original shipping carton and its llers have been lost, discarded, or damaged, a duplicate carton may be obtained  
from our Service Department for a nominal charge.  
Always ship PREPAID VIA UNITED PARCEL SERVICE (UPS) OR OTHER APPROVED CARRIER. DO NOT SHIP VIA PARCEL POST,  
since the packing was not designed to withstand rough Parcel Post handling.  
FREIGHT COLLECT SHIPMENTS WILL NOT BE ACCEPTED  
UNDER ANY CIRCUMSTANCES.  
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GFA-555se SPECIFICATIONS  
Power Rating (To FTC Requirements)  
200 Watts continuous average power into 8 ohms at any frequency between 20Hz and 20kHz with both channels  
driven at less than 0..04% THD.  
300 Watts continuous average power into 4 ohms at any frequency between 20Hz and 20khz with both channels  
driven at less than 0.04% THD. *  
600 Watts continuous average power into 8 ohms at any frequency between 20Hz and 20kHz at less than 0..09% THD,  
bridged. *  
IM Distortion (SMPTE)  
1 watt to 200 watts into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.009%  
1 watt to 300 watts into 4 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.009%  
IM Distortion (CCIF, Any Combination from 4kHz to 20kHz)  
200 watts into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.002%  
300 watts into 4 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.003%  
THD + Noise at 200 watts into 8 Ohms (Typical)  
20Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.004%  
1kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.003%  
10kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.006%  
20kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.010%  
THD + Noise at 300 watts into 4 Ohms (Typical)  
20Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.005%  
1 kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.004%  
10kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.015%  
20kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.025%  
IM Distortion, Bridged (SMPTE)  
1 watt to 600 watts into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.05%  
1 watt to 850 watts into 4 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.05%  
IM Distortion (CCIF, Any Combination from 4kHz to 20kHz)  
600 watts into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.005%  
850 watts into 4 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.005%  
THD + Noise at 600 watts into 8 Ohms, Bridged (Typical)  
20Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.004%  
1kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.004%  
10kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02%  
20kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.04%  
Frequency Response @ I Watt into 8 Ohms  
10Hz to 20kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +0, -0.25dB  
Power Bandwidth (-3dB). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Hz to 100kHz  
Dynamic Headroom Into 4 Ohms (1.7dB typical).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5dB*  
Signal to Noise Ratio, “A” Weighted  
200 watts into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110dB  
Gain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27dB  
Input impedance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10k ohms balanced; 100k ohms unbalanced  
* With supplemental cooling system.  
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Input Sensitivity  
200 watts into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.75V rms  
1 watt into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130mV rms  
Damping Factor  
2OHz to 2OkHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900  
Rise Time  
5kHz, 120V peak-to-peak square wave, 20% to 80%. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3μS  
Power Consumption (Continuous, Both Channels Driven)  
Quiescent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72VA  
Maximum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1500VA  
200 watts into 8 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675VA  
325 watts into 4 ohms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1180VA  
600 watts into 8 ohms, bridged. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1320VA  
General  
Power (available in 230V by special order). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120VAC—50/60Hz  
Chassis Dimension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15/16” (176mm) x 12-1/8” (308mm) x 16-15/16” (430mm)  
Maximum Dimensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1/2” (191mm) x 12-1/2” (318mm) x 17” (432mm)  
Weight. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 lbs. (16.3kg)  
Weight, Packed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 lbs. (18.1kg)  
Specications subject to change without notice.  
Copyrights/Trademarks  
Published by Advanced Sound and Image | Copyright © 2008 Advanced Sound and Image, LLC | All rights reserved  
Adcom and the Adcom logo are registered trademarks of Advanced Sound and Image, LLC  
No part of this manual may be reproduced or electronically transmitted without the express written consent of Advanced Sound and Image, LLC.  
Advanced Sound and Image, LLC shall not be liable for any errors contained herein or for any damages arising out of or related to this  
document or the information contained herein, even if Advanced Sound and Image, LLC has been advised of the possibility of such dam-  
ages. This document is intended for informational and instructional purposes only. Advanced Sound and Image, LLC reserves the right  
to make changes in the specications and other information contained in this document without prior notication. Advanced Sound and  
Image, LLC disclaims any obligation to update the information contained herein.  
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8541 East Anderson Drive, Suite 101  
Scottsdale, Arizona 85255  
Voice: 480.607.2277  
Fax: 480.348.9876  
www.adcom.com  
GFA-555se_manual_v1.1  
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