OWNERS MANUAL

GFA-7805 & GFA-7807
Multi-channel High-Current Power Amplifiers

WELCOME

Dear fellow ADCOM product owner, Welcome to the ADCOM family! For more than twenty years, ADCOM products have delivered excellent performance and value for customers around the world. Our products are designed by our experienced and demanding engineering team, built to the highest standards in our factory, and sold and serviced through dealers, custom installers, and other retailers whose primary goal is your complete satisfaction. We know you are anxious to hear your new amplifier in action, but please take a few minutes to read this owners manual before connecting the amplifier to your system. Because ADCOM amplifiers can put out tremendous power, it is particularly important that you connect your amplifier to your pre-amplifier and speakers while the amplifier is unplugged and your other equipment is turned off. This will protect the amplifier and other equipment from potential short circuits that may occur during installion. In addition, it is important that you allow for adequate ventilation around your amplifier and other equipment, since excessive heat buildup can shorten the life of any electronic product, including the amplifier. Once you have correctly connected your pre-amplifier and speakers to your new amplifier, you should be able to enjoy many troublefree years of performance. We conduct a thorough quality and performance test on each and every amplifier we build in our factory prior to shipment. In the rare case of a defect that may occur after shipment, we stand behind our amplifiers with a five-year parts and labor warranty. To register for this warranty, please complete and mail the enclosed warranty card back to ADCOM. Also, please keep a copy of your sales receipt with the owners manual so you may provide proof of eligibility for the warranty should the need arise. We know you will be very happy with the sound and performance of your new amplifier. We hope you will also consider other ADCOM products, such as our line of pre-amplifiers and DVD and CD players. In addition, we design and manufacture complementary products such as line conditioners/surge suppressors and speaker selectors. Please visit our web site, www.adcom.com, to learn more about our complete line of stereo, home theater, and distributed audio/video products. On behalf of all of us at ADCOM, I want to thank you for selecting our product for your home or business entertainment system. Sincerely,
Douglas Klein President ADCOM

TABLE OF CONTENTS

WELCOME.. 2 SAFETY INFORMATION.. 4 DESCRIPTION OF UNIT
GFA-7805 FEATURES.. 5 GFA-7807 FEATURES.. 5 WARRANTY INFORMATION.. 5
INSTALLATION & HOOKUP
UNPACKING THE GFA-7805/7807. 6 INSTALLING THE GFA-7805/7807. 6

OPERATION

FRONT AND REAR PANEL DIAGRAMS. 7 DESCRIPTION OF UNIT: REAR PANEL.. 8 DESCRIPTION OF UNIT: FRONT PANEL. 8-9 CONNECTIONS DIAGRAM.. 10 CONNECTING THE GFA-7805/7807. 11

TROUBLESHOOTING

RESOLVING PROBLEMS.. 12 CARING FOR YOUR GFA-7805/7807.. 13 SERVICE INFORMATION. 13 GFA-7805 SPECIFICATIONS.. 14 GFA-7807 SPECIFICATIONS.. 15
THE FOLLOWING PRECAUTIONS AND SAFETY INSTRUCTIONS ARE REQUIREMENTS OF UL AND CSA SAFETY REGULATIONS
Warning: To reduce the risk of fire or electric shock, do not expose this unit to rain or moisture.
POUR PREVENIR LES CHOCS ELECTRIQUES NE PAS UTILISER CETTE FICHE POLARISEE AVEC UN PROLONGATEUR, UNE PRISE CE COURANT OU UNE AUTRE SORTIE CE COURANT, SAUF SI LES LAMES PEUVENT ETRE INSEREES A FOND SANS EN LAISSER AUCUNE PARTIE A DECOUVERT.

ATTENTION

CAUTION
RISK OF ELECTRIC SHOCK DO NOT OPEN
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 PREVENT BLADE EXPOSURE.

The graphic symbol of a lightning flash with an arrow point within a triangle signifies that there is dangerous voltage within the unit and it poses a hazard to anyone removing the cover to gain RISK OF ELECTRIC SHOCK access to the interior of the unit. OnIy qualified DO NOT OPEN service personnel should make any such attempt. The graphic symbol of an exclamation point within an equilateral triangle warns a user of the device that it is necessary to refer to the instruction manual and its warnings for proper operation of the unit. Do not place this unit on an unstable cart, stand, tripod, bracket, or table. The unit may fall, causing serious injury to a child or adult, and serious damage to the unit. Use only with a cart, stand, tripod, bracket, or table recommended by the manufacturer or sold with the unit. Any mounting of the device should follow the manufacturers instructions, and should use a mounting accessory recommended by the manufacturer. Read all the safety and operating instructions before connecting or using this unit. Retain this notice and the owners manual for future reference. 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 surface that may block the ventilation openings; or placed in a built-in installation, such as bookcase or cabinet, that may impede the flow of air through its ventilation openings. The unit should be situated away from heat sources such as radiators, heat registers, stoves, or other devices (including amplifiers) 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. 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 qualified 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 exhibits a marked change in performance; or E. The device has been dropped, or the enclosure damaged. DO NOT ATTEMPT SERVICING OF THIS UNIT YOURSELF. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.

Any outdoor antenna must be located away from all power lines.
If an outside antenna is connected to your tuner or tuner/preamplifier, be sure the antenna system is grounded so as to provide 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 grounding 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 electrodes, and requirements for the grounding electrode. a. Use No.10 AWG (5.3 mm2) copper, No.8 AWG (8.4 mm2) aluminum, No.17 AWG (1.0 mm2) copper clad steel or bronze wire, or larger, as a ground wire. 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) copper, or the equivalent, when a separate antenna grounding electrode is used. See NEC Section 810-21 (j). EXAMPLE OF ANTENNA GROUNDING AS PER NATIONAL ELECTRICAL CODE INSTRUCTIONS CONTAINED IN ARTICLE 810. RADIO AND TELEVISION EQUIPMENT.

power lines

CAUTION POWER LINES
OUTDOOR ANTENNA GROUNDING
ground clamp service entrance conductors standoff insulators, b
mast antenna lead-in wire ground wire, a,b ground clamps
service entrance equipment
antenna discharge unit, c to external antenna terminals of radio receiver
power service grounding electrode system (e.g. interior metal water pipe) bonding jumper, d
ground wire, a,b ground clamps optional antenna grounding electrode driven 8 feet (2.44 M) into the earth if required by local codes.
NOTE TO CATV SYSTEM INSTALLER This reminder is provided to call the CATV system installers attention to Article 82022 of the National Electrical Code that provides guidelines for proper grounding and, in particular, specifies that the cable ground shall be connected to the grounding system of the building, as close to the point of cable entry as practical.

GFA-7805 FEATURES

Precision-matched devices used throughout the signal path 112,000 F of power supply-filter capacitance to optimize transient response 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 thermal-overload and distortion LEDs for all 5 channels High quality, gold-plated 5-way binding posts Balanced XLR inputs High quality, gold-plated RCA jacks Large independent internal heatsinks for greater cooling capability of output devices Convenient 12V DC power ON/OFF triggering Heavy gauge, anodized aluminum front panel Powder-coated, baked chassis and top cover for greater durability Cooling vents for greater efficiency and cooler operation while driving low impedance loads Forced convection temperature sensitive cooling

GFA-7807 FEATURES

Precision-matched devices used throughout the signal path 156,800 F of power supply-filter capacitance to optimize transient response 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 thermal-overload and distortion LEDs for all 7 channels High quality, gold plated 5-way binding posts Balanced XLR inputs High quality, gold-plated RCA jacks Large independent, internal 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 efficiency and cooler operation while driving low impedance loads Forced convection temperature sensitive cooling
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 benefits. 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. 5

INTRODUCTION

Congratulations on your decision to purchase the GFA-7805 or GFA-7807 multichannel power amplifier. The GFA-7805 and GFA-7807 have been designed to be high performance and musically accurate in a configuration specifically designed to integrate with any audio pre-amplifier. 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 amplifier, and before making any connections to it, please read these operating and installation instructions thoroughly.
UNPACKING THE GFA-7805/7807

Before your new ADCOM amplifier left our factory, it was carefully inspected for physical imperfections and tested for all electrical parameters as a routine part of ADCOMs systematic quality control. This, along with full operational and mechanical testing, should ensure a product flawless in both appearance and performance. After you have unpacked the GFA-7805/07, 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 amplifier 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-7805/7807
During normal home operation the internal heatsinks of the GFA-7805/7807 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 amplifiers long-term, trouble-free operation it is necessary to provide adequate ventilation for the heatsinks. Therefore, the GFA-7805/7807 should be kept away from external sources of heat such as radiators and hot-air ducts. The GFA-7805/7807 should never be placed with other heat-producing components in a cabinet or enclosure lacking free air flow. The top and bottom panel of the amplifiers 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-7805/7807. This is particularly important if your system includes low-impedance loudspeakers which are difficult to drive, or if you will consistently demand high volume levels from the amplifier and speaker system. Not only will heat generated by the amplifier affect the performance of equipment stacked on top of the GFA-7805/7807, but the free flow of air through the ventilating slots in the amplifier may be partially obstructed. If you observe these recommendations, the GFA-7805/7807 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-7805/7807 will ultimately depend on the care with which you make the connections between the amplifier, pre-amplifier, surround sound decoder 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-7805/7807.

GFA-7807 REAR PANEL

GFA-7807 FRONT PANEL
LF distortion alert > thermal protection >
(4) AC Fuse (5) AC Power Cord (6) On/Off Switch 7
(1) Input Jacks (2) Output Binding Posts (3) I2V DC Trigger
(7) Power LED (8) Thermal Protection LEDs (9) Distortion Alert LEDs
DESCRIPTION OF UNIT: REAR PANEL

(1) Inputs

The GFA-7805 and GFA 7807 have both balanced and unbalanced inputs for each channel. The unbalanced connection is made via the gold plated RCA jack and the balanced connection is made via the XLR input connection. Each channel also has a switch which selects the type of input for each channel. Make sure the switch is in the appropriate position for the type of connection you have choosen. For best performance, always use high quality interconnects. Your ADCOM dealer can help select the best cable for your needs.
is an overload within the GFA-7805/7807. If your fuse fails please contact your dealer or ADCOM directly for a replacement or servicing.

(5) AC Power Cord

The AC cord provides power to operate all the GFA7805/7807s 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-7805/7807.
DESCRIPTION OF UNIT: FRONT PANEL

(6) On/Off Switch

The On/Off Switch controls power to the power transformer and circuits of the GFA-7805/7807. Whenever the GFA-7805/7807 is energized the Power LED (7) will glow. To turn the GFA-7805/7807 on, press the push-button. It will remain in the engaged position while the unit is energized. To turn the GFA-7805/7807 off, press the push-button in and release and it will move to the disengaged position.

(2) Outputs

The GFA-7805s and GFA-7807s 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. 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 0.25 wide and maximum width of 0.57). The terminal will also accept bare wire (up to AWG1O) and banana type plugs (single or dual).

(7) Power LED

This LED will glow whenever the On/Off Switch (6) is turned on and the GFA-7805/7807 is energized. The Power LED indicates that there is AC voltage being fed to the amplifier, but it does not signify that all the amplifiers circuits are in operation. If, for example, one of the Thermal Protection LEDs (9) glows, that amplifier channel will not produce sound even though the Power LED may still glow. When the GFA-7805/7807 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 125C. 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 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

(3) I2V DC Trigger

The GFA-7805 and GFA-7807 are very high power amplifiers and as such must be directly connected to the wall outlet or an appropriate surge protector or AC line conditioner. It must never be connected to the switched outlets on the rear panel of a pre-amplifier. Usually this would mean that when you turn on/off your pre-amplifier you would have to turn on/off your power amplifier separately. We have, however, provided the ability to control the OFF/ON function of the GFA-7805/7807 by a l2V DC output jack on the rear of certain ADCOM pre-amplifiers. When using this feature the front panel Power Switch must be left in the in on position. To connect the preamplifier 12V DC output jack to the amplifier 12V DC jack, you will need a monaural mini phone plug to monaural mini phone plug cable. Contact your dealer for information on using this feature with ADCOM and other brand pre-amplifiers.

(4) AC Fuse

The AC Fuse protects the electronic circuits of the GFA7805/7807. This fuse, normally, will fail only if there
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) 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.

(8) Thermal Protection LEDs
The GFA-7805/7807 are provided with a thermal protection circuit which will shut down the individual amplifiers if its heatsink temperature reaches 85C. The Thermal Protection LEDs will light whenever the thermal protection circuit in 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 channels 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. Activation of the Thermal Protection circuitry in any of the amplifiers in the GFA-7805/7807 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.
WHENEVER CONNECTIONS TO OR FROM THE GFA-7805 & GFA-7807 ARE BEING MADE, BE CERTAIN THAT THE AC ON/OFF SWITCH OF THE AMPLIFIER IS IN THE OFF POSITION, THE AC CORD OF THE AMPLIFIER IS DISCONNECTED FROM THE AC WALL OUTLET AND THAT ALL ASSOCIATED COMPONENTS ARE OFF.

WARNING

Right Back Left Back Left Surround
unbalanced input input select balanced input
unbalanced input 12VDC trigger input select balanced input

output

AC fuse 15ABC 250V

120VAC 50/60 Hz

please visit www.adcom.com
WARNING: To reduce the risk of fire or electric shock, do not expose this appliance to rain or moisture. ATTENTION: Pour eviter tout risque de feu ou choc electrique, ` ` ne pas exposer cet appareil a la pluie ou a l'humidite. ` ` ` AVIS: Risque de choc electrique- ne pas ouvrir. `
serial number Model: GFA-7807 Power Amplifier Power consumption (max): XXXX W
Left Front Center Right Surround Right Front
CONNECTING THE GFA-7805/7807 TO YOUR SPEAKERS
When connecting the amplifier to the loudspeaker, it is vital to maintain proper polarity (positive to positive, negative to negative). On the GFA-7805/7807, 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. We recommend 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 firmly secured. Finger pressure is sufficient 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 finger 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 amplifier power in the cable, reduction of amplifier 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-7805/7807. The amplifier can drive these low-impedance speakers at more than adequate power levels with no difficulty. 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 difficulties even with these very low impedance loads unless you demand excessively high volumes levels from your system. We do not recommend that you run additional sets of speakers to the GFA-7805/7807. If you choose to add remote speakers in another room, we strongly suggest that a switching system to disconnect the non-home-theater speakers be incorporated when the surround sound (home theater) mode is in operation. A device such as the ADCOM GFS-3 or GFS-6 speaker selector is recommended. A Speaker Selector enables you to maintain good sonic integrity while giving you the flexibility to add speakers throughout your house. We suggest that you follow this chart below for maximum speaker lengths and minimum wire gauges. If longer runs are needed, we recomend that you consult with your ADCOM Dealer to maximize the performance of your system for your exact conditions.

up to 24 feet

up to 36 feet

up to 58 feet

RESOLVING PROBLEMS
Use the chart below to solve common situations that dont 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. No sound

POSSIBLE REASON

AC Power Cord(s) not plugged in. AC Fuse(s) failed. Transformer thermal protection engaged. I2V DC triggering malfunctioning. Preamp or source unit is not on. Connections in rear of amp are loose. INPUT(s) or OUTPUT(s) connector disconnected or loose. Speaker disconnected. Internal protection engaged. Ground loop (difference in ground voltages between components). Problem with source unit (CD, tape, etc.), or RCA cable connecting that source unit to the preamp. Some major appliance, dimmer, halogen or fluorescent light is creating interference.

POSSIBLE SOLUTION

Plug in AC Power Cord(s). Replace AC Fuse(s). Wait until unit cools down. It will reset. Reset power switch manually. Check connection of 12V DC trigger at source. Make sure whole system is on. Verify all connections on rear of amp. Verify both connections on that channel. Verify connection at speaker. Bring to Dealer or Service Center. 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. Make sure all appliances, dimmers and suspect lights are off.
Power LED glows, but no sound One channel not producing sound
Hum from all speakers at any volume Hum from all speakers (hum goes up or down with volume) Hum from the amplifier itself
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. 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, 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, 75) at the wall, or the first component the cable is connected to (i.e. the cable box, or VCR). If the hum is no longer present, you must insert a 75 Ground Loop Isolator before reconnecting the line. You should check with your ADCOM Dealer to obtain one. If the 75 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 amplifier is at least 6 from the Preamp and/or Processor. Usually putting another component between them is sufficient to minimize the hum. If this does not reduce the hum, turn the system off and disconnect all Inputs from the amplifier. If the hum still persists, then your Dealer or Service Center must examine the amplifier. If the hum disappears, try another set of RCA cables. Connect one RCA cable at a time to see if one specific 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.

CARING FOR YOUR GFA-7805/7807
Great care has been taken by ADCOM to ensure that your amplifier is as flawless in appearance as it is electronically. The front panel is a heavy-gauge, high-grade aluminum extrusion carefully finished 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 finish. If the front panel, top or sides become dusty or fingerprinted, 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-7805/7807.

SERVICING

ADCOM has a Technical Service Department to answer questions pertinent to the installation and operation of your unit. In the event of difficulty, 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 factory. 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: ADCOM Service 8551 East Anderson Drive, Suite 105 Scottsdale, Arizona 85255 USA
Phone, Fax or Email inquires to: Voice: (480) 607-2277 Fax: (480) 348-9876 Monday through Friday 9:00 AM to 5:00 PM MST Email: service@adcom.com
For Fax inquires, please include a return Fax number for the reply. When calling or writing about your GFA-7805/7807, 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 fillers 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.

GFA-7805 SPECIFICATIONS

Power Rating (To EIA/CEA-490-A Requirements) 300 Watts continuous average power per channel into 8 ohms at any frequency between 20Hz and 20kHz with all channels driven at less than 1.00% THD. 450 Watts continuous average power per channel into 4 ohms at any frequency between 20Hz and 20khz with all channels driven at less than 1.00% THD. THD + Noise at 300 watts into 8 Ohms (Typical) 20Hz. 0.012% 1kHz. 0.135% 10kHz. 0.12% 20kHz. 0.12% THD + Noise at 450 watts into 4 Ohms (Typical) 20Hz. 0.3% 1 kHz. 0.3% 10kHz. 0.27% 20kHz. 0.1% Frequency Response @ 1 Watt into 8 Ohms 10Hz to 20kHz. +0, -0.25dB Power Bandwidth (-3d B). 3Hz to 130kHz Dynamic Headroom Into 4 Ohms. 0.96 dB Signal to Noise Ratio, A Weighted 300 watts into 8 ohms. 112dB Gain. 29.67dB Input Sensitivity for 1 Watt output. 0.1 volts for 300 Watts output. 1.61 volts Input Impedance Unbalanced. 500K ohms Balanced. 10K ohms Damping Factor 1k. > 500

SERVICE MANUAL
7 CHANNEL POWER AMPLIFIER

GFA-7807

TABLE OF CONTENTS Introduction. 1 Test Procedures. 1 Parts List. 2 Voltage Conversion. 5 PCB Layouts. 7 Schematic. 9
8551 East Anderson Drive,Suite 105 Scottsdale, Arizona 85255 USA Tel: 480-607-2277 Fax: 480-348-9876 Web: http://www.adcom.com

INTRODUCTION

This service manual is intended to assist trained and qualified technical personnel in verifying the performance of, adjusting, and repairing the ADCOM GFA-7807 amplifier. The procedures described here are not intended for persons unfamiliar with the appropriate safety and test procedures. WARNING THERE ARE POTENTIALLY LETHAL VOLTAGES WITHIN THE GFA-7807 AMPLIFIER WHICH WILL BE ACCESSIBLE ONCE ITS TOP COVER IS REMOVED. DO NOT ATTEMPT FAMILIARIZATION, INSPECTION, OR ANY PROCEDURE WHATSOEVER UNLESS YOU HAVE DISCONNECTED THE GFA-7807 FROM THE WALL AC OUTLET OR OTHER SOURCE OF AC POWER AND THE POWERSUPPLY CAPACITORS ARE COMPLETELY DISCHARGED. THESE INSTRUCTIONS ARE PROVIDED FOR USE ONLY BY COMPETENT TECHNICAL PERSONNEL. DO NOT UNDERTAKE ANY SERVICE PROCEDURES IN THE GFA-7807 UNLESS YOU ARE TECHNICALLY QUALIFIED TO DO SO.

TEST PROCEDURES

All tests are performed with a 115V, low-distortion (less than 2% THD), AC-power source, 8-ohm resistive load (except slew rate), and a signal source of not more than 600 ohms. An 80kHz low-pass filter is employed during THD distortion measurements. Signal-to-noise measurements are A weighted. Damping factor is measured by comparing the 1 watt output voltage with and without an 8 ohm load. Slew rate is measured with an inductive load, and is derived with a dual-time-based oscilloscope reading the slope of a full power 5kHz square wave. DO NOT OPERATE THE AMPLIFIER AT FULL-POWER SINE WAVE ABOVE 22kHz OR FULL-POWER SQUARE WAVE ABOVE 5kHz. IMPORTANT BEFORE PROCEEDING WITH ADJUSTMENTS, MAKE SURE AMPLIFIER IS AT ROOM TEMPERATURE. CORRECT BIAS ADJUSTMENT IS CRITICAL TO THE PERFORMANCE OF THIS AMPLIFIER. MAXIMUM OUTPUT POWER, MINIMUM THD AND HEAT DISSIPATION ARE AFFECTED BY THE BIAS SETTING AND MUST BE CORRECT TO MAINTAIN THE SONIC QUALITY AND LONGEVITY OF THE AMPLIFIER. BIAS ALIGNMENT The component references are the same for all channels. Operate the amplifier without load or input connection for this adjustment. 1. Turn the amplifier on and allow to idle for 5 minutes. 2. Initial bias of individual modules shuld be adjusted to 3mv across the 0.2 ohm emitter resistors. Recheck module bias when amp modules are in the chassis and warm. - Insert a 0.1 ohm resistor in the top fuse location F2 ( Note: I did this by taking 2 each 0.2 ohm emitter resistors in parallel and soldered to a burnt fuse. ) - Measure voltage across the 0.1 ohm resistor check and adjust ( VR1) bias to 10 mV or 100 mA at this point. NOTE: The bias adjustment must be performed with the heatsink attached and the amplifier module installed in the chassis. DC OFFSET CHECK 1. Connect a millivoltmeter across the speaker output terminals and confirm a reading of 0mV +/- 10mV.
GFA-7807 SERVICE PARTS LIST
AMPLIFIER MODULE PCB SCHEMATIC LOCATION BR1, BR2 C01 ,C04 ,C13 C02 ,C03 ,C14 ,C15 C05 ,C09 C06 ,C17 ,C23 C07 C08 C10 C11 C12 C16 ,C20 C18 ,C19 C21 ,C22 D01 ,D07 D02 ,D04 ,D08 ,D09 ,D10 D03-D06 U01 ,U04 U02 U03 U05 F1 ,F2 K1 Q01 Q02 ,Q09 ,Q23 ,Q24 Q26 ,Q28 Q03 Q04 ,Q12 ,Q13 Q05 ,Q06 ,Q07 ,Q08 ,Q11 Q10 Q14 ,Q15 ,Q16 ,Q17 ,Q22 Q18 Q19 Q20 Q21 Q27 R01 ,R43 R02 ,R45 ,R56 ,R57 R03 ,R19 R04 R05 R06 ,R35 ,R38 R07 ,R14 ,R24 ,R36 ,R39 ,R40 ,RBRIDGE RECTIFIER CAPACITOR ELEC CAPACITOR ELEC CAPACITOR ELEC CAPACITOR ELEC CAPACITOR POLYPROPYLENE CAPACITOR ELEC CAPACITOR POLY CAPACITOR SIVLER MICA CAPACITOR ELEC CAPACITOR POLY CAPACITOR ELEC CAPACITOR POLYPROPYLENE DIODE ZENER 15V 1/2W DIODE DIODE IC IC IC IC FUSE RELAY TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR TRANSISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR KBU8J 10uF 25V 5600uF 100V 0.1uF 50V 100uF 10V 6800pF 63V 47uF 25V 100nF 250V 7pF 500V 47pF 500V 0.22uF 50V 100uF 100V 330pF 100V 1N965B 1N4148 1N4007 4N25N NE555N H11AA814 TL071 T6.3A G4A-1A-PE 2SA1380 2N3904 2SC4793 2N5401 KSC5200 2SC1567A KSA1943 2SA1837 2SC3502 MPSA06 MPSA42 2N3906 1K 10K 2W 5% 2K21 22K221 4.75K ADCOM PART NUMBER DESCRIPTION
SCHEMATIC R08 ,R13 ,R22 ,R37
ADCOM PART NUMBER 27004210 2
DESCRIPTION RESISTOR 100K
R09 R10 R11 ,R25 ,R60 R15 R18 ,R23 ,R27 R30 ,R59 R20 ,R21 ,R47 ,R49 ,R51 R26 ,R34 R31 ,R58 R32 R33 R41 R42 ,R53 R44 R46 ,R48 R50 ,R52 R54 R61 ,R62 TH1 U1 SW1 VR1 POWER SUPPLY PCB SCHEMATIC LOCATION C01 C02 C03 C04 CF D1-D7 D8 RL1 RL2 F2 F2 LED1 Q1 Q2 ,Q3 Q5 ,Q6 R1A ,R1B R2 R3 R4 ,R5 R6 R7 ,R9 ,R10 R8 R11 RT1 T1 U1 BR1 OTHERS

35007800

RESISTOR RESISTOR RESISTOR RESISTOR JUMPER RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR THERMISTOR IC SWITCH BIAS POT
1.21K 200K 10K 0.22 3W 11 5W 47.5K 866 49.9 6.81K 5.62K 1M 390K 2K 85 DEG C LM555 500
ADCOM PART NUMBER 19009800
DESCRIPTION CAPACITOR ELEC CAPACITOR ELEC CAPACITOR ELEC SPARK KILLER CAPACITOR ELEC DIODE DIODE RELAY RELAY STANDBY FUSE FUSEHOLDER POWER LED TRANSISTOR TRANSISTOR TRANSISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR STANDBY TRANSFORMER REGULATOR IC BRIDGE DIODE #W06F 1000uF 25V 220uF 16V 10uF 16V 0.01uF 400V 470uF 25V 1N4007 1N4148 G4A-1A-P G4A-1A-E 1A LTL1204 RED MJE15031 MPSA13 2N1K 0.5W 3.32K 10K 200K 100K 2.21K 20W 1A 13.5V 7812 W06/W02

27004200

24007402 21007812

SCHEMATIC LOCATION T2 T2

ADCOM PART NUMBER
DESCRIPTION MAIN TRANSFORMER 7805 MAIN TRANSFORMER 7807 FOOT FRONT PANEL HEATSINK POWER BUTTON POWER BUTTON FRAME DC FAN 12 VOLT 4 EA. TOP COVER Multi Voltage Models
GFA-7807 Voltage Conversion The GFA-7807 amplifier is produced in both a 120VAC only version and a multivoltage (120VAC or 230VAC convertible) version. The version can usually be distinguished by external inspection. The 120VAC only version has a fixed AC line cord. The convertible version has a detachable line cord. Internally, their are two differences. The toroid transformer in the convertible version has 2 primaries; the first primary has a black and brown lead, the second primary has a black and brown lead with white stripe. The toroid transformer in the 120VAC only version has only the brown and black lead (1 primary winding). Additionally, the connecting block mounted next to the power switch is different in both versions. In the multivoltage unit, this connecting block has 5 pair of mounting leads (as is shown in the figures below). In the 120VAC only version, the connecting block has only 3 pairs of mounts. The conversion procedure for the multivoltage GFA-7807 unit is listed below.
Conversion of Multivoltage Units 120V to 230V 1. Unplug the amplifier and remove the top cover. 2. Locate the connecting block mounted next to the power switch. 3. Move the transformer leads so they are configured as shown in figure 1. 4. Remove 2 Jumpers 120 VAC at the Power supply board and insert to 230 VAC for detail as figure 1. 5. Place a sticker on the rear panel at the AC Line show the new value is 230 VAC 50/60 Hz 6. Test the unit with a 230VAC source.

Figure 1: Transformer lead configuration for 230VAC operation (multivoltage units)
230V to 120V 1. Unplug the amplifier and remove the top cover. 2. Locate the connecting block mounted next to the power switch. 3. Move the transformer leads so they are configured as shown in figure 2. 4. Remove the jumper 230 VAC at the Power supply board and insert 2 jumpers at 120 VAC for detail as figure 2. 5. Place a sticker on the rear panel at the AC Line and new value operating voltage (120VAC 50/60Hz). 6. Test the unit with a 120VAC source.
Figure 2: Transformer lead configuration for 120VAC operation (multivoltage units)