Adcom GFA-555 User's Manual
Contents
1. front panel for your convenience The Output terminals on the GFA 555 are the standard 5 way binding posts The output terminals are spaced to permit the use of the so called Banana Plugs when using the amplifier as a stereo unit When connecting speakers to the GFA 555 you should always use the largest wire size lowest gauge number that is available to you We recommend at least 16 gauge 2 conductor cord zip cord for distances up to 25 feet For distance up to 50 feet 14 gauge wire should be used You may also wish to consider some of the commercially available speaker cables which have been designed to improve the connection between the power amp and the speakers When connecting the speaker wires correct phasing is required to obtain maximum bass response and to preserve a coherent sound when vocalists perform The simplest way to insure proper phasing is to inspect the wires being used Some form of coding is always employed whether a ridge or groove on one edge or side of the wire or the wires may be of different colors one copper wire and one silver For example to connect a speaker to the Left Channel of the GFA 555 using a length of color coded wire connect the copper colored wire to the Left Channel Positive Red output terminal on the amplifier Next connect the silver colored wire to the Left Channel Negative Black output terminal Now connect the other end of the copper colored wire to the Positive terminal of th2. ADCOM GFA 555 PRO POWER AMPLIFIER k OWNER S MANUAL E Brunswick NJ 08816 908 390 1130 GFA 555 PRO AMPLIFIER OWNERS MANUAL WELCOME It is very important that you read this owners manual thoroughly before turning on your ADCOM GFA 555 Power Amplifier Your ADCOM GFA 555 represents the most advanced thinking in audio amplifier design At 200 watts per channel the GFA 555 offers an exceptional value superior performance at a reasonable price Some of the outstanding features of this product are l 200 Watts per Channel 20Hz 20KHz into an 8 ohm load with both channels driven less than 0 09 Total Harmonic Distortion 325 Watts per Channel 20Hz 20KHz into a 4 ohm load with both channels driven with less than 0 25 Total Harmonic Distortion The ability to drive very low impedance loads Bridged mode power of 600 watts 20Hz 20 KHz into an 8 ohm load with less than 0 25 Total Harmonic Distortion Instantaneous Distortion Alert which indicates when distortion products are above the 1 level Power supply circuit breakers for overload protection Provisions for both Balanced and Unbalanced input signals This manual has been written to anticipate the kind of questions you may encounter while enjoying your GFA 555 power amplifier Please read it thoroughly to fully understand all of the features offered and how they can be used to maximize the performance of your audio system
3. Bends ov Individual level control is provided for each Stereo channel Sensitivity below is for level controls at max full clockwise position Balanced Tn pwt i side iis een OdBm Unbalanced InpUE una ae BV Balanced Input OVET LOADS oii 6 SiG so reiten Damping Factors e eoeneneveeeeeev eo seven oo LE EE SE E e gt 130 Dynamic Headroom 3 Las 2 0 008000000 0 vo eue vv z eee 2 kd 3 dB Protection Incoming AC power line Fuse 12 Amperes AGB Bt and B rails resettable circuit a breakers two per channel ii 7 Amperes Power Requirements win on special order 240VAC 60Hz version can 3 3 be SUDPLiCd eee cece cece cece ccncccccecs 117 VAC EOHZ Shipping Weights 0 ccc cece cece nec eceececescecee ss 34 lbs 15 5kgs Men Dimensions ha Heights na Saw Se ae g gate kun an 5 16 185mm i Width Leeeenesenesenzonsesssesenannnns ce 19 483mm Depth un sesssssseess sse l Z 1 4 311mm
4. SECTION 1 WHAT TO DO WHEN YOU OPEN THE BOX Before each GFA 555 left the factory it was carefully inspected for physical imperfections as a routine part of ADCQM s systematic quality control This along with full electrical testing should insure a product flawless in both appearance and performance After you have unpacked the amplifier inspect it for physical damage Save the shipping carton and all packing materials as they are essential to reduce to a minimum the possibility of transportation damage should the product ever need to be shipped again In the unlikely event that damage has occurred notify your dealer immediately and request the name of the carrier so that a written claim to cover shipping damage can be initiated THE RIGHT TO ANY CLAIM AGAINST A PUBLIC CARRIER CAN BE FORFEITED IF THE CARRIER IS NOT NOTIFIED PROMPTLY AND IF THE SHIPPING CARTON AND PACKING MATERIAL ARE NOT AVAILABLE FOR INSPECTION SAVE ALL PACKING MATERIALS UNTIL THE CLAIM HAS BEEN SETTLED SECTION 2 WHERE TO PUT IT AND WHERE NOT TO The GFA 555 utilizes large external heat sinks to dissipate heat from the power transistors The top and bottom panels of the amplifier have slots to allow air to circulate inside the amplifier Adequate air circulation must be available to ensure cool operation of the amplifier Therefore the GFA 555 should not be completely enclosed with other heat producing components and adequate space around the amplifier should be maintain
5. EIGHT COLLECT SHIPMENT CANNOT BE ACCEPTED SECTION 9 ADCOM PROTECTION PLAN U S A ONLY ADCOM offers the enclosed LIMITED WARRANTY Please read the details carefully to fully understand the extent of the protection offered by the warranty its limits and what responsibilities are required of you in order to obtain its benefits GFA 555 Pro SPECIFICATIONS Power output watts channel continuous both channels driven 20Hz 20kHz at lt 0 09 THD through either balanced or unbalanced inputs Be 8 SONS a ae ea ele oe DOO min Fa OBMBLe aan ae een 32 SE Bridged mono mode 8 ohms 20Hz 20kHz at less than 0 25 THD ccc cee ecw cece 600 min Bridged mono mode 4 ohms 20Hz 20kHz lt 0 25 TED ne TIN 14 min Intermodulation distortion SMPTE 4 1 ratio stereo mode at any level up to 200 watts continuous through either balanced or unbalanced inputes c cceceee 0 093 Intermodulation distortion SMPTE 4 1 ratio bridged mono mode at any level up to 600 watts min 8 ohms or 850 watts min 4 ohms through either balanced or unbalanced DUDUES i ai soe ea 0 25 Signal to Noise Ratio A weighted referred to 200 watts output 2 ecm cece cc ccc cesescee gt 110dB Input Impedance Balanced input 0 cc ccc ec ccc ee ee e600 ohms Unbalanced input depends on position of level CODEKOLS cc cece ccc cece cccccccceccecee22 Kohms min Input Sensitivity for 200 Watts Output N
6. amplifier designs currently available This leparture is the result of a careful study of all known amplifier technology circuits and parts The main feature of the GFA 555 is its outstanding ability to drive the vast majority of speakers to high sound levels while maintaining the sonic integrity of the music The Instantaneous Distortion Alert is a unique distortion detection circuit which reads all forms of distortion THD IM Slew Induced and DC Offset Peak LEDs one per channel will glow when distortion is above 1 regardless of the load impedance or reactance In use the LEDs may occasionally flicker under high volume listening If they glow brightly or are on most of the time that you are listening you are over driving your equipment and should tum down your volume control We consider the GFA 555 to be a truly significant contribution to the advancement of sound technology To ensure that the quality of construction is on par with the quality of the sonics a much neglected area in many other amplifiers the GFA 555 has been carefully developed with computer controlled metal fabrication techniques that maintain 0 005 of an inch tolerances throughout Full electrical inspection of each and every circuit board subassembly as well as the finished amplifier provide a mechanically and sonically superior product for your enjoyment At the time of its design we know of no other product on the market which offered the design and constructi
7. be noted that any time the circuit breakers trip it is an indication that the amplifier is cither encountering a short circuit or being over driven Check all input and output connections for loose wires and short circuits The input signal level should he reduced either through the use of the input signal attenuators on the GFA 555 or at the mixing console main output or volume control The most common cause of Thermal shut down is improper ventilation of the amplifier Please refer to Section 2 for proper installation instructions Ir ae Because of the great amount of electrical energy stored in the capacitors the design of the GFA 555 will allow music to remain audible for several seconds after the amplifier has been shut off We suggest that you wait until the red power LED has stopped glowing before turning off your preamplifier and other components This procedure will prevent turn off transients from reaching your speakers During the shut down procedure you may hear small noises through your speakers which result from capacitor discharge This is normal and is no cause for concern SECTION 5 SAFETY WARNING CAUTION TO PREVENT ELECTRICAL SHOCK DO NOT REMOVE THE AMPLIFIER COVER THERE ARE NO USER SERVICEABLE PARTS INSIDE REFER SERVICING TO QUALIFIED PERSONNEL ONLY i CAUTION BURN OUT OF THE OUTPUT STAGE BECAUSE OF FAILURE TO OBSERVE THE PRECEDING AND FOLLOWING PRECAUTIONS WILL VOID THE WARRANTY There is no such thing as a
8. bsolute reliability or protection when amplifiers are abused While the GFA 555 amplifier has been designed to operate reliably under normal conditions it may not be impervious to gross abuse There is one condition which must always be avoided This condition is called RF Detection and because ADCOM amplifiers have such an extremely wide band width RF Detection will almost certainly cause failure of the output devices if it occurs Damage to or failure of this equipment due to RF Detection is considered abuse and is specifically excluded from the ADCOM warranty The following acts cause RF Detection and MUST BE AVOIDED 1 Connecting the inputs or outputs while the amplifier is ON 2 Using the Thumb Test It is a dangerous habit to connect cables to the inputs touching the other end of the cable while the amplifier is ON This may not only cause amplifier failure but may destory your loudspeakers due to the high power surge emitted from the amplifier It is essential to follow the procedure of completely hooking up your system before turning anything on A few simple precautions will contribute to trouble free performance Because of the high power capability of the GFA 555 ADCOM will not be responsible for any damage to speakers or other components due to their inability to handle the amplifiers power output or any other misuse SECTION 6 WHY WE BUILT IT THE WAY WE DID The ADCOM GFA 555 represents a departure from many of the other
9. e Left speaker Connect the other end of the silver colored wire to the Negative terminal of the Left speaker Follow the same procedure for connecting the Right speaker to the Right channel outputs IT IS IMPERATIVE THAT THE MAIN POWER TO THE AMPLIFIER IS DISCONNECTED DURING THE HOOK UP PROCEDURE The GFA 555 PRO has a detachable grounded AC line cord This cord should be connected to the amplifier before plugging the unit into the AC wall outlet Remember all input and output connections should be made before plugging the amplifier into the wall outlet After the correct hook up procedure has been followed the AC line cord should be plugged into an outlet providing 120 volts AC 50 60 Hz BRIDGED MONO HOOK UP The ADCOM GFA 555 PRO amplifier can be used as an extremely powerful monaural amplifier without the use of any additional accessories or modifications a For mono operation the Stereo Bridged switch on the rear panel should be placed in the Bridged position In the Bridged mode oniv a single input cable is used The input cable to the GFA 555 should be plugged into the Right Channel input only The Right Channel input signal attenuator will function should amplifier matching be necessary When connecting a single speaker to the GFA 555 in bridged operation the Positive lead from the speaker should be connected to the Right Channel Positive Red output terminal on the GFA 555 The Negative lead from the speaker should be connected t
10. ed We recommend at least 3 inches on the top and 1 inch on the sides and rear for air circulation If the GFA 555 is going to be mounted in an enclosed cabinet it is recommended that the back of the cabinet have vents to allow air to circulate around the amplifier With these considerations in mind the GFA 555 should perform quite happily in any reasonable environment Of course such normal considerations as protection from excessive dust and moisture should always be observed The ADCOM GFA 555 power amplifier has been carefully designed with high quality components so that long term undiminished performance may be expected from the amp when it is operated in accordance with the instructions provided SECTION 3 WHERE AND HOW ALL THE WIRES GO All connections are conveniently located on the rear panel of the GFA 555 PRO Any suitable program source such as a control preamplifier or mixing board may be used ALL CONNECTIONS MUST BE MADE WITH THE AMPLIFIER UNPLUGGED AND THE AC POWER SWITCH OFF Inputs are provided for both Balanced and Unbalanced input signals There is a selector switch on the rear panel of the amplifier for Balanced and Unbalanced Input selection The jacks provided for Unbalanced input signals are standard 2 conductor 1 4 inch phone type The jacks provided for the Balanced input signals are for XLR connectors Input signal attenuators are provided for matching left and right signal levels These attenuators are mounted on the
11. o the Left Channel Positive Red output terminal Remember that when connecting the speaker wires you should maintain proper phasing to obtain maximum bass response and coherent sound quality SECTION 4 AMPLIFIER PROTECTION CIRCUIT Your GFA 555 power amplifier is equipped with externally mounted circuit breakers These Breakers are designed to provide overload protection for the amplifier There are two circuit breakers for each channel mounted on the front panel for easy access If any of the circuit breakers should trip a button in the center of the breaker will pop out Before resetting the breaker be sure to turn the power switch off lower the input signal level and check for short circuits To reset the circuit breaker simply depress the button that has popped out If the breaker trips again immediately recheck all connections for shorts and allow several seconds to elapse before attempting to reset the breaker again UNDER NO CIRCUMSTANCES SHOULD THE BREAKER BUTTON BE DEPRESSED AND HELD IN If any of the breakers cannot be successfully reset after checking all connections please refer to Section 8 Thermal cutoffs are also employed to protect the amplifier under high temperature conditions Should any of the thermal cutoffs activate Turn off the amplifier reduce the input signal level and make sure that the amplifier has adequate ventilation Allow several minutes for the thermostat to reset before resuming normal operation It should
12. o write or call us in the event of difficulty and we shall endeavor to offer prompt advice If your problem can not be resolved through our combined efforts we may wish to refer you to an authorized repair agency or we may prefer to authorize return of the unit to the factory To aid us in directing you to a convenient service station it would be helpful if you indicate which major city is accessible to your home Please address inquiries to ADCOM TECHNICAL SERVICE DEPT 11 ELKINS ROAD EAST BRUNSWICK NJ 08816 201 390 1130 When calling or writing about your amplifier be sure to include the model and serial number of your unit as well as the date of purchase and the dealer from whom the unit was purchased In the event that the unit must be retumed to us for service you will be instructed as to the proper procedure when you call or write for return authorization UNDER NO CIRCUMSTANCES SHOULD YOUR UNIT BE SHIPPED TO THE FACTORY WITHOUT PRIOR AUTHORIZATION OR WITHOUT THE ORIGINAL CARTON AND FILLERS If the original shipping carton has been lost or discarded or if the carton is not in good condition a duplicate carton may be obtained from our service department for a nominal charge Always ship PREPAID via UPS or other recognized surface carrier DO NOT SHIP VIA PARCEL POST since the packing will not withstand rough mail handling We are forced to refuse most Partcel Post shipments since they arrive in such poor condition FR
13. on quality of the GFA 555 at anything close to its selling price We sincerely hope that you ll agree SECTION 7 THE CARE AND FEEDING OF YOUR GFA 555 Great care has been taken hy ADCOM to assure that your amplifier is as flawless in appearance as it is electronically The front panel is heavy gauge high grade anodized aluminum If the front panel should become fingerprinted or smeared it can be cleaned with a damp soft cloth UNDER NO CIRCUMSTANCES SHOULD A STRONG OR ABRASIVE CLEANER SUCH AS SCOURING POWDER OR OVEN CLEANER BE USED ON ANY PART OF THE AMPLIFIER The amplifier is protected by a line fuse on the rear panel If the power is switched ON and the small red LED on the front panel does not illuminate after a few seconds shut off the amplifier unplug the AC line cord from the power outlet and check the AC line fuse If the fuse has opened replace it ONLY with a fuse of equal value REPLACEMENT WITH AN INCORRECT FUSE OR ONE OF A HIGHER RATING WILL NOT PROTECT THE AMPLIFIER AND WILL VOID THE WARRANTY If after replacing the fuse it blows immediately an electronic component failure or shorted output connection must be suspected No further attempts to replace the fuse or operate the amplifier should be made before rechetking all connections SECTION 8 IF YOU HAVE A PROBLEM OR QUESTION ADCOM has a technical service department to answer all questions pertinent to the installation and operation of your unit Please feel free t
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