ADCOM
P C W E R 4 M P
G F k - 5 5 5
ADCOM GFA-555 OWNERS MANUAL
WELCOME
It ia very important chat you thoroughly read th is owners manual b efote
turning your ADCOM GFA-555 power am p lifier on. (For those In a hurry* please
read S ections 1 -5 ).
Your ADCOM GFA-555 rep resents the most advanced th inking In audio am plifier
design . At 200 wacte per channel, the GFA-555 offe rs an exceptional value;
superior performance at a reasonable p rice. Some of the outstanding featu res of
th is product are:
- 200 w atts per channel* 20UZ-20KU2 * in to an 8 ohm load with both channels
driven with less than 0.09% t o ta l harmonic d is to r tion .
- 325 w atts per channel, 20Ha-20KHz, into a A ohm load w ith both channels
driven with less than 0.25% to t a l harmonic d is to rtio n .
- The a b ilit y to d rive very low impedance loads.
- Bridged mode power of 600 w a tts, 20Hz~20KH2, in to art 8 ohm load with le ss
than 0.25!? to ta l harmonic d isto rtio n .
- Instantaneous D istortion A lert which in d icates whenever d istortion products
are above the 1 % lev e l.
This manual has been w ritten to a n tic ip a te the kinds of q uestions you
might encounter w hile enjoying the f u ll b e n efits of your ADCOM GFA-555 power
am plifier. Please read i t thoroughly to fu lly understand a l l the fea tures offered
and how they can be used to maximize the performance of your audio system*
SECTION 1
WHAT TO DO WHEN YOU OPEN THE BOX
Before each GFA-555 l e f t the fa cto ry , it was ca r efu lly Inspected for
phy sical im perfections as a routine part of ADCOM's system atic q u ality control.
This, along w ith f u ll e lectr'ic a l te stin g , should insure a product fla w less in
both appearance and performance. After you have unpacked the a m plifier, inspect
it for any p h ysical damage. Save the ship ping carton and a ll packing m ateria ls
as they are ess e n tia l to reduce to a minimum the p o s s ib ility o f transportation
damage 3hould the product ever need to be shipped again. In the u nlikely event
that damage has occurred, n otify your dealer immediately and request the name
of the carr ier so that a w ritten claim to cover shipping damages can be in itia te d .
THE RIGHT ID ANY CLAIM AGAINST A PUBLIC CARRIER GAB BE FORFEITED IF THE
CARRIER IS NOT NOTIFIED FRQMPTLY 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 (AWD WHERE NOT TOt)
The GFA-555 u tiliz e s large ex ter nal h eat sink s to d issip a te heat from the
power tra n sisto rs . The top and bottom panels o f the am p lifier have slo ts to allow
air to c irculate in aide the a m p lified, Adequate a ir c ircu la tio n must be av ailab le
to assure cool operation of the amp. Therefore, the GFA-555 should not be complete
enclosed with other heat producing components, and adequate space around the amp
lif ie r should be m aintained. We recommend a t le a st 3 inches on the top and I inch
on the sid e s and rear for air c ircula tio n . I f the GFA-555 i s going co be mounted
in an enclosed ca binet, it is recommended that the back o f the cabinet have vents
to allow air to c ircu late around the a m plifier. With these consideration s in mind,
the GFA-555 should perform quite happily in arty reasonable environment. Of course,
such normal considerations as p ro tection from excessive dust and m oisture should
always be observed. The ADCOM GFA-555 power am p lifier has been c are fu lly designed
with high q u a lity components so that long term undlminished performance way be
expected from the amp when i t i s operated in accordance with the In structions
provided.
SECTION 3
WHERE (AND HOW) ALL THE WIRES GO
A ll con nections are conven iently loca ted on the rear panel o£ the GFA-555.
Any su ita b le program source, euch as a control pream plifier may be used* ALL
CONNECTIONS MUST BE MADE WITH THE AMPLIFIER UNPLUGGED AND THE AC POWER SWITCH OFF.
When making input aignal co nn ections, only high q u a lity shield ed (co-ax ia l)
audio cab le should be used. The input jack s accept the standard two-cotuluctor
RCA-type phono plugs.
The lin e cord should be plugged in to an AC o u tlet providing 120 v o lt s AC,
50-60 Hert2 . Output connections from the GPA-555 can be made to any standard or
ele c trosta tic lovdgpeafrer system.
When connecting speakers to the GFA-555, you should always use the larg est
wire s iz e (lowest gauge number) that is a vailab le to you. We recommend at lease
16 gauge, 2-conductor cord (sip cord) for d ista nces up to 25 feet. For d istan ces
of up to 50 fe e t, 14 gauge wire should be used. You a lso may wish to consid er
some of the commercially ava ila ble speaker cables which have been s p e cia lly designed
to improve the connection between the povfe* A m plifier and the loudspeakers. In a ll
ca se s, it is to your best sonic advantage to keep the w ire d istances as shocc as
possib le between the power am plifier and the loudspeakers. When connecting the
speaker w ires, correct phasing is required to obtain maximum bass response and CO
preserve a coherent sound when vocalistB perform. The sim plest way to ensure
proper phasing is to clo sely in sp ect the w ire being used. Some form of cading is
always employed, whether & ridg e or groove on one edge or sid e of the wire, or one
of the w lre3 may be tinned* Once determined, th is same coded w ire should be con
nected to the p o s itiv e term inal of the speaker system s. Then follow the same
procedure for the other loudspeaker. An alter n ate (but le a s r elia b le ) method for
checking proper phase response l 3 to connect two speakers and then p lace them
sid e by sid e. Play some mono program m aterial w ith heavy bass content through
the system. Now turn off the system , and reverse one pa ir of lea ds to one speaker.
Turn on the system and play the same passage again. I f th e b ass response has in
creased, leave the system as i t now is . If i t has dim inished, turn o ff the system
and rew ire i t as i t was o r ig in a lly s e t up. When making loudspeaker connections
care must be taken to avoid short c ircu its which w ill cause improper operation of
the a m p lifier ,
BRIDGED (MONO) HOOKUP
The ADCOM GFA-555 can be used as an extremely powerful monaural am plifier
without the use of any a dditiona l a c cesso ries or m o d ifica tion s.
For mono operation, the S tereo/Bridged switch on the rear panel should be
pieced in the bridged p o s itio n . In the Bridged mode only a single input cable is
used. The input cab le to the GFA-555 should be plugged in to the RIGHT CHANNEL
input only.
When connecting a sin g le speak&r to the GFA-555 in bridged operation, the
p o s itiv e term inal of the speaker should be connected to the righ_t channel p o sitive
(red) output p ost on the GFA-555. The n egative terminal of the speaker should be
connected to the l e f t channel p o sitiv e (red) output p o st. Remember that when
connecting the speaker w ires, yr>u should maintain proper phasing to obtain maximum
bass response and coherent sound q u ality.
AMPLIFIER PROTECTION CIRCUIT
Vour GFA-555 power am plifier is equipped with exte rn al and internal fu ses
which are designed to protect your loudspeakers from p ossible damage and also to
protect the amp its e lf under a l l but the s ev erest abuse o f operating condition s.
A therm al cutoff i s also employed to p rotect the a m plifier under high temperature
co ndition s.
Because o f the great amount o f e lectr ic a l energy stored in i t s ca pacito rs.
the design of the GFA-555 w ill allow music to remain audib le for several seconds
after the a m plifier has been shut o ff . We suggest that you vaic u n til the red
power LED has stopped glowing b efore turning o ff your pre-amp and other a ssociated
audio equipment:. This procedure w ill avoid tu rn-o ff tran sients from reaching your
speakers.
SECTION 4
SAFETY WARNING
CAUTION: TO PREVENT ELECTRIC SHOCK, DO NOT REMOVE COVER, NO USER
SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED PERSONNEL ONLY.
SERVICE TECHNICIANS NOTE
THE FILTER CAPACITORS USED IN TI1E GFA-555 RETAIN A CHARGE FOR SOME TIME
EVEN AFTER THE UNIT IS TURNED OFF AND UNPLUGGED. DO NOT TOUCH ANY INTERNAL
WIRING OR COMPONENTS INCLUDING THE INTERNAL FUSES UNTIL THE CAPACITORS ARE
FULLY DISCHARGED. SEE GFA-555 SERVICE MANUAL FOR ADDITIONAL WARNINGS.
CAUTION: Burn-out o f the output stage because of failu re to observe the
follow ing p recautio ns w i ll void the warranty*
There is no such th ing as ab so lute r e lia b ilit y or protection when am plifiers
are abused. While the GFA-555 am p lifier has been designed to operate relia b ly
under norwal con d itions, i t may not be Impervious to gross abuse. There is one
con dition which must always be avoided: This condition is called RF D etection and
because ADCOM a m plifiers have an extremely wide bandwidth, RF Detection w ill almost
certain ly cause fa ilu r e o£ the output devices i f i t occurs. Damage to, or fa ilu re
of the equipment due to th is reason i s considered abuse, and is sp e c if ic a lly
excluded from Che ADCOM warranty.
The follow ing acts cause RF D etection and MUST BE AVOIDED:
1. Connecting the inpu ts or outputs w hile the am plifier is on.
2. Using the 11 thumb t est." It is a dangerous habit to contifedt cab les to the
inp u ts, touching the other end of the cable w hile the am p lifier is on.
This may not only cause am p lifier failu r e but may destroy your loudspeakers
due to the high power surge em itted from the a m plifier.
XL i s e s sen tia l to fo llow the procedure of com pletely hooking up your system
before turning anything on! A few simple precautions w ill con tribu te to trouble
free pcrfortnance. Because o f the high power of the GFA-555, ADCOM w ill not be
respo nsible for any damage to speakers or other components due to th eir in abil i ty
to handle the a m p lifie r's power output or for any oth er m isuse.
SECTION 5
WHY WE BUILT IT THE WAY WE DID
The ADCOM GFA-555 rep resents a departure from many of the other cu rren tly
ava ilable a m plifier d esig n s, This departure i s the resu lt of ca reful study of a ll
known am p lifier technology, c ir c u its and par ts. The major featu re of the GFA-555
is i t s outstanding a b ilit y to drive v ir tu a lly any speaker, regardless of impedance,
to high sound le v e ls w hile m aintaining the sonic in tegrity of the music. By usin g
a 700 watt transformer along w ith 60,000 m icrofarads of f i l t e r capacitance, the
GFA-555 can provide continuous power, not only momentary power for demanding
musical transients. Also to n trib u tin g to the outstanding performance is the use
of 16 high-current output tr a n sisto r s along with p r ec isio n p arts se le ctio n o f the
components used in a ll audio c ir c u its ,
The Instantaneous D istortio n A lert c ir c u it is a unique d istortion detec tion
circu it which reads a l l forms of d istortion—THD» IM, slew induced, and DC o ff s e t.
Peak LEDs, one per channelj w ill glow when d is to rtio n is over 13 regardless of
the load impedance or reactan ce. In u se, the LED can occa sionally flick e r under
high volume liste n in g . If they §low b righ tly or are on most <?f the time that you
are liste n in g , you are overdriving your equipment and should turn down your volume
co n trol.
We consid er the GFA-555 a tru ly sign ifica n t contrib ution to the advancement
of sound technology. To ensure th at the qu ality of construction is on par with the
qua lity of s on ics, (a much n eglected area in many other a m plifiers) the GFA-555 has
been carefu lly developed w ith computer controlled m etal fabrication techniques thac
maintain ,005 of an inch to lerance throughout. F ull e lectr ica l inspection o! each
and every cir cu it board, sub-assem bly, as w ell as the fin ish ed am p lifier, provide
a so n ic a lly and m echanically superior product fox your enjoyment.
SECTION 6
THE CARE AMD FEEDING OF YOUR GFA-555
Great care has been taken by ADCOM to assure that your am p lifier Is as
fla w les s In appearance as I t is electr o n ic a lly. The front panel i s high-grade
anodized aluniinum, chosen for i t s d u rab ility and beauty. I f the front panel should
become fingerp rinted or smeared, i t can be cleaned w ith a damp, soft c loth .
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 am p lifier 1b p rotected by a lin e fu se on the rear panel, tf power Is
switched on and the small red LED on the front panel does not illu m inate a ft er a
few Beconds, shut o ff the am plifier , unplug the AC lin e cord from the power o u tle t,
and check the AC lin e fu 3e. If the fuse has opened, replace I t QNL’f with a fuse of
equal value.
REPLACEMENT WITH AN INCORRECT FUSE OR ONE OF A HIGHER CURRENT RATING WILL
NOT PROTECT THE AMPLIFIER AND WILL VOID THE WARRANTY.
If a fte r replacing the fuse, i t blows irnmedlately, an e lectr onic component
fa ilure must be suspected* No further attempts to repla ce the fuse should b£ made.
SECTION 7
IF YOU HAVE A PROBLEM OR QUESTION
ADCOM has a T echnical S ervice Department to answer a ll questions pertinent
to the in s ta lla tio n and operation of your u n it, Flease f e e l free to w rite or ca ll
ub in the event of any d if ficu lty * and we sh a ll endeavor to offer prompt advice.
I f your problem cannot be resolved through our conftirted efforts* we may wish to
refer you to an authorized rep air agency, or we may prefer to authorize return of
your u n it to the fa ctory. To aid us In d irec tin g you to a convenient service
sta tio n , i t would be h elpful i f you in d icate which major c ity is a c cessib le to
your home.
Please address in q u iries to:
ADCOM TECHNICAL SERVICE DEPARTMENT
11 ELKINS ROAD
EAST BRUNSWICK, NJ 08816
(201) 390-1130
Be sure to include the a e rial number of your u n it, date of purchase, and name and
address of dealer. In the event i t m ist be returned, an au thorization form and
proper packing in stru ctions w ill be forwarded to you. This au thorization form
should be returned w ith your u nit to id en tify i t and avoid unnecessary delay.
UNDER NO CIRCUMSTANCES SHOULD TOUR UNIT BE SHIPPED TO THE FACTORY WITHOUT
PRIOR AUTHORIZATION, OR WITHOUT ORIGINAL PACKING CARTON AND FILLERS.
If the o rigin a l shipping carton has been lo s t or discarded , or i f the carton is
not in good co ndition , a d uplic ate carton may be obtained from our Service Department
for a nominal charge.
Always 3hip PREPAID v ia UPS or other recognized surface c arr iers. DO NOT
SHIP VIA PARCEL POST, sin ce the packing w ill not withstand tough mail handling.
We are forced to refu se most P arcel P ost shipments since they arr£v<5 in such poor
cond ition . FREIGHT COLLECT SHIPMENTS CABNOT BE ACCEPTED,
SECTION a
ADCOM PROTECTION PLAN (U.S.A. ONLY)
ADCOM o ffe r s the enclosed one year LIMITED WARRANTY. P lease read the d e tails
ca r efully to understand f u lly the extent o f the protection offered by your warranty,
its lim its , and what r e sp o n sib ilities are required of you in order to ohtain it s
b en efits.
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