Adcom GFA-555 User manual

ADCOM
P C W E R 4M P
G F k - 5 5 5

ADCOM GFA-555 OWNERS MANUAL
WELCOME
It ia very important hat you thoroughly read th is owners manual befote
turning your ADCOM GFA-555 power am plifier on. (For those In a hurry* please
read Se tions 1-5).
Your ADCOM GFA-555 represents the most advan ed thinking In audio am plifier
design. At 200 wa te per hannel, the GFA-555 offers an ex eptional value;
superior performan e at a reasonable pri e. Some of the outstanding features of
th is produ t are:
- 200 w atts per hannel* 20UZ-20KU2* into an 8 ohm load with both hannels
driven with le ss than 0.09% to ta l harmoni d isto rtio n .
- 325 w atts per hannel, 20Ha-20KHz, into a A ohm load with both hannels
driven with le ss than 0.25% to ta l harmoni d istortio n .
- The a b ility to drive very low impedan e load s.
- Bridged mode power of 600 w atts, 20Hz~20KH2, into art 8 ohm load with le ss
than 0.25!? to tal harmoni d istortio n .
- Instantaneous D istortion Alert whi h in d i ates whenever distortion produ ts
are above the 1 % le v el.
This manual has been w ritten to anti ip ate the kinds of questions you
might en ounter w hile enjoying the fu ll ben efits of your ADCOM GFA-555 power
am plifier. Please read it thoroughly to fu lly understand a ll the features offered
and how they an be used to maximize the performan e of your audio system*

SECTION 1
WHAT TO DO WHEN YOU OPEN THE BOX
Before ea h GFA-555 le ft the fa tory, i t was a refu lly Inspe ted for
physi al im perfe tions as a routine part of ADCOM's system ati quality ontrol.
This, along with fu ll ele tr'i a l te stin g, should insure a produ t flaw less in
both appearan e and performan e. After you have unpa ked the am plifier, inspe t
it for any physi al damage. Save the shipping arton and a ll pa king m aterials
as they are essen tia l to redu e to a minimum the p o ssib ility of transportation
damage 3hould the produ t ever need to be shipped again. In the un likely event
that damage has o urred, notify your dealer immediately and request the name
of the arrier so that a w ritten laim to over shipping damages an be in itiated .
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 external heat sinks to d issip a te heat from the
power tra n sisto rs. The top and bottom panels of the am p lifier have slo ts to allow
air to ir u late inaide the am plified, Adequate air ir u la tion must be available
to assure ool operation of the amp. Therefore, the GFA-555 should not be omplete
en losed with other heat produ ing omponents, and adequate spa e around the amp
li f ie r should be maintained. We re ommend at le a st 3 in hes on the top and I in h
on the sid es and rear for air ir u la tio n . I f the GFA-555 is going o be mounted
in an en losed abinet, it is re ommended that the ba k o f the abinet have vents
to allow air to ir ula te around the am p lifier. With these onsiderations in mind,
the GFA-555 should perform quite happily in arty reasonable environment. Of ourse,
su h normal onsiderations as prote tion from ex essive dust and moisture should
always be observed. The ADCOM GFA-555 power am plifier has been a refu lly designed

with high qu ality omponents so that long term undlminished performan e way be
expe ted from the amp when it is operated in a ordan e with the Instru tions
provided.
SECTION 3
WHERE (AND HOW) ALL THE WIRES GO
A ll onne tions are onveniently lo ated on the rear panel o£ the GFA-555.
Any su itab le program sour e, eu h as a ontrol pream plifier may be used* ALL
CONNECTIONS MUST BE MADE WITH THE AMPLIFIER UNPLUGGED AND THE AC POWER SWITCH OFF.
When making input aignal onne tions, only high q u ality shielded ( o-a xial)
audio able should be used. The input ja ks a ept the standard two- otulu tor
RCA-type phono plugs.
The lin e ord should be plugged into an AC ou tlet providing 120 v o lts AC,
50-60 Hert2. Output onne tions from the GPA-555 an be made to any standard or
ele tro sta ti lovdgpeafrer system.
When onne ting speakers to the GFA-555, you should always use the largest
wire size (low est gauge number) that is available to you. We re ommend at lease
16 gauge, 2- ondu tor ord (sip ord) for distan es up to 25 fee t. For distan es
of up to 50 fe e t, 14 gauge wire should be used. You also may wish to onsider
some of the ommer ially available speaker ables whi h have been sp e ia lly designed
to improve the onne tion between the povfe* Am plifier and the loudspeakers. In a ll
ases, i t is to your best soni advantage to keep the wire distan es as sho as
possib le between the power am plifier and the loudspeakers. When onne ting the
speaker w ires, orre t phasing is required to obtain maximum bass response and CO
preserve a oherent sound when vo alistB perform. The sim plest way to ensure
proper phasing is to lo sely inspe t the w ire being used. Some form of ading is
always employed, whether & ridge or groove on one edge or side of the wire, or one
of the wlre3 may be tinned* On e determined, th is same oded wire should be on
ne ted to the p o sitiv e terminal of the speaker systems. Then follow the same
pro edure for the other loudspeaker. An alterna te (but lea s relia b le) method for

he king proper phase response l 3 to onne t two speakers and then pla e them
side by sid e. Play some mono program m aterial w ith heavy bass ontent through
the system. Now turn o ff the system , and reverse one pair of leads to one speaker.
Turn on the system and play the same passage again. If the bass response has in
reased, leave the system as i t now is . I f it has dim inished, turn off the system
and rew ire it as i t was o rigin ally s e t up. When making loudspeaker onne tions
are must be taken to avoid short ir u its whi h w ill ause improper operation of
the a m p lifier,
BRIDGED (MONO) HOOKUP
The ADCOM GFA-555 an be used as an extremely powerful monaural am plifier
without the use of any additional a esso ries or m odifi ations.
For mono operation, the Stereo/Bridged swit h on the rear panel should be
pie ed in the bridged p osition . In the Bridged mode only a sin gle input able is
used. The input able to the GFA-555 should be plugged in to the RIGHT CHANNEL
input only.
When onne ting a sin g le speak&r to the GFA-555 in bridged operation, the
p ositiv e terminal of the speaker should be onne ted to the righ_t hannel p ositive
(red) output post on the GFA-555. The negative term inal of the speaker should be
onne ted to the le ft hannel p ositiv e (red) output post. Remember that when
onne ting the speaker w ires, yr>u should maintain proper phasing to obtain maximum
bass response and oherent sound quality.
AMPLIFIER PROTECTION CIRCUIT
Vour GFA-555 power am plifier is equipped with external and internal fuses
whi h are designed to prote t your loudspeakers from p ossib le damage and a lso to
prote t the amp it s e lf under a ll but the severest abuse of operating onditions.
A thermal u toff is also employed to p rote t the am p lifier under high temperature
on ditions.
Be ause of the great amount of e le tr i a l energy stored in it s apa itors.

the design of the GFA-555 w ill allow musi to remain audible for several se onds
after the am plifier has been shut o ff. We suggest that you vai u ntil the red
power LED has stopped glowing before turning o ff your pre-amp and other asso iated
audio equipment:. This pro edure w ill avoid tu rn-off tran sients from rea hing 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 of the output stage be ause of fa ilu re to observe the
follow ing pre autions w ill void the warranty*
There is no su h thing as absolute r e lia b ility or prote tion when am plifiers
are abused. While the GFA-555 am p lifier has been designed to operate relia b ly
under norwal on ditions, i t may not be Impervious to gross abuse. There is one
ondition whi h must always be avoided: This ondition is alled RF D ete tion and
be ause ADCOM am plifiers have an extremely wide bandwidth, RF Dete tion w ill almost
ertainly ause failu re o£ the output devi es if it o urs. Damage to, or fa ilu re
of the equipment due to th is reason is onsidered abuse, and is sp e ifi a lly
ex luded from Che ADCOM warranty.
The following a ts ause RF Dete tion and MUST BE AVOIDED:
1. Conne ting the inputs or outputs w hile the am plifier is on.
2. Using the 11 thumb te st." It is a dangerous habit to ontifedt ables to the
inputs, tou hing the other end of the able while the am plifier is on.
This may not only ause am plifier fa ilu r e but may destroy your loudspeakers

due to the high power surge emitted from the am plifier.
XL is e sse n tia l to follow the pro edure of om pletely hooking up your system
before turning anything on! A few sim ple pre autions w ill ontribute to trouble
free p rfortnan e. Be ause of the high power of the GFA-555, ADCOM w ill not be
responsible for any damage to speakers or other omponents due to their inability
to handle the am p lifier's power output or for any other misuse.
SECTION 5
WHY WE BUILT IT THE WAY WE DID
The ADCOM GFA-555 represents a departure from many of the other urrently
availab le am plifier d esig n s, This departure is the resu lt of areful study of a ll
known am plifier te hnology, ir u its and parts. The major feature of the GFA-555
is it s outstanding a b ility to drive v ir tu a lly any speaker, regardless of impedan e,
to high sound le v e ls w hile maintaining the soni in teg rity of the musi . By using
a 700 watt transformer along with 60,000 mi rofarads of filt e r apa itan e, the
GFA-555 an provide ontinuous power, not only momentary power for demanding
musi al tra n sien ts. A lso tontributing to the outstanding performan e is the use
of 16 high- urrent output tra n sisto rs along with p re ision parts sele tion of the
omponents used in a ll audio ir u its,
The Instantaneous D istortion A lert ir u it is a unique d istortion dete tion
ir u it whi h reads a ll forms of distortio n —THD» IM, slew indu ed, and DC o ffse t.
Peak LEDs, one per hannelj w ill glow when d isto rtion is over 13 regardless of
the load impedan e or rea tan e. In use, the LED an o asionally fli k er under
high volume liste n in g . I f they §low brigh 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
on trol.
We onsider the GFA-555 a tru ly sig n ifi an t ontribution to the advan ement
of sound te hnology. To ensure that the quality of onstru tion is on par with the
quality of soni s, (a mu h n egle ted area in many other am plifiers) the GFA-555 has
been arefully developed w ith omputer ontrolled metal fab ri ation te hniques tha
maintain ,005 of an in h toleran e throughout. F ull ele tr i a l inspe tion o! ea h

and every ir u it board, sub-assem bly, as w ell as the fin ished am plifier, provide
a so n i ally and m e hani ally superior produ t fox your enjoyment.
SECTION 6
THE CARE AMD FEEDING OF YOUR GFA-555
Great are has been taken by ADCOM to assure that your am plifier Is as
flaw less In appearan e as It is ele tro n i a lly . The front panel is high-grade
anodized aluniinum, hosen for it s d u rability and beauty. I f the front panel should
be ome fingerprinted or smeared, i t an be leaned with a damp, soft 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 prote ted by a lin e fuse on the rear panel, tf power Is
swit hed on and the sm all red LED on the front panel does not illu m inate a fter a
few Be onds, shut off the a m plifier, unplug the AC lin e ord from the power o u tle t,
and he k the AC lin e fu3e. If the fuse has opened, repla e It 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 after repla ing the fu se, i t blows irnmedlately, an ele troni omponent
fa ilu re must be suspe ted* No further attempts to repla e the fuse should b£ made.
SECTION 7
IF YOU HAVE A PROBLEM OR QUESTION
ADCOM has a Te hni al Servi e Department to answer a ll questions pertinent
to the in sta lla tio n and operation of your un it, Flease fe e l free to w rite or a ll
ub in the event of any d iffi u lty * and we shall endeavor to offer prompt advi e.

I f your problem annot be resolved through our onftirted efforts* we may wish to
refer you to an authorized repair agen y, or we may prefer to authorize return of
your un it to the fa tory. To aid us In d ire tin g you to a onvenient servi e
statio n , i t would be h elp fu l if you in d i a te whi h major ity is a essib le to
your home.
Please address in q u iries to:
ADCOM TECHNICAL SERVICE DEPARTMENT
11 ELKINS ROAD
EAST BRUNSWICK, NJ 08816
[phone]
Be sure to in lude the aerial number of your u n it, date of pur hase, and name and
address of dealer. In the event it m ist be returned, an authorization form and
proper pa king in stru tions w ill be forwarded to you. This authorization form
should be returned with your unit to id en tify i t and avoid unne essary delay.
UNDER NO CIRCUMSTANCES SHOULD TOUR UNIT BE SHIPPED TO THE FACTORY WITHOUT
PRIOR AUTHORIZATION, OR WITHOUT ORIGINAL PACKING CARTON AND FILLERS.
If the original shipping arton has been lo s t or dis arded, or i f the arton is
not in good ondition, a du pli ate arton may be obtained from our Servi e Department
for a nominal harge.
Always 3hip PREPAID v ia UPS or other re ognized surfa e arriers. DO NOT
SHIP VIA PARCEL POST, sin e the pa king w ill not withstand tough mail handling.
We are for ed to refu se most Par el Post shipments sin e they arr£v<5 in su h poor
ondition. FREIGHT COLLECT SHIPMENTS CABNOT BE ACCEPTED,
SECTION a
ADCOM PROTECTION PLAN (U.S.A. ONLY)
ADCOM o ffe rs the en losed one year LIMITED WARRANTY. P lease read the d eta ils
a refully to understand fu lly the extent of the p rote tion offered by your warranty,
it s lim its, and what re sp o n sib ilities are required of you in order to ohtain its
b en e fits.