Adcom GFA-555 Pro User manual

:
ADCOM
GFA-555
PRO
POWER
=-
AMPLIFIER
Àk
_
OWNER'S
MANUAL
. Brunswick, NJ 08816
[phone]

GFA-555
PRO
AMPLIFIER
OWNERS
MANUAL
WELCOME
lt
is
very
important
that
you
read
this
owners
manual
thoroughly
before
tuming
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:
—
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.

SECTION 1
WHAT TO DO WHEN XOU 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 maintained. 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 happilv in anv reasonable environment.
Of course, such normal considerations as protection from excessive dust and moisture should alwavs 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
front panel for your convenience.
The Output terminals on the GFA-555 are the standard S-wav 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, vou should alwavs 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 the 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.
p For mono operation, the Stereo/Bridged switch on the rear panel should be placed in the Bridged position.
In the Bridged mode only 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 to 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 be noted that any time the circuit breakers trip, it is an indication that the amplifier is either
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 be 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.
aay oe

:
i
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1
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
„+
concem.
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 absolute 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
amplifier
designs
currently
available.
Thistleparture
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
turn
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
construction
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
by
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.

a ae cee ee ...
nn
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 ınust be suspected. No further attempts to replace the fuse or operate the amplifier should be made before
recheċking 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 to 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
[phone]
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 returned 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. FREIGHT COLLECT SHIPMENT CANNOT BE ACCEPTED.

ee
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.

1
Foie
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GFA-555
Pro
SPECIFICATIONS
Mee
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ra
ne
A
Power
output,
watts/channel,
continuous,
'
botħichannels
driven,
20Hz
-
20kHz,
at
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THD,
through
either
balanced
or
unbalanced
inputs:
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-
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<
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DADs
Sant
min.
Intermodulation
distortion
(SMPTE,
4:1
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stereo
mode,
at
any
level
up
to
200
watts
continuous
through
either
balanced
or
unbalanced
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distortion
(SMPTE,
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ratio),
bridged,
mono
mode
at
any
level
up
to
600
watts,
min.
(8
ohms),
or
850
watts
min.
(4
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through
either
balanced
or
unbalanced
DOA
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referred
to
200
watts
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Individual
level
control
is
provided
for
each
Stereo
channel.
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below
is
for
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controls
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max.,
full
clockwise
position.
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Dimensions
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|
|
TEAS
-
Heigh
€:
ua
42200
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5/16"
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(483mm)
Depth
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199;
1/4'
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