Adcom S.A.F.E. GFA-7705 User manual

G FA- 7 70 5
GFA-7/0/
s.a.f.e:
HIGH CURRENT, MULTI-CHANNEL
POWER AMPLIFIERS

GFA-7705/07 Features
• Precision-matched devices used throughout the signal path.
• 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.
• ADCOM-Universal pre-prepped chassis and internal power supplies for easy in-field upgradeability
from 5 to 7 channel configuration.
• Independent thermal-overload and distortion LEDs for all 5 (to 7) channels.
• S.A.F E.® Circuit: Self Annealing Fuse Equipped—automatic reset protection circuit in the event of
speaker or speaker wire dead-short.
• High quality, gold-plated 5-way binding posts.
• High quality, gold-plated RCA jacks.
• Large independent, internal heatsinks for greater cooling capability of output devices.
• Convenient 12 VDC power ON/OFF triggering.
• Heavy gauge, anodized aluminum front panel.
• Cooling vents for greater efficiency and cooler operation while driving low impedance loads.
Table of Contents
Introduction
Warranty Information. 4
Description of Unit— 20-Amp Device Notification .4
Rear Panel..
Front Panel..
Installation & Hookup
Unpacking the GFA-7705/07. 9
Placement of the GFA-7705/07.9
Quick Connection Diagram. 1 0
Connecting the GFA-7705/07. H
Caring for your GFA-7705/07. 12
Troubleshooting
Resolving Problems. 1 3
Service Information... 1 4
Specifications. 1 5
3

Introduction
Congratulations on your decision to purchase the GFA-7705/07 multi-channel power amplifier. The GFA-7705/
07 integrates very well with any other home theater system, such as Dolby ProLogic ™ or Dolby Digital ™ You
have made a wise choice that will reward you with exceptionally accurate and musical sound reproduction for
years to come. To realize the full potential of your new amplifier, please read these operating and installation
instructions thoroughly before attempting to make any connections to it.
ADCOM Protection Plan (NORTH AMERICA ONLY)
ADCOM offers the enclosed valuable Limited Warranty. Please read the details on the Warranty Card carefully
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, 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.
Description of Unit
The GFA-7705/07 is a 20-Amp Device.
GFA-7705/07 is high-power, high-current, wide-bandwidth design employing ADCOM’s Fast Analog Transform
(F.A.T.) circuitry with direct-coupled Power Rig output stages. All channels are completely monaural from
transformer secondaries through the output stages.
In order for this product to achieve its actual rated power output on all channels and to avoid repeatedly
throwing/popping the related electrical service panel circuit breaker, it is critical that the amplifier be
professionally installed on a 20-Amp household AC circuit and outlet, preferably dedicated but at minimum one
not shared with other large current-draw appliances or devices.
Common 15-Amp household circuits are easily and inexpensively converted to 20 Amp configuration by any high
voltage licensed electrician. 5 y 1 s
For this reason, the GFA-7705/07 ships Factory-equipped with a hard-wired, 20-Amp Plug on the AC Power Cord.
nnfr^p^AMnliDun^I P LUG ° R HARDWIRED AC POWER CORD TO EMPLOY EITHER A 15 AMP
OUTLET OR “AUDIOPHILE” TYPE DETACHABLE POWER CORD.
■ r^|^^7^^^^^^~^^^^~P R 000-0 T ' ^^ ARRA ~'^^ ^^^0^^^0—THE PRODUCTAN D PUCE THE USER AT EXTRFMF RISKflF
INJUR Y OR DEATH.
4

Rear Panel
Inputs (1)
The audio inputs for the GFA-7705 and 7707 are through high-quality, gold-plated RCA jacks to minimize hieh
RCA -T ■ *» ~* «* SZ5!S££1L L
manvc e b l FA wh 05 h /07 '* P [ eSerVed ’ you should use the quaUt^shiJ^
C0,Or ‘ C °S a 1 Specmca " y * ***** , OT « *WfcaUoo. YourZSca^Mp
select the best cable for your needs. (See Connecting the GFA-7705/07 for more information.) P
Inputs (1b)
Chassis knock-out for future expansion channel-card input jack (GFA-7705 only).
Outputs (2)
EssjSassisHssS®* “ ■ ™ S 1 vxzv
(See CONNECTING THE GFA-7705/07 for more information.)
Outputs (2b)
Chassis knock-out for future expansion channel-card output binding posts (GFA-7705 only).
5

WARNING
THERE ARE NO USER-SERVICEABLE PARTS OR FUSES INSIDE THE GFA-7705/07. In the event that the
amplifier’s rear-panel circuit breaker fails to reset (opens again when power applied to unit and unit
turned on) you must refer the amplifier to ADCOM Factory Service or ADCOM Authorized Service Center.
Do not open the amplifier nor remove the topcover-Hazardous and Potentially Lethal Voltage Present
and Warranty may be voided.
12VDC Triggering (3a)
ADCOM has provided the installer the ability to control the OFF/ON function of the GFA-7705/07 by a
12Volt DC output jack on the rear of certain pre-amplifiers and tuner pre-amplifiers. When using this
feature the front panel Power Switch must be left in the in “on” position. To connect, you will need a
monaural mini phone plug to monaural mini phone plug cable of appropriate length (not included) to
reach from the rear panel of the amplifier to the rear panel of the pre-amplifier. Contact your dealer
for information on using this feature with ADCOM and other brand pre-amplifiers. Although 12VDC is
optimal, the circuit will operate from approx. 5 to 30VDC. Center conductor (tip) is positive (+).
AC Circuit Breaker (3b)
The 15-Amp AC Breaker protects the electronic circuits of the GFA-7705/07. Normally, this breaker will
open only if there is an overload or a component failure within the GFA-7705/07.
If the Power LED (7) does not glow, it may be an indication that the AC Breaker has blown. If you are
using the 12VDC Triggering feature (above) it may be possible that there is no trigger voltage present or
a problem exists with that connection.
To determine if the problem is caused by a malfunction in the 12VDC system, remove the small plug
inserted into the 12VDC Triggering jack. Press the front panel power switch to turn off the amp, and
immediately re press the power switch. If the problem is caused by the 12VDC triggering circuit the
amp will turn on and the LED will glow.
DO NOT attempt repair of the 12VDC system. If you are not sure, or the amplifier displays other
symptoms, please consult the RESOLVING PROBLEMS section on page 13.
AC Power Cord (4)
The AC cord provides power to operate all the GFA-7705/07’s circuits. The GFA-7705/07 is a very high
power amplifier and as such must be directly connected to the wall outlet or an appropriate (non-
current limiting) surge protector or AC line conditioner of 20-Amp service capability.
NOTE: As previously described on Page 4, the attached plug is a 20-Amp fitting which, in order for the
amplifier to deliver its rated power output, should not be defeated in order to accomodate standard
15-amp household wall outlets.
Please consult with your dealer and/or licensed electrician for conversion of a 15 amp outlet and panel
circuit to a 20 amp circuit.
6

(5) (6)
(7) (8a, 8b)
Front Panel
On/Off Switch (5)
™ e^v“S,F. h ™ r /n7 et t0 frrr t,ansfor ™ r .«* »*
Power LED (6)
seconds to fully extinguish. t me t0 fade 001 com Ptetely. It may take up to 30
“ ' he GFA - 7 705, ° 7 . «* P°«r LED will no.
triggering, source *—« -
7

Distortion Alert LEDs (7)
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 vour
loudspeakers.
Thermal Protection LEDs (8a)
The GFA-7705/07 is provided with both a thermal protection circuit and a current overload circuit
which will shut down the individual amplifier's channels if its heatsink temperature reaches 85° C or the
amplifier’s outputs are shorted. The Thermal Protection LEDs will light when either of these protection
circuits are on 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 channel’s 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-7705/07 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.
S.A.F.E.® Protection Circuit (8b)
Self-Annealing Fuse Equipped: Instead of blowing internal protection rail fuses in the event of a dead-
short to either a loudspeaker or speaker cable leads, the GFA-7705/07 will enter into a self-protect
SAFE mode.
If the output of any channel of the amplifier becomes shorted the protection circuit will trip and
the individual Thermal Protection LED for that channel will light. The Protection LED will blink
approximately every 5 seconds as the circuit will attempt to reset; if the short has been corrected the
amplifier will resume proper operation. If the short is still present the channel will cycle off again.
The cycling of the protection circuit will continue until the short is corrected or the amplifier power is
switched off.
8

WARNING
Whenever connections to or from the GFA-7705/07 are being made, be certain that the AC On/Off Switch
(5) of the amplifier is in the OFF position, the AC Power Cord (4) of the amplifier is disconnected from the
AC wall outlet and that all associated components are turned off.
Installation & Hookup
Unpacking the GFA-7705/07
Before your new GFA-7705/07 left our factory, it was carefully inspected for physical imperfections and
tested for all electrical parameters as a routine part of ADCOM’s 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-7705/07 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.
Placement of the GFA-7705/07
During normal home operation the internal heatsinks of the GFA-7705/07 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 amplifier's long-term, trouble-free operation, it is necessary to provide
adequate ventilation for the heatsinks. Therefore, the GFA-7705/07 should be kept away from external
sources of heat such as radiators and hot-air ducts. The GFA-7705/07 should never be placed with other
heat-producing components in a cabinet or enclosure lacking free air flow. The top and bottom panels
of the amplifier’s 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-7705/07. Not only will heat
generated by the amplifier affect the performance of equipment stacked on top of the GFA-7705/07,
but the free flow of air through the ventilating slots in the amplifier may be partially obstructed. This is
particularly important if your system includes low-impedance loudspeakers which are difficult to drive, or
you will consistently demand high volume levels from the amplifier and speaker system.
If you observe these recommendations, the GFA-7705/07 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-7705/07 will ultimately depend on the care with which you
make the connections between the amplifier, preamplifier, surround sound decoder and the loudspeakers.
All input and output signal connections should be made only with high quality, low capacitance, shielded
cables following the recommendations in the Inputs and Outputs section of CONNECTING THE GFA-7705/07.
Quick Connections
For those of you who are in a hurry to hook up your amplifier into your system, we have included this
quick-connection section. The wiring is straight forward and expeditious if you use the proper cables
and follow this diagram exactly. If you have any difficulties or questions, please refer to the appropriate
section of this manual for complete descriptions and instructions.
9

Connecting the GFA-7705/07
Remember, that the Left and Right designations are as you are sitting down in your listening/viewing area
Theyareas fdSs ”*** and ° UtpUtS are gr ° Uped in 5 or 7 bracketed sets, one set for each channel.'
LB - Left Back (GFA-7707 only)
LS — Left Surround
LF — Left Front
C — Center
RF — Right Front
RS — Right Surround
RB - Right Back (GFA-7707 only)

Inputs (1)
To preserve the correct effects, be certain to connect the RCA cables to the proper RCA-input
connector. If the cables are color coded, then use this sequence for the connections:
^ ue ..Left Front
fted...Right Front
G feen ...Center
White with Blue Stripe....Left Surround
White with Red Stripe.Right Surround
The recommended maximum RCA cable capacitance should be less than or equal to 30pF per foot
when measured between the two conductors, and less than or equal to 50pF per foot when measured
between one conductor and the shield.
Outputs (2)
NOTE. The GFA-7705/07 is “polarity correct”. That is, it does not invert phase from input to output.
Any positive signals at its inputs will appear as a positive signal at its outputs.
In connecting the amplifier to the loudspeaker, it is vital to maintain proper polarity (positive to
positive, negative to negative). On the GFA-7705/07, the positive terminal is color coded RED and
labeled “+,” and the negative is color coded BLACK and labeled
The positive terminal on the corresponding loudspeaker will be color coded RED, or will be labeled “+,”
“pos,” "positive,” “8 ohms,” or “A ohms.” The negative terminal on the speaker will be color coded
BLACK, or will be labeled “neg,” negative,” “C,” “Common,” “G,” or “ground.”
It is necessary that your speaker cables be terminated with “U”-
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” (see diagram on right).
type spade connectors. These will give
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. Recommended
capacitance of the speaker wire should not exceed 50pF per foot. This insures high frequencies will not
be rolled-off.
11