Adcom GFA 4702 Service Manual

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SERVICE MANUAL

ADCOM®

defaiis you can hear

CAR AUDIO
POWER AMPLIFIER

GFA-4702

TABLE OF CONTENTS
Introduction ....................................... 2
Specifications and Features ............. 3
Wiring Configurations ....................... 4
Parts Lists ......................................... 5
Notes ................................................. 8
Schematics ........................................ 9

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TECHNICAL SERVICE DEPARTMENT
11 ELKINS ROAD
EAST BRUNSWICK, NJ 08816
PHONE: (908) 390-1130
FAX: (908) 390-9152

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Welcome To ADCOM Car Audio

The ADCOM GFA-4000 series car amplifiers offer the consumer a new level of sound quality in the mobile
environment. Audiophile sound quality is now unleashed to the streets in what ADCOM calls The

Ultimate Power Trld.

tn servicing the GFA~4000 series amplifiers you will see the straight fonNard, bare bones, high quality
construction, and attention to detail that has been engineered into this line of power amplifiers. You will
see that most repairs are very straight forward, and easily located.

The GFA-4702 is of a unigue amplifier design. The power supply section is in a separate chassis and the
amplifier section occupies another separate chassis. The two sections are connected by two umbilical
cables. The high current is transferred by a 7-conductor color coded cable. and the regulated, high voltage
is transferred by a smaller vain Molex° terminated cable.

Attention to the hook-up of these amplifiers is essential. as the amplifier will not perform optimally if not
configured properly. The biggest difference you will find in hook-up of these amplifiers is the input
configuration. The GPA-4000 series uses a Balanced input configuration. As you know this reduces
noise induced into the amplifier at the input. For more information on the hook-up, and on the theory
behind the Balanced input configuration. please refer to the Technical Details Manual.

The GPA-4702 is a 70 watt per channel RMS amplifier into a 4 0 load. The amplifier can be configured to
run in a bridged mode, and is stable into a 1 9 load. The input to the amplifier consists of one (1) XLR
connector, in a Balanced Configuration. The XLFi connector 3 pin configuration is: Bill - Ground; m
- +" Right on; mg - -" Right Ch; £10.31 - + Left Ch; m -" Left Ch. The amplifiers with XLFi cables
are more effectively utilized when used with the GFI-440W 4600. they allow polarity inversion to be done
with a pin jumper, and provide a conversion from unbalanced RCA's to balanced XLR connectors. The
GFI is also useful for configuring in Mono-Stereo set-ups. The GFl-44OO provides balance line conversion
and polarity selection. The GFI-4600 provides all the features available in the GFI-4400, as well as the
addition of a two way crossover. In lieu of a GFI unit, the GFY-t and GFY-4 cables may be used to
configure the unit as desired. The GFY-t is used for Mono bridging, while the GFY-4 is used for stereo
operation. Refer to page 4 for wiring configurations, or to the Technical Details Manual for further
information.

The GFA-4702 provides level controls for the positive input, these should be set at full during testing.
When bridging the amplifier, the input is applied to the negative input of one channel (Le. - On A), and the
positive channel of the other channel (is. . Ch B). The Speaker (or load) is then put across the positive

speaker terminals of channels A at B (i.e. . from Ch As + to Ch B s "+).

Service Notes:

0 The enclosed schematics are version 1.5, and include all current updates to the original design. It you
encounter changes in the circuit on a unit you are servicing, please call ADCOM Service, at (908)390-
1130, to find out it the changes are factory authorized, if the unit was modified by a third party, or if the
unit is from a production run prior to the implementation of the printed updates.

0 When replacing parts in the GPA-4000 series amplifiers. always use the same type. and rating.

0 When replacing the MOSFET devices, use only the same type of devices removed. The MOSFET
devices also MUST be matched in the output stages, and front and circuits. Use care as these are
static sensitive devices, and require all special handling precautions associated with static sensitive
devices.

Remember that ADCOM Service is available from 9:00 am to 6:00 pm for inquires, or you can fax us at
(908)390-9152.

This service literature. nevehengeaiany time without notice.
K.Karagan 6/1/95