Adcom GFA 4304 Service Manual

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SERVICE MANUAL

ADCOM®

defails you can hear

CAR AUDIO
POWER AMPLIFIER

GFA-4304

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 FIOAD
EAST BRUNSWICK, NJ 08818
PHONE: (908) 390-1130
FAX: (908) 390-9152

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Welcome To ADCOM Car Audio

The ADCOM GPA-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 Trip".

In servicing the GPA-4000 series amplifiers you will see the straight forward. 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 straightforward, and easily located.

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
coniiguration. 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 Manuat.

The GPA-4304 amplifier produces 30 watts RMS per 4 channels into a 4 Q load. The amplifier can be
configured to run in a bridged mode, and is stable into a 1 S2 load. The input to the amplifier consists of
two (2) XLR connectors, in a Balanced Configuration. There is one (1) XLR connectors for channels A a
B and one for channels C & D. The pin configuration for the XLR connector is: Ein_1 - Ground: mg - +"
Right Ch; Egg; - u." Flight Ch: Pin 4 - +" Left Ch; M -" Left Oh. The amplifiers with XLR cables are
more effectively utilized when used with the (EH-440014600, they allow polarity inversion to be done with a
pin jumper, and provide a conversion from unbalanced RCA's to balanced XLFt connectors. The GFl is
also useful for configuring in Mono-Stereo set-ups. The GFl4400 provides balance line conversion and
polarity selection. The GFl-4600 provides all the features available in the GF|~4400, as well as the addition
of a two way crossover. In lieu of a GFl unit, the GFY-t and GFY-4 cables may be used to configure the
unit as desired. The GFY~1 is used for Mono bridging, white the GFY-4 is used for stereo operation. Refer
to page 4 for wiring configuration.

The GPA-4304 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 (i.e. - Ch A), and the
positive channel of the other channel (i.e. - Ch B). The Speaker (or load) is then put across the positive
speaker terminals of channels A & B (i.e. - from Ch As +" to Ch Bs +").

Service Notes:

0 The enclosed schematics are version 1.5, and include all current updates to the original design. If you
encounter changes in the circuit on a unit you are servicing, please call ADCOM Service, at (908)390-
1130, to find out if 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 end circuits. Use care as these are
static sensitive devices. and require all special handling precautions associated with static sensitive
devices.

Ftemember that ADCOM Service is available from 9:00 am to 5:00 pm for inquires. or you can fax us at
(908)390c9152.

ElliesechstI-immaxmg at anytime withoumefise

K.Karagen 6/1/95