This is the 11 pages manual for Adcom GFA 4302 Service Manual.
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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 -œThe
Ultimate Power Trip".
In servicing the GFA-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 straight forward, 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
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-4302 amplifier produces 30 watts RMS into a 49 load. The amplifier can be configured to run in
a bridged mode. and is stable into a i .(2 load. The input to the amplifier consists oi four (4) RCA
connectors, in a Balanced Configuration. There are 2 RCA connectors per channel, one for the positive
input and one for the negative (out of phase) input. The other balanced mode which is called Passively
Terminated Balanced Configuration, has the signal applied to the positive input, and the -œsignal" ground
(chassis) of the head unit applied to the negative input. The amplifier can also be used in the bridged
mode or the MoStm (Mono + Stereo) configuration. Basic diagrams are displayed on page 4. For more
detailed configurations, refer to the Owner's Manual or the Technical Details Manual.
The GPA-4302 provides level controls tor the positive input, these should be set at full during testing.
When bridging the amplifier, the input is applied to the positive input of one channel (Le. - Ch A), and the
negative channel of the other channel (i.e. - Ch B). The Speaker (or load) is then connected as so: "A+" is
the positive lead, and -œB+" is the negative lead. RCA shorting plugs must be inserted into all unused input
jacks for proper operation.
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, ii the unit was modified by a third party, or ii the
unit is from a production run prior to the implementation of the printed updates. Also see page 8 for
most common differences.
0 When replacing parts in the GPA-4000 series amplifiers, always use the same type, and rating.
0 When repiacing 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
Remember that ADCOM Service is available from 9:00 AM to 6:00 PM EST for inquires. or you can fax
us at (908)390-9152.