Adcom GFA 4404 Service Manual

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For Qualified Service Personnel Only

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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 GFA-4DOO series amplifiers you will see the straight fomard, bare bones, high
quality constnrction. 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 it not configured properly. The biggest difference you will find in hook-up of these
amplifiers is the input configuration. The GFA-4ooo series uses a Balanced Input configuration.
As you know this reduces noise coming into the amplifier on 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 GFA-MM is a 40 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 (2 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: m - Ground; Pi_nz . +' Right Ch; Bin-3 - '- Right Ch; Pin 4 - + Left Ch; EM
Left on. The amplifiers with XLR cables are more effectively utilized when used with the GH-
4400/ 4600. they allow polarity inversion to be done with a pinjumper. and provide a'converslon
from unbalanced RCA's to balanced XLR connectors. The GFI is also useful for configuring in
Mono-Stereo set-ups. The GFI-4400 provides balance line conversion and polarity selection.
The GFl-4600 provides all the features available in the CPI-4400. as well as the addition of a two
way crossover. in lieu of a GFI unit. the GFYJ and GFY-4 cables may be used to configure the
unit as desired. The GFY-3 is used for Mono bridging, while the GFY-4 is used for stereo
operation. Refer to the Technical Details Manual for further information.

The GPA-4404 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 (Le. - on B). The Speaker (or load) is then

put across the positive speaker ten-ninais of channels A d B (Le. - from Ch A's '+' to on as +').

Service Notes:

0 The enclosed schematics are version 1.4. 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 or 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.

Remember that ADCOM Service is available from 9:00 am to 4:00 pm for inquires. or you can

fax us at (908)390-9152.

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K. Katagan 2/25/94