This is the 11 pages manual for Adcom GFA 4404 Service Manual.
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For Qualified Service Personnel Only
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 +').
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
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.
K. Katagan 2/25/94