PIONEER GM-X644
Service Manual

Setting the Unit
Gain Control
Adjusting the gain controls A and B will help match the output of the car stereo to the Pioneer amplifier. Normally, set the gain controls to the �NORMAL� position. If the output is low, even when the volume of the car stereo is turned up, turn these controls clockwise. If there is distortion when the volume of the car stereo is turned up, turn these controls counter-clockwise.
� If you only use one input plug, set the gain controls for speaker outputs A and B to the same position. � When using with an RCA equipped car stereo (standard output of 500 mV), set to the NORMAL position. When using with an RCA equipped Pioneer car stereo with max. output of 4 V or more, adjust level to match the car stereo output level. � If you hear too much noise when using the speaker input terminals, turn the gain control counter-clockwise.

Connecting the Unit
CAUTION

Connection Diagram
� Make sure that wires will not interfere with moving parts of the vehicle, such as the gearshift, handbrake or seat sliding mechanism. � Do not shorten any wires. Otherwise the protection circuit may fail to work when it should. � Never feed power to other equipment by cutting the insulation of the power supply wire to tap from the wire. The current capacity of the wire will be exceeded, causing overheating. Fuse (30 A) Special red battery wire [RD-223] (sold separately). After making all other connections at the amplifier, connect the battery wire terminal of the amplifier to the positive (+) terminal of the battery. Fuse (30 A) Ground wire (black) [RD-223] (sold separately). Connect to metal body or chassis.

Power Indicator
The power indicator lights when the power is switched on.

� Disconnect the negative (�) terminal of the battery to avoid the risk of short-circuit and damage to the unit. � Secure the wiring with cable clamps or adhesive tape. To protect the wiring, wrap adhesive tape around it where they lie against metal parts. � Do not route wires where they will get hot, for example where the heater will blow over them. If the insulation heats up, it may become damaged, resulting in a short-circuit through the vehicle body.

Grommet

To prevent damage
� Do not ground the speaker wire directly or connect a negative (�) lead wire for several speakers. � This unit is for vehicles with a 12-volt battery and negative grounding. Before installing it in a recreational vehicle, truck or bus, check the battery voltage. � If the car stereo is kept on for a long time while the engine is at rest or idling, the battery may go dead. Turn the car stereo off when the engine is at rest or idling. � If the system remote control wire of the amplifier is connected to the power terminal through the ignition switch (12 V DC), the amplifier will always be on when the ignition is on� regardless of whether the car stereo is on or off. Because of this, the battery could go dead if the engine is at rest or idle. � Speakers to be connected to the amplifier should conform with the standards listed below. If they do not conform, they may catch fire, emit smoke or become damaged. The speaker impedance must be 1 to 8 ohms. But in case of two-channel and other bridge connections, the speaker impedance must be 2 to 8 ohms. � Install and route the separately sold battery wire as far away as possible from the speaker wires. Install and route the separately sold battery wire, ground wire, speaker wires and the amplifier as far away as possible from the antenna, antenna cable and tuner. � Cords for this product and those for other products may be different colors even if they have the same function. When connecting this product to another product, refer to the supplied Installation manuals of both products and connect cords that have the same function. Connecting wires with RCA pin plugs (sold separately).

RCA input

Amplifier with RCA input jacks

External Output If only one input plug is used, do not connect anything to RCA input jack B.

Car stereo with RCA output jacks

Front side

Input Select Switch For two-channel input, slide this switch to the left. For four-channel input, slide this switch to the right.

LPF (Low-Pass Filter)/HPF (High-Pass Filter) Select Switch Input Select Switch
For two-channel input, slide this switch to the left. For four-channel input, slide this switch to the right. Set the LPF/HPF select switch as follows according to the type of speaker that is connected to the speaker output connector and the car stereo system: LPF/HPF Select Switch
LPF (left) OFF (center) HPF (right)

RCA output jack

RCA input jack B RCA input jack A

Speaker Channel
Four-channel Two-channel Three-channel Speaker output A Three-channel Speaker output B

Speaker Type
Subwoofer Other than subwoofer Subwoofer Other than subwoofer Subwoofer Other than subwoofer Subwoofer Other than subwoofer

Power
Nominal input: Min. 65 W Max. input: Min. 100 W Nominal input: Min. 170 W Max. input: Min. 240 W Nominal input: Min. 65 W Max. input: Min. 100 W Nominal input: Min. 170 W Max. input: Min. 240 W Speaker terminal See the �Connecting the Speaker wires� section for speaker connection instructions. Fuse (25 A) � 2

Audio frequency range to be output
* � 40 to 120 Hz Full range * 40 to 120 Hz �

Speaker Type
Subwoofer Full range Full range

Remarks
Connect a subwoofer. Use if you want to cut the very low frequency range* because it is not necessary for the speakers you are using.

Back side

Connecting wires with RCA pin plugs (sold separately).

Cut Off Frequency Control
If the LPF/HPF select switch is set to LPF or HPF, you can select a cut off frequency from 40 to 120 Hz.

* See the �Cut Off Frequency Control� section.

System remote control wire (sold separately) Connect the male terminal of this wire to the system remote control terminal of the car stereo (SYSTEM REMOTE CONTROL). The female terminal can be connected to the auto-antenna relay control terminal. If the car stereo does not have a system remote control terminal, connect the male terminal to the power terminal through the ignition switch.