Zapco ST-4B 4-Channel Class AB Amplifier

Safety Precautions

• Always disconnect the vehicle's negative battery terminal before beginning any installation.
• Ensure all wiring is properly routed and secured to prevent damage or short circuits.
• Use appropriate gauge wiring for power and ground connections to handle current demands.
• Avoid mounting the amplifier in locations exposed to excessive heat, moisture, or direct sunlight.
• Consult a professional installer if you are unsure about any part of the installation process.

Mounting the Amplifier

Select a mounting location that provides adequate ventilation for the amplifier to dissipate heat. Common locations include under a seat, in the trunk, or behind a panel. Ensure the mounting surface is solid and secure. Use the provided mounting screws to firmly attach the amplifier.

Dimensions: 12.2 x 2.05 x 7.17 inches (L x H x W).

Wiring Connections

Proper wiring is crucial for optimal performance and safety. Refer to the diagrams below for connection points.

Figure 1: Input and Control Panel. This image displays the left side of the Zapco ST-4B amplifier, showing the High-Level Input (HI-IN), Front and Rear RCA Inputs (IN), RCA Outputs (OUT), Gain controls, and Crossover switches (HPF, LPF, FULL) for both front and rear channels. Power and Protection indicator LEDs are also visible on the right.

Figure 2: Power and Speaker Output Panel. This image displays the right side of the Zapco ST-4B amplifier, showing the speaker output terminals for Front and Rear channels (Left and Right, with Bridged options), the main fuse, and the power input terminals (+12V, REM, GND).

Power Connections (Refer to Figure 2)

• +12V (BATT): Connect to the positive terminal of the vehicle's battery using an appropriate gauge power cable with an inline fuse (not supplied, but essential for safety) located within 18 inches of the battery.
• REM (Remote): Connect to the remote turn-on output of your head unit. This wire turns the amplifier on and off with your car's audio system.
• GND (Ground): Connect to a clean, unpainted metal surface of the vehicle's chassis. Ensure a solid, low-resistance connection. Use the same gauge wire as the +12V connection.

Input Connections (Refer to Figure 1)

• RCA Inputs (IN): For head units with RCA pre-outs, connect the front and rear RCA cables from your head unit to the corresponding "IN" jacks on the amplifier.
• High-Level Inputs (HI-IN): If your head unit does not have RCA pre-outs, use the high-level input connector. Connect the speaker wires from your head unit's speaker outputs to the HI-IN terminal block. Ensure correct polarity (+/-).

Speaker Output Connections (Refer to Figure 2)

• Stereo Mode: Connect your speakers to the "FRONT" and "REAR" speaker terminals, observing correct polarity. The amplifier is stable into a 2-ohm stereo load.
• Bridged Mode: For higher power output to a single speaker (e.g., a subwoofer), bridge two channels. Connect the speaker to the designated "BRIDGED" terminals (e.g., Front Left + and Front Right -). The amplifier is stable into a 4-ohm bridged load.

Initial Power-Up

Once all connections are made and verified, reconnect the vehicle's negative battery terminal. Turn on your car's audio system. The "POWER" LED on the amplifier (refer to Figure 1) should illuminate green, indicating normal operation. If the "PROTECTION" LED illuminates red, refer to the Troubleshooting section.

Controls and Adjustments (Refer to Figure 1)

• Gain Control (MIN/MAX GAIN): These rotary controls adjust the input sensitivity of the amplifier to match the output level of your head unit. Start with the gain set to minimum (fully counter-clockwise). Gradually increase the gain until you achieve a clear, undistorted sound at your desired volume level. Avoid setting the gain too high, as this can introduce distortion.
• Crossover Switches (HPF/FULL/LPF):
  • HPF (High Pass Filter): Allows frequencies above the set point to pass through to the speakers. Useful for front/rear speakers to prevent low bass frequencies from distorting them. Adjustable from 80Hz to 3kHz.
  • LPF (Low Pass Filter): Allows frequencies below the set point to pass through. Primarily used for subwoofers. Adjustable from 50Hz to 250Hz.
  • FULL: Disables the crossover, allowing the full frequency range to pass through.
• Bass Boost (0dB/6dB/12dB): This switch provides a selectable bass boost at a specific frequency. Use sparingly and adjust to taste. Excessive bass boost can lead to distortion and speaker damage.

Cleaning

Periodically wipe the amplifier's exterior with a soft, dry cloth to remove dust and debris. Do not use harsh chemicals or abrasive cleaners. Ensure ventilation fins are clear of obstructions.

Fuse Replacement (Refer to Figure 2)

The amplifier is equipped with an internal fuse for protection. If the amplifier fails to power on, check this fuse. Always replace a blown fuse with one of the exact same type and rating to prevent damage to the amplifier or vehicle's electrical system.