1. Introduction
The Infinity REF-551A Reference Mono Amplifier is designed to deliver pure power in a compact chassis, suitable for various vehicle installations. This amplifier incorporates advanced topology, variable electronic crossovers, and bass boost control for precise audio system tuning. It features high- and low-level inputs for compatibility with both aftermarket and factory car stereo systems. The REF-551A is also compatible with certain advanced driver assistance systems (ADAS) and Harman HALOsonic technologies, which can enhance the in-car audio experience by reducing noise and simulating engine sounds.
What's in the Box
- 1 x Infinity REF-551A Amplifier
- 1 x High-level input wiring harness
- 2 x Spare fuses
- 2 x 2-color brand stickers
- 1 x Quick start guide
Figure 1: Top view of the Infinity REF-551A Reference Mono Amplifier, showcasing its compact design and Infinity branding.
2. Safety Information
Please read all instructions carefully before installing and operating your amplifier. Failure to follow these instructions may result in serious injury or damage to the product or vehicle. Keep this manual for future reference.
- Power Source: Connect the amplifier only to a 12V DC negative ground electrical system.
- Wiring: Ensure all wiring is correctly routed and secured to prevent pinching or damage. Use appropriate gauge wire for power and ground connections.
- Fuses: Always replace fuses with the same type and rating as specified. Do not bypass fuses.
- Ventilation: Install the amplifier in a location that allows for adequate air circulation to prevent overheating. Do not cover the amplifier with carpets or other materials.
- Professional Installation: If you are unsure about any part of the installation process, seek assistance from a qualified professional installer.
- Hearing Protection: Prolonged exposure to high volume levels can cause permanent hearing loss. Use caution when adjusting volume.
3. Setup and Installation
Proper installation is crucial for optimal performance and safety. Choose a mounting location that is dry, well-ventilated, and secure. Avoid mounting the amplifier where it will be exposed to direct sunlight, excessive heat, or moisture.
Mounting the Amplifier
Secure the amplifier firmly to a solid surface using appropriate screws. Ensure there is enough space around the amplifier for air circulation.
Wiring Connections
Before making any connections, disconnect the vehicle's negative battery terminal to prevent electrical shorts.
Power and Ground Connections
- +12V (Power): Connect a heavy-gauge power cable directly from the vehicle's positive battery terminal to the +12V terminal on the amplifier. Install an appropriate fuse holder (not supplied) within 18 inches (45 cm) of the battery.
- GND (Ground): Connect a heavy-gauge ground cable from the GND terminal on the amplifier to a clean, unpainted metal surface on the vehicle's chassis. Ensure a good electrical connection.
- REM (Remote): Connect a remote turn-on wire from your head unit's remote output to the REM terminal on the amplifier. If your head unit does not have a remote output, the amplifier features auto signal detection, which can turn it on/off by sensing an audio signal.
Figure 2: Rear view of the amplifier, detailing the power, ground, remote, and subwoofer output terminals. Note the fuse compartment.
Audio Input Connections
- Low-Level Input (RCA): For head units with RCA pre-outs, connect RCA cables from the head unit to the amplifier's INPUT (LO) terminals.
- High-Level Input: For head units without RCA pre-outs, use the supplied high-level input wiring harness. Connect the speaker wires from your head unit to the harness, then plug the harness into the amplifier's high-level input.
Speaker Output Connections
Connect your subwoofer(s) to the SUB terminals on the amplifier. Ensure correct polarity (+ to + and - to -) for optimal performance. This is a mono amplifier, designed for a single subwoofer or multiple subwoofers wired to a mono load.
Figure 3: Front view of the amplifier, displaying the RCA input, input level switch, gain, bass boost, and phase controls.
4. Operating the Amplifier
Once installed, you can adjust the amplifier's settings to optimize sound performance for your vehicle and subwoofer setup.
Controls and Adjustments
- INPUT LEVEL (LO/HI1/HI2): This switch adjusts the input sensitivity to match the output voltage of your head unit. Set to 'LO' for low-level (RCA) inputs. For high-level inputs, select 'HI1' or 'HI2' based on your head unit's output.
- GAIN (MIN/MAX): The gain control matches the amplifier's input sensitivity to your head unit's output. Start with the gain at minimum, then slowly increase it until you hear distortion, then back off slightly.
- FREQ (Crossover Frequency): This knob adjusts the low-pass filter frequency. It allows only frequencies below the set point to pass to the subwoofer. Adjust this to blend the subwoofer output smoothly with your main speakers.
- BASS BOOST (0dB/+9dB): This control provides a boost at 45Hz to enhance bass impact. Use sparingly to avoid distortion.
- PHASE (0°/180°): This switch adjusts the phase of the subwoofer output relative to the main speakers. Experiment with both settings to find the one that provides the most impactful and cohesive bass response.
5. Maintenance
The Infinity REF-551A amplifier requires minimal maintenance. Follow these guidelines to ensure its longevity:
- Cleaning: Periodically wipe the amplifier's exterior with a soft, dry cloth. Do not use harsh chemicals or abrasive cleaners.
- Ventilation: Ensure that the amplifier's cooling fins and ventilation openings remain clear of dust and debris.
- Connections: Occasionally check all wiring connections to ensure they are secure and free from corrosion.
6. Troubleshooting
If you experience problems with your amplifier, consult this section for potential solutions before contacting support.
No Power / Amplifier Not Turning On
- Check the main fuse near the battery and the fuses on the amplifier. Replace if blown.
- Verify that the +12V power wire is connected securely to the battery and the amplifier.
- Ensure the ground wire is securely connected to a clean metal chassis point.
- Check the remote turn-on wire connection. If using auto signal detection, ensure the head unit is on and producing an audio signal.
No Sound Output
- Confirm that the head unit is on and playing audio.
- Check all audio input connections (RCA or high-level harness) for proper seating and continuity.
- Verify speaker wire connections at both the amplifier and the subwoofer. Ensure correct polarity.
- Adjust the amplifier's GAIN control. It might be set too low.
Distorted Sound
- Reduce the GAIN setting on the amplifier.
- Check for proper impedance matching between the amplifier and the subwoofer(s).
- Ensure the subwoofer is not overdriven. Reduce the head unit's volume or bass boost.
- Check for loose speaker wires or short circuits.
Amplifier Overheating
- Ensure adequate ventilation around the amplifier. Clear any obstructions.
- Check the speaker impedance. Running the amplifier below its minimum recommended impedance can cause overheating.
- Reduce the GAIN setting or BASS BOOST.
7. Specifications
| Feature | Specification |
|---|---|
| Model | REF-551A |
| Output Power (2Ω) | 550W RMS x 1, <1.0% THD+N |
| Output Power (4Ω) | 370W RMS x 1, <1.0% THD+N |
| Max Power | 1300W Peak |
| Signal-to-Noise Ratio | >80dB (ref 1W output @ 4Ω) |
| Number of Channels | 1 (Mono) |
| Item Dimensions (L x W x H) | 11.5 x 9.25 x 4.25 inches |
| Item Weight | 7.28 pounds |
| Material | Metal |
| Mounting Type | Surface Mount |
8. Warranty and Support
Warranty Information
The Infinity REF-551A Reference Mono Amplifier comes with a 1-Year Manufacturer Warranty. This warranty covers defects in materials and workmanship under normal use. Please retain your proof of purchase for warranty claims. The warranty does not cover damage caused by improper installation, accident, abuse, neglect, or unauthorized modification.
Customer Support
For technical assistance, troubleshooting beyond this manual, or warranty service, please contact Infinity customer support. Refer to the contact information provided in your quick start guide or visit the official Infinity website for the most up-to-date support details.
