Sky High Car Audio FXB 800.4 4-Channel Amplifier

Sky High Car Audio FXB 800.4 4-Channel Amplifier

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The Sky High Car Audio FXB 800.4 is an ultra-compact Class D full-range amplifier that delivers useful four-channel speaker power from a chassis measuring barely over 5 inches long. It produces up to 225 watts RMS per channel at 2 ohms while fitting into spaces where many conventional amplifiers will not.

This makes the FXB 800.4 a practical choice for amplified door speakers, component systems, coaxial speakers, midrange drivers, custom doors, motorcycles, powersports vehicles, factory-system upgrades and other installations where space is limited.

Browse more Sky High Car Audio products, compare our complete selection of 4-channel amplifiers or view all car audio amplifiers.

Real Four-Channel Power in an Extremely Small Amplifier

At 14.4 volts, the FXB 800.4 produces 130 watts RMS per channel at 4 ohms or 225 watts RMS per channel at 2 ohms. That gives customers enough clean power for many upgraded daily-driver speaker systems, higher-output coaxial speakers, component sets, midrange drivers and compact pro-audio installations.

The FXB 800.4 is not limited to four-channel operation. It can also be bridged to produce up to 400 watts RMS across two channels at 4 ohms, giving installers more flexibility when the system needs fewer channels with additional power.

Customers building a complete Sky High speaker system can compare Sky High full-range speakers, Sky High midrange speakers, Sky High midbass speakers and Sky High tweeters.

RMS Power Ratings at 14.4 Volts

Four-Channel Mode

• 225 watts RMS × 4 at 2 ohms
• 130 watts RMS × 4 at 4 ohms
• 900 watts RMS combined at 2 ohms
• Minimum stereo impedance: 2 ohms per channel

Two-Channel Bridged Mode

• 400 watts RMS × 2 at 4 ohms
• 260 watts RMS × 2 at 8 ohms
• Minimum bridged impedance: 4 ohms

Important impedance notice: The FXB 800.4 must not be operated below 2 ohms per channel in four-channel mode or below 4 ohms when bridged. Calculate the completed impedance of every channel before connecting the speakers.

Flexible Speaker-System Configuration

Run four independent channels for front and rear speakers, bridge one channel pair when one section of the system needs additional power or bridge both channel pairs to create a compact two-channel amplifier.

The amplifier includes selectable HPF, full-range and LP-BP crossover modes. A two-channel or four-channel input-selection switch also provides additional signal-routing flexibility for different system layouts.

These controls make the FXB 800.4 useful for daily-driver speaker upgrades, custom doors, mids-and-highs systems, motorcycle installations and modern vehicle integration. The final crossover and gain settings should always be selected around the exact speakers being powered.

FXB 800.4 Features

• Ultra-compact Class D full-range four-channel amplifier
• Up to 225 watts RMS per channel at 2 ohms
• Fully bridgeable at 4 ohms
• Full-range frequency response from 10 Hz to 25 kHz
• Operating-voltage range from 10 to 16 volts
• HPF, full-range and LP-BP crossover selection
• Two-channel or four-channel input selection
• Metal detent crossover adjustment controls
• Tiffany-style RCA connections
• Reversible Sky High emblem for different mounting positions
• Power, clipping and protection indicators
• Fanless design
• 85% rated efficiency at full power
• 95 dB signal-to-noise ratio
• 180 damping factor
• Less than 0.1% total harmonic distortion
• Thermal, overload, DC-output, short-circuit and input-voltage protection
• 4-gauge power and ground terminals
• 10-gauge speaker-output terminals
• 90-amp fuse rating
• Compatible with the SHCA modular mounting ecosystem
• Compatible with SHCA Universal Amp Key mounting options
• Passive-cooling and color-customization options available separately
• One-year manufacturer defect warranty

Ultra-Compact Dimensions

• Width: 5.9 inches
• Length: 5.39 inches
• Height: 2.1 inches
• Quantity: One amplifier

Measure the intended mounting location before ordering and leave additional room for power wire, speaker wire, RCA cables, adjustment access and ventilation. Because the amplifier uses a fanless design, it should not be sealed inside an unventilated compartment or mounted where heat cannot escape.

Although its compact size makes it useful for motorcycle and powersports installations, the product is not identified as waterproof or marine-rated. Install it where it will remain protected from water and direct moisture.

Plan the Wiring and Electrical Support

The FXB 800.4 uses 4-gauge power terminals and carries a 90-amp fuse rating. Power and ground wire should be selected around the conductor material, cable length, expected current demand and complete system—not terminal size alone.

Browse compatible car audio amplifier wiring kits and power, ground and speaker wire. Use properly sized fuse protection near the power source and keep the amplifier ground short, secure and connected to clean bare metal.

If the factory radio is staying in the vehicle, confirm whether the system needs a line-output converter, DSP or another integration solution before beginning the installation.

Match the Amplifier to the Speakers

Do not choose speakers only by their advertised peak-power rating. Match the FXB 800.4 using the speaker RMS rating, individual impedance, number of speakers per channel, wiring configuration and amplifier output at the completed channel load.

At 4 ohms, each channel produces 130 watts RMS. At 2 ohms, each channel produces 225 watts RMS. Make sure every speaker or completed group of speakers connected to a channel can safely work with the available power.

Running several speakers on one channel changes the final impedance. Parallel wiring lowers impedance, while series wiring raises it. Never connect a speaker configuration below the amplifier’s 2-ohm-per-channel minimum.

Gain and Crossover Setup

Set amplifier gain using a clean signal and treat it as an input-sensitivity adjustment—not a volume control. Use appropriate high-pass crossover protection for door speakers, coaxial speakers, mids and tweeters so they are not forced to reproduce frequencies below their intended operating range.

Our car audio speaker tuning guide explains amplifier gain, crossover settings and speaker-system setup in more detail.

Who Should Choose the FXB 800.4?

The Sky High FXB 800.4 makes sense for customers who want meaningful four-channel power in the smallest possible footprint. It is a strong match for amplified daily drivers, upgraded door speakers, component systems, compact custom doors, motorcycles, powersports vehicles and factory-system integration.

Choose the FXB 800.4 when 130 watts RMS per channel at 4 ohms or 225 watts RMS per channel at 2 ohms matches the speaker system. If the speakers need substantially more power, compare the larger FXB 1400.4 or FXB 2600.4 instead of operating this amplifier below its minimum impedance.

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