BRAX MX4 PRO – Reference-Level 4-Channel Amplifier

The MX4 PRO represents BRAX’s pursuit of absolute performance in car audio amplification. During development, every part of the amplifier was re-evaluated, refined, and enhanced, no matter how small. This attention to detail has resulted in an amplifier that pushes technical and acoustic boundaries further than before. The MX4 PRO stands as a new standard for high-end audio in vehicles.

This model blends premium components, advanced engineering, and signature BRAX craftsmanship. As with all BRAX amplifiers, each power transistor is individually selected and matched by hand using equipment developed in-house. This unique selection process ensures minimal tolerances and exceptionally accurate performance.

A large portion of the MX4 PRO’s capability comes from its power supply design. Each pair of channels receives its own stabilized and independent voltage supply, giving each amplifier section ideal operating conditions. Custom ultra-low ESR capacitors and encapsulated toroidal transformers supply more than 1,800 watts of clean power. A redesigned quad-layer PCB allows extraordinary current flow, helping the MX4 PRO deliver a consistent 4 x 300 W RMS into 4, 2, or 1 Ohm loads.

The MX4 PRO also bridges traditional analog amplification with modern digital integration. When used with the BRAX DSP, its digital inputs offer a new level of volume control. The DSP encodes volume data in the SPDIF signal, and the amplifier decodes it to adjust the analog volume stage directly before the output section. This preserves full signal resolution and avoids the losses found in typical digital volume adjustments.

Each amplifier is built to order, recorded by serial number, and assembled with meticulous care. The MX4 PRO is truly a handcrafted piece of high-end engineering.

Main Features

• Two stereo digital inputs (optical and coaxial) supporting up to 192 kHz sampling

• DiSAC volume control system when paired with a BRAX DSP

• Quad-layer PCB engineered for optimized power delivery and signal stability

• Gold-contact relay switching for clean input transitions

• No coupling capacitors in the audio path for improved impulse response

• Extremely high damping factor exceeding 1,400 @ 4 Ohms

• Synchronized power supply for the lowest possible noise

• Highly regulated and complex switch-mode power supply

• Eight-point-contact capacitors totaling 40,000 μF with very low ESR

• Massive 300 A choke coil for smoothing power peaks

• Dedicated connector for BRAX power stabilizers

• High-current speaker protection via precision relays

• Custom toroidal transformers with high-permeability cores

• 32 matched MOSFETs selected for ultra-low tolerance

• Individual serial number engraved on stainless steel

• Stable 300 W RMS output per channel at 4, 2, or 1 Ohm

• Active cooling with a temperature-controlled fan

• Heavy aluminum heat sink for ideal thermal performance

Special Technology: DiSAC Volume Control

Most car audio systems adjust volume in one of two ways:

1. Volume controlled at the source (head unit)

Common but often reduces digital resolution, especially when a DSP is used, because lowering the source volume discards audio bits.

2. Volume controlled inside the DSP

Better for resolution, but digital attenuation can still slightly affect signal purity.

BRAX’s solution: DiSAC

When used with a BRAX DSP, the MX4 PRO follows a different system.
The DSP outputs audio at full resolution and embeds the volume commands within the SPDIF data stream. The amplifier reads this information and adjusts the analog volume stage just before the output transistors.

This means:

• The digital signal stays at full resolution

• Volume control happens in the analog domain

• No loss of detail at low listening levels

• Maximum sound quality at every volume setting

This control method is exclusive in the car audio world and demonstrates BRAX’s goal of achieving the cleanest signal handling possible.

Start-Stop Support

The MX4 PRO can continue operating even if voltage drops to 6 V during engine start, thanks to its stabilized power supply design.

Technical Specifications

Output Power (RMS)

• 4 x 300 W @ 4 Ohms

• 4 x 300 W @ 2 Ohms

• 4 x 300 W @ 1 Ohm

• 2 x 600 W bridged @ 4 Ohms

• 2 x 600 W bridged @ 2 Ohms

Amplifier Type: Class AB

Inputs

• 4 x RCA

• 2 x Optical SPDIF (32–96 kHz)

• 2 x Coaxial SPDIF (32–192 kHz)

• 1 x Remote In

Input Sensitivity: 1.0 – 8.0 V
RCA Input Impedance: 10 kΩ

Audio Performance

• DA converter: BurrBrown 24-bit

• Frequency response: 10 Hz – 80 kHz

• SNR (digital input): > 116 dB (A-weighted)

• SNR (analog input): > 116 dB (A-weighted)

• Distortion (THD): < 0.0005%

• Damping factor: > 1400

Electrical Details

• Operating voltage: 9 – 16 V (down to 6 V for 5 seconds)

• Idle current: 8.5 A

• Fuse: 6 x 25 A LP-Mini (APS)

• Additional features: Color Protection System, BRAX Stabilizer connector, Start-Stop compatibility

Dimensions & Weight

• 79 x 360 x 360 mm

• 12.0 kg net weight