SKU 12842 Category

Is it possible to make the best amplifier in the world even better? Our engineers were faced with this enormous challenge during the development of the MX4 PRO. Because at the level of a BRAX product, it is important to always question and optimize every detail, even if it seems insignificant at first glance. Only in this way is it possible to push the boundaries – both sonically and technically – further and further. In the end, we succeeded in redefining the standards in amplifier construction with the MX4 PRO. It is the perfect symbiosis of state-of-the-art components and congenial circuit improvements, without neglecting the previous virtues and traditions for which the BRAX brand enjoys the highest reputation worldwide.

It is still a matter of course that Audiotec Fischer is the only manufacturer ever to use only hand-selected transistors for the production of each BRAX amplifier, which are divided into over 300 classes using self-developed measuring devices and assembled accordingly. This unique method guarantees not only the lowest series tolerances, but above all unique measurement and performance values.

Above all, however, the enormous effort involved in supplying power to all assemblies also plays a significant role in the overall performance. Separate and stabilized power supplies for two channels each guarantee optimal working conditions for the individual amplifier stages. The electrolytic buffer capacitors specially manufactured for Audiotec Fischer with extremely low internal resistance thanks to 8-way contacting are now just as legendary as the encapsulated high-performance toroidal transformers, which can shake more than 1,800 watts of power supply power out of their sleeves. A completely revised PCB layout with four solid copper layers ensures maximum power delivery capability – so it is not surprising that the MX4 PRO with 4 x 300 watts RMS can provide even more power than ever at the speaker terminals.

But that’s not all – the MX4 PRO is also a prime example of bridging the gap between analogue amplifier technology and the digital age. For the volume control of the digital signal inputs, a hitherto unique effort is made. As an absolute novelty in the CarAudio segment, in conjunction with the BRAX DSP, the signal level is controlled without reducing the digital resolution only immediately before the output stages that drive the loudspeakers and thus completely lossless in the analogue signal level. The volume information is embedded by the BRAX DSP in the digital SPDIF data stream and decoded again in the MX4 PRO. This alone illustrates the striving of our engineers for absolute perfection.

And, of course, this meticulousness continues in production. Each individual device is manufactured exclusively to order individually according to customer requirements and recorded in a service database with the corresponding serial number. This makes each amplifier a real one-of-a-kind, which can rightly adorn itself with the title “High-End Car Hifi made in Germany”.


  • Two digital stereo signal inputs in SPDIF format (optical and electrical) up to a sampling rate of 192 kHz
  • DiSAC (Digital Signal Analog Controlled) volume control for the digital signal inputs, controllable via the BRAX DSP
  • Optimized PCB layout with quad multilayer baseboard for maximum current and signal flow and higher output power
  • Lossless switching of input signals via relays with gold-plated contacts
  • Elimination of coupling capacitors in the signal path as far as possible for the best possible pulse behavior
  • Enormous damping factor of over 1,400 @ 4 ohms for maximum speaker control
  • Maximized signal-to-noise ratio through power supply synchronization
  • Extremely elaborately designed, regulated switched-mode power supply
  • Eight-contact electrolytic capacitors with a total capacitance of 40,000 μF and lowest possible internal resistance as well as 300 A interference suppression choke for buffering the pulse currents on the operating voltage
  • Separate connector for BRAX power stabilizer
  • Loudspeaker protection circuit via the highest quality high-current power relay
  • Specially developed toroidal transformers made of highly permeable core materials with the highest possible saturation currents
  • 32 hand-selected high-end MOSFET transistors for lowest tolerances and optimal measured values
  • Engraved serial number in the stainless steel nameplate
  • Impedance-independent output power of 300 watts per channel
  • 4-, 2- and 1-ohm stable
  • Processor and temperature-controlled fan in the bottom plate
  • Solid heat sink made of a special aluminum alloy for optimal cooling of the power supply and power amplifier transistors

Special Features:

DiSAC (Digital Signal Analog Controlled) volume control in conjunction with the BRAX DSP

In a car hi-fi system, there are typically two different ways to adjust the volume.
a) The volume is controlled in the signal source (e.g.dem car radio):

This method is most commonly used, but has the disadvantage that when a digital signal processor (DSP) is controlled in the signal chain, its full signal resolution is only used if the volume at the source is set to maximum. Otherwise, bits are “lost”, so that the precision of the sound suffers, especially at very low volumes. However, this loss can occur even if there is no DSP connected between the radio and the amplifier, because most radios nowadays include a digital volume control, which is also lossy.

b) The volume is controlled in the digital signal processor (DSP):

In this case, the signal source always delivers maximum signal level, so that the downstream DSP is always optimally controlled and no information is lost, e.g. during AD conversion. Via a remote control connected to the DSP, the volume is then digitally controlled in the signal processor, which is not possible at very low volumes, however, without sound losses.

The perfect solution

The MX4 PRO, in conjunction with the BRAX DSP, therefore follows the most consistent and elaborate way to avoid sound losses from the outset when adjusting the volume with the exclusive, proprietary “DiSAC” technology. This principle works optimally if the signal source itself either does not contain any volume control or a high basic volume is set on it. The signal is thus always processed in the BRAX DSP at an ideal level without reducing the resolution at any point. To adjust the desired volume, either the URC.3 remote control or the DIRECTOR is used.

The special feature is that the volume information evaluated by the remote control in the DSP is embedded in the digital audio data stream of the SPDIF outputs of the BRAX DSP and thus transmitted to the MX4 PRO. In the MX4 PRO, this information is extracted from the data stream and used to control the analog volume controls behind the amplifier’s DACs. This means that the volume adjustment takes place losslessly at the ideal point, i.e. only directly before the power levels that drive the speakers.

This type of volume control is absolutely unique in the car hi-fi sector and shows that no effort has been spared with this amplifier to redefine the sound scale.


Performance RMS
– @ 4 ohms 4 x 300 watts
– @ 2 ohms 4 x 300 watts
– @ 1 ohms 4 x 300 watts
– bridged at 4 ohms 2 x 600 watts
– bridged at 2 ohms 2 x 600 watts
Amplifier technology 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 RCA 1.0 – 8.0 volts
Input impedance RCA 10 kOhm
Input impedance high-level
Exits 4 x speaker output
Output voltage RCA
Signal converter for digital input BurrBrown 24-bit DAC
Band 10 Hz – 80 kHz
Bass Boost
High Pass
Flank steepness high / low pass
Slope Subsonic / Low Pass
Signal-to-noise ratio digital input > 116 dB (A-weighted)
Signal-to-noise ratio analog input > 116 dB (A-weighted)
Total harmonic distortion (THD) < 0.0005 %
Damping factor > 1400
Operating voltage 9 – 16 volts (max. 5 sec. down to 6 volts)
No-load current consumption 8.5 A
Fuse 6 x 25 A LP mini plug-in fuse
Additional Features Colour Protection System, BRAX Power Stabilizer connection, start-stop capability
Dimensions (H x W x D) 79 x 360 x 360 mm
Net weight 12.0 kg



The power supply in the MX4 PRO ensures the internal power supply even in the event of short-term dips down to 6 volts. This ensures that the MX4 PRO remains fully functional even when the engine is started.

BRAX -DiSAC-Volume-Control_DE