4 Channel Class-D Amplifier with DSP

Turnkey solution with integrated DSP
Up to 3000W on a single 4 ohm channel
Super-compact design
Built-in active PFC
Versatile input configuration

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  • Features
  • Block Diagram
  • Specifications

Integrated DSP

On board 64bit DSP with freely configurable signal path. IIR+FIR filter capability.

Universal Power Supply & PFC

Power supply with worldwide operation from 100-240Vac. Its active power factor correction circuitry ensures efficient use of the mains power system

Sonic Performance

Our proprietary control loop provides a load independent frequency response and low harmonic and intermodulation distortion.


The SMA-2 amplifier module measures just 250mm x 100mm, making it ideal for use in smaller cabinets.

Low Idle Loss

Low idle loss (heat) through the use of a proprietary control loop which relaxes the output stage’s dead time. Only a small 2mm aluminium sheet of 240x110mm is needed for cooling.

Versatile Input configuration

SMA-2 signal inputs comprise 4 analog inputs, AES3/SPDIF and I2S. Further GPIO pins are available for signal LEDS and preset selection.

Block Diagram

In the illustration below a simplified block diagram of the SMA-2 hardware is displayed. The heart of the system is the DSP which not only does the processing of the audio signals according to the needs of the user, but also controls the internal household of the whole module to ensure worry-free, reliable operation anywhere, any time and in any conditions.

At the top left there are four balanced analog line inputs, one digital SPDIF/AES and one I2S input which all can be simultaneously processed by the DSP.

Below, some lines intended to externally control the module are provided. There are some general purpose I/O lines which can be used to connect external switches or indicating LEDs, some ADC inputs to connect for instance to an external potentiometer to implement volume control and, last but not least, a user selectable SPI/I2C serial interface to enable external communication with more advanced user applications which may require this.

The SMA-2 also accommodates Auxiliary standby power for powering optional user applications (+ and –15V) for enabling low standby power applications.

On the right side of the diagram you can see the four Digital to Analog converters, which drive their corresponding Class-D amplifier.

Operating temperature range 0 to +50°C Full load over entire voltage range
Isolation 3000VAC Class I construction
Max. Operational Altitude < 2000m
Max. Standby Power < 500mW Module in Standby mode; User application < 10mW
Max. Active Idle Power < 20W Amplifier active; Channels not driven
Mains inputs
Input Voltage range 100 – 240VAC
Input Frequency 50 – 60Hz
Input Current < 12A @ 230VAC
Inrush Current < 80A Over entire voltage range
Input Protection Internal T6.3AH/250VAC fuse
Analog Audio Input
Input Impedance 20k
Max Full Scale Input Voltage 21dBu
Digital Audio Input
Digital I/O voltage levels 3.3V
Max Sample Rate 192kHz
Audio output channels 
4x SE 750 W @4ohm 1kHz, 1% THD
2x PTL 1500 W @2ohm
2x BTL 1500 W @4ohm
1x PBTL 3000 W @4ohm
1x PTL + 2x SE 1500 W @2ohm + 2 x 750 W @4ohm
1x BTL =2x SE 1500 W @4ohm + 2 x 750 W @4ohm
Max. THD+N 0.01% 20Hz – 20kHz; Pout < Pr/2
Typ. CMRR 70dB
Max. Output Noise 70uV 20Hz – 20kHz
Min. SN Ratio 100dB
Frequency Response 20Hz – 20kHz
Auxiliary Output Voltages
Typ. Auxiliary Output Voltage 1 12V +/- 1V Disabled in standby
Typ. Auxiliary Output Voltage 2 12V +/- 1V Disabled in standby
Max. Auxiliary Output Current 250mA Available in standby

SMA-2 is an amplifier module featuring four output channels specifically designed for multi-way loudspeakers as well as subwoofers by setting up its output configuration to match the application. The highly compact design, integrating all four channels, makes the APEX SMA-2 a unique product, capable of delivering up to 3000W on a single 4ohm channel, granting the highest power available for driving all speakers on multi-way systems.

It combines the switch mode power supply, two Class-D power amplifiers, a powerful Analog Devices ADAU1462 DSP supported by high performance ESS Technology Analog to Digital and Digital to Analog  conversion stages and all the necessary analog circuitry, optimized for optimal sonic performance on a single, compact PCBA. The customization is basically done by means of the small input connector PCB, together with the mechanics, which still allow you to determine the layout of the connectors and controls, with the potential for additional input sources or networked audio. This will enable you to keep control over the general look of your brand.

The SMA-2 module features the APEX GlidePath direct drive technology, first introduced in the two channel SMA-1. GlidePath is a proprietary Class-D technology where the DSP system is an integral part of the amplifier system. Other than one capacitor at the audio input side to protect amplifying DC voltages, the audio signal path traveling through the ADCDSP-DAC-AMPLIFIER is completely DC coupled.

GlidePath direct drive technology delivers major advantages over regular Class-D amplifiers, including significant improvements in cone excursion and transient response.  A module equipped with GlidePath technology will clip later due to the fact that the peak levels on both sides of the sinus are close to equal. In addition, GlidePath has more output at the initial impuls (+10%) and the cones swing less after the signal stops even at 200Hz (-10% excursion). All these improvements are very clearly audible and result in a cleaner, more powerful low end experience compared to traditional Class-D designs.

The output power for each amplifier channel can be assigned through the software, creating numerous possibilities, from high power bridged submodules to 4 x identical power modules or a combination of different power options.

APEX SMA-2 is a turnkey power amplifier module for OEMs which enables a fast time to market. With its very small size of 100x250mm it fit even the smallest cabinets. It features up to 8 preset selections and field firmware updates. The highly efficient double power supply (one PSU for 2 channels) with active PFC allows worldwide input voltage range. Custom printing is offered with a scratch-free polycarbonate overlay.