Digital Interface AK4118

The Rasptouch Digital AK4118 has a digital interface card based on a AKM AK4118 chip. It converts the audio streams from the Raspberry Pi to an S/PDIF & I2S signal. The coaxial output is driven by a DS8921 chip and the I2S output is configured by default to broadcast the DSD frame via PCM (DOP) for use with ESS technologies (ES9038Q2M & ES9038Pro). An internal circuit automates the detection of non-PCM streams in order to avoid bothering the user when reading DSD files.

The digital stage uses its own power supply with an ADP151 LDO regulator ensuring excellent signal stability while minimizing electronic noise. In addition, a Pulse PE-65612NL isolation transformer can cleanly separate the audio circuit from the logic circuits and the power supply.

Connectivity

The RaspTouch offers a wide connectivity that allow you to take full advantage of your audio system. Most of the connection of the Raspberry Pi 4 with its 2 USB-A 2.0 ports & 2 USB-A 3.0 ports, its Micro SD port and its Ethernet port. The USB ports enables the device tio work with all kinds of compatible peripherals:

• Hard Drives of USB storage
• USB WiFi Dongle
• External USB DAC
• Keyboard / ouse ...

The AK4118 digital interface has two digital SPDIF outputs (coaxial on RCA port and optical on Toslink port) as well as an I2S output on HDMI port (LVDS).

The power is supplied by a DC 5.5 / 2.1mm base connected to an integrated linear power supply allowing good stability. The optimum input voltage is 7 to 9V DC and can go up to 12V maximum.

The ON/OFFbutton not only turns off the power, but starts shutting down the system beforehand. The configuration of this function is available as a native plugin under Volumio.

Please note, despite the native WiFi connectivity of the Raspberry Pi 4, the latter has been sacrificed to install the reader in an aluminum box isolated from disturbances. The wifi connection therefore requires an external USB adapter (Wifi Dongle).

Software

Announcing himself as a free system, the RaspTouch comes without operating system. This choice depends on your other devices, the ambition of the project and the expected functionality.

The device is ready as far as electronics are concerned, So it remains to choose an operating system and mount it on a micro-SD card. Many softwares are available to meet all your expectations: piCorePlayer, Max2Play, OpenELEC, Volumio ...

Depending on the software, you can access the following features:

• Complete Support and unlimited Multiroom
• Remote Play audio files stored on a media server connected to the network (NAS)
• Remote reading from a UPnP source.
• Playback from USB source (hard disk, USB key)
• DLNA Management
• Support Qobuz
• Support Airplay