Got the XMOS 384KHz USB Interface
Follow the discussion of this board and XMOS technology in general in the diyaudio thread: [link].
The new board
The new chip from XMOS
Cannot tell from the chip markings what part is it. It is “missing” the part number. But it is definitely a “U” part as there is no separate USB controller chip. Here is the datasheet of one version of the part: [link]
The previous generation XMOS devices required a separate USB interface chip (foto from here: [link]):
The audio clocks. According to the datasheet, pin 1 is the enable pin and pin 3 is the output pin. Looks like the enable pin is controlled by the XMOS chip, enabling/disabling the clocks for the corresponding sample rate.
The local ultra low noise LDO (excuse the left over cotton fibers from my cleaning :-)). You can bypass the USB power by removing FB1 and provide external 5V.
The 2 LC filters for filtering the output from the built in DC-DC converters. Here is place to add larger caps and increase the filtering.
Solid ground plane. CN1 is for external powering (instead of using USB power).
If you read the datasheet and compare the topology of this board you will find that the manufacturer has followed the build and layout recommendations from XMOS. In fact it is so simple, that not following the manufacturer’s recommendations is kind of hard 🙂
The new XMOS chip has several advantages over the old device
- Built-in USB receiver
- Requires much less external components and thus it has been optimized to be implemented on a 2-layer board
- Built in voltage regulators. The internally generated regulated power is further filtered by external LC filters – Here is an area to mod: add capacitance to increase the filtering 🙂
- The clocks can be positioned much closer to the device than in the previous design
Apparently 384KHz support was added by diyinhk according to this lively discussion at diyaudio [link]
FEATURES OF THE MODULE (From the manufacturer)
- 6.5uVrms Ultralow noise LDO. -The TI LP5900 [link]
- Solid ground plane (a must for high speed digital circuit)
- No Via in active circuit (via inductance always create jitter problem)
- FOX Xpresso ultra low ppm oscillators and Murata capacitors sourced from Digikey USA. -The two Xpresso 22.579 2MHz and 24.576 MHz clocks. Not the ultimate in low jitter, but pretty low jitter. See the graph below
- Gold plated USB connector
- Compact size 50mm x 30mm. -That is even smaller than the Amanero which is 30×70 mm approx.
- USB powered but can be externally powered by removing FB1 and connect 5V to CN1 (warning: over-voltage or reverse-voltage can damage the XMOS chip immediately. Any modification will void item warranty)
- Can optionally install series resistor to I2S lines (by cutting the traces)
Comparing the Xpresso clocks with Crystek.
I first checked it by plugging it to a Macintosh computer. Native MacOS supports up to 352K and 384K sample rate.
On the PC, it requires device drivers.
Version 1.63.0 is the latest driver from Thesycon.
No indication of 352K/384K capability for WASAPI shared mode. This may in fact a limitation of Windows mixer as it expects to resample every audio stream to the selected sample rate. However, in WASAPI exclusive mode, this part (the mixer) is totally bypassed and the output sample rate from the player application is passed directly to the hardware.
The driver also supports ASIO
CONNECTING TO DAC
Connected the board to my old Buffalo II DAC (80 MHz clock) and tested all sample rates from 44.1KHz all the way to 384KHz. With the 80MHz version of the Buffalo II DAC, 352.8KHz and 384KHz work fine with oversampling turned off. All sample rates work as advertised. Modern designs are pretty robust, especially this version of the XMOS chip which requires only a few external components.
The socket in the XMOS device matches the socket pin arrangement for the latest version of the $99 ES9018 board and a ribbon cable can be used. For the Buffalo simple cat-5 twisted pairs can be used.
Here is an implementation from a reader with diyinhk $99 DAC board:
The XMOS is hiding…