Inside FiiO D3
I was intrigued by this DAC based on the industry-leading Wolfson SPDIF receiver WM8805. According to the specifications it is capable of 24bit/192KHz operation and it only costs $30
Just like any good DIYer, the first thing I did was to take it apart…
The famous Wolfson WM8805 SPDIF receiver. Even though it is capable of muxing up to 8 SPDIF sources, it is configured in hardware mode and therefore it is configured to have a single input into the receiver. The device has a coax and a toslink input and these are selected with a single pole switch. Notice also the use of a seam-sealed crystal instead of the more traditional can (most likely for size).
The WM8805 interfaces a Cirrus Logic 4344 DAC (“344″ indicates fixed I2S configuration). This DAC has pretty decent specs at 105 db SNR and -90 db THD+N, a cut above the DACs found in this price range (in reality, you can’t find any DACs at this price range which is a new low)
The analog output of the DAC connects to a TI LMV358 opamp
You can see the I2S lines (the 4 diagonal traces), ready to be tapped…
The power is supplied by an external 5V DC switching supply through a standard mini-USB connector. The 5V line (the uppermost trace from the USB connector) connects to a 6.8 (R37) ohm resistor and to the main PS capacitor. This provides a first stage RC filtering to the incoming power.
The 5V incoming is filtered through L5 and further regulated with a simple discrete Zener diode circuit (basically a shunt regulator) to 3.3V which feeds the DVDD (pin 1, digital core suppy) of the WM8805. This is pretty good filtering and regulation. This line also feeds PVDD (Pin 11, PLL supply) filtered through L2, and feeds the Toslink module through L1. Good use of ferrites for noise filtering.
The zener regulated line also feeds the DAC, with a simple cap bypass.The 102 resistor you see in the photo powers the LED to show Power-on condition. One of the advantages of the 4344 DAC is that it requires minimal external components. In the case of power, it only has a single power line.