Fiio D3: Power Supply Tweaks
Now, turning our attention to the other end of the spectrum: the Fiio D3. This little DAC seems pretty popular according to the number of customer feedback at Amazon:
I had purchased and reported about the Fiio D3 a long while back. The D3 was interesting because it was selling for under thirty bucks and yet it implemented a Wolfson WM8805 SPDIF receiver which is typically found in much higher-end devices. (Note: the original version implemented the Wolfson chip. The latest version has switched to the Cirrus CS8416 SPDIF receiver)
I hadn’t even listened to it until now.
The first thing I did was to do some measurement on the power section. The motivation to do this came from the datasheet: The Cirrus 4344 DAC can operate at 3.3V and at 5V. At 5V operation, you get 2 dB better performance pretty much across the board.
By measuring the voltage on the power pin of the DAC (VA, Pin 9), the DAC is actually operating at 4.8V which is pretty much the specification for best performance.
At first I thought the operating voltage was 3.3v because there is a zener diode regulating to 3.3V for the Wolfson part and thought that voltage was used throughout the device. Not true. Every chip has its own dedicated “supply line”.
In addition, the output stage OpAmp is also operating at the same 4.8V. Therefore, there is no need to do any modding here to get the better performance.
This 4.8V is directly coming from the external supply. So any improvements to the external supply and/or any improvement in the filtering should directly benefit the analog components of the DAC.
Actually this 4.8V may be regulated/filtered by the “power circuitry” you see in the upper right corner of the photo below. I’ve not traced this circuit, so I don’t know what it does, but it is related to the +V supply that powers the DAC and OpAmp.
I proceeded to mod the input capacitor. Space is very tight, so must use similar sized capacitor. I used a standard class ELNA 1000 uF capacitor, bypassed with a 22nF film cap. The original was 470 uF, 16V. Detail after removing existing capacitor:
After the large capacitor, the power line is filtered through a ferrite, and then bypassed by two ceramic capacitors. It then connects to V+ in the opamp
Detail after replacing capacitor and bypassed with film cap
LISTENING TEST (for the power supply)
I connected the D3 to the optical spdif output of a Denon DVD player. And listening with a NAD receiver and small monitor speakers. At the same time I also connected the analog outputs of the Denon DVD player to the receiver for easy comparison.
The FiiO D3 is powered by an included wall DC 5V DC adapter. There has been reports that this is a noisy adapter. However at normal listening volume, with the player in PAUSE, there is absolute no noise that can be heard from the speakers even with the ear next to the speaker. If the volume is cranked up all the way, then there is some faint hissing when listening next to the speaker, whereas with the analog output of the DVD player it is completely silent.
I used a ferrite with a few turns turns at the plug end of the power cable and combined that with a 1000uF capacitor across the + and – terminals forming an LC filter.
Result: no difference. Still hear a faint hiss when cranking the power all the way up. I’ll leave the capacitor in place, since it probably helps.
Next, I used a linear 5V supply, and spliced a mini USB plug with a built in ferrite.
Result: no difference. Still hear the faint hiss when I crank up the volume all the way. At normal listening levels, there is absolutely no noise.
Conclusion: the included switching power supply seems plenty good with respect to low noise. A linear supply may be an improvement in other areas…