FET Audio | Hi-End Audio & Electronics DIY Electronics & Repair

Having understood DIYAUDIO member Alex_twn to modify an Apple AirPort Express to output I2S signal to converter FDA-1B to a wireless “AirPlay” DAC, I have not done anything for more than a year.  The main reason is that the US$99 AirPort Express will become useless with Zero second hand value after modifications. Secondly there is no clear indication of the position of the I2S signal inside the AirPort Express circuit boards and tracing the circuit will be difficult for many DIYers.  Thirdly the quality of the internal Master clock jitter of the AirPort Express is still unknown!  Since the AirPort Express has an Optical Digital output socket in optical mini plug format (shared with the analogy output), there is a simple solution to use optical connection between AirPort Express and FDA-1B.  With the WM8804 input receiver quality in FDA-1B, the sound performance will sure has very high assurance level.

Here is my version of wireless FDA-1B DAC playing from a 4 years old notebook with winxp & iTunes.  I use the Airport Utility for windows version 5.5.3 due to my windowXP version. Also I create a new wireless network for the AirPort Express so that it will not increase too much wireless traffic for my original D-Link wireless Router DIR-652 (note this router is connected to internet via a boardband modem).  The connection between AirPort Express and DIR-652 is by a Lan Cable.  With this connection, both the wireless networks can also be able to access internet.  Note that the Optical cable must be one end with mini plug for AirPort Express and the other end with square plug for FDA-1B Optical input.  The total cost of upgrade is only US$115 and it is really a simple upgrade relative to the XMOS solution!  Awesome, it is wireless for both PC and Mac platforms!!!

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The daughter board is to be used with FDA-1B DAC.  It can use two chips – SRC4192 or AD1896.  Note that the price of this FDA-1B ASRC board is HK$800 (about US$100).  It will be fully assembled and tested before shipment.

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With SRC4192 chip, the output sample frequency can be set to 48k, 96k or 192k by two jumpers.  With AD1896 chip, the output sample frequency can be selected at 96k, 48k or 32k.

An XO with frequency 24.576MHz is used as the master clock in the ASRC board.  Through hole type DIP or 5x7mm SMT type XO can be soldered on the pcb but a DIP XO will be provided by default as shown above.  Only 3v3 XO can be used.

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Circuit: FDA-1B ASRC Ckt

Jitter measurement is show in below 3 charts for SRC4192 chips:

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Here is the history of the past versions of FDA-1B for past 1.5 years.  I am still searching for the photo of V3 but I believe I did not take any photo of it due to the poorly design of the digital input selection.

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During the development process in V1, many regulators had been tested on the PCM1794A for both the 3.3V and 5V regulators and eventually the simple LM317T plus AMS1117 regulators were selected for it most balance sonic performance.  The lesson learnt here is that expensive and high performance low noise regulator might not sound best in this design.  Also various SMT and Through-hole transistors were tested.  Resistors and capacitors were also tested at various locations to see how much it will affect the sound.  Of course the most important evaluation were the ASRC chips like AD1896, SRC4192 and CS8421.  After many hours of listening, AD1896 with 96k Fs output is rated the best sound ASRC chip in this platform.  For the digital input on the 4th selection – I2S/USB, PCM2707 (USB 16bit 48k) was evaluated but the sound was just too ordinary.  Later XMOS USB reference design was plug into the I2S input and the sound is just too good to be true.  Other receiver chips were evaluated like DIR9001, WM8804, WM8805 and CS8416.  The best sound chip is WM8804, then WM8805, then CS8416 and last is DIR9001.  In fact I would say the WM8804 and XMOS reference design sound equally good in FDA-1B. Thus I have no urgency to move to USB yet as the CD-PRO2 transport and the Logitech Classic media player is providing digital source music with no issue at all in both V13 and V15c versions.

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In the final version V13, it is basically a SMT version mainly designed for mass production.  Then a through-hole (TH) version V15c was created for the DIY market.  So here is why I start to sell the FDA-1B DIY DAC from April 2012.

FDA-1B Rev History – Summary of the revision change history

V1 – Through-Hole version – evaluate regulators, ASRC and 4th digital input + CS8416

V2 – Convert to SMT in digital section + CS8416

V3 – SMT and WM8804 with digital input switch.

V4 – Layout improvement, use relay for digital input select + WM8804

V5 – Layout improvement

V10 – Layout improvement

V13 – Improve I2S bus timing, add SMT pads for IV section; full SMT version for mass production

V15c – DIY version for DIY market

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Note that a new revision manual is released today.  The new revision added two attachment 6 & 7 total 5 pages at the end of the manual.  Attachment 6 is the Balance mode external I2S connection and attachment 7 is the rear panel dimensions.

FDA-1 PCM1794A DAC Manual_r6

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Note that this FDA-1 DAC kit is all SOLD out! 

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