New FDA-1B ASRC Board

May 15th, 2012

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.


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.


Circuit: FDA-1B ASRC Ckt

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



New FDA-1B Development History

April 30th, 2012

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.


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.


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


FDA-1 PCM1794A DAC Kit Revision 6 Manual

January 14th, 2012

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


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

XMOS USB Audio 2.0 Reference Design Jitter Measurement

January 9th, 2012

The XMOS demo board sold for $149 in digikey.  The firmware need to be loaded before the board can be used.  There is a digital out from the USB 2.0 demo board and thus it will be a easy interface from USB to FDA-1 optical input.  What you need to do is to get an optical cable to link up output of demo board and input of FDA-1 Toslink.  I have tested this mode and the sound is better than using Ti PCM2707 USB receiver with I2S output.


On board, there is a I2S connector and thus the clock jitter measurement is taken at the MCLK, BCLK, LRCLK locations.  The jitter at MCLK from 48k to 192k Fs is from 10 to 13 pico second respectively which are excellent.  In fact the MCLK is taken directly from the onboard crystal oscillator after the buffer logic IC.  For jitter at other clock like BCLK (Bit Clock) and LRCLK (Word Clock, Fs), they are as high as 800 pS or above.  For any DAC using the MCLK as the clocking reference (like FDA-1), the result should be very good.

Attached is the document of jitter measurement for reference:

Jitter measurement by Lecroy DDA-120

From all the measurement, the lowest jitter mode is to set the output of the USB 2.0 at 24 bit with 48k Fs.

With a more accurate period jitter machine Wavecrest DTS-2070C, the jitter at MCLK is measured at only 4.6ps.  See attached document:

Jitter measurement by Wavecrest DTS-2070C

Lecroy DDA-120 Jitter measurement

December 2nd, 2011

I acquired this machine for a month from Seagate Singapore but this set do not have the JTA software option for jitter measurement.  I have asked Lecroy for the cost of JTA option but they want to charge me 5k USD ! Anyway DDA-120 is for disk drive analysis and it has a simple jitter measurement using period@level function.  Also it has period, frequency, sigma and histogram function which is good enough to do some clock signal jitter measurment as below:

 I have also taken some measurements of DAC chips as in attached file.  They are WM8804, CS8416, DIR9001; SRC: CS8421, SRC4192 & AD1896.  The measurement is on the MCLK (master clock) of the DAC FDA-1 in different test version durng development.

Jitter Measurement