Archive for the ‘DAC’ Category

XMOS USB Audio 2.0 Reference Design Jitter Measurement

Monday, 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

FDA-1 PCM1794A DAC Clearance Sales – 50% off!

Thursday, July 21st, 2011

* * * 50% OFF * * *

FDA-1 PCM1794A DAC clearance Sales and while stock last!

NEW prices in the STORE page.

I have updated a new user manual as below:

PCM1794A DAC Manual_r5

XMOS USB 2.0 Reference Design – USB 24bit/192k

Thursday, June 23rd, 2011

I buy this XMOS USB 2.0 reference design evaluation board from Digikey for US$141.91.  It can receive USB 2.0 24bit/192k Fs signal and output to SPDIF optical and I2S besides stereo analogy input/output.  The board will require firmware programming before it can be used.  Details can be found in XMOS website.

Digikey item: 880-1017-ND


For I2S, the signal is labelled on the board  and I use 2.54mm pin header for connection to my PCM1794A DAC board.  The USB board use the power from USB connection at about 150mA and thus do not need any outside power supply.  The good thing about the reference design board is that XMOS provide all the details of design, schematic, pcb layout and software to make it work in almost any platform that can accept I2S or optical signal.


Since I use Windows system and thus I need to install a Thesycon drivers which is also free from XMOS website after registration. The diver works with the USB2.0 reference design boards without any issue but it will beep once every 30mins of use.  Overall it is a complete design and easy evaluation of the performance by both industry or DIYers.


Photo shows how I mount it piggyback on a daughter board and then plug into my DAC main board.

FDA-1 PCM1794A DAC for Sale / PCM1794

Friday, April 1st, 2011

Last Update: April 1st, 2011

Change U11 from TA7805 to L4941BV for a more dynamics and details sound.  TA7805 remains a good mellow sound signature.  The kit will only provide TA7805 as standard.

Update: Oct 14th, 2010

There is some minor update on FFT measurement in Rev 4 manual.

FDA-1 PCM1794A DAC Manual Rev 4.1

FDA-1 PCM1794A DAC Manual Rev.5 (Updated Aug 23, 2011)

FDA-1 PCM1794A DAC Manual_r6 (Update on 12th Dec, 2011)

FFT measurement and power supply connection diagrams are added in this Rev 4 Manual.


These kits are designed to replace the obsolete PCM63 balance DAC kit (aka D1V3 and D1V33).

Please click on the link below to download complete manual for Product Specifications, Circuit Description, Circuit Diagrams, Assembly Instructions, PCB Layout, Interface Specifications, Bill of Materials and FFT measurements: PCM1794A DAC Manual Rev3

Price information refer to Store page:


A. Introduction:

  • These DACs are designed for the serious audiophile. They utilize the best DAC chip -PCM1794A that is capable of producing a super dynamic range of 127dB in stereo mode and 132dB in mono mode!
  • The I/V and analogy sections are custom designed and use 100% discrete components.  The I/V converter is a “Current Steering” topology and the analogy section is a pure ‘Class A’ non negative feedback driver and output buffer stages. With this combination, the sound will be musical, dynamic, accurate and real.
  • In Single End version, the DAC uses one circuit board with one PCM1794A DAC chip working in Stereo Mode. In Full Balance version, the DAC uses two circuit boards (one Master and the second Slave) and two PCM1794A DAC chips, each configured in mono mode (namely Mono L and Mono R) to deliver super dynamic range of 132dB.
  • Users can start with Single End version to see if the performance is up to the expectation of Hi-Fidelity. To protect your investment, a very clear and simple upgrade path is built into the design. Users of the Single End version can easily upgrade to the True Full Balance version anytime by adding a second slave DAC board! The sonic improvement of the Full Balance version brings new meaning to the word ‘High-Fidelity’!
  • These ‘serious audiophile’ DACs are peppered with high quality audiophile grade components that are selected because of their complementary sonic signatures after many exhaustive hours of listening tests.  Audio transistors, Paper-In-Oil capacitors, Silmic II capacitors and Dale resistors are widely used in the DACs.
  • However, the most important feature is that these DACs sounds musical, dynamic, open and warm with an unparalleled resolving power. These are truly remarkable DACs capable of holding themselves against any branded DAC costing many times more!

B. Specifications:

  1. DAC chip: Texas Instruments PCM1794A 24bit/192k best in class DAC
  2. Digital Receiver: Crystal CS8416 24bit/192k digital receiver
  3. I/V and Analogy Filter: Discrete transistor I/V (current steering) operating in pure Class A mode with NO global feedback for the best sonic performance
  4. Digital Input: SPDIF, AES, Toslink and I2S Bus (RCA, XLR female, Optical and 8×2-pin header)
  5.  Bit/Sampling Frequency: Up to 24bit/192k
  6. Analogy Output: Stereo Channels (Single End) @ 1.5Vrms (expandable to Full Balance output by using two boards @ 3Vrms)
  7.  Output Impedance: 150 ohm Single End mode; 300 ohm Full Balance mode
  8. Auto muting for noiseless operation when no audio/digital signal is detected or when a digital error occurs (e.g. AC-3 signal) or when powering up or down
  9. Power supply: AC 17~18V x 2, 0.5A and AC 8~9V x 1, 0.5A; total consumption 7W/board
  10. Display LEDs: PLL Lock, 48k, 96k and Mute (for CS8416 input only)
  11. Distortion: Typically at or less than 0.02% 1kHz at FS, 20kBW Single Ended @ 1.5Vrms.  At full bandwidth typically no more than 0.04%.
  12. Board: 6 x 8 inches double sided 1.6mm gold plated FR4; 6 x M3 supporting holes; max height part 35mm.

C. A lot of Audio grade components are included in the kit:

1.      Elna silmic II capacitors in all analogy power supply

2.      Russian PIO K40Y-9 for Low Pass Filter in IV section

3.      Sanyo OS-Con capacitors in digital supply

4.      Panasonic film capacitors for supply bypass

5.      Vishay Dale resistors in all signal path

6.      Low ESR filter capacitors by NCC or Panasonic

7.      High speed rectifiers BYV27 series

Refer to Bill of Materials for component provided in the kit.

D. Pictures:

FDA-1 PCM1794A DAC Upgrade!

Sunday, February 20th, 2011

This is a simple upgrade:


Change U11 7805 regulator to ST L4941BV.  The different is the sonic of the sound – more dynamic and clean.


LM7805 is a more mellow sound with less clarity but it is still very good.