Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz - diyAudio
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Old 22nd July 2014, 01:44 AM   #1
soekris is offline soekris  Denmark
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Default Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz

I have been working on a little side project, now it's time to present it for everybody here....

It's a DAC module based on a discrete R-2R sign magnitude DAC design, with FPGA based reclocking and custom digital filters, < 1 ps jitter clock generator, with 28 bit resolution so there is headroom, oversampling up to maybe 3.072 Mhz. Up to 24 bit / 384 Khz input from SPDIF, I2S and USB (via USB to I2S interface board), with isolation on the I2S interface. The board will be very flexible, with digital volume control and filter parameters that can be downloaded, a possibility is also to add digital crossover filters, but that will probably not be ready for first production lots, although the board is firmware upgradable over a simple serial connection.

The basis R-2R network has an output voltage of 1.4V RMS and output impedance of 1.2 Kohm and can therefore drive a lot of things directly.... There is also onboard balanced output drivers that can drive high impedance (>= 300 ohm) headphones directly. The power supply is also onboard, just add a 5W toroid transformer.

It is a small mostly surface mount PCB, and yes, I have working prototypes, see below.... But it's not really something for home assembly, with the FPGA in BGA package and 600 pcs SMT parts.... So yes, if there is enough interest it will go into real production, with sales though two existing online shops in US and EU.

Performance of first prototypes using 0.05% resistors is better than expected, see 1 Khz -1 db and -60 db FFT plots. I believe that the sound quality will be the absolute best, better than any Delta Sigma DAC, in class with discrete DAC's from totaldac and msb technology. And for way way less cost :-)

Update on Nov 6:

Thanks for all the nice words and interest. The board will definite go into production, leadtime on the precision resistors is the limiting factor, I'm trying for a ship date of late November for the first batch of 240 boards, then more boards in December. Planing for about 25% 0.01% version, 50% 0.02% version and 25% 0.05% version. Final pricing is:

0.05% resistor version USD 170 / EUR 137
0.02% resistor version USD 235 / EUR 190
0.01% resistor version USD 325 / EUR 263

Shipping cost and any local taxes to be added.

They will become available to order though two existing webshop (no info there yet, so do not contact them):

http://www.soekris.com for American and Asia markets.
http://www.soekris.eu for EU and European markets.

Once boards are ready to ship I will take orders in sequence using a priority list based on postings and private messages here in diyadio. To get on the priority list, send a private message here on diyaudio. Do not post on the list, and do not send emails. I will not confirm simple request to get on the priority list, but try to answer all technical questions. Please note that the first batch is already sold out, next batch is close to sold out, but I will make more, as many as needed....
Attached Images
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File Type: jpg fft_-1db.jpg (172.3 KB, 5076 views)
File Type: jpg fft_-60db.jpg (161.4 KB, 4760 views)

Last edited by soekris; 19th December 2014 at 04:16 PM.
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Old 22nd July 2014, 02:41 AM   #2
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Very cool project, soekris!
Count me in for one 0.02% version. Otherwise a 0.05% version is fine for me, too.
A fully assembled board is prefered, otherwise I can also solder the SMT parts myself if you have pre-soldered the FPGA.

However, it seems the analog output portion can't be bypassed. Here in diyaudio many of us have our own flavor of analog stage (opamp, discrete, tube, output transformer, etc). It would be much better and certainly would garther more interest if you could add a jumper for us to use the onboard analog stage or our own analog stage. The real jewel of this design is the digital portion.

Last edited by rredline; 22nd July 2014 at 02:54 AM.
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Old 22nd July 2014, 02:57 AM   #3
soekris is offline soekris  Denmark
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Actually yes, the output drivers can be bypassed, the "raw" R-2R DAC outputs before buffering are available on connector J7, at line level voltage and low impedance.

Not that the output buffers are that crappy, a LM49710 driving a LM49724....
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Old 22nd July 2014, 03:19 AM   #4
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Quote:
Originally Posted by soekris View Post
Actually yes, the output drivers can be bypassed, the "raw" R-2R DAC outputs before buffering are available on connector J7, at line level voltage and low impedance.
Great! Just saw it. At first I thought JP7 signal is came from opamp but turns out it is from DAC.

Last edited by rredline; 22nd July 2014 at 03:24 AM.
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Old 22nd July 2014, 06:12 AM   #5
CFT is online now CFT  United States
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Very nice!
Please count me in for one 0.02%.
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Old 22nd July 2014, 06:31 AM   #6
dex-rex is offline dex-rex  Australia
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Tempting! Count me in for a 0.02% version. Freq. graph would be welcome ...
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Old 22nd July 2014, 06:45 AM   #7
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interesting project... I would like to have one although i have 3 dacs already...

Can I ask for the reclocking is using the on board clock or the incoming clock ? Also upsampling can be bypass ?
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Old 22nd July 2014, 07:23 AM   #8
tuyen is offline tuyen  Australia
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Consider me keen for a board
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Old 22nd July 2014, 07:37 AM   #9
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Very nice design, it is quite compact and it is a joy to look at. I think it is the smallest discrete R2R DAC I have ever seen.

Some concern: with a resolution this high and "naked" resistors even some dust can disturb things isn't it ?
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Last edited by jean-paul; 22nd July 2014 at 07:40 AM.
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Old 22nd July 2014, 07:46 AM   #10
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+1 of the 0.02% version or 0.01% if is not outrageously expensive...
BTW what is the size of the board?

Last edited by Nikola Krivorov; 22nd July 2014 at 07:48 AM.
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