Author Topic: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz  (Read 8936 times)

Offline Tuyen

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http://www.diyaudio.com/forums/digital-line-level/259488-reference-dac-module-discrete-r-2r-sign-magnitude-24-bit-384-khz.html

"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 optical 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 :-) My plans are for two board versions, one with 0.05% resistors for maybe USD 170, and one with 0.02% resistors for maybe USD 240, one with 0.01% resistors is also a possibility, but it might be to expensive....
"





Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #1 on: July 22, 2014, 04:23:06 PM »
Thoughts?   I'm interested in putting my name down for 1 board.  I've always liked the idea of the TotalDAC, but just too costly for my taste.   This seems like a cheaper option but based on similar concept.    Could be good!?

Offline kajak12

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    • http://killerdac.com/forum/index.php
Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #2 on: July 22, 2014, 10:42:16 PM »
go for it tuyen
still discovering the link between electronics and audio reproduction.so much to learn and so little time

Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #3 on: July 23, 2014, 12:04:01 PM »
Indeed I will!   Noticed klacto has posted his interested for one too.    :)

Seems like DSD will be possible too through the programmable FPGA according to the designer.

"Hi Soekris
i have some question that need to ask . The r2r dac is possible to accept a DSD format file ?"

"At some point, should be easy to convert from DSD to PCM in the FPGA..."

« Last Edit: July 23, 2014, 12:08:31 PM by Tuyen »

Offline ozmillsy

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #4 on: July 23, 2014, 01:03:53 PM »
Seems like DSD will be possible too through the programmable FPGA according to the designer.

"Hi Soekris
i have some question that need to ask . The r2r dac is possible to accept a DSD format file ?"

"At some point, should be easy to convert from DSD to PCM in the FPGA..."

Conversions are not ideal.   May as well just convert in software. 

There are 2 issues with *any* kind of conversion (hardware or software);
1) volumes of the recorded DSD material
2) high frequency filtering 

The reason why tools like Audiogate or Saracon are a better option,   than an "on the fly" converter (software or hardware based),   is you can check the headroom and re-run the conversion to optimise the volume.    There are also better dithering and filtering options.   These things can and do make a difference, for different types of music.      When it is done in hardware,  it is generally 1 setting for all, and the type of dithering will be pretty basic.

I like the idea of a purpose built DSD dac,  which is optimised purely for DSD playback.   Such a device could be quite affordable, if done well.    There is no problem having multiple front ends,  from my perspective.  :)
« Last Edit: July 23, 2014, 01:06:08 PM by ozmillsy »
It's all about the music,, not the equipment.

Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #5 on: July 23, 2014, 01:22:07 PM »
I hear what you are saying Oz.  I see the logic!

What about the USB to I2S module that Danny and Terry are playing with?  Is conversion also happening in that case?

Link to the module - http://jlsounds.com/i2soverusb.html

Offline ozmillsy

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #6 on: July 23, 2014, 03:07:26 PM »
What about the USB to I2S module that Danny and Terry are playing with?  Is conversion also happening in that case?

Link to the module - http://jlsounds.com/i2soverusb.html
I don't believe so.    As I understand, DSD over PCM is an encapsulation and transportation method.     I don't know if this method has any timing implications,   but after transportation the data itself should be presented to the dac chip in DSD form.    Danny is streaming the DSD data into a SACD player,   what type of chip that player has I am not too certain.   I think it might be a delta sigma type Burson chip,  not sure.

It comes down to the type of chip, and if we are talking about a 24bit pcm chip,  then a conversion needs to happen somewhere (inside the chip, or somewhere upstream).
« Last Edit: July 23, 2014, 03:09:31 PM by ozmillsy »
It's all about the music,, not the equipment.

Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #7 on: July 23, 2014, 03:39:57 PM »
Thing is Oz,  this design is not based on any traditional DAC chip :)    Thus what makes it different...

There are many discrete resistors in an array that are controlled by the programmable FPGA chip (which is not a DAC chip).

Danny is sending DSD via I2S into a Burr Brown PCM1738 DAC (in his Pioneer).    My shanling SCD-t200C uses the same chip (DSD capable, hence why it can play SACDs!)

Correct me if I'm wrong Danny/Terry?     Also how would a purpose built DSD DAC differ to this design?   

cheers!

Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #8 on: July 23, 2014, 03:44:32 PM »
Designer's replies:

"Hi Soekris
That means is to use FPGA to convert file format to PCM then decode? This is the only way to do ? Can not be native decode the dsd format? Ok if yes , is possible to upsampling to DXD format first to decode (optional choice on firmware).
Thanks for your prompt reply."

"DSD is a one bit delta sigma modulated signal at 2.822, 5.644 Mbs or higher, afaik, you just feed it do a 50-70 Khz lowpass filter to get the analog signal back.
On a parallel DAC like mine you have to do an equivalent digital lowpass filter, then feed it in parallel form to the R-2R network, not really any conversion as such...."

"Hi Soekris
If I am nit misunderstood that means we just only need a digital filter to get analog signal to feed in the r2r dac only? If yes this is a extra benefit to all user .
Thanks"

"No, DSD is digital serial signal, a digital lowpass filter in the FPGA convert it to a PCM digital parallel signal. See Direct Stream Digital - Wikipedia, the free encyclopedia for more info on DSD."

Offline ozmillsy

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #9 on: July 23, 2014, 05:28:57 PM »
The key bit in that post is about the digital filtering.

You cant easily edit (or filter) DSD data.     

Quote
On a parallel DAC like mine you have to do an equivalent digital lowpass filter, then feed it in parallel form to the R-2R network, not really any conversion as such...."
<snip>
"No, DSD is digital serial signal, a digital lowpass filter in the FPGA convert it to a PCM digital parallel signal. "


Why filter at all?    Because 1 bit data has excessive high frequency noise,  that starts kicking in at about 40k and rises from there.       

I have a Shanling SACD player aswell,  it has PCM1794 chips in it, and these are also DSD capable.   But what is not clear,   is what the chip itself is doing?   It accepts the incoming DSD stream,  and then what?     I think there is converting going on,  but to multibit delta sigma.  Not 100% sure.

http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html#MultiBit


Purists argue that single bit delta sigma,  with analog filtering, is the simplest and cleanest approach.  I don't know if this is true, I don't have first hand experience.

« Last Edit: July 23, 2014, 05:31:03 PM by ozmillsy »
It's all about the music,, not the equipment.

Offline klackto

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #10 on: July 23, 2014, 06:43:02 PM »
Indeed I will!   Noticed klacto has posted his interested for one too. 

Hi Tuyen 
Yep, put my name down for one.
For that sort of money thought it could be fun to get one and build a tube buffer stage for it ......  but then again reading this forum is putting evil ideas about crowns, double crowns, deulunds, vintage chokes,wadias,battery powered clocks etc etc etc in my head.   ;D

Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #11 on: July 23, 2014, 07:23:15 PM »
Same thought here. Not crazy outlay for something quite unique and should be bit of fun.   

Spending the same amount of money for 1 duelund capacitor is not my idea of fun anymore!  ha ha

Offline ozcal

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #12 on: July 24, 2014, 03:25:59 PM »
Thanks T , put my name down for a board too.
Listening with my ears :)

Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #13 on: July 24, 2014, 03:28:01 PM »
Nice G.  Saw that!       Must catch up soon?  Interested in some of those new toys you have built. :)

Noticed fellow forumer PixelPlay put his name down for 1 board too.

Offline zenelectro

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #14 on: July 25, 2014, 04:00:21 PM »
I don't believe so.    As I understand, DSD over PCM is an encapsulation and transportation method.     I don't know if this method has any timing implications,   but after transportation the data itself should be presented to the dac chip in DSD form.    Danny is streaming the DSD data into a SACD player,   what type of chip that player has I am not too certain.   I think it might be a delta sigma type Burson chip,  not sure.

It comes down to the type of chip, and if we are talking about a 24bit pcm chip,  then a conversion needs to happen somewhere (inside the chip, or somewhere upstream).

Just as a point of interest, AKM semiconductor has a line up of ultra quality converters coming next year.
They include ADC DAC and SRC (format conversion). All do PCM up to 32 bit / 768kHz (yep) and DSD up to 11mHz (DSD256=quad speed)
The format converter / SRC  can convert any of these formats to any other with very high precision.

Not sure where the market is heading but this should open it up a bit, especially WRT pro audio DSD recording / editing.

PS for anyone sending me PM's and emails, currently running pretty easy, a few weeks out of hospital and it's
going to be a slow steady road for quite a few months.

cheers

Terry

Offline Rob181

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #15 on: July 26, 2014, 08:14:13 AM »

PS for anyone sending me PM's and emails, currently running pretty easy, a few weeks out of hospital and it's
going to be a slow steady road for quite a few months.

cheers

Terry

Great to hear that your are SLOWLY on the mend...

Offline vitavoxdude

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #16 on: July 27, 2014, 04:00:55 AM »
 ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;)
Great tho hear you are back on the road to recovery, go Zen go  ;D ;D ;D ;D ;D ;D
V
We all like different things so lets all agree to disagree and if any common ground is found then worship it.  Mine is the KD hence being present on this forum.

Offline zenelectro

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #17 on: July 28, 2014, 10:39:34 AM »
;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;) ;)
Great tho hear you are back on the road to recovery, go Zen go  ;D ;D ;D ;D ;D ;D
V

Many thanks Vita and others, your encouragement and + energy is appreciated ! 

It's a damn slow frustrating road, I can tell you - they have made some pretty massive changes to my insides!  :o

However I'm slowly recovering and looking toward a positive future.  ;) ;) ;) ;) ;)

cheers

Z
« Last Edit: July 28, 2014, 10:41:32 AM by zenelectro »

Offline Tuyen

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #18 on: February 02, 2015, 09:22:50 PM »


Quite cute and compact design!

Offline omodo

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Re: Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
« Reply #19 on: February 03, 2015, 09:41:39 AM »
I'm quite interested to see what you think of it, particularly through the WE rep coils, either the unbuffered (600 ohm iirc?) or buffered outputs should be ok. Have only seen opinions from sabre/ds dac owners so far, which imho aren't all that valid :P