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Old 26th August 2011, 08:01 AM   #81
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Quote:
Delta Sigma DAC's are supposed to be less sensitive to jitter
no, DS DACs has less output levels, from 2 (PWM, PDM) to 78, step size (sample-to-samole amplitude difference) is much bigger then for Nyquist dacs (16bit - 65536 output levels), sensitivity to jitter is much bigger.
There is proportional between jitter, frequency and slope of a signal (step size, step density).
Quote:
Do the modulations on the clock fold over from the actual clock or the sample rate?
Yes, jitter modulating HF quantization noise folding it down to baseband.
Quote:
I'm not clear what the effect of jitter on the clock system will be
the same, phase modulation of input signal
Quote:
Phase jitter, time domain jitter, phase noise, residual FM are all different descriptions of the same phenomena
yes, but measurement methods are not the same -> numbers are not the same
Quote:
Interesting, the HF component may be less important
For Nyquist dacs and 2562\8741 only 10Hz-10kHz is important
Quote:
Perhaps not, but how would they differ?
differs absolutely, for DS depending on order of modulator, levels of the DAC, filtering in digatal domain and at discrete-to-continuous time interface.
Quote:
The original breed of DS DACs (Bitstream from Philips - example TDA1547) had switched-capacitor (SC) architecture. This means the clock can jitter but that doesn't translate into an amplitude variation at the DAC's output.
no, translate, but less then a simple CMOS PWM output
Quote:
I wonder if that's what Nazar was referring to in mentioning 'digital filter'
no, digital filtering is digital filtering, not the filtering at discrete-to-continuous time interface

Quote:
the Cirrus DACs I think have SC filtering after the DAC itself
CS, AK, WM, and PCM4104 all has DCT (Direct charge transfer) DACs, but different
Quote:
a paper by Bob Adams (ADI) seemed to suggest that AD parts don't, but don't quote me on that
AD and TI dont use DCT dacs because DCT dacs are very power consuming and complicated
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Old 28th August 2011, 02:56 AM   #82
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Default First mission: Modding the WM8741 DAC

I have a WM8741 DAC. It has two WM8741 working in differential mono mode and a WM8805 DIR. I was full with expecting but got a bit disappointment on the clarity I don’t know why. I suspect it was the LPF design problem but I didn’t confirm. I am gonna mod it by my I2S FIFO now.

On board, there are two relays switching between internal and external I2S sources. Just disassemble them by a SMT soldering station and bridge the I2S signals by input and output cables linked to the FIFO. The MCLK goes separately by a 50 ohm coaxial cable. I make use of an on board 5V LDO power the FIFO. The FIFO board together with the frame of the clock board was fixed to the base by 4 screw standoffs. I attached the pictures. Things look pretty easy.

I ran it by a $3 oscillator just to confirm everything is OK. It sounds almost the same quality level as the WM8805 did. Not like my AD1955 DAC which sounds quite different with and without the FIFO. I think there might be two reasons: 1, the WM8805 has better jitter performance than DIR9001 and need the FIFO equipped with a bit better secondary clock to get improvement; 2, the WM8741 is not as sensitive as AD1955 to the MCLK jitter. However the clarity problem is still there, I believe it was analog problem and has nothing to do with the digital audio signals.

Anyway, I’ve already started collecting the oscillators other than $3 ones for the later on testing and evaluation. I’m gonna try different clocks the next steps.
Attached Images
File Type: jpg WM8741DAC1.JPG (583.9 KB, 1328 views)
File Type: jpg WM8741DAC2.JPG (570.0 KB, 1253 views)
File Type: jpg DACchip.JPG (549.9 KB, 1170 views)
File Type: jpg wm8805.JPG (515.1 KB, 1127 views)
File Type: jpg FIFOhookup1.JPG (508.7 KB, 1135 views)
File Type: jpg FIFOhookup2.JPG (577.3 KB, 550 views)
File Type: jpg FIFOhookup3.JPG (413.4 KB, 475 views)

Last edited by iancanada; 28th August 2011 at 03:26 AM.
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Old 28th August 2011, 09:46 AM   #83
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Hi Ian, I look at you pictures, DAC is very poorly designed (maybe by audiophiles)

Quote:
I ran it by a $3 oscillator
what type?
Quote:
Not like my AD1955 DAC which sounds quite different with and without the FIFO
nothing surprisely

Quote:
the WM8805 has better jitter performance than DIR9001 and need the FIFO equipped with a bit better secondary clock to get improvement
8804 has 100Hz LPF corner frequency, 9001 - 10kHz (absolutely dont reject necessary input jitter), 8804 with external good generator has jitter <50ps RMS (find the time I measure exactly), 9001 - 50...60ps RMS. 9001 very poorly designed, very sensitivity to "glitches", dont work stable.

Quote:
the WM8741 is not as sensitive as AD1955 to the MCLK jitter
Approximately 50 times lower

Quote:
I believe it was analog problem and has nothing to do with the digital audio signals
this DAC is all complete problem)


Quote:
from 2 (PWM, PDM) to 78
must be "from 2 (PWM, PDM) to 64"
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Old 28th August 2011, 05:02 PM   #84
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Nazar:
How are you measuring jitter? Method, hardware and type will help in making meaningful comparisons.

I have not been impressed with the sonics from Wolfson (not sure why) and have heard other reports to the same effect. I have also heard from very skilled designers that the Wolfson spdif receiver is a nightmare to get working and the net results from the really easy to use AKM were better.
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Old 28th August 2011, 08:22 PM   #85
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Quote:
How are you measuring jitter? Method, hardware and type will help in making meaningful comparisons.
I need to go office one company who produce generators. Methods all standard, high speed DSO & Spectrum analizer. (Agilent, Rhode&schwarz)
Quote:
I have also heard from very skilled designers that the Wolfson spdif receiver is a nightmare to get working and the net results from the really easy to use AKM were better.
I use 8804 since he was produced, very good reciever with no problem at all, all others receivers (dir,cs,ak,ym,phil) has almost NO rejection of jitter in right range (LPF corner freq. >10kHz), needs second PLL
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Old 28th August 2011, 09:10 PM   #86
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Quote:
Originally Posted by Nazar_lv View Post
8804 has 100Hz LPF corner frequency, 9001 - 10kHz (absolutely dont reject necessary input jitter), 8804 with external good generator has jitter <50ps RMS (find the time I measure exactly), 9001 - 50...60ps RMS. 9001 very poorly designed, very sensitivity to "glitches", dont work stable.
Approximately 50 times lower"
Hi Nazar, Thank you so much for confirming what I suspected.

Quote:
Originally Posted by Nazar_lv View Post
this DAC is all complete problem)
must be "from 2 (PWM, PDM) to 64"
I wanted to try WM8741 and WM8805, that was only reason I bought this DAC. But the clarity problem make me having some negative feeling on them. You said the DAC was all complete problem, do you have any idea to improve the clarity of WM8741?
What you mean 'must be "from 2 (PWM, PDM) to 64"'? Thanks. Ian

Last edited by iancanada; 28th August 2011 at 09:17 PM.
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Old 28th August 2011, 09:42 PM   #87
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Quote:
Originally Posted by Nazar_lv View Post
I need to go office one company who produce generators. Methods all standard, high speed DSO & Spectrum analizer. (Agilent, Rhode&schwarz)
I use 8804 since he was produced, very good reciever with no problem at all, all others receivers (dir,cs,ak,ym,phil) has almost NO rejection of jitter in right range (LPF corner freq. >10kHz), needs second PLL
And following from your earlier comment thgose each measure in different ways, depending on how they measure. The phase noise analyzer measures the obvious way, the scope several possible ways. I just ran across this really good background on the subject (which will save a lot of difficult explanations for others who happen on this):http://www.designcon.com/newsletter/...aper_april.pdf

I can measure directly to 30 pS RMS but that doesn't seem to be enough and its only cycle to cycle measurement. Any info you can provide from your experience will help in determining my next steps.

I understand that you have had success with the Wolfson receiver. I have read their white paper on the different cutoff on the PLL. Its interesting but the programming looked to be a major issue. Is there anything special you did?
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Old 29th August 2011, 06:45 AM   #88
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Quote:
Any info you can provide from your experience will help in determining my next steps.
http://www.sitime.com/support2/docum...easurement.pdf
Quote:
Is there anything special you did?
no, only correct PCB layout, and i use hardware mode because i dont need some special functions in software mode.
Quote:
do you have any idea to improve the clarity of WM8741?
of course, i work now with this dac, but its not a diy project.
Quote:
What you mean 'must be "from 2 (PWM, PDM) to 64"'? Thanks. Ian
corrections to my post 81

Quote:
Quote:
I ran it by a $3 oscillator
what type?
Regards,
Nazar
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Old 30th August 2011, 07:18 AM   #89
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Quote:
Originally Posted by iancanada View Post
I have a WM8741 DAC. It has two WM8741 working in differential mono mode and a WM8805 DIR. I was full with expecting but got a bit disappointment on the clarity I donít know why. I suspect it was the LPF design problem but I didnít confirm. I am gonna mod it by my I2S FIFO now.

On board, there are two relays switching between internal and external I2S sources. Just disassemble them by a SMT soldering station and bridge the I2S signals by input and output cables linked to the FIFO. The MCLK goes separately by a 50 ohm coaxial cable. I make use of an on board 5V LDO power the FIFO. The FIFO board together with the frame of the clock board was fixed to the base by 4 screw standoffs. I attached the pictures. Things look pretty easy.

I ran it by a $3 oscillator just to confirm everything is OK. It sounds almost the same quality level as the WM8805 did. Not like my AD1955 DAC which sounds quite different with and without the FIFO. I think there might be two reasons: 1, the WM8805 has better jitter performance than DIR9001 and need the FIFO equipped with a bit better secondary clock to get improvement; 2, the WM8741 is not as sensitive as AD1955 to the MCLK jitter. However the clarity problem is still there, I believe it was analog problem and has nothing to do with the digital audio signals.

Anyway, Iíve already started collecting the oscillators other than $3 ones for the later on testing and evaluation. Iím gonna try different clocks the next steps.
I also have this WM8741 DUAL DAC, too
I think there're some problem on LPF, If you see input point before Opamp you can jump these signal to external voltage gain and use them.

Too many different sound and more liquid if you use only 16BIT function. After I used >176.4KHz there'remany noise and error signal I don't knor why ?

Lyricxx Audxx ?

Thanks
Anadigit
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Old 30th August 2011, 12:43 PM   #90
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Quote:
Originally Posted by ANADIGIT View Post
I also have this WM8741 DUAL DAC, too
Thanks Anadigit, Yes we got the same toy. It seems the designer made a lot of effort, but he didn't get the right answer, as well as went through very careful test.
Thank you so much for those suggestions, I'll go through the LPF and the whole analog section this weekend to see if I could make it better.
Ian
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