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Old 31st October 2011, 01:23 AM   #11
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Um, you can't. Oversampling is built in to the way that chip works.
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Old 31st October 2011, 01:24 AM   #12
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by tiefbassuebertr View Post
How can I realize a non oversampling DAC with the PCM1794?
All possible modes of operation are explained in the datasheet, the only one that might possibly interest you is the defeat internal digital filter mode.
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Old 31st October 2011, 11:11 AM   #13
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Quote:
Originally Posted by abraxalito View Post
Um, you can't. Oversampling is built in to the way that chip works.
Thank you. This means, for non oversampling DACs only TI's (Burr-Brown's) types "PCM63", "PCM1702" and "PCM1704" are suited therefore.
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Old 31st October 2011, 12:03 PM   #14
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Yes if you only count TI's DACs in the audio classification. However there are other DACs which can potentially be used for audio - for example the DAC8831:

Digital to Analog Converter - Precision DAC (=<10MSPS) - DAC8831 - TI.com

and the DAC8581 (which I suspect is doing sterling duty in the Metrum Octave dac now heavily in demand):

Digital to Analog Converter - Precision DAC (=<10MSPS) - DAC8581 - TI.com
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Old 31st October 2011, 01:25 PM   #15
marce is offline marce  United Kingdom
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A quick note on grounding etc, there is no professional advantage or knowledge that isn't available to all, the definitive source of info on grounding is Henry Ott, 'Electromagnetic compatability Engineering. There is also a whole wealth of information regarding grounding on the web and at sites such as Ti etc. But first point of reference is H. Ott.
Heres a few links that may be of interest.
http://www.hottconsultants.com/techt...gnd-plane.html
http://www.elmac.co.uk/pdfs/Lord_of_the_board.pdf
An intuitive, practical approach to mixed-signal grounding
http://focus.ti.com/lit/an/sbaa052/sbaa052.pdf
http://focus.ti.com/lit/ml/slyp167/slyp167.pdf
http://www.ieee.org.uk/docs/emc1206a.pdf
http://www.icd.com.au/articles/Split...s_AN2010_6.pdf
http://www.analog.com/static/importe...0Grounding.pdf
http://www.analog.com/static/importe...als/MT-031.pdf
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Old 31st October 2011, 06:50 PM   #16
AWaudio is offline AWaudio  China
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Good! Thanks. Huge work to merge the paper into engineering. In my understanding grounding is part of the power supply design that focus on isolation. Photos attached above is with a naked transformer, it's going to be replaced by encapsulated ones. Again for given components, the most important thing is the current loop and power supply. I was trying to isolate the power supply and filter the noise locally for each stage by heavily de-coupling RC filter, typically a rubycon and a WIMA.Sounds better than my Marants CD.
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Old 1st November 2011, 12:53 PM   #17
marce is offline marce  United Kingdom
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Grounding (or more correctly providing a return current path) as the second link sugest is the MOST important signal on the board. In fact power delivery systems are becoming quite problematic with high density high speed, lots of switching nodes for noise and just being able to cope (i.e. PC motherboards, a prime example!). I'm just about to depart to an engineering day where a lot of the info is gonna be on power integrity by this guy.
Power Integrity Aware Complex PCB Design
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Old 3rd November 2011, 08:04 AM   #18
AWaudio is offline AWaudio  China
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High speed digital system power supply is a similar but yet not identical problem with that of the audio circuit. One main reason is the error and noise get "zero-cleared" so long as it does not excced the threshold level, while for analog circuit this is a diffrent story as any fluctuation can be accumulated stage by stage, and get noticed by human ears in an audio system.

So in my mind, take the DAC for example, there are basically two modules, one module ouput a digital I2S, another take the I2S as input, and the interconnection between this two. In this model I think the most important thing is "isolation". Ideally the second stage only cares about the relative voltages between the I2S data/clock and the digital ground PIN of the DAC chip, while in real word, if the two modules are powerd by a same power, cross talking happens due to the common power, the first stage digital part is more like an dynamic load, this dynamic load brings in noise to the power supply, and the noise feed back to the analog stage. So it's better to have proper "isolation" for the power of this two module, either by seperated transformer, seperated winding, or something else, while in my mind a seperated regulator with a PSRR value of large than 75 or 80dB value should be fairly enough.

In my mind the risk of improper grounding comes from the improper "sharing" of some of the current path for the power supply, here we are back to the word "current path", yes current path is the most important.

I used to build HDI digital boards of up to 800MHz Core CPU clock, but the philosiphy of "sweet sound" should be more than the nosie/EMC/EMI things. No idea what they are but will always be in exploring. BTW do you read the AES magazine? I just begin to do it.
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Old 3rd November 2011, 10:28 AM   #19
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Quote:
Originally Posted by AWaudio View Post
I've tested a typical negative feedback tone controlling circuit with opamps opa2604, and thin film capacitors. Indeed it's able to adjust the EQ obvious with lots of dBs. However it's not that sweet.... any more ideas.
Check out this thread:
Ultimatest Passive Tone Control Network based on James-Baxandall's topology wanted

Now some other questions:

1) How much are the shipping cost to Germany of the DAC, mentioned about the ebay-URL from post #1 ?

2) Do you know the difference in sonic character to a DAC equipped with PCM1704?

3) Which section shows the first picture of the second attached PDF ??

Thank you for your advices.
Attached Files
File Type: pdf PCM1794 USB DAC AW Audio Shanghai-I.pdf (127.2 KB, 97 views)
File Type: pdf PCM1794 USB DAC AW Audio Shanghai-II.pdf (184.5 KB, 42 views)
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Old 3rd November 2011, 11:09 AM   #20
AWaudio is offline AWaudio  China
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Appreciate very much for your post about Tone Control information, I'd read it carefully later. I once tried the classic passive and active tone control filter in this E-100 DAC and at last I decide not to include it at this moment, but I do want to include some good performance circuit to enable the EQ. For you question.
1) It's 38$ for 3KG and 45$ for 4KG by Fedex, arriving at around 4 ~6 biz days. I've no idea how much it exactly weighs, may tell you later.
2) No idea have not compared it with PCM1704, maybe you can do it and share the result
3) It's the power supply of the whole machine, two seperated channels of LM317/337, with fully protection diode and sufficient WIMA Rubicon capacitor for filter, 4700uF/63V*2 for main filter. It sounds dead quiet, leave the input or press the pause of your CD player, turn the volume to max you hear nothing as if it's not powered on.

Last edited by AWaudio; 3rd November 2011 at 11:14 AM.
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