NOS PCM 1704 DAC PCB group buy interest - diyAudio
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Old 17th June 2014, 08:05 PM   #1
kinku is offline kinku  United States
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Default NOS PCM 1704 DAC PCB group buy interest

Hi,
I am in the process of a Non oversampling DAC construction with PCM 1704 chip. I am wondering if anyone interested in a group buy of PCB. Assuming the PCB cost would be close to 50-60 per board for now. If more people are interested the cost will go down a little bit more. The PCB will be professionally designed and made with high quality materials. Lets see.
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Old 18th June 2014, 07:21 AM   #2
rol is online now rol
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More info and pics please
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Old 18th June 2014, 11:18 AM   #3
kinku is offline kinku  United States
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Default Schematic

Here is the schematic of proposed Board. Awaiting suggestions and interests.
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File Type: png pcm1704 filter.png (73.5 KB, 194 views)
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Old 18th June 2014, 01:00 PM   #4
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DAC with two PCM1704
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Old 18th June 2014, 01:39 PM   #5
kinku is offline kinku  United States
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Yes, but with modified LP filter .....and no more noisy regulators.

Last edited by kinku; 18th June 2014 at 02:05 PM.
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Old 19th June 2014, 09:58 AM   #6
vzs is online now vzs  Europe
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What is the idea behind combining different LP filters topologies: SK, MFB?
What filter order do you plan to use?

There's no reclocking after the delay - don't you care about jitter?

Easier way of doing the I2S splitting and delay is with Ian's I2S-PCM board (in another thread).

Last edited by vzs; 19th June 2014 at 09:59 AM. Reason: spelling
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Old 19th June 2014, 10:06 AM   #7
kinku is offline kinku  United States
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Vzs there is no filter that can have all the characteristics we want. To filter out the images after DAC we need a 10th order or higher filter.
I2S-PCM board is a good idea but so far I have found everything comes with a price. If you improve jitter ,you will introduce something else.( noise ).Thanks though.
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Old 19th June 2014, 10:20 AM   #8
vzs is online now vzs  Europe
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Quote:
Originally Posted by kinku View Post
Vzs there is no filter that can have all the characteristics we want. To filter out the images after DAC we need a 10th order or higher filter.
I thought about a less generic answer for this.
e.g. SK topology for this... MFB for that...
bessel type for this.. equiripple for that...

Forgot to ask: what sample rate will this run at?

Quote:
Originally Posted by kinku View Post
I2S-PCM board is a good idea but so far I have found everything comes with a price. If you improve jitter ,you will introduce something else.( noise )
Don't you think those 5 shift registers will dirt your ground plane being closer to the DACs themselves?

Will you use a board similar to Pavouk's v1.0 ?
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Old 19th June 2014, 11:29 AM   #9
kinku is offline kinku  United States
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The post DAC filter is the hardest part to implement in Non oversampling DACs. You can either ignore the presence of those images and depend on your Amplifier ,pre amp band width limiting abilities to block them from being reproduced through speakers. And your ears will filter out everything that is not needed. Or you can argue that those images will cause IMD in amplifier and hence need a brickwall filter to cut everything above 20KHz. But no filter is always better than best filter. I decided to go with something in between. I am ignoring the first image at 22.1KHz and decided to get rid of all others using a filter( using 44.1KHz CD material). Inverse Chebyshev works reasonably ok for that purpose or a Butterworth if you are ready to include more opamps. The DAC board will support up to 24bit 96KHz( not sure about192KHz, and I do not think I will need that sampling either). For using 96Khz material you do not need such a higher order filter but if source is 44.1KHz yes you do need one.
With power supply
There is three supplies one for digital and one for shift registers and one for analog OPAMP.During board design( not done by me, but a qualified engineer) the measures will be taken to limit ground planes interacting with each other. The board will not be similar to Pavouk as it seems a lot of auto routing and do not considered as properly designed( no offense) by PCB design engineer and he never claimed that it is designed by a professional either. I did read about it . Considering the expensive DAC chips involved I will not be doing the PCB design myself but will be using professionals to do it. Provided there are enough people interested.
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Old 19th June 2014, 02:19 PM   #10
vzs is online now vzs  Europe
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I know there is no free lunch in engineering but do you think that a good software 8x oversampling with a digital filter having a less steep rolloff (this goes with optimized time-domain performance that allows more aliased images to leak into the audioband but still much less then NOS) + a 2nd-3rd order Bessel is worst then using a 10-12th order filter and leaving most of the lower sideband of the first image in?

Would be interesting if you would implement those filters as separate small modules insert-able into a 8pin DIP socket (with res/caps of 0603 or 0805 size and a SOIC IC this would be fairly easy) so you could easily jump them in-out and see whats better.
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