Inboard or outboard DAC: Pros and Cons? - diyAudio
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Old 14th August 2004, 11:27 PM   #1
niles is offline niles  United States
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Default Inboard or outboard DAC: Pros and Cons?

I think I have settled on the PCM 1794 to base an upgrade to my Sony x707es cd player. As I see it, I have two ways to go:

1. Build a board and minimal output stage to place in the player and use the transformer and components of the existing CD power supply. In this implementation I would add a Text clock to feed both the DAC and transport a high-quality 16.934Mhz clock. Pros are: less parts and an integrated package, with less overall cost. I dont know about implementing the clock distribution, seems I have read that shielded lines and other considerations are necessary. I would appreciate some comments about this. I can design the DAC board to incorporate Jung regulators for the analog supplies without too much extra work (I think). This seems to be the most elegant solution and is how I am presently leaning.

2. Build an outboard unit with a dedicated power supply. Pros include more space to work with, a dedicated tranny and the ability to use more than one source. Cons include the additon of an SP/DIF conversion in the signal chain, but a re-clocker could be added. Clearly more expensive. However the Rakk dac is available for rolling output stages and I would get to design a really cool enclosure.

I would appreciate any of you sharing some of your hard won lessons so that I might avoid making some expensive mistakes in this process. If you have some technical observations about what works and doesn't work, I would also appreciate you sharing that information. Thanks in advance--

Niles
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Old 16th August 2004, 10:56 PM   #2
niles is offline niles  United States
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Well, I guess I blew my first post here 'cause it looks like you guys are reading this but you aren't replying. So, let me try to increase the interest with requests for your know-how:

What do you think are the advantages and disadvantages of inboard versus outboard conversion.

Specifically, what is lost in an S/PDIF encode/decode process, if anything given todays reciever chips?

What is the advantage to designing a stand-alone DAC in terms of the power supply?

Does the PCM 1730 sound as good as the 1794 (cause I have samples of the 1730)?

Has anyone sucessfully modified a CD player with a new DAC/output stage and liked the result?

Exactly what is necessary to distribute the clock signal from a DAC board to the transport inside a CD player to prevent leaking and contamination of the ground planes?

Anything else you want to contribute? Anyone? Anyone? Bueller?
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Old 17th August 2004, 06:35 AM   #3
Netlist is offline Netlist  Belgium
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Hi Niles
Guess you'll have to wait for someone with enough 'digital brains' to pass along and answer your question.
Some of them seem to be on holiday. And I have no clue
At least you’ve got a reply…but no answer.

/Hugo
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Old 17th August 2004, 11:09 AM   #4
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Default DAC

More of the Pros and Cons of the 2 designs you have already mentioned.
To get you a little bit more clear about the reclocking:
- if you do not use resampler, /asrc/ you remain with the jitter of the Digital SPDIF receiver.... which is high.
- if you do use a resampler /ASRC/ it is some type of digital filter and it affects the overall sound , but reduces jitter. However, the jitter reduction is not infinite, it is like a filter - something will always be there at the ouput. Moderns ASRCs like AD1896 sound very good. Of cource the design cost is very high. But you can use the outboard DAC for every piece of digital source equpment you have!
For PSU designs - you generally need a good low noise supply for those circuits, despite of being internal or external. You will find very good designs around if you do a search.
1794 vs 1730 - I think 1730 is very good too, almost as the 1794. Pay more attention and compare the pass-band - stop-band chars in the two datasheets, if they are idnetical, probably the chips are too I did such comparisions for AD1853 and AD1955, wich are the same, excluding more formats support for the latter as well as higher output current and so a 3 dB increase in the Dynamic Range.
Best Regards,
Kaloyan Mahinov
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Old 9th March 2007, 09:13 AM   #5
dowser is offline dowser  Switzerland
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Did you ever progress this Niles? Considering doing a DIY DAC inside my X707ES as well.

Thanks, Richard
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Old 9th March 2007, 10:38 AM   #6
weissi is offline weissi  Europe
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I can confirm that PCM1730 sounds good. Have compared it to AK4395 and CS4398. To me it sounds best (although the to others are placed an a E-MU and PCM1730 is linked to a PCM2707)
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