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In Reply to: RE: How about a different approach: replace Juli@'s analogue PCB posted by cics on March 29, 2009 at 11:27:57
cics,This idea of you has me very intrigued. I think there are several ways we could go on this...
1. Develop a new board using the PCM1794A that you mentioned above. I do like it's digital filter disable mode, but it does only do 24-bit.
2. Develop a new board using the AK4399 that I'm getting. It is another of the current 'superchips, most notably used in Alex Peychev's $30,000 NWO 3.0-GO modified Esoteric UW-1. It also has the digital filter disable mode, but it is a 32-bit chip... I'm not sure how much that matters, but it's good from a numbers perspective.
3. Develop an easy-to-implement mod of the ESS Sabre DAC, which has gotten a LOT of favorable press. What makes this an attractive option is the availability of Twisted Pear's ready-to-implement boards including an output IV stage. If the pricing for the new boards will be the similar to the last generation, this may be the most expensive of these options... but take the least development. This newest one is 32-bit AND also has the filter disable mode, so it remains a top contender. One good thing... the supporting I/V stage and power supply boards seem very highly developed.
4. A budget upgrade based on modifying the Juli@'s analog out, similar to what I did this last weekend. I don't yet know how good it will be, it hasn't fully run-in yet, but it's sounding very nice at three days in. Bass is especially well defined and strong, a significant jump over the stock card.
In the new-DAC world, I especially like the idea of dis-engaging the on-chip digital filter... I suspect there are significant gains available just doing that.
I am also expecting that it will be important to provide a separate power supply for best sound. As long as nothing goes too awry this next weekend, I hope to try that with the Juli@. I do have all the parts in-house now and started laying out the raw supplies last night. 4-6 hours of work on Saturday and it should be running. I'm also very interested to see how much of a difference it really makes in my setup where I start with the linear/hybrid supplies powering the computer. I still expect a significant bump, but it may not be as much as when separate digital-interface and DAC supplies are added to a computer SMPS-based setup.
Here's my version of your wish-list:
1. Phase I power mod to add additional filtering caps on the Juli@ digital board and on the DAC option chosen. Phase II power mods going to separate supplies for the digital And , either a linear or battery.
2. Phase I DAC mod to upgrade the Juli@. Phase I to implement one of the three DACs above (or any new contenders that emerge).
3. Output stage may have several options to choose from. The Twisted Pear setups offer nice turn-key stages. I do like the idea of a nice tube stage. I also like the idea of your multiple output voltage choices.
4. Location inside the computer case to minimize the I2S line length. Packaging to minimize RF and EMI interference would be important, such as your faraday cage. Mounting the I2S connections directly on the Juli@, maybe the entire DAC board, would be trick.
5. Balanced out via Neutric or Hicon XLR connectors. Un-balanced out also available.
If we want to investigate the PCM1794A or AK4399 options, it's probably worth getting a couple of the evaluation boards on-order.
One thought I have is that this is more of a DIYAudio-type of thread than most of the ones I see on the Asylum (except for the Tube DIY forum here). So I've started a thread for cMP2 mods there:
http://www.diyaudio.com/forums/showthread.php?s=&postid=1788543#post1788543
I don't know if you've seen it there, but Peter Daniel has posted a bit about his version of an AOB and later a cMP2 in the last few pages of his AudioSector-chip amp kits, dacs, chassis thread:
http://www.diyaudio.com/forums/showthread.php?s=&postid=1788548#post1788548
It was his implementation that was half of the inspiration to go to the linear/hybrid supplies... and the other half goes to the Asylum's Ryeland for his linear P4 power supply.
I invite consideration of moving that thread there, I suspect that the DIY nature of that board will get us more input than we'll see here.
My recent 2 cents.
Greg in Mississippi
Edits: 04/01/09Follow Ups:
Greg,
interesting thoughts!
Just a brief correcting remark on the ESS Sabre for now: The current version is the ESS Sabre32, it is 32 bit (not 24) and the deemphasis and FIR filters both can be disabled.
Regards
Robert
Robert,
That's good to know and I updated my post above.
Honestly, if Twisted Pear had not be out of the Buffalo DAC at the time I'd decided which one to order, I'd probably have one of them now instead of waiting for the AK4399 DAC board. I don't feel bad going with the AK4399, but I liked the maturity of their design.
Two questions I have for the group...
One, you mention that the deemphasis is defeatable. One question I have is what happens with emphasised CDs? I happen to know (because I once made a CDP based on a CDP650 that had a demph-on LED) that a few of my CDs are emphasized. Will they play wrong. It's not like I stay awake at night worrying about this, but I am curious.
Second, does anyone have any tips on programming these things. It looks like the AK4399 will need programming to set the filter bypass on... and I wouldn't be suprised if the others didn't too. I suspect that the info on how to do this is in the ESS Sabre DAC thread on DIYAudio, but I haven't taken the time to look yet.
Again, thanks!
Greg in Mississippi
Juli@'s ASIO drivers remains the best I've seen to date.
New analogue board plugs onto this using I2S interface which I assume will support 24 bit DACs only (a deal breaker for 32 bit DACs). Alfred uses this interface for the Buffalo / Sabre DAC. Alfred: can you confirm 32 interface?
I'm not religious about 24 or 32 bit: important factors are SNR and the ability to bypass internal reconstruction filter. My AA Prestige SE uses the PCM1792 DAC which is excellent. Both AKM and ESS Sabre are excellent 32 bit DACs and yes the Sabre would be a brilliant choice (even better than 1794) given that we can disable its filter and includes IV stage & PS refinements.
So lets go with the Sabre and add RCA outs as well.
Will look into Peter Daniels' work as well. DIY thread is a great start (PS - my loyalties lie with AA).
Regarding Juli@ i2s out and ESS Sabre32:
Not sure wether Juli@ i2s out will work with ESS Sabre32 "as is" right away, will have to test. If it doesn't, this can likely be fixed by choosing a different PCM audio interface format - ESS Sabre32's default is 32-bit but can be set to 24-bit by programming the registers.
Documentation is light and so far, my readings suggest Sabre 2008 allows for disabling "Demphasis" only. Can't get any info on Sabre 2018.
Just thinking aloud:
The ESS Sabre32 has 32bit PCM audio input stream as default - would it be possible and would it make any sense to have SRC resample to 32/192...? Haven't thought about this yet, but apparently Asus Xonar soundcards can output 32bit (at least Xonar DX can, see test here: http://www.atomicmpc.com.au/Review/116715,asus-xonar-dx-pci-e.aspx) - not sure if Juli@ can.
Anyone any thoughts if 32bit make any sense?
.
32 bit i2s and filter disable confirmed
Edits: 04/04/09
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