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RE: How about a different approach: replace Juli@'s analogue PCB

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: 04/01/09
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