[aos]

Well, it's over a year since I embarked on this project, and almost a year since the first prototype worked. This one marks - almost - the end of my journey to portable sound bliss. So as posting "long awaited" pictures of everybody's favorite projects is a recent trend here, I thought I'd chime in with my own baby. I finished drilling only yesterday, and I didn't do a particularly good job, but I don't care.

 

[jude]

That's pretty dang studly, man.

I know you've mentioned it before in other posts, but what's in it? That info would go well with the photos.

 

[maczrool]

Nice work. I take it the revisions to your last PCB worked out? When can we see schematics and an overview of operaton/construction? I know you changed a few things since the article on Headwize.

I'm still gathering parts and thinking out the design of my PDAC project. No NPC filter. Had to go with BB.

Stu

 

[morsel]

Very sexy, aos.

 

[aos]

I had the insides of this version of portable DAC posted at Headwize a while ago, but I must say that the previous version looked way cooler from the inside (that one is my avatar). The article on Headwize will be updated at some point when I manage to find some time. Though the basic design is the same, there are a few major differences - coax in, combo mini optical/electrical in jack, I added an analog filter after DAC chip as in datasheet just to be safe (as there's no digital filtering) and the analog stage had a major revision by adding star grounding and voltage regulation for each chip. The result is far better bass than before as well as all-around better sound. There are still a few annoyances in this particular specimen though, it refuses to work at anything but 44kHz (it should work up to 96kHz) and it shuts down digital section only partially when used as amplifier (DAC should shut off to save power but it doesn't do that completely).

Batteries can of course be used but as a battery pack plugged in DC jack. That's why I shortened the case - there's no point in having batteries in case that doesn't have battery compartment, and you can't have one for 10AA's (or 2 LiIons). Otherwise a 12V adapter does the trick.

 

[maczrool]

Quote:

I added an analog filter after DAC chip as in datasheet just to be safe (as there's no digital filtering)

AOS,

So did you stick with the component values listed for the filter in the AD1866 datasheet or did you adjust them. I think the values presented will give you too wide a bandwidth for it to do any good. It seems like it is probably somewhere in the 35kHz range, but I could be wrong. Since your PDAC as it is used, has a Nyquist frequency of 22.5 kHz, you would obviously need to filter above that.

Stu

 

[aos]

I stuck with values as specified and the sound is still great. You're right that it won't attenuate all that much in first hundred kHz or so but it will cut the broadband noise overall and make sure and kind of carrier and clock frequencies in hundreds of kHz and MHz are attenauted.

 

[Gariver]

This portable DAC is the best DIY project I've seen at Head-Fi or Headwize! It is truly amazing! Congratulations aos!!!

 

[Audio-Me]

When you figure out how to get it to do upsampling, you should make one in a 5 1/2" slot enclosure for use with a PC (coax input in the back, hp out in front). DVD (software dolby hp) would be awesome, as well as music and games.

 

[maczrool]

aos,

I was looking at the schematic for the PDAC and noticed that you used an inverter between the right latch on the AD1866 and the LRCKO on the DIR1703. How did you realize that that was needed? I will be running into a similar situation with a DF1706 digital filter and an AD1868 and don't know whether the inverter is necessary or not.

Thanks,
Stu

 

[Audio-Me]

All in one DIY system:
transport
pdac (move to gilmore output stage later on)
hp jack
both analog and digital i/o
in one box
hell you could go even further and add a 50wpc all FET power amp in a separate case

 

[aos]

maczrool, you have a pm...

Inverter is needed because L/R is indicated with 0 and 1 from DIR while latching of data into DAC chip is done on one of the edges (rising or falling, can't remember). So for one of the signal needs to be inverted. Current shemactics is more complex because G protection in Sony PCDPs causes nasty pops as they send so much noise that the DIR cannot decode signal properly - so I had to add some circuitry to minimize pops (which seem to happen in right channel only).

Bear in mind, this is not "an ultimate DAC". It's a portable DAC. I have Marc Heilinger DAC and using PDAC amp with EL2009 and the sound is clearly significantly superior to PDAC alone. It's a compromise.

 

[maczrool]

Quote:

Inverter is needed because L/R is indicated with 0 and 1 from DIR while latching of data into DAC chip is done on one of the edges (rising or falling, can't remember). So for one of the signal needs to be inverted.

It's falling edge. Thanks!

Stu

 

[elrod-tom]

Excellent. Something like this would be the next ideal upgrade for my work rig. What's the build cost??