Support Head-Fi.org by
starting all of your
Amazon.com shopping by
clicking here.
____________________________________________________________________
Today's Featured Head-Fi Blog: A Japanese headfier's monologue (Sasaki)
____________________________________________________________________
Please help
support Head-Fi by becoming a Contributing Member
CLICK
HERE -- Contributing Members, thank you
for your generous support! --
Rants: - there - in or at that place; to or into that place; at that point or stage; in that matter, respect, or relation; used interjectionally to express satisfaction, approval, encouragement or sympathy, or defiance
- their - of or relating to them or themselves especially as possessors, agents, or objects of an action; his or her
- they're - they are
Now, I'm not a design expert of any kind just yet, but perhaps we can design our own portable, full on DAC/amp solution using some of Wolfson's better DACs. I realize there are already solutions available along these lines, but none fitting the I2S input requirement. stevenkelby, you mentioned using the Headamp Pico for its I2S input, but that DAC/amp converts USB to I2s. Unless we open it up and route some wires, we can't do it without voiding the warranty. I'm not sure how we'd go about doing this, but is it a viable solution having a portable DAC/amp running off a 9V? That's quite a huge energy loss converting down to 3.3V, so maybe running off some AAs would be wiser. Before we even go there, we should probably pick out a DAC that'll work. I'm thinking something along the lines of a portable full-on DAC, like a portable TPA Opus DAC (okay, maybe not that far). I'm looking at some Wolfson DACs over at Mouser, and a couple of the models jump out immediately. They all seem to be designed for DVD players or digital set-top boxes, but if somehow we can plow through with the design, I think the head-fi community would be better for it. I'm no Alf, cetoole, Jambo, justin w., Ray Samuels, etc., but I can offer my limited knowledge and unbridled passion and enthusiasm to this kind of project. Please, someone with actual knowledge help me out here. I've had a class in digital logic design, but I'm not sure how much of it actually applies here.
Rants: - there - in or at that place; to or into that place; at that point or stage; in that matter, respect, or relation; used interjectionally to express satisfaction, approval, encouragement or sympathy, or defiance
- their - of or relating to them or themselves especially as possessors, agents, or objects of an action; his or her
- they're - they are
Heh, I was wondering if anyone here was thinking of doing this from the interest the "iMod" thread is getting... I've been thinking about it ever since I got water inside my iPod a few short months back. The most obvious problem is the 0.5mm pitch QFN the Wolfson DAC comes in.
Beyond that, while searching around, I came across this (scroll down to 12-23-07) where someone took apart an iPod video and found that it had a non-standard I2S interface. That does sound like something Apple would do... It's possible that not all iPods are like that though, especially since MSB seems to be able to do it.
Myself, I was thinking of tapping the 4 I2S signals out to the dock connector, and using an external portable DAC+AMP. I have two ideas for tapping into the I2S lines, but I don't know how much of a problem signal integrity would be. Perhaps a ASRC(?) would be needed somewhere along the line.
The DVD player type DACs (generally) have the plus points of better performance and hardware control, but the down sides are their power consumption. They're all around the 70-80mW though from the datasheets I have looked at, which I guess is tolerable. I noticed you haven't mentioned the WM8740/1, they're Wolfson's best DACs which are worth looking at if you want best performance possible, and the power consumption for the WM8740 is ~80mW at 3.3V. Also, the WM8740 has differential output, so you don't need any caps on the output.
I'm willing help out where I can, although I'm afraid my ipod is staying in one piece! And I also have my own project doing my head in at the moment as you can see in the Jambo DAC thread lol.
Now, I'm not a design expert of any kind just yet, but perhaps we can design our own portable, full on DAC/amp solution using some of Wolfson's better DACs. I realize there are already solutions available along these lines, but none fitting the I2S input requirement. stevenkelby, you mentioned using the Headamp Pico for its I2S input, but that DAC/amp converts USB to I2s. Unless we open it up and route some wires, we can't do it without voiding the warranty. I'm not sure how we'd go about doing this, but is it a viable solution having a portable DAC/amp running off a 9V? That's quite a huge energy loss converting down to 3.3V, so maybe running off some AAs would be wiser. Before we even go there, we should probably pick out a DAC that'll work. I'm thinking something along the lines of a portable full-on DAC, like a portable TPA Opus DAC (okay, maybe not that far). I'm looking at some Wolfson DACs over at Mouser, and a couple of the models jump out immediately. They all seem to be designed for DVD players or digital set-top boxes, but if somehow we can plow through with the design, I think the head-fi community would be better for it. I'm no Alf, cetoole, Jambo, justin w., Ray Samuels, etc., but I can offer my limited knowledge and unbridled passion and enthusiasm to this kind of project. Please, someone with actual knowledge help me out here. I've had a class in digital logic design, but I'm not sure how much of it actually applies here.
I too would choose WM8740. It uses about 24mA at 3.3V, which isn't too bad if you're using AA cells (typically 2500mAh+), whatever amp topology you choose, it will likely use a lot more. Choose opamps carefully and you should get good battery life (I'd guess about 16h is possible).
It's probably possible to fit a WM8740 DAC and (SMD) opamp-based amp into the smallest Hammond with two AAs, if you're very careful with your layout. I don't think you'd manage cramming a charger in there too though. If you choose a larger case, it should be easy.
Be warned that I might get bored and do a layout for you .
Actually, error, I thought of listing you in that "group of people that I am not," but I already submitted the post.
How did I miss the WM8741? It's listed in Mouser under "Stereo DACs, High End." *rolls eyes*
Part of the rub becomes whether or not we should include the amp, much like what justin w. is doing with his Pico. The initial amp that comes to mind is the PPAS. In fact, they're so small we could probably fit two for ultimate in balanced configuration. I'll bookmark the WM8741 and read endlessly. I'll also try to grab one of the professors at school and see if they can guide me a little.
How does USB power sound? I want to regulate it, but it would have to be cut down a bit. I vaguely recall a similar problem in the Alien DAC. But fear not, even in the tiny Hammond 1445C801(BK) we can fit some sort of DC-DC converter.
Rants: - there - in or at that place; to or into that place; at that point or stage; in that matter, respect, or relation; used interjectionally to express satisfaction, approval, encouragement or sympathy, or defiance
- their - of or relating to them or themselves especially as possessors, agents, or objects of an action; his or her
- they're - they are
Part of the rub becomes whether or not we should include the amp, much like what justin w. is doing with his Pico. The initial amp that comes to mind is the PPAS. In fact, they're so small we could probably fit two for ultimate in balanced configuration. I'll bookmark the WM8741 and read endlessly. I'll also try to grab one of the professors at school and see if they can guide me a little.
I think you should be able to fit a decent amp in a small case without making any major compromises. It's your project, but I don't see a reason to exclude it. The other thing is that you need either a) output caps or b) 4 amp channels (balanced) - if you include the amp, you can do a balanced solution, otherwise you probably need to include the caps since not many portable amps are balanced.
How does USB power sound? I want to regulate it, but it would have to be cut down a bit. I vaguely recall a similar problem in the Alien DAC. But fear not, even in the tiny Hammond 1445C801(BK) we can fit some sort of DC-DC converter.
So you're planning on stealing power from the iPod, or are you talking about having it plugged to a computer all the time? I think you should include batteries for your DAC/amp myself, the iPod batteries are small and you'll drain the whole shebang quickly. A couple hours of use doesn't seem enough for anyone, and then you can't even use it unamped!
You'll definitely need a DC-DC of some kind or you'll have no overhead whatsoever to drive your cans - or you have to use small and inappropriate 9Vs. I'd say 2AAs is about optimal - battery life should be similar to an iPod and it's small enough. You'll need quite a few regulators for an 'audiophile' approach though, I count a minimum of 4 (step up, linear for amp, linear for avdd, linear for dvdd), 5 would be better for battery life (extra dc-dc to 5.5V or so for the low voltage lines). Check out how dsavitsk did his HPDAC supply, you could probably poach most of that design, just respec it for 3V input.
I'm really not sure why the AlienDAC chose the REG101 in SO8 package. The regulator itself is quite impressive; few match its specifications - but very few low noise regs are made in SO8 package so you cant' substitute anything! Plus it's a larger package than the alternative SOT23 that has lots of similar regulators with the same pinout. Neither has great availability right now though, so I wouldn't recommend them for a new project since TI can't seem to keep them on the shelves. There are tons of good switching chips out there, but I'd probably use the TPS61040 dsavitsk chose. I would probably use LP2985s for the Vdds. Not sure what would be good for the amp, would have to do some looking.
That Fairchild device is a switching step-down converter - not sure why you'd need one of those - you should probably be using linear regulators for all your final regulation, and you need a boost converter from the batteries. Everything you listed is also physically rather large. Look for regulators in SOT23 or SO8 - you don't need to handle a lot of power dissipation, and you need as much space as you can get. Since you've got the DAC to deal with, no point in trying to do a non-SMD board or anything .
After doing a bit of looking around, TPS61040 looks good for DC boosting, 3.3V regulation can be done by the in-stock-at-Digikey Diodes Inc. AP131, with the LM7805 covering the 5V bit. I'm thinking of powering the DAC with USB power, and if possible we can stuff the thing in the Hammond 1445C801. That way it would operate like the Alien DAC, where we could stack the iPod on the DAC. Further, unlike the HPDAC, we could choose our own amplifiers. Even with this theoretical design, we could make a portable and full-on version. But before we go on, I need to do some more learning.
=T
__________________
"Ears that hear and eyes that see - the LORD has made them both." Proverbs 20:12
Team University-fi | Team Edmonton-and-Surrounding-Urbanities(1)(2)
Rants: - there - in or at that place; to or into that place; at that point or stage; in that matter, respect, or relation; used interjectionally to express satisfaction, approval, encouragement or sympathy, or defiance
- their - of or relating to them or themselves especially as possessors, agents, or objects of an action; his or her
- they're - they are
We can probably explain the reg101 thing as an heritage of the "Guzzler USB DAC" on which the alien dac is originally based. I'm pretty much responsible for it
When we (Guzzler and I) designed a battery powered USB dac in February 2004 (!), the reg101 was readily available from digikey. When I started the layout, I was a real newbie when it came to smd parts. The reg101 was available, easy to solder and probably the "best" integrated LDO regulator out there. Why not pick it ?
When Guzzler later designed a small usb-to-spdif converter, the reg101 was considered too expensive and was also getting harder to source. He then switched to the TI TPS793* ldo regulators. Those are still available by the thousands at digikey. You need to get the adjustable version to go up to 5V though.
The so8 reg101 was still the regulator we picked for our tentative "all-out" transportable USB dac with Ble0t.
I've had a class in digital logic design, but I'm not sure how much of it actually applies here.
I've been thinking about it ever since I got water inside my iPod a few short months back. The most obvious problem is the 0.5mm pitch QFN the Wolfson DAC comes in.
