[threepointone]

the problem with that diy mp3 player (and pretty much every other DIY DAP on the internet right now) is that it all relies on a dedicated MP3 decoding chip for all the audio decoding. This means none of them, as far as I know, can support FLAC/AAC/OGG/WMA/whatnot, and even if they could, you'd have to pretty much start over from scratch to make them accept any new formats. One of the goals of this project is to make a DAP that's actually as capable or more capable than teh stuff on the market.

oh and a reminder: first version isn't portable at all--it's a desktop DAP. I'll start working to make it portable (which will require some compromises with the audio quality) after the desktop version is done. But it also depends on your version of portable--if you'll do anything for your audio (like that guy in the headphones forum who stuck a subwoofer (?) into his backpack for extra bass), i'm sure you could stick a huge battery pack and stick the DAP into your backpack. . .

Price? no idea really--it's way, way, way, way too early to think about that. I'm pretty sure it'll be <$500, probably a lot less, but like all the other DIY stuff, it'd really depend on how you customize everything. Since many of the parts for this project aren't really available in smaller quantities without sampling (which can't be counted on) I'd imagine I (or someone else) would have to break up the chips into kits, or sell the individually. This would also drive down costs somewhat.

 

[OverlordXenu]

Well, desktop isn't too bad. At least then you can use it at work or something.

Still, sounds GREAT.

 

[flecom]

im actually working on my own "audiophile" DAP... its going to be in a smallish hammond case with a built in battery and a decent dac/headphone amp so that its at least fairly portable... i will post pics when i get closer to being done

im thinking if i can actually get it working reliably im going to look into the costs of making them and maybe offer them to head-fi members... but thats probably 6 months off before i can really think about that

its going to have a 2~3" color screen, MP3, MP4, FLAC, etc...

 

[threepointone]

cool, more people! someday head-fi's going to beat apple. . .OPEN SOURCE HARDWARE!!!! =)

 

[OverlordXenu]

Quote:

Originally Posted by threepointone /img/forum/go_quote.gif cool, more people! someday head-fi's going to beat apple

I doubt that would be hard. It's not like Apple is an innovator or something. (Except maybe a hardware manufacturer controlling their phone in the US. That is something never done before.)

 

[balou]

Quote:

the problem with that diy mp3 player (and pretty much every other DIY DAP on the internet right now) is that it all relies on a dedicated MP3 decoding chip for all the audio decoding.

and even worse, it has a DAC, headphone amp and digital potentiometer already integrated (all non-bypassable). And the headphone out requires an output capacitor...


I just read this on the Wolfson page:
Quote:

Fully dfferential voltage outputs

um.. did I get that right, the possibility for a balanced output?

I also read the description on the SCF5250... this chip is quite amazing, IDE and SPDIF onboard, added DSP instruction set... I wanted to ask how you plan to attach the HD, but my question has been answered. This will also allow direct attachment of a CF card for the later portable version... nice.

 

[threepointone]

yep, balanced outputs =) an example is already in the datasheet. I'd have to figure out how to get balanced outs in the dual differential configuration, though (dual differential supposedly would perform even better)

Yeah, the scf5250 is a great chip--only problem that's come up (other than 20-bit audio max) is that it might be getting a bit old, and there's a possibility that it might be obsoleted by the time everything gets finished (it's about 1 or two years old now?). The MCF5253 appears to be the best replacement (as far as I can tell, it does everything as good or even better than the scf5250--it even has builtin usb), but it only comes in a BGA package--I'm still thinking about whether or not I should switch over. With a BGA package, I'd have to do some sort of adapter board solution (schmartboard licensing?) or manually batch toaster-oven-reflow them and distribute them, since you obviously can't reach any of the pins with a soldering iron.

 

[flecom]

Quote:

Originally Posted by balou /img/forum/go_quote.gif and even worse, it has a DAC, headphone amp and digital potentiometer already integrated (all non-bypassable). And the headphone out requires an output capacitor... I just read this on the Wolfson page: um.. did I get that right, the possibility for a balanced output? I also read the description on the SCF5250... this chip is quite amazing, IDE and SPDIF onboard, added DSP instruction set... I wanted to ask how you plan to attach the HD, but my question has been answered. This will also allow direct attachment of a CF card for the later portable version... nice.

most DACs have balanced outputs, in the I/V stage they get turned into single-ended on most players...

 

[balou]

oh, another question: are you going to add the 32mb dram which are supported by the chip? in the standalone version, caching reduces noise and RF interference (would be definitely a plus) and power consumption (not so important). but in the battery-powered version, caching becomes absolutely crucial. A 1.8" HD consumes 100mA of power while idling - that's also one of the reasons why iPodlinux only has about half the run time compared to the standard ipod os, it seems like they haven't really implemented hd power down (at least not on the 5g ipod). Oh, and it gets a bit more drop proof (if drop occurs while hd is in power down, which it is most of the time)

 

[threepointone]

you have to be careful about balanced outputs in DACs these days--things are getting more and more integrated, and a lot of the new DACs don't need a I/V stage and can't do balanced. the pcm2702 in the alien dac can't, for example, and a lot of the stuff designed for portable players can't.

I'm going to try to avoid thinking about the power consumption issues for the portable player until later--it's probably the most difficult thing for making something portable. The maximum sdram for the chip is already being included in the non-portable design (256Mb or 32MB), and I see no reason why it shouldn't be included in the portable design. Again, though, I'm going to avoid thinking about the portable design for now--honestly I'm not even sure if i'll stick with the SCF5250 or a coldfire chip at all, as I haven't even begun to think about the power budget / battery size of the portable player. For all I know, if memory prices go down enough, it might be designed primarily for flash memory.

 

[Cauhtemoc]

Quote:

Originally Posted by threepointone yep, balanced outputs =) an example is already in the datasheet. I'd have to figure out how to get balanced outs in the dual differential configuration, though (dual differential supposedly would perform even better)

In dual differential mode each DAC outputs the same data on both channels. Just add the signals together with two resistors. There is an example of this in the WM8740 datasheet.

 

[Rescue Toaster]

Quote:

Originally Posted by balou /img/forum/go_quote.gif oh, another question: are you going to add the 32mb dram which are supported by the chip? in the standalone version, caching reduces noise and RF interference (would be definitely a plus) and power consumption (not so important). but in the battery-powered version, caching becomes absolutely crucial. A 1.8" HD consumes 100mA of power while idling - that's also one of the reasons why iPodlinux only has about half the run time compared to the standard ipod os, it seems like they haven't really implemented hd power down (at least not on the 5g ipod). Oh, and it gets a bit more drop proof (if drop occurs while hd is in power down, which it is most of the time)

The trick with the portable hard drives is the most important factor is the speed at which you can read data from the drive relative to the speed data is consumed by the DAC, no matter how big the cache is. When playing .WAV or FLAC, you need a good disc driver so you can fill your cache quickly and get the drive shut back down. A basic no-DMA no-irq polled interface will have horrible performance, and if you're only pulling data off the disc at say twice the speed you're using it, no matter how big your cache is, the drive will be on 50% of the time. Cache size only determines how often it cycles on & off.

EDIT: Don't forget that non-DMA'd hard drive access can eat up a lot of CPU time that you might want for FLAC decoding or DSP processing.

 

[balou]

Quote:

the most important factor is the speed at which you can read data from the drive relative to the speed data is consumed by the DAC, no matter how big the cache is.

Fortunately, the SCF5250 microprocessor has a DMA controller chip already integrated, so reading the data at sufficient speeds shouldn't pose a serious problem. Of course, if you had to write your own IDE accessing routines using only generic IO ports, this would be quite a problem.

 

[OverlordXenu]

Any news, per chance?

 

[antonyfirst]

Ok guys, a balanced lineout DAP is my portable dream. If someone makes one, I'll buy it in a blink!