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Old 29th December 2003, 09:01 PM   #1
harba68 is offline harba68  Norway
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Question portable hd-source?

first: i'm quite a newbie to diy-audio, but i'm very interested in higher-end portable (...and transportable in bags!) headphone listening.

lately the possibilities of portable listening have expanded greatly, now with the ppa amp, and now lately also with battery powered dacs. but the lack of a battery powered, quite high-end battery powered source is very irritating (imo). some pcdps have opt. outs, but the jitter that is introduced makes them very hard to use as nice transports. the headphones are there aswell.

so my question is. how hard would it be to make a battery powered source (f.i. using this battery board: http://www.tangentsoft.net/audio/ppa/bb/) consisting of:
- hard drive
- some sort of buffer
- some kind of controller that could play wav, and some lossless compression formats (like flac)
- presicion clock to reduce (eliminate?) jitter (like the lc audio xo3 clock, or some other diy-clock). how power hungry are these clocks, btw? are there possible to drive of batteries?
- the battery life wouldn't have to be very long, something around 10-12 hours would be sufficient.
- the user interface *don't* have to be fancy, just a usb2 of firewire interface, and the hd pops up as a usual hard drive in the pc, so you can drag&drop files to the player.

would something like this be possible to do?! imagine a portable device consisting of this source, the aos' dac and a ppa... portable musical bliss...

some links:
www.head-fi.org
www.headwize.com
elvencraft.com/ppa/
tangentsoft.net/audio/ppa
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Old 29th December 2003, 10:35 PM   #2
MCLL is offline MCLL  Hong Kong
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Old 30th December 2003, 02:42 AM   #3
Benjlv is offline Benjlv  United States
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this seems perfectly doable. What you will need to do is find a decoder chip out there to decode the formats you wish to decode. Then from there it should be relatively simple if you know your stuff. You will have a hard disk and a microcontroller, USB, USB 2.0 or 1394 interface (1394 and USB 2.0 will be much more difficult than just regular USB, The regular USB interface has many controller chips out there, but look around anyways) Anyways you'll have the hard disk, microcontroller, display, controls, the decoder, a DAC, and a head phone drive circuit. Also probably some sort of charging circuit. Ideally you would implement some sort of lithium ion charger to gain the battery life you seak, also in the interest of size and battery life you will want to use a notebook hard disk.

make sense?

well anyways here is some food for thought. Is a portable MP3 player. Much of it will apply to what you are doing, but i imagine bandwidth issues will become a problem with wav files being streamed instead of mp3's
http://www.myplace.nu/mp3/index2.htm

there are many other decoder chips other than the VS1001 used in this project. This particular one has a built in DAC which obviously wont be what youre looking for.
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Old 30th December 2003, 03:03 AM   #4
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The hardest part of this would be the programming. The electronics are fairly simple, but you'd probably need to program in some form of assembly.
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Old 30th December 2003, 03:43 AM   #5
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Why not just get an iPod?

Click the image to open in full size.

Rompurs are we'll see new lower priced units next week @ MacWorld Expo.

dave
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Old 30th December 2003, 04:01 AM   #6
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additional rumor is that apple is entering the flash player market as well.

i'd say if you're going to go the non-diy route, look into alternatives to the iPod. not to bash it, but i haven't been able to find any S/N specs on it, whereas (some) other HD players publish theirs. (most notably, Creative's Nomad Jukebox 3 specs 98dB SNR from their lineout, with THD at 0.1%)

i currently own an unopened iPod, a xmas present, which i'm trying to decide whether to exchange for the JB3.

a few months ago i saw someone posting some progress on designing just the project you're asking about, over on the DIY forums at headwize.com. i can't seem to find them now, but if you search around you might have luck.
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Old 30th December 2003, 04:48 AM   #7
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Quote:
Originally posted by faustian bargin
but i haven't been able to find any S/N specs on it, whereas (some) other HD players publish theirs.
And how realistic are the numbers? Sterophile, i believe did a full test on it.

Will the other player lay uncompressed AIFFs -- i can't listen to MP3s.

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Old 30th December 2003, 02:58 PM   #8
Benjlv is offline Benjlv  United States
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while the ipod and creative zen are very nice products I dont think they are quite what he is looking for. They are meant to play mp3s at a respectable sound quality. They arent what i would call a high definition source.

http://www.modeemi.fi/~vesas/iPod_Audio.pdf
thats a punch of tests on the ipods audio output.

http://www.audiosense.org/results/po...iPod%20Mp3.htm
more tests

Creative claims the following for the Zen
Signal to Noise Ratio: up to 98dB
Channel Separation: up to 75dB
Frequency Response: 20Hz - 20kHz
Harmonic Distortion Output: <0.1%

in a test they found the following
RMAA Tests

Tested chain: Creative Zen hp out - ESI Waveterminal line-in
Operating mode: 16-bit, 44 kHz


Test Test Signal Creative Zen WAV Creative Zen MP3
Frequency response (40 Hz - 15 kHz), dB +0.00, -0.00 +0.05, -0.23 +0.18, -0.63
Noise level, dB (A) -97.8 -92.1 -92.1
Dynamic range, dB (A) 95.5 89.6 89.4
THD, % 0.0003 0.0047 0.0048
Intermodulation distortions, % 0.0057 0.014 0.015
Crosstalk, dB -92.0 -87.3 -85.2

that table can be better seen towards the bottom of this page.
http://www.digit-life.com/articles2/creative-zen/

Perhaps moding a zen or ipod would be a better idea? That way you dont have to design a new interface and write all that assemble code and so on...

this is off a another forum
"The rest of the device [iPod] uses a dedicated MP3 decoder and controller chip from PortalPlayer, a Wolfson Microelectronics Ltd. stereo digital-to-analog converter, a flash memory chip from Sharp Electronics Corp., a Texas Instruments 1394 firewire interface controller, and a power management and battery charging IC from Linear Technologies Inc."

perhaps there are some I2C lines in there that can be tapped...hmmmm
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Old 30th December 2003, 03:12 PM   #9
Benjlv is offline Benjlv  United States
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the ipod uses a Wolfson Microelectronics WM8731

http://www.wolfsonmicro.com/products...codecs/WM8731/
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Old 30th December 2003, 04:59 PM   #10
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Quote:
Originally posted by Benjlv
while the ipod and creative zen are very nice products I dont think they
are quite what he is looking for.
The iPod can play full resolution CD tracks as AIFFs. If used as such it can outperform many a CD player (some costing much more than the iPod) -- a large part of the performance is that it is streamed off HD.

As such Stereophile gave it runner up in Digital product of the year, the Editors Choice award, and the Budget Product (?).
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