audiophile diy DAP?

[kramer5150]

interesting discussion...

I was thinking of something in a non-portable chassis, ~500M capacity (or whatever size drive gives the most G per$), and optical / coax digital output. Could be either wall-wart powered, or have a dedicated P/S. Forget portability, that will drive cost up and audio fidelity down (we already have portable players for that). If it plays lossless files, and has an optical/digital output it could rival a good mid-fi CD deck.

[threepointone]

Originally Posted by Cauhtemoc

The I2S protocol is not as complicated as you think. All you need to make an interface is three shift registers, a counter and an AND gate. Let me know if you need a schematic.

I would use a CPLD however, they are not as bad as you think. You can find a couple of ready made I2S interfaces over at OpenCores, or you can make your own.

I was just wondering, how are CPLDs be programmed? Can it be easily programmed by a microcontroller? I'd rather not need any external programmers for the system

Originally Posted by kramer5150

I was thinking of something in a non-portable chassis, ~500M capacity (or whatever size drive gives the most G per$), and optical / coax digital output. Could be either wall-wart powered, or have a dedicated P/S. Forget portability, that will drive cost up and audio fidelity down (we already have portable players for that). If it plays lossless files, and has an optical/digital output it could rival a good mid-fi CD deck.

So far that's exactly what i'm doing--it'll have spdif output, use a 2.5" hd (up to maybe 200GB or so by now?), wall-wart powered, and play lossless =)

btw, I split the audio design section here: Ever shipped to Canada before?

[Cauhtemoc]

Originally Posted by threepointone

I was just wondering, how are CPLDs be programmed? Can it be easily programmed by a microcontroller? I'd rather not need any external programmers for the system

Depending on which CPLD you use, a programmer can be as simple as a parallel port, a buffer and a couple of resistor. They're not too dissimilar from the EEPROM programmer I posted earlier.

[threepointone]

I've been thinking about the case dimensions, and I made a couple of mockups of some of the hammond 1455 cases (the nice aluminum ones). To me it seems that the 1455Q1601 is probably the best candidate. It's 160mm x 120mm x 30.5mm (~6.3" x 4.75" x 2"), which might seem a bit big but when I made a model it's definitely a reasonable size, especially when compared to other desktop audio equipment.

The 2" height gives pretty good clearance for most LCDs and allows enough height for any low-density audiophile power supply caps / heatsink for the linear regulator. It'll also help with the modular design of the DAP, which will probably involve some elevated boards. 2" does actually look a bit high, but it's not as easy to find LCDs for the next shorter hammond case, at about 30mm (really about 27mm actual available height; most LCDs seem to have outlines of <30mm)

The large amount of board space allows a 2.5" HD to fit pretty snugly on one end and provides enough room to isolate it from any of the audio circuitry. it also gives more room for any modules and the potentially complex audio section in the DAP

If anyone wants me to, I can post pics of the mockups of the cases / LCDs / HD I made to get an idea of what size the DAP will be

[labmat]

Originally Posted by threepointone

If anyone wants me to, I can post pics of the mockups of the cases / LCDs / HD I made to get an idea of what size the DAP will be

I'd love to see what you've come up with.

[Danielj]

Hi 3.1 Sounds like you are making good progress...would very much like to se mock up pics posted

keep up the good work
Dan

[OverlordXenu]

I haven't read through this thread, so I don't know if this has been said, but here is my suggestion. As said by the OP, RockBox and a 2.5" laptop harddrive. Since this will be audio, an extremely small monochrome/two-tone/whatever display/LCD, something that will just display song info and directors and the like, low power. Instead of making the device bigger to include a DAC and battery, forget that. Just include an optical out (possibly a built-in high quality cable?), and some terminal so one can use external batteries.

That would make the device as small as possible, and if someone is a true audiophile, they won't mind having something like a MicroDAC, external amp, and external battery pack.

[Danielj]

Hi the OP here...
So far it seems that first build will be wav only with a 2.5 HD.
Wallwart type PS so yes an external battery pack would be possible and recommended. The design implies the use of line out, so an external headphone amp or other amp source would be needed. Also implied is an optical out for those who want to use an external DAC; however the design needs to have its own high quality DAC so as to not force the extra expense of an ext. DAC We decided that the internal DAC needs to be of the highest quality possible...this has been a high priority for the design concept. Size of unit has been determined to be less of a priority than quality. transportable but not necessarily portable.

Of course the particulars on the tech side are still being figured out by 3.1 and the other electro wizards involved in the project. As for myself I am just an end user hoping these guys can come up with something that qualifies as a superDAP

[Danielj]

Hi guys....there are some threads in the portable audio forum where folks are discussing the desire for audiophile daps. I pointed them to this thread as i know people are working on this.There hasnt been any recent postings, so how is the research and development going on this project?
thanks Dan

[threepointone]

been a bit busy and it's been slow--came back from vacation a short while ago. a couple of friends of mine said they'd start working on it with me after they come back from vacation in a couple of weeks, so it might speed up. Unfortunately, it's going to be quite a while before something solid comes out. atm I'm waiting for a digikey order to come in and then I can start working on the digital section,.

So far, here's the plan:


basics:
- modular design (probably storage module, microcontroller module, USB module, user interface module, and DAC/SPDIF module). This will ease development, debugging, soldering, and allow for customizability. For now I'm using SIP sockets, but later I'll look for something that takes up less space and might be a bit nicer in terms of the parasitics
- onboard diagnostic debug lights (after looking at how many connections there are on the board, this would be pretty darn necessary for debugging)
- (might be removed if I end up needing more board space for everything else) optional built-in BDM programmer for myself and developers for easier debugging
- (might, but probably won't, change) hammond 1455Q1601 case (about 6"x5"x2"--a bit thick, but personally I think the LCD would have to be too small otherwise)
- scf5250 microcontroller, as discussed before
- basic eeprom-based bootloader (more fail-safe than a hard drive based bootloader, at least during initial development)

Basic modules:
- storage: 2.5" HD
- USB: ISP1561 / cypress peripheral controllers for the USB (depends on whether or not I can get samples)
- DAC: WM8740 (digits might be mixed up) for the DAC. I might even use something simpler--the DAC board is modular, anyway, so it doesn't really matter what I stick in here for the first revision.
- SPDIF: directly from the scf5250, with a simple reclock circuit
- user interface module: bunch of tactile play/pause/stop switches, and a simple graphic LCD. I would have gone for an OLED, but it appears that some serious problems are cropping up with supply--optrex, one of the most accessible suppliers of OLED screens, just completely pulled out of the display market. digi-key is only stuck with a couple if tiny OLED modules left in inventory and most other OLED module manufacturers have discontinued their lines. Sparkfun does have a color OLED available from a different OLED screen, but it's a bit more complicated than necessary (color screen) and a bit smaller than I was hoping for. If anyone knows somewhere I could get a monochrome (or grayscale) OLED with a module size of around 60mmx45mm-ish, tell me!


Things on hold for future revisions of the board (i.e. "feature creep" section):
- ultra-low jitter clocking - I've figured out some way to get less jitter than probably anything available commercially. It's pretty complex, though, and I'm almost certain that I can't avoid four-layer boards if I really wanted to implement it. The clock distribution / clocking IC also sucks up quite a bit of power, though, and would probably require another microcontroller to control all of the clocks.
- CPLD for 24-bit audio; the SCF5250 only supports 20-bit. I'm not sure if it'll be really that important, though, as some people seem to think going over 16/44.1, the original format of the audio, isn't a good idea anyway.
- flash-memory based bootloader
- differentially driven expansion port using RJ45/CAT-5 wiring: connect other modules (maybe video out, DSPs, ethernet, DACs slaved to the clock line, etc. . .)
- compactflash/securedigital storage module: the SCF5250 already has controllers for these formats, and some people might not mind sacrificing storage space for less EMI/RFI that might come from the hard drive
- capacitive touch sensor for front panel interface
- nicer screen
- built-in headphone amplifier for the front panel
- movie playback
- enough feature creep already!

As you can see, I'm trying hard to make it as simple as possible =) hopefully this will make it a bit easier for me to actually come out with something in a reasonable amount of time, and make debugging a lot easier.


hm... whoa--sorry for the uber-long post!

[OverlordXenu]

Sounds amazing. Is that the same DAC that the iPod uses? Or is it better? I wonder what the best portable DAC is, and if you could get your hands on it...

Are you going to be making these, offering them in kits, or what, exactly?

[werdwerdus]

any ballpark price range? Also, I'm guessing that it's going to be a line level output only, and not a volume adjustable?

[Cauhtemoc]

Originally Posted by OverlordXenu

Sounds amazing. Is that the same DAC that the iPod uses? Or is it better? I wonder what the best portable DAC is, and if you could get your hands on it...

The iPod uses a WM8975. The WM8740 is much, much, much better.

[Danielj]

thanks 3.1 for the update...keep up the good work
Dan

[xnothingpoetic]

maybe someone can improve this design?

http://www.hackaday.com/2005/11/14/simple-mp3-player/