I'm just glad someone's still paying attention here.
Are you kidding? I'm taking notes for my next install. Not that I'll be able to replicate even half of what you've achieved here, but still I'm stealing ideas.
OK, below is the mini-build log for my custom DAC project. Here's the link to the post where I described all the important design details: 2011 MINI Cooper CarPC Build
Please read that post before asking any "why did you do it this way?" sort of questions, the answer is probably already there
Here's a really quick summary for the lazy:
This is a custom-designed 10-channel DAC to interface my Mac Mini CarPC, to date I've not seen anything remotely like it. I designed the circuit (with a bit of borrowing from existing designs out there), sourced the component parts, did the printed circuit board layout, and then built the board assemblies.
This is a no-compromise SQ design. I wasn't content with just using off-the-shelf equipment from a Sweetwater Music catalog. I'm looking for very high SNR numbers to my amplifiers, to get a great dynamic range (my amps will likely be modded too). I will be attempting to compete with this system in March at the IASCA spring break nationals (and the MECA event there as well). Hopefully I can get my acoustic issues fixed by then.
I'm using the MiniDSP USBStreamer (image below) as my USB-to-I2S bridge (I2S being the most common electrical protocol that audio DAC chips use). This component is responsible for virtually all of the jitter (or lack of it), since it's providing all of the clocking signals to the DAC.
Rather than use an expensive and complicated 8+ channel DAC chip, I decided to use individual low-cost stereo DAC chips and go with a "stacking" design. The clock signals are "fanned out" to the individual boards (with care taken to route the traces properly and prevent signal reflection. This design allowed me to do a lot of pcb layout tricks where I could keep all of the clock and analog signals guarded with a ground trace (which prevents signal crosstalk), and keep an uninterrupted ground plane (which prevents a lot of nasty EMI and other bad stuff from happening).
Total cost of the DAC project so far is $89 in component parts, $2.50 each for the custom circuit boards, and $145 for the MiniDSP USBStreamer. That's less than a lot of the shitty pro-audio equipment, and I'll hopefully have better specs....
Here's a picture of the MiniDSP USBStreamer, 10-channel USB-to-I2S converter. The yellowish stuff on the USB connector is a piece of insulating Kapton tape.
Here's the original block diagram that I proposed back on October 31:
Here's the schematic of the DAC PCB. I decided on the ESS9023P DAC chip because of the low-parts count, i.e. the KISS approach. Keep in mind that there will be five of these boards stacked on top of each other (for a total of 10 channels) to complete the final design.
J1 is the connector to the MiniDSP USBStreamer. Each board can be configured to route either of the four I2S streams to the chip, via R5-R8.
IC1 is the DAC chip, the ESS ES9023P. It's specs are pretty good, but chip specs aren't as important as getting the board layout and component part selection right.
IC2 is a 3.6V low-dropout ultra-low-noise voltage regulator. I love Linear Technology parts, but they think their shit doesn't stink and therefore have very high prices; I opted to use the Micrel MIC5205-3.6YM5 instead (as have a few other hobby DAC designs).
SHIELD1 is an EMI shield (i.e. a faraday cage).
FB1 is a ferrite bead, which is used as an input EMI filter to the power supply.
You guys know what resistors and capacitors do hopefully, no need to explain those
Beginning of the build phase:
Powering up for the first time. Checked the voltage regulator output voltage, and a few other test points.
A close-up shot of the first board while powered up and playing a 1 kHz sine wave. Disregard the flux and wire leads sticking out, those will be gone after the testing phase.
Here's the 1 kHz sine wave coming out of the DAC, and the 5V lab supply:
Next step was to install the EMI fence. As mentioned earlier, this is a faraday cage to keep out the nasty electromagnetic radiation that plagues my BMW-designed car
Now with the EMI fence's "lid" installed.
The bottom of the PCB is a solid ground plane. I've never really seen a DAC that managed to have this before. RF guys use this technique religously, but consumer electronics do not (ever). A solid ground plane does many things for a pcb layout: It acts as a faraday cage for stray EMI (in both directions, i.e. radiated and susceptibility). It provides a quick "return path" for high-speed RF signals (keep in mind that my I2S clock lines are ~24 MHz with VERY high rise times. Any upset here will cause EMI and worse yet, jitter problems. Lastly, the solid ground plane provides a very beefy ground system with extremely low resistance, so that every point on the pcb seems the same ground potential (same reason you guys use beefy ground wires on your amps ). The holes on the board are "vias", they're plated copper and pass the ground plane to the front side of the board (but you guys already knew that, right?? )
One more shot of the first guinea pig board.
I'm still waiting on one connector to get here, and will need to order some standoffs to attach the boards together. I'll post back later with more pictures and hopefully a listening test.
2011 MINI Cooper S :: [build log] :: [new CarPC project]
HAT L6SE, L3SE, L1 Pro R2. 4x Alpine SWR-843D, 2x JL XD700/5, 2x XD500/3, Alpine H800, RUXC800, Mac Mini CarPC
Are you kidding? I'm taking notes for my next install. Not that I'll be able to replicate even half of what you've achieved here, but still I'm stealing ideas.
Show this thread to guys at a shop (not mine) and ask what they would charge for something like that, and no matter what they say, ask "Why so much?" LOL
OK. More to say, it is really cool!
I wished I have similar skills, it would save me $$$ for my upcoming home audio DRC project.
Couple of questions though:
1) You opted for USB transport for all the digital audio supply. Are you going to use USB isolator to stay away from PC noise?
2) Are you sure USB 2.0 bandwith is enough to supply 10 channels with 24 bit 96 kHz streams as you planned?
And I am really interested to know how your PC would detect these 5 DACs in the same order every time you power up your system. Is it something that USB streamer is responsible for? What about ASIO support ???
I spent the last four days with the full-blown flu, so pardon my lack of major progress. I really wanted to work on this project instead of rest, but my extremely high fever was making it impossible to get out of bed, let alone concentrate. Here's what little bit I did get done today:
Component assembly of the remaining four boards:
Each module is conveniently labeled 1 through 5:
Here's the complete assembly, from the back. Notice the TOSLINK in and out connectors on the MiniDSP USBStreamer, and the connectors that pass the signals back and forth between the modules.
And finally, a shot from the front. Next step is to design and fabricate a nice metal enclosure for the whole thing to sit in.
Channel 1 thru 8 have been tested and are working. Channels 9 and 10 still require a TOSLINK-to-I2S bridge to squeeze the maximum 10 channels out of the MiniDSP USBStreamer. For this, I'm planning on hacking up the $25 FiiO D3, as described by the Hifiduino blog.
2011 MINI Cooper S :: [build log] :: [new CarPC project]
HAT L6SE, L3SE, L1 Pro R2. 4x Alpine SWR-843D, 2x JL XD700/5, 2x XD500/3, Alpine H800, RUXC800, Mac Mini CarPC
Neil,
Sorry about the flu. Glad you seem to be recovering.
I am so impressed by your implementation and thank you for sharing it. It is so inspiring to see such well-crafted components created by an individual (with your micro-factories ).
Wish I could hear and see it in person, but I moved from Orlando long ago and now live near Boston. Please continue to describe it well. Good luck and thanks.
Sorry I wasn't able to review your design. Obviously, it's going just fine.
There were a few really stupid mistakes that noone caught I noticed them only a few minutes before submitting the pcb order to Shenzhen. Also, I'm surprised noone caught the "2Vpp RMS" caption on the block diagram which makes no sense (if you did catch that one, give yourself a pat on the back)
I still can't wait to give it a listening test later on, but I'm going to have to get the enclosure finished and some software written on the PC side.
On a separate note, I have been playing with active matrix surround sound extraction with great success. I can basically do what the MS-8 does with Logic7 (although in a much more rudimentary way), which is split stereo music into front, center, left, rear left, rear right, and sub. More on that in a later post.
2011 MINI Cooper S :: [build log] :: [new CarPC project]
HAT L6SE, L3SE, L1 Pro R2. 4x Alpine SWR-843D, 2x JL XD700/5, 2x XD500/3, Alpine H800, RUXC800, Mac Mini CarPC
On a separate note, I have been playing with active matrix surround sound extraction with great success. I can basically do what the MS-8 does with Logic7 (although in a much more rudimentary way), which is split stereo music into front, center, left, rear left, rear right, and sub. More on that in a later post.
Subscribed.
And it's not even a thread yet.
Quote:
Originally Posted by subwoofery
What I wanted to say is that amps ... sound the same.
Yea, that will be a separate thread There's just so much to it (just ask Andy W. or read some of his posts on the subject in the MS-8 thread). I've coded up several different algorithms so far: passive matrix (i.e. L-R and L+R), Dolby Pro Logic 1, and a few different approaches of Dolby Pro Logic II. Next will be to tackle Logic 7. But here's the thing... Logic7 is much more complicated, especially when the left and right channels are slightly less than correlated. This complication is by design, as Harmann/Lexicon believed that this would gain them a slight edge over Dolby Pro Logic. No idea how long it will take to wrap my head around it.
2011 MINI Cooper S :: [build log] :: [new CarPC project]
HAT L6SE, L3SE, L1 Pro R2. 4x Alpine SWR-843D, 2x JL XD700/5, 2x XD500/3, Alpine H800, RUXC800, Mac Mini CarPC
I spent the last four days with the full-blown flu, so pardon my lack of major progress. I really wanted to work on this project instead of rest, but my extremely high fever was making it impossible to get out of bed, let alone concentrate.
2011 MINI Cooper S :: [build log] :: [new CarPC project]
HAT L6SE, L3SE, L1 Pro R2. 4x Alpine SWR-843D, 2x JL XD700/5, 2x XD500/3, Alpine H800, RUXC800, Mac Mini CarPC
Two more custom circuit boards have been designed and ordered (these are my last two, I swear )
The first is an ultra-low-noise power supply board for the FrankenDAC. The second is the Arduino Brainstem that I described in a previous post (it ties together the knobs, buttons, switches, and other bits of the CarPC that need to be integrated in a clean way. I had prototyped this circuit out on a breadboard earlier and am now going through the steps to make a finalized rugged version. It has some new features that I added, I'll explain them when I get the boards back from China.
After this step, I'll finally be able to install everything in the car. I for one can't wait for all of these custom pieces to come together
2011 MINI Cooper S :: [build log] :: [new CarPC project]
HAT L6SE, L3SE, L1 Pro R2. 4x Alpine SWR-843D, 2x JL XD700/5, 2x XD500/3, Alpine H800, RUXC800, Mac Mini CarPC
Re: 2011 MINI Cooper CarPC Build
Press here
). The holes on the board are "vias", they're plated copper and pass the ground plane to the front side of the board (but you guys already knew that, right?? 
Linear Mode
