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|3rd March 2009, 11:06 PM||#11|
Join Date: Dec 2007
Boards arrived yesterday!
They look sooo goood the factory seems to have done an excellent job. Invoice was 540€ final just for the boards and solder stencil, but it looks incredibly neat work. Each were individually optically and electrically tested, something I won't have to deal with too. Hehe.
Ok ok will post you a handful of photos taken with my phone tomorrow - got no digital camera.
Components are currently shipping - ES9018s included, yay.
Caps and so on still are waiting on Mouser's stock to ship to France.
So in 1 week will start the great mess: check if everything's ok, and how to improve the performance up to the desired level.
I let you imagine the number of options that can be tried, from voltage regulator, type of caps, I/V filtering, topology, etc etc... If I get mad, don't worry.
I already see some small mistakes I made... but these are very small ones that really don't matter at this prototyping stage. Well I can tell you: clearance between some of the pins of the ESS chip is a bit small and they will be a pain to solder (but I have 0.1mm precise stencil to counter that).
And, stupid me, I put the sot23 diodes in the bad position on my relay commands. Stupid, no? Well, I'll use good old through hole parts soldered on the connector, that's not that bad.
You'll soon know what works, how it works, how much it would cost, and how much you can buy them from me!
|4th March 2009, 01:25 AM||#12|
Join Date: Jan 2007
Are you going to use the (dfm audio made) diceII prom module as your dice center board solution?
I am very interested in that diceII prom module. With a group buy we could easily lower its price.
Also I would be even more interested in your module boards if we were using both the same hardware.
|4th March 2009, 10:51 AM||#13|
Join Date: Dec 2007
Well I'm not going to use the DFM for several reasons:
- It can only output 12 channels of i2s at full speed
- Dice II is going to be discontinued (I hope they will output an incredible replacement!)
- It's not exactly what I want, nor is it cheap.
Hell, my final boards would cost me around 100-150$ to do exactly what I want!
But as there is a design stage involved, I need to buy that $2000 EVM to save hassle. I'll try to ask for some help from the TC guys, if they could lend me one or something like that.
I don't want to go through an ocean of unknowns as I don't know enough about high frequency electronics. I studied them but I was just too bad at it... To be honest, the only parts that I fear are: the connection to memory (impedance matched?), the impedance matching for the FireWire part, the clock distribution, the bootloader.
Apart from that, it's just laying i2s tracks with LVDS drivers in the end - a board that I could lay in a few days, wouldn't be these "impedance controlled tracks". Stuff like microstrip etc...
I'll try to contact one of my old professors and see if any of them wants to give me hf pcb layout lessons.
|4th March 2009, 01:07 PM||#14|
Join Date: Dec 2007
Price for the stuffed board should be 250$
You'll need a few extras to use it:
- A µC. I'm going to work with Seeduino and will release the code. At $20 this µC board, you can't go wrong - and you can easily control everything that would go around your dac!
-Power supplies regulators, at least two (3.3V and 1,2V), more (up to 7) as quality is required. I'll have regulators boards to spare, between 10 to 15$ each board. I'll let you pick your mains to DC adapter - you could use TP ones with excellent results.
- Input circuitry. Make this on veroboard for spdif, you may also use the SPDIF to i2s modules from Twisted Pear too if you don't want to design or solder anything.
- Optionnal output circuitry. With just resistors, the Sabre will work in Voltage Out mode. With I/V, it will work in current output mode with far better performance.
TP's IVY is, again, a reference. I may have a few I/V channels based on the THS4131 to spare too. Too soon to give you any more info.
|6th March 2009, 04:48 PM||#16|
Join Date: Dec 2007
A few considerations, for what they may be useful...
Considering an I/V filter based around a THS4131.
With the gain setting resistor in the FB loop.
With a cap in parallel with this resistor, and no damping resistor with it (seems unnecessary).
Results from sim, not direct calc, results should be about the same.
A 10n cap will provide a filter with Fc(-3db)=96kHz.
@20kHz, amplitude is 0.24dB under nominal
@20kHz, phase shift is -14°
A 6.8n cap will provide a filter with Fc(-3db)=130kHz.
@20kHz, amplitude is 0.12dB under nominal
@20kHz, phase shift is -9°
Without this FB cap, what if we filter via post-filtering like on ESS's 9008 datasheet? (just too lazy to copy the filter schematic... A symetrical resitor-cap-resistor-cap filter).
With 1k resistors and 470p as in the datasheet,
Fc= 106kHz, dA=0,18dB, dp=-14°
With 22 ohms resistors and 18nF,
Fc= 117kHz, dA=0,127dB, dp=-8°
These are values I chose and computed today to choose between filtering schemes. I may associate them too. Things to try! I give them here if it can save hassle to anybody.
Also note that I provided space for a pi input filter. On spice, they create a really MAD peak near 1.5Mhz. Max L that can be fitted in this space is a 120nH. To start getting LP filtering effect you have to use caps in the µF range (without adding resistor to the DAC's output though). And you still have an insane peak just before the slope (don't know the english word for that). Definately useless. I though small 2nF caps could help remove very HF from the chip, thus avoiding any demodulation effect, but it seems to prove worse.
|7th March 2009, 05:15 AM||#17|
Join Date: Oct 2003
I think most, if not all, of your potential customers would want to know what they are getting on the stuff board for $250, in addition to what are NOT, as you have already listed. For example, a Bill of Material and Schematics would be great.
|7th March 2009, 12:52 PM||#18|
Join Date: Dec 2007
Yeah you're right.
Regarding the schematics, I'll post one later on imageshack. I wanted to post the exact BOM but realised it wouldn't look nice nor be fully usefull. Of course I'll post details, but do you really need the reference of each resistor? I'll post details. If you want the BOM I'll post it.
So what is it exactly?
An ESS 9018 or 9018 Sabre Reference universal boards.
ALL sabre's input are tied to a connector with a series and a resistor to ground so you can input ANYTHING the Sabre can accept and have the correct input impedance and current adequation.
ALL sabre's outputs are tied to a high quality connector (2.54 latching header gold-on-copper low impedance from 3m).
ALL sabre's commands are tied to connectors: i2c, connector to engage or disengage pull-ups on i2c lines, reset/addr inputs, mute/locked outputs.
ALL power supplies (AVCCR, AVCCL, AVDDR, AVDDL, VCC, VDD, Clock) tied to a 30 pins header with remote SENSE and Ground sense lines. Sense lines can be cut (remove 0402 shunt) near the load to avoid picking up interference if you don't use sensing.
Ultra low jitter clock: Crystek's lowest jitter noise part CCHD-950, 80Mhz, 25ppm (lowest drift version available). -162 dBc phase noise.
=> Grounding and bypass questions
- Full uninterrupted ground plane on all the board.
- Full star grounding with no shared via (with a very few exceptions for some non-critical shared vias where I couldn't stuff an additionnal one).
- 100nF NP0/C0G on EACH supply pin of the chip. Caps chosen to be NON MICROPHONIC.
- Solid Polymer Capacitor, 100µF, 15mohms ESR on each supply rail. NON MICROPHONIC too. Chosen to filter out HF.
- Big (very big) bead from Fair Rite on each supply rail. 600 ohms at 100Mhz. Insanely low DC resistance bead : 6,2mOhms.
- Star power distribution on dedicated layer and via quite large planes.
Note that the 100nF bypass caps are under the chip, so current flow in one direction on top layer, then on the opposite on bottom layer ==> ultra small loops that cancel RF emissions.
=> PCB things
- Gilded 4-layers, 35µ copper (double than standard), 0.15mm trace/space, 0.3mm vias. 2 silkscreens. That's why the bare PCB is expensive!
- Well partitionned layout: no digital things near analog lines and vice versa (of course).
- Perpendicular crossing of lines on seperate layers to avoid interference.
- Shields (screens) on each layer, that can be tied to local ground plane or remote earth.
- Separate small ground plane on top layer for clock with a single big via to ground plane layer to avoid clock interference leaking into nearby components. Ultra short and straight path from clock to chip.
- Shield between each power supply pin, strip, plane... on every layer.
- No shield between each side of differential signals (if one signals couples on one line, you want it on the other to cancel, not going to ground!).
Shields between each channel, and virtually about any line going to the chip.
Differential pairs length and impedance matched.
- Half of the connectors pins dedicated to shielding. Locally tied to ground on outputs only, so you can avoid ground loops by directly grounding through heavy gauge wire each board. On outputs because the you want to send the noise where it is less critical - outputs, what you want is clean signal at the next board's input.
- Everything SMD to lower series inductance.
- Quality components, 100ppm resistors even on non-critical lines.
There probably are some other details (I spent a very long time designing this board!) but I just don't remember them right now.
Please note that I keep less than 10% of the price for me - considering I do all the soldering! It all goes to pretty expensive components, boards, and 0.1mm copper stencils. Would I sell 100 boards it would not even pay my lab power supplies!
These are prototypes of a much more complicated setup I plan for future commercial use - if everything works as hoped.
So the classic legal stuff: boards are protected by copyright with a registered copy of the design and restricted to DIY use only.
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