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ADC S/PDIF DIY project


SounDuke
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I'd like to use the 8 adat optical channels in my motu traveler in order to use 4 additional stereo analog ins. I don't want to buy an alesis AI3 for this purpose (very expensive in my opinion), so after reading some discussions about using the AK's and CS I asked myself if you guys have made something similar. I was considering using the al1401. Is it possible to adapt it to the ADC/preamp Pilo designed (he published it in the portal sideproject forum)? Using 4 al1101 (so 4 ADC circuit based on pilo schematics to have preamps too) I could have 4 stereo channel digital stream which can be routed to a single AL1401 for ADAT conversion. Please correct me if I'm wrong. I would like to convert S/PDIF and AES EBU too for 2 additional analog stereo ins, maybe using after the above mentioned Pilo's preamp a CS8402A  encoder. Please help me :D

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Well here's my plan: the motu traveler supports up to adat 8 channel @ 48Khz and 4 @ 96 Khz (conforming to adat protocol) .

anopther good  thing is that the traveler has WDCLK output. I could make 8 preamps with al1101 ADC streaming to an AL1401 and  synchronise them with the word clock output of the Traveler. Do you think I'll need SMPTE sync too or it will be enough sample accurate? I don't know how to sync smpte

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first, my schematic are here : http://membres.lycos.fr/blendinpulse/adat/

Some (like the dac) have been done with D2k, I have other one (like with pcm1804) which was done with Gillesdeshays. Everything started when we want to mods the emu10k1 SBlive.

Maybe I should upgrade the adat stuff page with more info? (I didn't get a lot of feedback, so I never take the time to put more stuff on it).

I think you can use every preamp (analog side) you want with almost any ADC IC, as the al1401 chip (ADAT enconding) can works with a lot of different interface (inter-IC communication). As I said before I never use SPDIF yet, but it shouldn't be ore complicated than ADAT :)

Now for the clock : for some chip (adc or dac) you need a high frequency clock (generally 256xSampling frequency, ie 12.288Mhz for 48Khz). I built a small generating clock for this. Sync stuff are also possible, but if you just have the wordclock, it may work with al1101, as this chip only require the sampligin frequency clock, but if you want to use others adc (or dac), you will need the higher freq clock. In this case you need to build a Phase Lock Loop clock to recover the 256xfs clock from the wordclock.

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Well I'm beginning to understand your design. Very cool! Congratulations. But:

In the buffer module description you state for ADC connectors: "there are 4 connectors for 4 adc boards (...)"

If I want to use the 8 adat channels at 48Khz, I'll need 8 ADC's to have 8 analog channels in 8 adat channels. How to connect 2 adc's to a single input in AL1401? In other words, how to stream 8 channels in the AL1401 which provide only one pin for channel 1/2?

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In the buffer module description you state for ADC connectors: "there are 4 connectors for 4 adc boards (...)"

If I want to use the 8 adat channels at 48Khz, I'll need 8 ADC's to have 8 analog channels in 8 adat channels. How to connect 2 adc's to a single input in AL1401?

If you look at the ADC-Schematic you'll see that every adc board has two channels. So 4 ADC boards are 8 channels ;D)

@pilo: Realy cool project.

Raphael

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@Sonduke :

first, the clock generator is not the hard parts :) and I think it's important. Even if you want to use the WDclock output from anpther device, I think you need a PLL to recover a proper clock (I didn't make it yet, but I have a schematic, not very hard). With a clock generator you can use the converter as master device, which is needed with some sound card (for example the RME digi32/8 can only record when in slave mode!).

For the psu, I built one around a simple tx and some 78xx regulator (there are 8 voltage : +12v/+5v/-5v/-12v for analog and +5v/+3.3v for digital).

The aim of the project was to built something modular... the adc schematic works fine, the ADAT schematic and PCB (from the al1401 and al1402 datasheet) have change (for mechanical purpose mainly). The buffer module... I have a lot of trouble with this one (CEM trouble).

Something cool would be to redesign the buffer module. FOr example adding the PLL stuff on it, then the frequency divider, some logic for inverting some clock (needed for IIS protocols), and then buffer (without buffering the clock signal, it won't work). That's not a lot of work, but as you can see, I built only single sided PCB...

And as raphale said, an adc is stereo (2 channels), so you need 4 of them to make 8 channels :) .

@Raphael:

thanks ;) it's cool to hear good feedback from this project, which takes nights and days to make working!!

So take care with the schematic that are on line, I should make an update with the right one. I only have 2 adc now (4 inputs), and I don't have time to play with it :(

and the link to the rightaudio mark test :

http://membres.lycos.fr/blendinpulse/adat/test/DIGI32_8 Out (1+2)(1)_13.htm

For the price : you can buy al1401 and al1101 at profusionplc, other IC are I think easy to find. I etch the pcb my self, so they was cheap. I think it cost me about 200/300euros and 25000000000hours of works lol for an 8 channeles input and 2 channels out :) I should make more photos of it, but I don't have a lot of free time, which is very boring, but I hope to have some when I finish the school (in about 5 months).

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