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Old 9th December 2012, 04:56 AM   #3361
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progress on adding my spdif-out board.

I removed one of the input XLR's to make room for a pair of rca's. those will be 4 channels worth; I will not do 6 channels as its too much work and I only really need 4

the i2s wires are in place and strain-relieved by some hot-melt glue and a 2x3 header. a ribbon and IDC connector will go from there to the actual transmitter board.

had to stop there as this was all I could get done today. I put things back together and the unit still functions, so at least no harm done yet

tomorrow I'll do the perf board and actually wire it up.
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Old 10th December 2012, 04:24 AM   #3362
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almost ready to test out with one of the transmitters.
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Old 10th December 2012, 07:41 PM   #3363
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getting closer...

perf board mounted to chassis (I hate drilling but it had to be done) with stand-offs. its in securely, now. easy to remove for service, too.

i2s cable is made (I love IDC cables. its a joy to make these.)

spdif-out cables were some junk 75ohm composite tv wiring from 'yellow to yellow' patch cords. nothing high grade but better than bare wire, to be sure.

left to be done: find a clean enough 5v and ground tap and then do some testing.
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Old 11th December 2012, 06:12 PM   #3364
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partial success (the perf board does work) but its not working with the behringer yet.

I've verified the wolfson perf board by connecting its i2s to the usb audio widget, where I have the 4 i2s lines ready and easy to tap into. things work fine there, with this new board.

but when installed in the behringer, I'm not getting audio data out of the spdif transmitter. I see spdif lock-on via my dac led but only white noise comes out.

lr-clock is seen at 96khz via my scope and counter, so I know I have that line right. I'm not so sure that the master clock is clean enough to be dragged across inches of wire, though. that might be what's stopping this from working. any comments or ideas?
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Old 11th December 2012, 07:39 PM   #3365
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Have you checked the SDIN, SDOUT, CSB and GPO0 status flags, these should indicate any errors in hardware mode (which seems to be quite complex to set):
http://www.wolfsonmicro.com/document.../en/WM8805.pdf

Search "Table 17".
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Old 11th December 2012, 08:22 PM   #3366
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I have more info (and some scope pics to upload of the waveforms, later on).

short summary: I compared a known good working config for the wolfson (96k audio file played over the 'usb audio widget') to the lines on the behringer (which is always 96k, at the output). result: the audio widget puts out 24mhz (and some fraction; the right number) but the behringer puts out 12.something (which is exactly half of what the wolfson needs).

I think the hardware mode (that I am running wolfson at) only wants to see the higher master clock freq, not a lower one. 12.something is too low and it wants 24.something. I know that 24.something works when I connect my new perf board setup to the audio widget and steal its i2s lines. music plays perfectly and glitch-free (I ran this mode for a few hours today to verify my wm8805 perf board build). and so, I know my build is ok and the hardware config of the 8805 is ok. the audio widget works with it and my dacs decode the spdif-out just fine.

the voltage levels even look more or less ok for i2s. and all the lines seem to be 'right' in that wordclock is 96k and bitclock is a few mhz and a constant wave and data is about bitclock speed but variable wave. master clock is the fastest but only 12.something.

so, this won't work just by hooking things up, as-is. at least not with this spdif transmitter chip.

I might look into doubling the 12.something and feeding that to the wolfsons. or I could look into another spdif transmitter chip, but that seems a bit drastic to me.
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Old 11th December 2012, 09:46 PM   #3367
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both devices shown with rigol scope captures.

the data and bit and wordclocks all look right! ignoring probing sloppiness and actual shape quality, for now.

the only thing that is 'wrong' is the master clock. its half of what the wolfson wants in order to work, at least in pure hardware mode for the 8805 chip.
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Old 11th December 2012, 10:07 PM   #3368
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looking further at the wm8805 datasheet, in hardware mode (what I'm using, since its controller-less) the mclk MUST be 256 * Fs. fs = 96000 and so that's 24mhz roughly that the master clock has to be in. this fully explains why things 'didnt work' direct from the behringer. the dcx puts out 128Fs and not 256Fs on ITS master clock. bingo. akm chips work that way but the wolfson does not (again, in hw-mode).

so, I either have to find somewhere on the dcx that is already 256Fs or I have to clock-double to make use of this wolfson chip. or try another spdif transmitter chip.
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Old 12th December 2012, 12:28 AM   #3369
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some good news. I tried a spare cs8406 chip I had and it did work! at 128*Fs, you can jumper THAT chip in hardware mode to run. the wolfson, well, not so much.

I guess that's that, unless I feel like doing software controller stuff for the wolfson. (not right now, I don't!)

so, save yourself hassle and use my results. the wolfson is not right for this particular task. not unless you want to clock-double the 12 into a 24 for the 8805 to run at.
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Old 12th December 2012, 12:42 AM   #3370
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Quote:
Originally Posted by linuxworks View Post
some good news. I tried a spare cs8406 chip I had and it did work! at 128*Fs, you can jumper THAT chip in hardware mode to run. the wolfson, well, not so much.

I guess that's that, unless I feel like doing software controller stuff for the wolfson. (not right now, I don't!)

so, save yourself hassle and use my results. the wolfson is not right for this particular task. not unless you want to clock-double the 12 into a 24 for the 8805 to run at.
Linuxworks, congrats on your results. I love your spirit and the fact that nothing could stop you. Now that I am thinking somewhere in this thread I believe, there was a guy who was trying to achieve the same thing. Unfortunately I have no chance of finding it, but it was many years ago and many pages back in this thread. He was successful as well, picking up the signals and transmitting them further.
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