I am looking for using the wm8805 for simple i2s to spdif converter board and have checked the wm8805 datasheet and some schematics from other implementations. In some diy implementations I found from the internet the TX0 is put directly to toslink output jack while in some other implementations there is a voltage divider implemented + 0.1uF cap before the spdif output. Is the voltage divider and cap really needed and what is the purpose of it?
For example this project uses 210 and 110 resistors and 0.1uF cap. https://www.dimdim.gr/diyaudio/spdif-receiver-with-the-wm8805
Mika
For example this project uses 210 and 110 resistors and 0.1uF cap. https://www.dimdim.gr/diyaudio/spdif-receiver-with-the-wm8805
Mika
They are meant to make the output impedance and signal levels compliant with the S/PDIF specification. The IC presumably puts out full-swing CMOS levels. The components are needed when you want a coaxial S/PDIF output, but not when you want an optical output, because the optical transmitters are usually designed for a full-swing CMOS input signal.
The divider is to bring the output level from the CMOS driver's 3.3V to consumer S/PDIF level of .5-.6V. The values are chosen to give an approximately 75 ohm termination impedance (actually 72 ohm here). The capacitor is to prevent any DC offset at either end from passing.
There is one additional component to the voltage divider: the assumed 75 ohm termination at the receiver. 110||75 is 44.6 ohms, resulting in .58V with 3.3V out, or .52V at the minimum guaranteed output with 3.3V supply (.9xVDD).
If you want to send 3.3V instead but still across 75 ohm coax, then replace the divider with a single 75 ohm to ground.
There is one additional component to the voltage divider: the assumed 75 ohm termination at the receiver. 110||75 is 44.6 ohms, resulting in .58V with 3.3V out, or .52V at the minimum guaranteed output with 3.3V supply (.9xVDD).
If you want to send 3.3V instead but still across 75 ohm coax, then replace the divider with a single 75 ohm to ground.
In my case I want to send the spdif audio signal to optical toslink jack. For that purpose I have looked either the FCR6842032T or FCR684204T and to my understanding for them I can feed the 3V3 signal. So in this case I should use one 75 ohm terminator resistor to ground? And then just the 0u1F cab before connecting to the jack to filter the dc offset noice?
Purpose for my circuit is to feed the audio via optical cable to Hosa ODL-312 that I use for converting the optical spdif audio to AES/EBU signal via XLR cable to my speakers.
Purpose for my circuit is to feed the audio via optical cable to Hosa ODL-312 that I use for converting the optical spdif audio to AES/EBU signal via XLR cable to my speakers.
@MarcelvdG is correct and beat me to it (just like with the first reply 😀). I'm curious, why the conversion to optical before AES, instead of just converting S/PDIF to AES directly? Is it related to device locations?
Digital AES question was a good, thought that also for second version. The project is not originally my own so wanted to try out first something that is close to original one in here:
https://hackaday.io/project/162309-spdif-from-echo-dot
I could not find the kicad files for that project, so I am now kind of redoing schematics and routing first with only a some small changes so I can verify the functionality. I think I want to add later the possibility to playback also on dot's own speaker and probably switch the ATMega168-A to some other chipset with wifi or bl support.
If I would use digital XLR instead of Toslink, then I could to my understanding still use the same TX0 signal from WM8805 for output? (signal for all speakers would go via xlr cable to first speaker and then from there to second one with genelecs)
Btw, my current version of kicad 7 project (mostly schematics, only started looking for possible component placement) is attached on this kicad bug report thread
https://forum.kicad.info/t/new-track-start-position-problem-on-kicad-7-10-rc1/47006:
https://hackaday.io/project/162309-spdif-from-echo-dot
I could not find the kicad files for that project, so I am now kind of redoing schematics and routing first with only a some small changes so I can verify the functionality. I think I want to add later the possibility to playback also on dot's own speaker and probably switch the ATMega168-A to some other chipset with wifi or bl support.
If I would use digital XLR instead of Toslink, then I could to my understanding still use the same TX0 signal from WM8805 for output? (signal for all speakers would go via xlr cable to first speaker and then from there to second one with genelecs)
Btw, my current version of kicad 7 project (mostly schematics, only started looking for possible component placement) is attached on this kicad bug report thread
https://forum.kicad.info/t/new-track-start-position-problem-on-kicad-7-10-rc1/47006: