SPDIF receiver with external clock

kevinkr

Administrator
Paid Member
The Wolfson WM8804/05 will do what you want, but only in software mode, otherwise the xo has to run at 12MHz. And yes it is hard to get, but available, check with Wolfson - their sales offices are quite responsive and they will tell you where you can get their parts.

AFAIK there is no other "readily" available receiver chip that is even close to being able to do what you propose.

FWIW the Wolfson chip is a very good performer.
 
I don't know if any of these chips will do what you actually want.

They all use PLLs to lock onto the incoming signal.

You don't want a PLL for this clocking scheme... You just want to clock in the SPDIF and remove the bi-phase, the overhead preamble bits, and the post user and data bits. A PLL will just muck up the works.

Do any of these chips allow the PLL to be disabled?
 
rossl said:
I don't know if any of these chips will do what you actually want.

They all use PLLs to lock onto the incoming signal.

You don't want a PLL for this clocking scheme... You just want to clock in the SPDIF and remove the bi-phase, the overhead preamble bits, and the post user and data bits. A PLL will just muck up the works.

Do any of these chips allow the PLL to be disabled?

The WM8804/05 are quite a bit different than the usual PLL scheme, they actually have two PLL and the master clock is derived from a crystal reference clock scaled by the second PLL to match the clock recovered from the spdif signal. Doing as you propose I think would require a custom FPGA programmed to do what you propose, a project beyond the capabilities of many diy folk, myself included.
 
I think I se the problem!

The right way will be to use a MCU to control the WM8805 and have is bypass the internal PLL - then it shold work.

Perhaps this is the way I shold take, as the DAC in mind (PCM1792) can be used as a volumecontrol in software mode.

It's early morning here now, but what do I "muck up" if I feed the PLL in the receiver with an external clock and also run my transport using this clock signal?

/R
 
Yes, you need to put your receiver in slave mode.

I did this with CS8412, it's pretty easy, just read the datasheet and check the mode pins. You can do it with the other chips also, proably. CS8412 has a 2-sample FIFO (double buffer) so the delay/phase between the clocks does not matter (the datasheet mentions this) as long as they are the same frequency.

Including a SPDIF transmitter is a good idea since it will allow you to slave your soundcard. But you can also use the SPDIF output of your player (most players will output silence on the SPDIF even when not playing, which works to slave a soundcard, I tried).

Be careful about power up sequence since some players will just act crazy without a clock (for instance smashing the lens repeatedly into the disc 10 times per second -> lifetime of the lens actuators at this regime was about 2 minutes on the CD723, may it rest in peace, lol).

When you build it, you should check for proper operation (no sample skip) by viewing the various signals on the scope and use a proper test signal (for instance, a string of samples 0000-FFFF-0000-FFFF).

In order to slave your CDP you will need to transmit the clock. I suggest either fiber optics or differential lines. Optic transceivers will not handle 16 MHz though. Both allow you to separate the grounds. For differential you could use a very cheap Ethernet transformer from DigiKey since both clock and SPDIF are transformer-friendly). Coax isn't good for this because the shield needs to be grounded at both ends, or else it makes a very effective antenna, differential is much better. Ground the shield at one end only.

There are some RS422 receivers which will work at the frequency you need, I forget the part numbers right now, check the parts search at DigiKey.

I plan to use a SATA cable in my next rig, this is nice because you get 2 differential lines specced to 3 GHz, so you can't fukup when connecting, it costs $1, and the connectors cost $0.5.
 
WM8805

Hi,
I'm a bit of a newb to this forum, but spotted a post relating to the WM8805. I have been struggling to source a couple of these chips to hook up to some WM8741 DAC chips I already have.

Any chance anyone has a couple of WM8805's still lying around that they are willing to do a deal on?

Any help would be greatly appreciated

Regards

Chris