SAA7220 SP/DIF help

[buzzforb]

Wanting to add a SP/DIF output to my CDB482. I know Pin 14 is the digital audio out on the chip but my question concerns the values posted in the datasheet. Is it necessary to maintain the exact values or can others be used? Values are somewhat unusual. How would these be calculated and is it dependant on the ratio of the two resistors 315 and 91. Would the cap need changing if it was possible to use different R values.

[SoNic_real_one]

Those resistors are calculated to give a 75 ohm output impedance while reducing the digital signal to the proper 1Vpp level required for SPDIF...
Capacitor is just to block the DC, is not there to be a HF filter.
Another way to do it (in many Philips players) is using a transformer - it loads less the output of the 7220.

[buzzforb]

Do you mean use a 1:1 ratio trafo? How would it be wired? Could you elaborate as I am new to this!

[SoNic_real_one]

I don't think those used where 1:1 (based on the resistors used), maybe 3:1...

[amc184]

Even though your player doesn't output S/P DIF it probably has patterns and tracks on the PCB where the components to do that job could have been installed. Philips often made one PCB to suit different models, and where a function wasn't needed the parts weren't installed.

I'm pretty sure I'll have a CD player mainboard lying around somewhere that'll have the parts you need to add a S/P DIF output to your player (mainly the signal transformer), do you want me to have a look?

Another thing; there's a few different CDB482 / CD482 models, what decoder and DAC is yours using? SAA7210 and TDA1541 or SAA7310 and TDA1543?

[buzzforb]

Mine has the SAA7210 and 1543. No 7220 unfortunately, which would have made it easy. I have considered taking the PSaudio route and pulling the I2S from the 7221 and running it directly into the cs4398 chip on my DAC. I have heard this is possibly a good mod in terms of sound quality.

[amc184]

Ah, no SAA7220, that complicates things a lot. The way you talked about pin 14 on the first post made me assume you were talking about a version that had a digital filter.

If you want to add a S/P DIF output I'd recommend having a look at Twisted Pear Audio's kitset.

If you want to go the I2S link route you'll have to decide on what sort of physical layer you want to use. PS Audio did specify a physical layer, but it involves quite a bit of work, and is probably more complex than adding a S/P DIF output, even though it may not appear that way on the surface.

[SoNic_real_one]

I was thinking also about SAA7220, when I READ THE TITLE (it says SAA7220 SP/DIF help).
And also when I read about pin 14.

[buzzforb]

Forgive me, I sent the post right before opening up the CD player. According to most list it was suppose to have a 7220 in it. Guess not. From all that i gather, adding the SP/DIF will be just as difficult as the PS Audio route. I am trying to find am accurate service manual for my version of the 482. I will check out the Twisted Pear site and see what he has. I really don't know how this thing is working. I thought the 7220 was the decoder chip that sent the info to the DAC. If it is not doing it, what is? Also, the 1543 is no where near the 7210, and i always thought that idea was to kep the I2S trace as short as possible.

[buzzforb]

Here are some photos