[vdr] Re: RGB output on J2:

[Stefaan Coddé <stefaan.codde@pandora.be>]

Reinhard Walter Buchner wrote:

>> Note to RGB:
>> I will not combine the sp-dif with the RGB on one board due to the 
>> extra costs for the PCB design,

>Well, it's just a matter of proper shielding (PCB traces) and an
additional buffer IC (for the coax). (Another point which >shows that
the afore mentioned PCB from ebay isn't designed very well. There is no
top layer to shield the 1MHz digital 
>sound traces)

The digital out need no real grounding plane but the ground plane of the
design should cover the one sided
board as much as possible.
The RGB part does need a two layer PCB where the bottom is also the GND
sield
and if it's combined with the ditital audio out, then best a shield
between the two.
It's even not a bad idea to put all of this in a metal tuner alike box.

>> second, my sp-dif solutrion will not contain a optical
>> output cause optical  has more problems with jitter.

>Sorry, but no, it doesn't. Have you scoped the output?
>I see no difference in raw DVB output and and the output
>of the TOSLINK (actually the input of my Denon amp)

This has nothing to do with the toslink modules itself.
The jitter is caused by the way the light travels thru the cable.
As long as short cables are used, then that's not a big problem.
but long cables induce jitter anyhow. That doesn't mean that coax has
it's
weak points tho.

>> the coax solution offers just a better connection and
>>I see no reason to pay extra...

>Well, there is one simple reason: Optical is much more
>common than coax input and if one (like me) has one
>HiFi component that *only* has coax output,  these
>people are out of luck with your solution.

>Secondly the opto output provides galvanic isolation and
>there is no *mess* to make it HiFi conform (both problems
>are solved on my board, which has opto & coax digital out)

Coax is isolated even well, to prevent ground loops a small transformer
is used. (20:2)
What mess to make it hifi comformed? It just needs to be 0.5V at 75ohm.
Heer too, resistant to short circuit.

>> toslink modules are not that cheap...for a lower quality connection. 
>> btw, using toslink modules is very easy.

>TOSLink cost about 3 Euro each (good quality)
Feel free to use it, I just ignore the toslink mainly due to cable
jitter.
I have two TORX en TOTX modules here but still will not use them.

>> RGB safety : I want a fool proof solution so..in case of
>>voltage spikes or even short  circuit, the DVB card should
>> stand it.

>Already taken care of on my protection and signalsorter piggyback PCB
;o))
I'll skip the piggiback solution :-)






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