distribute S/PDIF or I2S, passive?

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Hi all,

Would it be possible to connect more than one DAC-receiver to a single S/PDIF line with just a passive circuit. If I increase the 75Ohm to reduce loading maybe this would be possible.

Or should I use the I2S output to distribute the digital data. Or is passive a no-no-no and should I go to the shop and buy some digital buffer, make a powersupply, a circuitboard etc etc. I was hoping to avoid that :rolleyes:

Greetings,
Thijs
 
Jean-Paul,

CATV splitters start at 5 MHz up to 860 or 1000 MHz, the attenuation will be at least 3,7 dB from in to outputs. Most probably a little more at 5 MHz.

Will this not be a problem?

Besides this they use F connectors which is a resonable connector for "last mile CATV" but can not be compaired with a 75 ohm BNC connector. A professional splitters returnloss at low frequenties will be something like 18 dB, maybe lower at 5 MHz. There are only two high quality brands that I know of: Comega and Tratec.

A last remark regarding the F connector is about the difficulty of using professional crimp-connectors, this requires a special tool. NEVER USE THE TWIST ON types, it should be forbidden to sell these!

regards,

Peter
 
I actually thougth serious about it for a brief moment. But I just finished a article on the history of the S/PDIF standard and it says something like 100KHz up to 6MHz (not higher??), so the TV eas dropped from my mind.

How about connecting two DAC to a single CS8414 I2S output?

Regards,

Thijs
 
Hi,

I suggest adapting one DAC to have a "loop-through".
In other words, the original coax goes to the receiver chip, but insted of being terminated with 75 ohms, is also connected to a second coax which is routed to the a new connector on the back-plate. This is the output to the second DAC. When a second DAC is not connected, you must connect a 75 ohm termination to this socket. You can make a term in an RCA plug.
This is common practice with video, and while the return loss figure will deteriorate a little, I think it's a better solution than those already suggested.

Cheers,
 
Thanks dhaen,

To compare my DAC efforts, I have put them all in one housing chassis, complete with selector switch, volume controll and output buffer as a giant DAC/preamp/Headphone-amp combo.

So all DACs (4) are in one housing. The digital source is a coax for a philips CDplayer or a CD-rom with S/PDIF TTL out, converted tot 1Vpp 75Ohm out. One DAC has a fixed (SMD) 75 Ohm. Could I terminate all other DAC with 220 Ohm to reduce signal loss?

Regards,

Thijs

Thijs / trying not to be obnoxious with all his questions.
 
Hi Thijs,

If you want to use this method. you should loop-through each DAC using no termination, and only terminate the final one in the chain.
There might be problems though, with so many loop-throughs. Another consideration is possible interference from one receiver chip to another: although they should at least be synchronous;)


Really, the best method would be to use a distribution amplifer. It should not be difficult to build one. As an "off the shelf" solution, you could try a video DA.

Cheers,
 
Deteriorate a little???

I suspect it will deteriorate a lot. Measure the rho of one of these setups......I bet the RL will be worse than 20 dB due to capaciitve loading. That is more than enough to cause a lot of jitter.

The resistors are used to present a 75 ohm impedance at all ports. I believe that the rho of such a setup will be lower than the daisy chain type.

Don't make me measure this...........................

Jocko
 
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