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Old 22nd May 2003, 09:48 AM   #1
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Default distribute S/PDIF or I2S, passive?

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

Greetings,
Thijs
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Old 22nd May 2003, 10:24 AM   #2
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Use a good splitter for 75 Ohm ( TV )
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Old 22nd May 2003, 06:16 PM   #3
Peter K is offline Peter K  Netherlands
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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
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Old 22nd May 2003, 06:28 PM   #4
tiroth is offline tiroth  United States
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Magic T?

I would go active. S/PDIF levels are so low already. You add a little jitter with the buffer but it solves a lot of other problems.
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Old 22nd May 2003, 07:05 PM   #5
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You missed the in my post. Never tried it but maybe it works for testing purposes ? I wouldn't fiddle around too much with SPDIF, it is already difficult with only one device connected to it
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Old 22nd May 2003, 07:33 PM   #6
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A "Y" splitter can be made connecting three 25 ohm resistors at a common point. One free end is the input, the other two are the outputs. Works good for most frequencies. Has 6 dB loss.

Jocko
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Old 22nd May 2003, 07:35 PM   #7
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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
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Old 22nd May 2003, 07:39 PM   #8
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Hi Jocko,

Thanks, I just missed your post. The 25 Ohm resistors are for the attenuation of reflections? I must say I'm very unexperienced in HF stuff.

Regards,

Thijs
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Old 22nd May 2003, 07:45 PM   #9
dhaen is offline dhaen  Europe
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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,
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Old 22nd May 2003, 07:52 PM   #10
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Quote:
I think it's a better solution than those already suggested.
You succeed in more useful content.
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