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
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
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
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
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.
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.
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 😀
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 😀
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
Jocko
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
How about connecting two DAC to a single CS8414 I2S output?
Regards,
Thijs
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
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
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,
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,
You succeed in more useful content.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.
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,
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,
Tschrama,
The selector switch you are mentioning is at the output of the DAC's I suppose (?) Why not using some 75 Ohm coaxial relais at the input of the DAC's.
Regards,
Peter
The selector switch you are mentioning is at the output of the DAC's I suppose (?) Why not using some 75 Ohm coaxial relais at the input of the DAC's.
Regards,
Peter
Hi Peter K,
Yes the selector is at the output of the DAC. The input was constant connected to the S/PDIF line. I could use relais etc. but I wanted to keep it simple.
Thanks you all your anwsers. I give it all some thought.
Regards,
Thijs
Yes the selector is at the output of the DAC. The input was constant connected to the S/PDIF line. I could use relais etc. but I wanted to keep it simple.
Thanks you all your anwsers. I give it all some thought.
Regards,
Thijs
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
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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