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4-Channel S/PDIF Input - interference between inputs / ground / locking issues
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miero  
#1 Posted : Thursday, November 24, 2011 1:28:13 AM(UTC)
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Is there some wiring recommendation for 4-Channel S/PDIF Input board?

I'm having lock drops (1-2 per second) when playing 192kHz sampled data into one input and on the second one a unused TOSLINK input module is connected. Sometimes the lock is lost on <192kHz data.

Following helps to reduce/eliminate drops of lock:
1) only the one input is connected into 4ch SPDIF module.
2) or the Buffalo 3 is disconnected from IVY module (i.e. metal case too). Of course there is no sound, but also the LED is not blinking.

What needs to be fixed? Isolate everything from metal case, use coax for all spdif connections, use the very short cable between buffalo and 4ch input module, etc?

Edited by user Thursday, November 24, 2011 1:30:54 AM(UTC)  | Reason: Not specified
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Russ White  
#2 Posted : Thursday, November 24, 2011 6:37:16 AM(UTC)
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Hmmm. My suggestion (especially in your case) would be to definitely isolate the input jacks from the case. It sounds like may have a ground loop. These can manifest themselves in ways other than hum.

Edited by user Thursday, November 24, 2011 6:39:09 AM(UTC)  | Reason: Not specified
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miero  
#3 Posted : Thursday, November 24, 2011 4:33:43 PM(UTC)
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Oh, I've found out why... it was not the ground loop but a hidden antenna!

Mine 4ch S/PDIF board has not have soldered R3 and R4 yet.
The massive drops of lock disappears after inserting those resistors at their place.

But it was funny to play with it - the interference was disappearing when the optical cable was connected to TOSLINK module, and also it helped to raise 4ch S/PDIF board 10cm above the case... :-)
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miero  
#4 Posted : Monday, November 28, 2011 3:57:04 PM(UTC)
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Adding missing R3/R4 resistors has helped, but there were still some issues
with drops of lock using coax and 192kHz material.

I've found that unconnected input with R2 is interfering other inputs;
e.g. touching "-" terminal with screwdriver caused instant blinking of lock led.

As a workaround I've connected/shorted the "+" and "-" terminals of that input.
The SPDIF lock is now stable even on 192kHz.

Do anyone other observe similar behavior on R2 input?
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Brian Donegan  
#5 Posted : Monday, November 28, 2011 5:06:36 PM(UTC)
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I assume you mean input 2. Do you have all of the components installed for that input (termination resistors, etc)?
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miero  
#6 Posted : Tuesday, November 29, 2011 5:16:48 AM(UTC)
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Yes, all components on the board are installed.
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Russ White  
#7 Posted : Tuesday, November 29, 2011 6:22:46 PM(UTC)
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There is nothing special about input #2. :)

You may want to double check all of the solder joints etc. You can also try joining -IN to the GND on that input and/or the others if it is consumer level input.

The secondary side of each transformer is terminated to GND (usually by 75R for consumer level). If your using TTL level signals into the module you may want to decrease the value of that termination resistor (from 10K to say 1K) but even 10K should be just fine. :)

Also be sure your ribbon cable to the DAc is as short as possible. Also make sure your IDC connectors are making good contact.

I am not having any trouble running all four at 192/24 from 2 consumer sources and 2 AES. My termination Rs are 75R and 110R.
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Russ White  
#8 Posted : Tuesday, November 29, 2011 7:31:25 PM(UTC)
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One other great solution would be to use a voltage divider immediately at the output of the TOSLINK module to turn the TTL output of the TOSLINK module to consumer level. 210R series then 110 ohms to GND will do that nicely. Then you can terminate that input with 75ohms like the others.

Edited by user Tuesday, November 29, 2011 7:31:58 PM(UTC)  | Reason: Not specified
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