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Old 19th November 2011, 10:55 AM   #1
TBKK is offline TBKK  Germany
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Default Static or digital sound by using DAC

I got an problem;

i hear an digital sound looks like static sound when connected the
digital output to an DAC i have convert the SPdif TTL to COAX
does anyone knows this problem
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Old 19th November 2011, 11:15 AM   #2
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I was always under the impresion that SPDIF was a coaxial connection. Maybe you mean you converted a Toslink or other optical to coaxial.
Please forgive me if i am wrong.

Regards Ian
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Old 19th November 2011, 12:53 PM   #3
TBKK is offline TBKK  Germany
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I only hear this with using THE digital output
Of THE dvd rom to be sure i have converted THE ttl
To normal voltage use for coax
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Old 19th November 2011, 01:28 PM   #4
DF96 is offline DF96  England
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How did you convert the voltage levels? What voltage do you end up with?
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Old 19th November 2011, 02:03 PM   #5
TBKK is offline TBKK  Germany
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Spdif digital from CDROM = 5 v ttl
I have this with capacitor and two resistors
And THE DAC Locked good.
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Old 19th November 2011, 02:15 PM   #6
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"Two resitors" - that's your problem.
The coax SPDIF is a 75 ohm input. In order to build a passive divider you need to end up with the same impedance at the source - so your divider should be 75 ohms to ground.
That would overload any CDROM digital output, since those are made to work with 1 kohm loads.
If you do a divider with unmatched impedance (1 kohm), you will have "reflections" of the signal on the connecting cable (especially if it is short) and you end up with noise.

Last edited by SoNic_real_one; 19th November 2011 at 02:17 PM.
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Old 19th November 2011, 08:35 PM   #7
TBKK is offline TBKK  Germany
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Do you have an schematic for so i can try
I have use also with 100 nF PE65612 paralel 75 ohm to ground same problem
Use several DAC and dvd-rom and CDROM players

Last edited by TBKK; 19th November 2011 at 08:45 PM.
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Old 19th November 2011, 08:48 PM   #8
TBKK is offline TBKK  Germany
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Can i messure the reflection?
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Old 19th November 2011, 10:01 PM   #9
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http://www.epanorama.net/documents/audio/spdif.html
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Old 20th November 2011, 09:34 AM   #10
jaycee is offline jaycee  United Kingdom
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You'll find most DAC inputs are 5v tolerant - you should be able to connect your TTL input directly to it.

SPDIF is a bitstream protocol, and can be passed over any medium. TTL is just 0-5v square wave. "Coaxial" is 75 ohm transformer coupled, 0.5v peak-peak. AES/EBU is a balanced 100 ohm signal. TOSLINK is an optical transmission system.
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