Static or digital sound by using DAC

[TBKK]

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

 

[madtecchy]

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

 

[TBKK]

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

 

[DF96]

How did you convert the voltage levels? What voltage do you end up with?

 

[TBKK]

Spdif digital from CDROM = 5 v ttl
I have this with capacitor and two resistors
And THE DAC Locked good.

 

[SoNic_real_one]

"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.

 

[TBKK]

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

 

[TBKK]

Can i messure the reflection?

 

[SoNic_real_one]

http://www.epanorama.net/documents/audio/spdif.html

 

[jaycee]

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.

 

[TBKK]

Yes it woks also if i connect the digital output to the dac but the sound is totally better
when converting it but then i hear an static sound



I have now

---100 NF ---00000--|----------- digital


....................T1.... 75 ohm


-------------00000 --|----------- GND

 

[SoNic_real_one]

Maybe the voltages after divider are not right levels? See the previous link for values.

 

[TBKK]

I now have only 100nf serial in the digital line and GND direct to the
DIR1701e receiver. But the sound is to white.
Does it help to use 75 ohm paralel?