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Coax output circuit (SPDIF)
Coax output circuit (SPDIF)
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Old 10th June 2003, 05:12 PM   #1
Vinnie R. is offline Vinnie R.  United States
diyAudio Member
Join Date: Apr 2003
Location: Boston Area
Default Coax output circuit (SPDIF)


I am now using my Denon 2800 with an external DAC. I have the service manual for the Denon and have been looking at the coax output circuit. I noticed that the spdif signal passes through some inverters, transformers, caps, inductors, etc. before it reaches the coax RCA-type jack.

I am only running 1M of Monster M1000D digital cable, and was wondering if the digital output circuit of my Denon can be improved.
In it's simplest form, I've seen a schematic online where only 1 cap and two resistors (1 in series, one in parallel) were used (I guess to convert TTL to SPDIF). Is this a case of "simpler is better" or are all the buffers and EMI stuff in the path benefical to the digital dignal. Put another way, would a simpler circuit add or reduce jitter and other eye pattern parameters like Extinction Ratio, overshoot, etc.

Also, if a 75ohm impedance cable is important, then why does the signal pass through crappy PCB traces and connectors before it reached the jack. Isn't this messing it up somewhat?

Thanks for all your input,

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Old 10th June 2003, 05:20 PM   #2
tiroth is offline tiroth  United States
diyAudio Member
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
This has been discussed before. Look especially for some comments from Jocko about how to do things right.

Short form:
Get rid of the RCA and use a 75 ohm BNC
PCB traces don't have to be controlled impedance b/c they aren't transmission lines
A quality pulse transformer is a good thing
Be careful how you terminate your cables or you'll blow your savings
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