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Troubleshooting S/PDIF Output

filmis

filmis

Active Member
Since my new Nakamichi amp has a bunch of digital inputs, I've been trying to make the most use of them as the DACs on there really sound fantastic.

I'm modding a Denon LA-2150K laserdisc to output the digital audio (yes, most laserdiscs had digital audio, though it was also analog-capable).

Luckily, the onboard CXD2500AQ DSP offers pin 60 as TTL-level S/PDIF digital signal. Holding pin 59 high enables the digital output and I get a good, strong signal.

I'm trying to troubleshoot the attached circuit. Those resistor values should provide the desired change in voltage range, from 0,5V to the required -0.5,0.5V. However the actual output ends up being more like 0-1V and doesn't seem to dip below zero. Naturally my DAC refuses to do anything with this.
I'd like to keep the component count low for now--just a proof of concept will suffice for now--but is there any obvious fault or alteration I should make?Untitled.png
 
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filmis said:
I'm trying to troubleshoot the attached circuit. Those resistor values should provide the desired change in voltage range, from 0,5V to the required -0.5,0.5V. However the actual output ends up being more like 0-1V and doesn't seem to dip below zero. Naturally my DAC refuses to do anything with this.
Click to expand...

I missed this when first posted. I'm not sure why you have a DC offset in the output - seems like the 100nf cap should be blocking it. But if you haven't run across a solution yet, I wonder if another cap on the output side would do the trick, as below. A while ago I struggled with one of those cheap chinese HDMI audio stripper boxes, wanting to convert its optical out jack to coax; I'd removed the LED emitter and played around with a simple transistor buffer circuit (copied from the schematic of a Sony DVD player) for a while. Couldn't get that to work, then tried replacing the buffer with a single electrolytic cap. Don't remember the value offhand, might have been something like 10uf. Tested it first with a cheap DAC to be safe, found it worked, and am now using it with my Bryston BDA-1.

spdifoutidea.png
 
I ended up driving a TOTX177 from the output directly instead. That works fine, so I'll stick with that for the time being.
 
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