Mod CD/LD players with digital coaxial output - need help!

[Assyst1606]

Hi all,
I wanted to mod my players with a coaxial digital output so as to connect it to my DAC.
I got this circuit from the web.
I tried it on my old Sony CD (model CDP 590) player which uses a CXD2500Q chip, on pin 60 (digital out) but there is no sound output from the DAC.
I tried it on my old Pioneer LD (model CLD-D580) player which uses a Sanyo LC7868 1K chip, on pin 43 (digital out), again there’s no sound.
I don’t think is the thin copper wire that I used between the output resistor & the RCA connector.
Anyway if anyone have done this mod (that is moding your player with a digital output so as to connect it to an external DAC), if u don’t mind do share with me your knowledge & experience.
Thanks!

[dangus]

Yes, I've done that with a Hitachi VIP-RX8 (guts built by Pioneer) laserdisc player. It used the CXD2500AQ chip, and had traces and locations on the board for a Toslink output. Since at the time it was hard to get Toslink devices, I put in a little buffer board and an RCA jack output. I think the circuit I used was a lot like yours.

Maybe the output has to be enabled? Pin 59 is the "Digital Out On/Off Control"; High for On, Low for Off.

CXD2500AQ at Alldatasheet.net

[Assyst1606]

Hi Dangus,
Thanks for the reply. I'm not good in electronics, may i know how to enable pin 59?
Is it possible that i can copy your circuit & try it out?
Thanks!

[kevinkr]

Originally posted by Assyst1606
Hi Dangus,
Thanks for the reply. I'm not good in electronics, may i know how to enable pin 59?
Is it possible that i can copy your circuit & try it out?
Thanks!

Stupid question I know, but did you remember to connect the power and ground pins on your 74HC04??

[dangus]

Pin 59 could be connected directly, or through a resistor (10k or so) to the same supply voltage the chip uses, probably 5V. The datasheet should explain what is OK to do.

If I remember, maybe I will open up the player and take some pictures (I didn't have a camera with macro at the time I did the mod.). I've got a sketch someplace of the board layout, or maybe I can get a shot of the backside of the board if I didn't mount it too permanently.

[Assyst1606]

Hi Kevinkr,
Yes, i did. 5V to pin 14 & gnd to pin 7 of 74HC04.

Hi Dangus,
I'll be happy if u can provide more info with pictures.
I read a number of articles but none mentioned about enabling pin 59 of the CXD2500Q.

Thanks!

[dangus]

Here's a scan of a portion of my notes that shows the schematic and board layout. I think I used the HC14 just because it was handy.

[Assyst1606]

Hi Dangus,
Thanks! I can see u are using HC14, what's the different between it & the HC04?
U didn't mentioned about enabling pin 59 on the CXD 2500Q chip.
So i guess that is not needed.

Here's another TTL to SPDIF circuit -


So confusing now, wonder which circuit will really work?

[Mooly]

Hi,
The 14 is a Schmitt trigger type, probably the best choice but the 04 should work fine.
I have seen it mentioned somewhere that some DAC inputs use a 0 - 5 volt logic level.
I can't see anything wrong, and when I last experimented with something similar ( adding an optical output ) I found it not critical at all. Whether the circuit inverts or not didn't matter.

[kevinkr]

Originally posted by Mooly
Hi,
The 14 is a Schmitt trigger type, probably the best choice but the 04 should work fine.
I have seen it mentioned somewhere that some DAC inputs use a 0 - 5 volt logic level.
I can't see anything wrong, and when I last experimented with something similar ( adding an optical output ) I found it not critical at all. Whether the circuit inverts or not didn't matter.

Probably doesn't make much difference in this application since the inverter is driven by a good square wave, but hysteresis is implicated as a major contributor to jitter in spdif applications.

Spdif has a specific range of amplitude levels that work (well) above that range things can get very funky with receiver chips latching, etc. Below a certain level most receiver front ends won't lock properly.

400 - 500mVpp with everything properly terminated is a good number to aim for. (See my posts in the shigaclone thread for much more detail on this issue.)