How to get your beloved CD-player from the eighties into the Digital Domain

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Hello,

Some days ago, I finished my work in upgrading my Nakamichi OMS-5EII with a S/PDIF output.
This CD player was developed in 1986, (bought mine in 1990) so this post might be interesting for those, who own a player from this time, when a digital output was not common.
The OMS-5EII, as well as the OMS-7EII have a PCM decoder from Sony, CX23035.
Sony used it also for the first consumer model with S/PDIF out named CDP-552ESDII. It came to the market the same year as the Nakamichi.
So, If this PCM decoder is used (I.e. the Denon DCD-1500 has it, and probably many other japanese high end CD players ), chances are very good for upgrading.

I am not a technician at all, so I want to give big thanks to some people, I think three of them are users in this forum, for helping me:

- At first to Ray, who developed the schematics for the digital output
- Jobstens (www.jobstens.de), who checked them and gave me many tips
how to handle ESD and heat-sensitive devices
-Frank who proposed a I2s output
-Uwe (http://beis.de/Elektronik/Electronics.html) for practical tipps in wiring the board and providing the output transformers needed.
-Stefan for proposing a company which solders SMD devices

I do not have a scope or anything like that, so building the digital output was a matter of "plug and play".
If it did not work, it would have been impossible to find errors.

For upgrading, Ray and Jobstens proposed the DIT4192 from TI, a digital transmitter which does not need a controller. An octal buffer, 74HC240N was used for transferring the signals from the CX23035 to the DIT4192.
One problem was, that the Nakamichi worked internally with a
master clock rate of 156fs, but the DIT4192 needs 384fs.
I bought a clock from Tentlabs, which provides both frequencies: 8.4672 for the Nakamichi ´s CX23035 and 16.9344 for the DIT4192.
One nice side effect of the upgrade is, that the Nak now sounds "fresher" because of this almost jitter-free clock.
I also replaced all electrolytic capacitors of the "Nak", (also on the D/A Board) but this did not have any audible effect to my ears.

I did not want to stress the power supply of the Nakamichi, so the tentlabs XO and digital output circuitry got their own power supplies.
But shortening the pins of the S/PDIF (even though a decoupling transformer was implemented) made the laser loose track.
But with the buffer being connected to the Nak´s 5V power circuitry, everything works fine.

The only problem was (and still is), that my DAT-recorder (Sony ZA-5ES) does not recognise the S/PDIF signal.
Experimenting with several modes of the DIT4192 did not help.
But my sample rate converter (Z1-SRC), my portable DAT (AIWA HD-S1) and soundcard (ESI Juli@) receive the S/PDIF with no problems, so I blame it on the Sony.

The next and final step would be implementing an up to date D/A board which can be hooked on the S/PDIF out. But the Nak sounds fine, I will see...

One request: If anybody reading this post lives in the Berlin area and has a scope, it would be fine to meet.
Before and also after the upgrade, the Nak has sometimes problems to find a track when skipping over a longer distance. I replaced the laser three years ago and did also replace the motors when doing the upgrade but it had no effect, so I think it is a matter of realignment...

All the best,
Sal

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One photo of the Nak´s digital board...

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And a top view...

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The Nak reassembled...