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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Hi Salar,
Nice going! I'd very much like to have a digital output on my OMS-7 too! My biggest problem is time.

Your tracking problems are partially alignment and partly because that model really never did track that well on defects or bumps. Your problem sounds like straight alignment.

That head (Sony KSS-123A I think?) can have a problem where the centre post used to keep the lens in alignment can become sticky. This mostly affects focus as the lens assembly has to move up and down the post. With power off, the lens should move completely freely up and down on that post.

-Chris
 
Well, I did my mod 12 years ago... CD was at its heights
BTW, my Nak runs fine - but I overgreased some years ago. When there is time, i will have to clean the mech`s gears because the grease shortens the life of the belt.
There is one alignment I was never able to do, I do not remember the details,
but some frequency has to be injected into one IC to align the servo gain.

I did serve a second OMS-5II in November 2017
which I bought as non functioning from ebay. I found out that the belt was somehow transformed to tar, replaced it, cleaned everything and it ran fine.
I did start further alignment and was very happy to find out that everything was still up to the sweet spot. Gave it to my best friend who is very happy to own a Nak.

@Chris I still have an OMS- Mark One on the shelf with the big laser (Probably Toshiba or NEC, I do not recall the naming) If there is a need for one, I am happy to help out
 
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Hi Salar,
OMS-5 or OMS-7? It is an NEC head. It's pretty large. If you remove the grey cover on a dead one you can see how the optics are laid out. The head is very much like an optics lab and you can see why these heads were so darned expensive when new. These very much are the best heads ever put into a CD player. Interestingly, it is a single beam system on a linear tracking mechanism. The alignment procedure is exacting and if followed, you end up with a system that will track just about anything. Of course, there is also the servo board modification that is very extensive. I'm really glad I set mine up.

What's wrong with the one on the shelf??

-Chris
 
I forgot to mention: OMS5 and OMS 7 are identical. Same with the II-models. The only difference were a different VFD and IR Receiver, different keyboards, extra headphone board.
VFD, receiver and keyboards are passive components, driven by the same IC on the main board.
This difference made 1000$ in price.
It did cost only 600$ when ordering the parts as spare parts - front panel and remote included!
 
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Hi Salar,
I would be surprised if they were the same, but never having seen the Toshiba head, I can't say.

You are correct about the differences between the OMS-5 and OMS-7 models. The price difference between list prices and parts is kind of reversed, wouldn't you say? Normally the parts would be many times the difference between the list prices.

-Chris
 
I worked in a supermarket for about six weeks to afford my Nak OMS-5
and made a $1000 loan. This was in 1990. Got a service manual the same year
and I was a bit shocked to find out it covered both models
and the main boards are the same. A defective OMS-7 I bought later(just a voltage regulator was blown) gave the proof...
 
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Hi Salar,
That was never concealed from us. It was a very good thing that they were essentially the same machine. The person who bought the OMS-5 didn't lose anything except the remote control functions. The OMS-3 and OMS-4 used the same chassis and transport. The D/A section was different. At least the person who bought the OMS-3 got a good transport. The OMS-2 and OMS-1 were completely different animals. The OMS-2 had the TDA-1541A dual D/A converter. The transports were not nearly as good as the one in the OMS-3/4. I also have an OMS-4 to go along with the OMS-7. I got that later after the OMS-7. I didn't buy it new. I got it from a customer that didn't want to pay for a new head, I think I gave him 3 or 4 hundred dollars for it, maybe more. Then, I did the servo board mod, put a new head in it and set it all up. It has been a fantastic machine.

Having one manual cover more than one model isn't that uncommon. But I have to say that at least Nakamichi didn't try to hide anything. Did you also put the wired remote connector in the rear panel (and also a new rear panel?)? Teac was one company that would have a base model, then one of two models built on that base. These used the same service manual. Denon was another, Yamaha had separate manuals for each of their products.

-Chris
 
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Well, no. The OMS-5/7 used the TDA1540 DAC which was 14 bit. The OMS-5/7 still sounded great and used the entire Philips chip set. I would very much like to convert it into a PCM-1702 DAC using the DF-1700 digital filter. That should sound pretty amazing.

-Chris
 
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