Any ideas to improve this PCM-54K based DAC?

[Salar]

It is from a Nakamichi OMS-5EII. Sounds thin compared to newer players.
The link to the schematic is:
Schematic

And the board layout:

Thanks in advance,
all the best, Salar

 

[rfbrw]

What do you want to do with it ? There are a number of possibilities.

 

[Salar]

Hi rfbrw!
Well, as you might remember, I do not know anything about electronics, even after upgrading my Nak with a digital out, where you were so kind to help me.
To comparisons: i bought a cheap audiolabs DAC with upsamßpling. Compared to the audiolabs, the nak sounds sweter. But i was very surprised, when I bought a mint, second generation Toshiba (XR-Z70) and compared it to the Nak. Tha nak now lacked bass and the Soundstage of the Toshiba is wider - but has hrsh treble.
23 years ago, when I made the same test, the Nak won clearly over the Toshiba.

I did add a Tentlabs clock last autumn to the nak and also replaced 3 Capacitors of the D/A board´s power supply (2200 u) with Blackgates and changed the decoupling capacitors of the analog outs (1u).
So, some questions for sound Improvement:

Should I replace/bridge the optical decouplers?
Any other capacitors which should be replaced?
Any decoupling of the PCM 54Dacs (i.e power to GND) needed?
Should resistiors of higher values be replaced?
Is there any other opamps i could replace the original ones with?
Maybe, some later DACs (PCM56/PCM63 are even pin compatible? (I doubt...)
All the best salar

 

[deuginthesky]

Many many op amps are better than the LF353:
-opa2134
-AD8620
-LM4562...

I usually replace diodes with faster one, like the very fast BYV27-200, bypass caps with MKP2 film capacitor.
I also like to put some Clarity caps (PX grade minimum) as filters just before the RCA, always find an improvement

My 2 cents, MFG

 

[rfbrw]

Should I replace/bridge the optical decouplers?

You could.

Any other capacitors which should be replaced?

The filter caps C508 - C513 may be worth a look though I must admit to being a bit of a capacitor sceptic, i.e. I'm not convinced it will make much difference.

Any decoupling of the PCM 54Dacs (i.e power to GND) needed?

It would better to see what the manual says about aligning the 3 MSB's of each dac for minimum distortion. That is what the three pots are for. Over 23 years things may have drifted through aging.

Should resistiors of higher values be replaced?

Unless it has changed value why bother ?

Is there any other opamps i could replace the original ones with?

Unless it has stopped working, there would be little point. It is a servo. Anything cheap and similar will do the same job. That isn't to say some joker out there hasn't got an OPA627 at 15Euro doing servo duties in place the 0.80Euro LF351.

Maybe, some later DACs (PCM56/PCM63 are even pin compatible? (I doubt...)

Nothing pin compatible but you could replace just the dac or the whole board depending what you what to do. Is there a particular dac chip you want to use ?

 

[Salar]

Hello rfbrw
I guess, i will replace the optocouplers on the Nak´s board in the future.
I did now compare the Nak to other dacs and the Nak still holds up against them very well...
Upgrading the nak with a tentlabs clock was the only audible improvement in the last time, at least to my ears...

But another important question:
I am now running three power supplies in the Nak:
The Nak´s own power supply, another for the clock feeding the Nak´s main board and the diy SPDIF transmitter and a third power supply for the transmitter itself. (the octal buffer between the main boards decoder and transmitter is connected to the main board´s power supply.) So, the only ground connection between those three circuits are the signal cables of the clock.
Should I connect those three circuits/pcb´s to ground somewhere else to prevent ground loops running through the wiring?
All the best,
Salar