Optical vs Coaxial output

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I have a Technics SLPG-620 modified with an LC low jitter clock. The CD is fine but I wish to use it as a transport taking advantage of the good transport (CDM4) and low jitter clock. The problem is that this CD offers only an optical digital output. Many think that this output is inferior to the coaxial output. How can I get a coaxial output from my CD? Is it worth it?

Thank you
George
 
Hello,

i have the same question...

at one, you may just put a TORX-176 between.

Better would be a proper digital output stage. Hoerwege (www.hoer-wege.de) sells a digital output stage at 40 Euros, which is of good quality. Consideriing they must work economically, i think one might built it by itself for less than 10 Euros. Schematic wanted!

Everybody tells me coaxial is better than optical. So I believe ...

Regards
Christian.
 
Hello,

thanks for the schematic,

as I understand, this one is a kind of a optical input for a DAC, which means you would have to connect the TORX176 to the optical output of your cdplayer. You could build it as a converter into a separate box...

I would like to see a kind of schematic which shows the opportunity to be connected BEFORE the optical output thing, which must convert electrical signal to otical, does it? Or is the laser beam of the disc drive just brought to the optical output without converting anything?

Cheers
Christian.
 
If you need to use your CD Player as a transport, the best "traditional" (that is, compatible with any commercial DAC) arrangement should be to reclock the SPDIF stream immediately before it goes out from the transport unit.

This would require to put the clock not near the original clock station (provided the unit goes on working in this way....) but as near as possible to the output reclocking unit, that should in my view be as near as possible to the output line driver.

I have mounted something similar with a low noise clock I will not mention in my Pioneer PDS-505 a couple of years ago, and it works really fine.

I think I prefer its sound to the Mimik one (costed just 5+ times more...), but, to be honest, the difference is so small that I am not completely sure of what I would say if I had designed the Mimik... you know, your sons are always the best... ;)

As soon as I have time, I'm going to publish an article about this on TNT.

As far as I know, I think there is at least one similar commercial product [by Net Audio, I think]. I have not tested it yet, nor am I completely sure it does exactly the same...

Last, and best, but for sure drastical solution: go all the way and mount the clock in the DAC (by the way, it also is a less polluted environment and this should utterly help).

Take the clock back to the transport with a coaxial wire. Drive the CS841x Receiver output and the DAC with clock signals derived from the local clocks (disregarding the PLL reconstructed clock): the disregarded reconstructed clock should in any case be synchronous (even though with an unknown phase rotation and added jitter) with the local clock, as this one is the only one driving all the units in the loop...

This is the arrangement supported by Wadia and Sonic Frontiers, by the way. And probably also my next step...

hope this helps

Giorgio
 
Hello,

thanks for your responses.

Actually, I am planning to tweak a Pioneer PD-S507 as a CD Transport Unit and the DAC will be a TDA1543 solution (by Doede Douma, see www.dddac.de, using Guido Tent Clock at 16.9344MHz

Gorgio, your PD-S505 should be very similar to my 507. I have already ordered the Service Manual to see things more clearly. Please, can you suggest certain things to do with this unit? I heard that the UK version of this cdp has a coaxial digital output, maybe this is shown in the service manual, so i will simply build this in. Otherwise my very above question ist still the most important one. Apart from that, can you tell me what exactly you did with it? What/how you reclock?

I am planning to exchange electrolytics by Panasonic FC and Oscons, bypassing them with foil capacitors, replacing Diodes with BYV27/200 (I have them on hand) etc. Any help would be appreciated. In case of you do not want to publish things here, you can send me an email to post at krishu dot de. But I think everybody would like to know ;)

Apart from this, does your Pioneer transport read CD-RW discs?

Cheers
Christian.
 
Output

The optical transmitter has an electrical input. All you have to do is find the pin on the transmitter with digital signal and tap off that. However, my own feeling is that once its in digital format, its not really important whether it goes optically or by wire.

However, if you do believe optical is inferior, then using an opto to electrical converter is silly because you still have the opto in the signal path.
 
How can optical transmission be inferior? Coax transmission is susceptible to noise. Even though optical transmission is limited by distance, there is no possibility for electrical noise. I image bandwidth is limited as well, but for PCM transmission, is optical really that bad?
 
Having recently designed an optical S/PDIF receiver for work, the one thing I can tell you is that the optical transmitter/recevier combination can distort pulse widths significantly - al least 10 to 20 ns IIRC. This is because of a significant difference between rise time and fall time of a pulse. This pulse width distortion can (depending on the clock recovery scheme used) increase jitter in the receiver.

In all other respects I would agree that an optical solution would be better, offering increased noise immunity as well as electrical isolation between transport and DAC.
 
Ahh, I understand now. All transmission methods have their flaws and choosing the right one in a design depends on the application. My question is for using the S/PDIF output from a cd-rom drive. For transmitting the output to a CS8420, which is the best method for a maximum of 6ft cable lengths with 16 and 24 bit audio up to 96kHz?
 
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