does AES/EBU help if i implement reclock?

[garbage]

hi all

i have a monica 1545a dac and want to do the reclocker circuit as suggested at the same site for it.

question is, will an AES/EBU 110ohms transformer (assuming i am using balanced XLR cable from the transport) at the input of the CS8412 make any difference or should i just stick to RCA 75ohms and use normal coaxial cables?

thanks.

[hwb]

Hi!

Basically Coax is the better solution for digital audio interconnection, as it is designed for HF signal transmission, opposite to ordinary twisted pair cable. Even special 110Ohms digital microphone cable is always worse in transmission quality compared to Coax.

Regarding transformers, have a look at Cirrus' AN134, there you will find some references to background knowledge. Especielly Scientific Conversion has some interesting Papers about the influence of transformers on Jitter.

HTH,
Holger

[Jocko Homo]

Mostly true, but not for exactly those reasons.

Main problem with AES/EBU is the connector. While it is a 110R connector, it is unusable due to excessive reflections.

There are twisted pair cables designed for data transmission, that would work well if the proper connector was used. But sourcing them will be a problem, so coax does win out. As long as its impedance is matched to the impedance of the TX and RX circuits, as well as the connector.

Don't believe everything that Scientific Conversions says. In order for the jitter to be low, the reflections must be low. They provide no information on that, just a lot of their ideas about noise performance.

Jocko

[garbage]

looks like i'll go with plain jane.

initially wanted to order some sc939-06 trans from scientific conversions.

cheers
garbage

[hwb]

Yocko, you wrote: "Main problem with AES/EBU is the connector. While it is a 110R connector, it is unusable due to excessive reflections."
I think you've forgotten a "not" in your sentence. XLR is no 110Ohms connector and never will be. Even Neutrik's XCC Series, especially designed for the use with AES/EBU, has a lower impedance. It is kind of stupid, that the AES has specified XLR as connector for this signal.

The TP digital audio cables have 110Ohms, but usually +/- 10%. And if you bend the cable you get some inhomogeneities within the cable causing a decrease in signal quality, whereas a coax cable has by nature a more narrow tollerance and better homogeneity.

At least in professional applications with longer cable runs I will always prefer coax together with BNC connectors and transformers at the end.

Holger

[Jocko Homo]

I hate to tell you, but it really does measure 110R. If you can eliminate all the extraneous garbage on the TDR trace.

Forget the impedance.......it will never work as the pins are so far apart that it will have too many reflections.

You are correct that the cables that you refer to will have problems. Back in my telecom days, we had twisted pair cables for balanced transmisson that worked quite well.

The reason that they worked is that you could not bend them. Much too rigid. Basically, the only place that we used them was in elevator shafts, to transmit data between locations many floors apart.

And, yes...........transfomers on the end!

Jocko

[hwb]

Hmm, I've had a discussion with a representative of Neutrik on this topic, he told me, that the impedance of a XLR is lower than the required 110Ohms. But I don't want to argue about that, we both agree that a XLR is unsuitable for AES/EBU, no matter if it has the correct impedance or not.

BTW, I have heard some rumour that the AES is thinking about a new connector for AES/EBU or using a coded XLR variation. If that was true, they would badly need a reality check, coming up with this idea ten years after they have issued their standard...

[Jocko Homo]

They needed a reality check years ago. The first version allowed for.......what was it..............3 TX and 7 RX on each cable??? Something like that. I tried to tell the AES, but would they listen...............

Eventually, they figured out part of it, and went to one T/R only. Still, the whole concept is flawed.

I guess if you include all the stray capacitance in the impedance, it would be lower than 110R. But it is no longer resistive, so like you said, it still doesn't matter.

Jocko

[Jocko Homo]

Anyway........we have strayed a lot here.

What you are refering to is commonly called an asynchronoius reclocker. Elso is fond of them, as are a few others. I have no use for them. Seems like another flawed concept.

Secondary PLLs, or ASRCs, are the only real ways to get rid of the jitter on the DAC.

Jocko

[stolbovoy]

Originally posted by Jocko Homo
Secondary PLLs, or ASRCs, are the only real ways to get rid of the jitter on the DAC.

What about source clocking + reclocking from master XO placed close to DAC chips?