John Swenson tutoring paper: "Considerations regarding usage of external reference clocks" (EtherREGEN and other): Sine vs. square, impedance, cables—and a money saving surprise at the end.

Many of our friends here at Audiophile Style have been waiting for us to publish John Swenson's introductory explanations concerning choosing and implementing an external reference clock—be it for connection to an EtherREGEN or some other audio device.

[I take the blame for the delay. John gave me the first draft of his paper just over two months ago. The concepts were pretty clear but I think he wrote it late at night so it needed a few editing/formatting passes. I finally had time this past week to prepare it for presentation.]

Here is a link to the PDF for offline reading: Considerations regarding 10MHz external reference clocks...

And below are the JPGs of the pages.

We do not expect that this paper will answer all questions about the complex realm of high-frequency reference clocking, but it is a start. Nor does this paper get deeply technical and there are some generalizations.

After reading it, feel free to ask questions.

As teased in the thread title, at the end of the paper we present a shortcut to getting stellar performance out of less than state-of-the-art clocks.

If there is interest, we may begin stocking the item mentioned--mostly for convenience of our overseas clients as the company selling the small, inexpensive item charges $120 for shipping to destinations outside the USA.

Enjoy!

--Alex C.

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Very clearly written and helpful.  Thank you!

Not sure if that little gizmo is needed for the Cybershaft, but I'm curious to try it.  If you stock it, I'll purchase through UpTone.  

Great white paper! Really explained everything in great detail, but easy for a clock neophyte like myself to understand! 
Thank You @JohnSwenson @Superdad !!

20 minutes ago, LowMidHigh said:

Thank you for the pointed white paper. 99% clear.

 

Since I use a quality Ref10 clock, I'm left  wondering about my cables.

 

How much does attenuation plays a rule in a 1.5 cable? Professional companies gives  their specs @ 100m runs. 

For example, the attenuation of Canare LV-77S @ 100' is 1.0. Can things get any lower? LV-61S @ 100' is 1.3.

 

 

Secondly, if performance can be improved, can anyone recommend a low attenuation 75ohm cable?  By the meter or feet is better, as I solder my BNC cables myself.

Raw attenuation doesn't matter, it is how the attenuation changes with frequency that matters. So the numbers you quoted don't make any difference, what you need is the attenuation vs frequency graph. The flatter the graph below 1GHz the better. The problem is you cannot compare graphs from different companies since the scales are almost always different. Even within the same company the scales are frequently different.

The Canare LV-77S spec sheet has a table for this with several of their models. You can tell by looking at this table that the LV-77S has significantly less change with frequency than the others do. This is the information you need to look at to compare cables.

Note this is only if you are using square wave output, if you are using sine wave it doesn't matter.

John S.

@Superdad

Reading this, I will find it a shame that Uptone does not eventually market an external clock for those who wish to connect one to an Etherregen. At least the customer will have fewer questions and we would have a "Uptone" design.

Hope you are working on this external clock project ..... because I am already a potential customer for this clock

6 hours ago, LowMidHigh said:

Regrettably, the Canare and the  Belden measurements don't fully overlap, but where the do, the 1694A does measure better. 

 

But the Canare LV-77S sounds better!  Trust your ears, it's not just about measurements.

21 minutes ago, James Stephens said:

Are there any other clocks, besides I imagine the Mutec Ref 10 and Ref 10 SE 120 (?), for which we might expect the square wave output into an ER to surpass its sine wave output (+ of course the Mini-Circuits filter)?

[When you accidentally posted your question in AfterDark’s “Filter group buy” thread I answered there. But since you caught that the question is more appropriate here, I’ll just repost my long answer below...]

Hi James:

While I understand what you are asking, the phrasing of the latter part of your question does not really fit. You seem to imply that there are first-rate clocks that offer both square and sine waves from the same box. That’s not the case with the Mutec (square only) nor any of the better boxes from Asia (mostly sine) that I am aware of.

As John explained in his paper, it takes a lot of care to both produce a really good square wave AND to preserve that quality (via cabling) all the way to the target device. Not that it can’t be done.  And OXCO modules (the circuits in the cans along with the crystal) are available with square wave output. But how that is implemented and handled varies greatly.

Also, some companies (and I have no idea about what AfterDark does to offer square wave in some models) use sine>square circuits between the OCXO module and the output.  There exist a couple of chips that do this extremely well, but then there are the rest which are rather poor at it (and then the truly terrible squarer mess that is in the BG7TBL boxes).

So with inexpensive square wave output clocks you really never know what you will get. Yet with sine wave clocks you need to be very careful to filter to a very clean wave—best done at the endpoint target device end.

Back to your question—which likely was more meant to be something like:
“Can a really low-phase noise sine wave output clock—terminated with the Mini-Circuits filter—outperform a first-rate square wave box such as a Mutec REF10 SE20 (assuming $$$ also spent on a cable for that square wave)?

I certainly can’t answer that and I think John would decline to as well without making extremely careful (and rather difficult to set up) measurements.  And even the characteristics of the receiver in the endpoint target would likely have significant affect on such a comparison.

I write all the above primarily so that we can all begin thinking about these things from the proper angles. It’s confusing stuff! 

28 minutes ago, Superdad said:

 

[When you accidentally posted your question in AfterDark’s “Filter group buy” thread I answered there. But since you caught that the question is more appropriate here, I’ll just repost my long answer below...]

 

Hi James:

While I understand what you are asking, the phrasing of the latter part of your question does not really fit. You seem to imply that there are first-rate clocks that offer both square and sine waves from the same box. That’s not the case with the Mutec (square only) nor any of the better boxes from Asia (mostly sine) that I am aware of.

 

As John explained in his paper, it takes a lot of care to both produce a really good square wave AND to preserve that quality (via cabling) all the way to the target device. Not that it can’t be done.  And OXCO modules (the circuits in the cans along with the crystal) are available with square wave output. But how that is implemented and handled varies greatly.

Also, some companies (and I have no idea about what AfterDark does to offer square wave in some models) use sine>square circuits between the OCXO module and the output.  There exist a couple of chips that do this extremely well, but then there are the rest which are rather poor at it (and then the truly terrible squarer mess that is in the BG7TBL boxes).

So with inexpensive square wave output clocks you really never know what you will get. Yet with sine wave clocks you need to be very careful to filter to a very clean wave—best done at the endpoint target device end.

 

Back to your question—which likely was more meant to be something like:
“Can a really low-phase noise sine wave output clock—terminated with the Mini-Circuits filter—outperform a first-rate square wave box such as a Mutec REF10 SE20 (assuming $$$ also spent on a cable for that square wave)?

 

I certainly can’t answer that and I think John would decline to as well without making extremely careful (and rather difficult to set up) measurements.  And even the characteristics of the receiver in the endpoint target would likely have significant affect on such a comparison.

 

I write all the above primarily so that we can all begin thinking about these things from the proper angles. It’s confusing stuff! 

First off, John explicitly says in the paper that he suspects a good square producing clock + low  attenuation cables would outperforms a sine clock + a filter. I'm quoting:

"Just remember that the best possible result is still going to be using a square wave clock box with a REALLY good sine to square converter, everything being just right inside the box—AND you use a really low-attenuation-with-frequency cable."

Secondly, I believe you misconstrue James' question. He  was interested to know if there were other excellent square-producing clocks, apart from Mutec's, which could outperform a sine+filter. Put differently, could you list the brands whom he could trust to have the proper internal circuitry to produce a stellar square wave.  

24 minutes ago, LowMidHigh said:

Secondly, I believe you misconstrue James' question. He  was interested to know if there were other excellent square-producing clocks, apart from Mutec's, which could outperform a sine+filter.

Seems it was, but I wanted to clarify and to expound a bit on the choice and decision process. 

24 minutes ago, LowMidHigh said:

Put differently, could you list the brands whom he could trust to have the proper internal circuitry to produce a stellar square wave.  

We are not presently surveying the whole clock market, nor would it be possible to assess any models without looking very closely as their circuits (really good clocks are not cheap!) 

However, John did this with the BG7TBL that I sent him and found quite a lot to criticize in that piece with regards to the squarer circuit. In fact, even the sine from the OXCO itself goes through the lousy squarer circuit and then a poor filter I think. Maybe he will speak of what he found as I think it might be educational. Certainly that box was not designed with audiophiles in mind. Would have been better just to run the OXCO module in the thing straight to a BNC jack.

Still, as he pointed out, putting the Mini-Circuits low-pass filter on it at the target device end will yield cleaner and much more worthwhile sine wave.

19 minutes ago, LowMidHigh said:

I have a question fo my own here to John. Given we have the figures for both the Bedlen 1694A and Canare LV-77S, which of the two would he recommend over the other? Going by the numbers alone, the Bedlen is superior, but some people here claim that the Canare "sound" better. Kind of a contradiction, so I hope he could weigh in. 

Five of your six posts in this thread have been about clock cables for square wave clocks. But the thrust of the paper and the concepts we are wishing to speak about are not that. You could start a new thread on clock cables or perhaps revive one such as this which already exists: