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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.


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7 minutes ago, JohnSwenson said:

There is no such thing as full jitter rejection, it doesn't exist, so any real circuit has to have SOME jitter sensitivity. A major issue is to look for what units are being used for jitter. Some companies have decided that 1ns of jitter is "essentially zero jitter", so if they can get their jitter down to 1ns, they consider that to be all that is necessary and market that as zero jitter. BUT there is a whole world below 1ns. This is where everything we are working on here resides. If a company says that no matter what the input is the signals going into the DAC have 1ps or less, THEN you can say they really do have an effective jitter rejection. But I don't think anybody is actually making that claim.

 

So unless some company really has come up with something truly amazing, I think that these things being talked about here will still be useful, even with DACs that say they have "near perfect" jitter rejection.

 

John S.

Thanks John!

I am not experienced in reading Jitter measurements, but all I have seen provide DB Vs frequency as an indication of Jitter or lack of it

How does it relate to the time domain? here is an example, does this show Jitter performance better than 1ns?

 

Hugo_2_Jitter_Graph.png

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11 hours ago, GMG said:

Thanks Martin, 

Sure, but are saying that the clock adds to the clean up of the ground noise?

 

Via a reclocker like ER or Mutec, the output will have less jitter and phase noise.

 

You can't reclock to better than the clock accuracy.

 

Getting rid of ground plane noise requires very good grounding connection or grounding boxes.

 

Both of these contribute to the ultimate sound quality.

TP-Link MR6400 4G router > Uptone EtherREGEN reclocker > Sonore Signature Rendu SE streamer > Gustard U18 DDC > Gustard X26 Pro DAC > Belles SA-100 power amp > Usher Dancer Be-20 speakers. AfterDark clocks x 2. PS Audio P3 & P10 regenerators.

https://theaudiostandard.net

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  • 5 weeks later...
10 hours ago, GMG said:

@JohnSwenson, Sorry for a slightly off topic question, but I have a question related to the Low Pass Filter suggested in the paper

 

Would it make sense to add such a filter to the input of a DAC? maybe with a 1Mhz cut-off frequency

 

Came across this:

https://audiowise-canada.myshopify.com/products/gnd-zro-signal-ground-isolation

I presume you are talking about S/PDIF, a low pass filter is not good for this since it is a square wave with complicated frequency components going up quite high. The low pass filter would destroy the signal.

 

That filter you link to on the other hand IS a useful device. Since leakage current is primarily low frequency, a HIGH PASS filter attenuates the leakage current while letting the signal you want (S/PDIF) go through. It probably has a significant attenuation for low impedance leakage, but probably not effective for high impedance leakage. So for most systems it is probably useful but not a complete solution.

 

John S.

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  • 1 month later...
On 3/28/2021 at 12:10 AM, Superdad said:

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.

Here are examples of various BG7TBL's products:

 

3EFB8B0F-203C-4AA1-9894-67D626A2069F.thumb.jpeg.0efc3bcf485d76b7c1e35a17c4d5fdf6.jpeg

 

95636520-141C-45B4-BC90-E6C4ABC7E0EA.thumb.jpeg.559061f25dd5944ae951067a79688b02.jpeg

 

7D0649FF-014F-4D15-9309-F3A86C661285.thumb.jpeg.2689236a1a8d5a4748d7ac42296f524f.jpeg

 

34888AAA-082A-449A-A731-B0CCB26222BA.thumb.jpeg.52f6c679c6ad89df73b6eda5a168b450.jpeg

 

Mini-Circuits (from datasheet):

 

B058F9C3-1644-4F62-A668-8D9F33DF73C1.thumb.jpeg.e33656788baff9b2187466ae76728937.jpeg

 

It can be seen that simple LCL low pass filters are responsible for creating a square wave signal at the output, exactly as in the Mini-Circuits and Crystek filters (circled in yellow). Blue circled where there is no LCL filter at the output and the sine wave signal at this output accordingly. So how do the recommended Mini-Circuits filters differ fundamentally from LCL filters in BG7TBL's products? Only more steep filter?

 

 

 

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  • 1 month later...
On 3/27/2021 at 10:51 PM, Superdad said:

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

Can you specify the names of those two chips?

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On 4/22/2021 at 4:38 PM, Superdad said:

John’s examination of the BG7TBL’s circuits revealed, it does not at all qualify as having a “really good sine-square converter.”  It is actually quite poor in that regard. On the opposite side of the solar system in comparison to a Mutec REF10 for square wave performance.

What criterion (indicator) do you use to assess the quality of the conversion of sine to square? On what basis do you draw this conclusion about the quality of the conversion of sine-square to BG7TBL and Mutec? Based on product schematics analysis, measurement analysis (which?) or something else? Have any measurements of BG7TBL been taken in order to infer extremely low quality of square wave at the output of the clock?

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41 minutes ago, Mihaylov said:

Can you specify the names of those two chips?

The Linear Tech LTC6957 is state of the art for that.

 

29 minutes ago, Mihaylov said:

What criterion (indicator) do you use to assess the quality of the conversion of sine to square? On what basis do you draw this conclusion about the quality of the conversion of sine-square to BG7TBL and Mutec? Based on product schematics analysis, measurement analysis (which?) or something else? Have any measurements of BG7TBL been taken in order to infer extremely low quality of square wave at the output of the clock?

Yes, John analyzed the circuits of the BG7BTL unit I sent him, gave details of his findings publicly, and also made measurements at various places in the circuit.  Someone else here published the nasty-looking square wave output of it as well. It really would have been better if the BG7TBL guy just installed those reclaimed OCXOs on a plain board with nearly no circuitry. (That's about what AfterDark does, but with new-old-stock CTS clocks which they grade with their Symmetricom.)

 

The Mutec REF10 is in an entirely other league.

 

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23 hours ago, Superdad said:

Someone else here published the nasty-looking square wave output of it as well.

If you're referring to this message, the square wave distortion is caused by impedance mismatch: the output clock impedance and cable impedance is 75 ohm, and the oscilloscope input resistance is 50 ohm.

 

1856821415_BG7TBLSquareWavePulseTrain-s.thumb.jpg.c63d0312010c4928b06491662564d8e0.jpg

 

Mutec shows the same bad curve when impedances are mismatched.

image.png.0daddcf47734b6713395bddf5cdeeb68.png

 

 

 

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  • 2 months later...
On 5/10/2021 at 4:00 PM, JohnSwenson said:

As the ER paper mentions reclocking can itself generate ground plane noise which can partially negate its effectiveness.

 

The jitter on the clock doing the reclocking is very important. If the clock used for reclocking is has higher jitter than the what you are reclocking it makes things worse. So reclocking only makes sense when you have or can generate a clock that is better than what your data has. There are methods of extracting a clock and lowering its jitter so it can be used to reclock the data, this is what most S/PDIF "reclockers" do, but this can only go so far, it is really only useful when the data has a lot of jitter. If your data is already quite low jitter then using this process makes things worse.

 

Hi, @JohnSwenson

 

There may have been relevant context prior to this statement that I have taken out by mistake, but this comment seems to imply that reclocking devices added in series is "likely" to make things worse as you say. I've not been one to do or test this but of course people here have put two EtherRegens inline and so on. And I'm asking about Ethernet and USB where reclockers have, to my ear, definitely improved most things. And there again people have "stacked" reclockers in series. (Maybe crossing over from one, um, protocol (is that the right term for this change of data?) to another increases jitter or something, I dunno.)

 

So it makes sense that some have found stacking to make things worse per your comment above, and I guess my question with the EtherRegen more specifically is that if one has a sufficiently good streamer or DAC, say, with a better clock than the EtherRegen, then it's likely the EtherRegen will do more harm than good?

Alex knows that I just purchased a JS-2 for use with the manta ray Aries streamer, and that's a different topic (yes it's a solid improvement, thank you!) and because the manta ray is such an old unit I'd think the EtherRegen should help (my ears say yes). But, what if I had a streamer or a DAC or combo that's more modern and more high end with a similar clock as the EtherRegen with Ethernet as an input?

 

Forgive me if this is an oversimplification (I'm sort of guessing it is) and I'm asking just to clarify the practical implication of your statement.

 

 

Sum>Frankenstein: JPlay/Audirvana/iTunes, Uptone EtherRegen+LPS-1.2, Rivo Streamer+Uptone JS-2, Schiit Yggdrasil LiM+Shunyata Delta XC, Linn LP12/Hercules II/Ittok/Denon DL-103R, ModWright LS 100, Pass XA25, Tellurium Black II, Monitor Audio Silver 500 on IsoAcoustics Gaias, Shunyata Delta XC, Transparent Audio, P12 power regenerator, and positive room attributes.

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2 hours ago, feelingears said:

So it makes sense that some have found stacking to make things worse per your comment above, and I guess my question with the EtherRegen more specifically is that if one has a sufficiently good streamer or DAC, say, with a better clock than the EtherRegen, then it's likely the EtherRegen will do more harm than good?
 

As a user, this has NOT been my experience.  My streamer/DAC has excellent measured performance (and sounds great), but it was improved by the eR.   In my setup, copper ethernet goes to the eR (then to another eR) and from there copper ethernet feeds the ethernet input of the streamer/DAC.

 

I think you will find that many folks here who use the eR have well-regarded setups, including, of course, their streamers and DACs.  In fact, it is interesting to me that so many different kinds of setups benefit by the eR.  

Grimm Audio MU1 > Mola Mola Tambaqui > Mola Mola Kaluga > B&W 803 D3    

Cables:  Kubala-Sosna    Power management:  Shunyata    Room:  Vicoustics  

 

“Nature is pleased with simplicity.”  Isaac Newton

"As neither the enjoyment nor the capacity of producing musical notes are faculties of the least use to man...they must be ranked among the most mysterious with which he is endowed."  Charles Darwin - The Descent of Man

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Yeah, that has been my general impression lurking the clock threads and such. I've avoided "over-reclocking" in part due to diminishing returns and the fact that 90% of my listening is Red Book or 24/96. And my rack is spaghetti enough with cables sticking out three sides and not just the back. 😉

Sum>Frankenstein: JPlay/Audirvana/iTunes, Uptone EtherRegen+LPS-1.2, Rivo Streamer+Uptone JS-2, Schiit Yggdrasil LiM+Shunyata Delta XC, Linn LP12/Hercules II/Ittok/Denon DL-103R, ModWright LS 100, Pass XA25, Tellurium Black II, Monitor Audio Silver 500 on IsoAcoustics Gaias, Shunyata Delta XC, Transparent Audio, P12 power regenerator, and positive room attributes.

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@JohnSwenson

How much will “the moat” going from B to A degrade the phase noise (or jitter) ?

How much phase noise is needed from an external clock to overcome the degradation ? If it’s  even is possible to think like that. 

 

Could the opticalModule deLux used with optical out, be equal in measurements compared to the EtherRegen in a B to A setup, or may even be better, since no moat present ? 

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