Article: SOtM sNH-10G Network Switch Review

[Superdad]

42 minutes ago, STC said:

Hi Ken, could you update the link?  It is taking to a paypal page...

 

The link is correct but it looks like at this morning moment www.sotm-audio.com has been hacked!  The supposed PayPal link t goes to is to lure the unsuspecting into signing in with their PayPal credentials.  

[Superdad]

23 hours ago, The Computer Audiophile said:

perhaps this is why Sonore will create its own sfp module?

 

Really? That would be news if true. 

Perhaps you are thinking of their fortcomimg FMC, called opticalModule. But its SFP cage will be supplied with a standard Gigabit fiber SFP module.

[Superdad]

Besides, the North Pole is not nearly as cold as it used to be. 

[Superdad]

26 minutes ago, plissken said:

This ignorance is beyond the pale.

 

You’re calling @PeterSt ignorant?

What a sweet guy you are.  No wonder you are so well liked... 

[Superdad]

10 hours ago, Jud said:

Way back near the dawn of digital, people like Ed Meitner were already discussing “logic induced modulation,” and right up to the present day folks like ESS talk in white papers about lowering noise getting into the chip.  It’s a situation where the level of noise may not be quite so important as even small changes in it (changes in noise on ground = jitter at the clock), so at least theoretically you don’t want things in the playback chain to be changing noise characteristics while engaging in playback.

 

To what extent this or anything to do with jitter may be audible has always been a subject of some discussion and controversy.

 

Seems a good place to reprint a post of @JohnSwenson's from October 2017:

 

The hypothesis goes thusly:

ALL crystal oscillators exhibit frequency change with power supply voltage change. This is known and well measured. A cyclical change in voltage causes a cyclical change in frequency which shows up in phase noise plots. For example if you apply a 100Hz signal to the power supply of the oscillator you will see a 100Hz spur in the phase noise plot. 

 

A circuit that has a digital stream running through it will will generate noise on the power and ground planes of the PCB just from the transistors turning on and off that are processing that stream. This effect is very well known and measured. Combine this with the previous paragraph and you have jitter on the incoming data stream producing varying noise on the PG planes that modulates the clock increasing its jitter.

 

The above has been measured.

 

But shouldn't ground plane isolation and reclockers fix this? At first glance you would think so, but look carefully at what is happening. What is a reclocker? A flip flop. The incoming data with a particular phase noise profile goes through transistors inside the flip flop. Those transistors switching create noise on its internal PG traces, wires in the package and traces on the board. This noise is directly related to the phase noise profile of the incoming data. This PG noise changes the thresholds of the transistors that are clocking the data out thus overlaying the phase noise profile of the local clock with that of the clock used to generate the stream that is being reclocked. This process is hard to see, so I am working on a test setup that generates a "marker" in the phase noise of the incoming clock so it becomes easy to see this phase noise overlaying process.

 

This process has always been there but has been masked by the phase noise of the local clock itself. Now that we are using much lower phase noise local clocks this overlying is a significantly larger percentage of the total phase noise from the local clock.

 

Digital isolators used in ground plane isolation schemes don't help this. Jitter on the input to the isolator still shows up on the output, with added jitter from the isolators. This combination of original phase noise and that added by the isolator is what goes into the reclocking flip flop, increasing the jitter in the local clock. Some great strides have been made in the digital isolator space, significantly decreasing the added phase noise which over all helps, but now the phase noise from the input is a larger percentage, so changes to it are more obvious.

 

The result is that even digital isolators and reclocking don't completely block the phase noise contribution of the incoming data stream. It can help, but it doesn't get rid of it.

 

For USB (and Ethernet) it gets more complicated since the data is not a continuous stream, it comes in packets, thus this PG noise comes in bursts. This makes analysis of this in real systems much more difficult since most of the time it is not there. Thus any affects to an audio stream come and go. Thus just looking at a scope is not going to show anything since any distortion caused by this only happens when the data over the bus actually comes in. To look at anything with a scope will take synchronizing to the packet arrivals. Things like FFTs get problematic as well since what you are trying to measure is not constant . It will probably take something like wavelet analysis to see what is really happening.

 

The next step in my ongoing saga is to actually measure these effects on a DAC output. Again I have to build my own test equipment. The primary tool is going to be an ADC with a clock with lower phase noise than the changes which occur from the above. AND it needs to be 24 bits or so resolution. You just can't go out and buy these, they don't exist. So I build it myself.

 

I have done the design and have the boards and parts, but haven't had time to get them assembled yet. Then there is a ton of software to make this all work. Fortunately a large part already exists, designed to work with other systems but I can re-purpose it for this.

 

So it's not going to be right away, but hopefully not too off in the future I should be able to get to actually testing the end to end path of clock interactions all the way to DAC output.

 

John S.

===========

 

FYI, his elaborate clock test set up--we call it the Golden Gate Bridge--has been through a couple of iterations and John has been working ever more actively on it--even this very day.  But mostly in-between product development work. 

[Superdad]

35 minutes ago, incus said:

So the noise of your Emotiva is greater than anything that's come before it? Interesting.

 

Yeah, well @plissken paid $300 for his marginally built DAC with $0.50 master clocks, and $2.00 opamp output stage, so its not much surprise that nothing upstream can be heard. 

[Superdad]

1 hour ago, plissken said:

Let me remind everyone you are the one that disappeared at What's Best Forum when you initially said you would blind A/B your own ISO Regen product in your own home when someone was going to purchase air fair.

 

Knock it off Pliss. First of all, what someone misconstrued as an invitation to my home never was.  I have blind A/B'd our products many times in my own home.  The ISO REGEN did not even exist when the aforementioned exchange occurred.  And my decision to stop participating in that forum had nothing to do my not inviting hostile parties to my house.  I simply had no further interest in arguing with close-minded people.

 

In case you have not noticed, there is a very wide market with plenty of competition and companies (including my own) offering 30-day, money-back guarantees on products that produce better signal integrity before the DAC input.  Don't you think if such products were useless and ineffective the market for them would have dried up long ago?  [That's a rhetorical question, I already know your answer and could care less what you think. ]

 

1 hour ago, plissken said:

What DAC do you use 😉

 

Holo Spring Level 3.

 

1 hour ago, plissken said:

I don't know what's worse: My faith in my $300 (I purchased second hand but basically new in box) or your lack of faith in your DAC and your product, er I mean ears.

 

Dream on buddy.