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beerandmusic

CLOCKS, what should we look for in next generation

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I am a "believer" in advancement of clock upgrades to improve the D->A chain.

I know a lot is being done in the way of mods, and I believe that future products will take note and include upgrades in this area.

 

That said, what should we look for in the way of clock upgrades in future equipment?

 

I know sotm has the sclk-ex and mutec makes clocks, and i am sure there are numerous clocks that would work similarly to improve the d->a chain.

So what should we keep are eyes open for in next generation players and dacs, if we aren't ready to jump on the high priced SOTM sclk-ex "off the shelf" gear today, and if we don't want to mess with mods.

 

I know if i go with a usb dac, that i will want galvanic isolation, but I am leaning toward network players now.

What marketing should i look for in upcoming equipment to know that they have taken advantage of advancements in clock circuitry?

 

 

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Clocks are critical for DACs, there will always be new ways to make these stable, but product development can take years. Creating a clock is quite an accomplished art (and science).

 

How good the internal clocks are within DACs and how DACs are wired to accept external clocks is another development path. On the one hand, the DAC's clock is good enough to listen to, but the DAC manufacturer is not that proficient in clock technology, so let an external clock have a shot.

 

There's going to be a debate on 50 or 75 Ohm systems.

 

There are those that subscribe to the mediocre view that Ethernet and USB transmissions don't require an inbuilt clock as part of the protocol as sufficient buffering in the receiver exists to pad this out. For data, the existing system works OK. For audio, I need to be convinced. This is another story.

 

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1 minute ago, mansr said:

Ethernet and USB audio implementations have flow control, so there is no need to embed a clock signal with the data stream. This is a fact just as the sun rises in the east.

There's my point.

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How is the suggestion that having the DAC and the player use the same clock removes jitter relevant, if at all?

I read that somewhere...i will see if i can find the article to share.

 

Also, what is all the hoopla around the sCLK-ex in the SOTM relevant in recent advances?

 

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Clocks are an established technology. The offset frequency vs phase error offset plot pretty much tells the entire picture of the clock itself. If the manuf doesn’t provide such a plot you have no way to tell what you are buying. Prices have dropped recently and it’s possible to get a great DAC clock oscillator for $20 or do. 

 

The DAC circuitry itself as well as the power supply greatly affect the phase error. Plugging a great clock into crappy electronics doesn’t do much. Waste. If it’s onky $20 you are wasting NBD.

 

I haven’t seen a phase error plot of the sclk-ex it might be good, it might not.

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31 minutes ago, beerandmusic said:

Also, what is all the hoopla around the sCLK-ex in the SOTM relevant in recent advances?

 

Crystal clock oscillators are an established technology governed by physics. The advance is that an excellent phase error clock is available for $20 ie the crystek: CCHD-957.pdf

http://www.crystek.com/crystal/spec-sheets/clock/CCHD-957.pdf

 

If the specifications aren’t better, particularly at 1Hz offset where the error is highest, then the clock is not better.

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excerpt:

2) A few companies made proprietary links whereby if you purchased both the transport and the DAC from the same company, they could eliminate the jitter introduced by the interface completely. These all used a separate signal line for the clock, whereby the master audio clock was in the DAC box and sent upstream to the transport. This is a relatively elegant system, but there was certainly no attempt to try and create or promote any industry-wide standards for this.
 
----
it would seem to make sense to me that if one manufacturer made both the player and the dac, (and in one box without need for interconnects) the design could be optimized to reduce noise/jitter....or is this article (2013) so old that we are already beyond that with interfacing the player and dac where jitter is no longer an issue?
 
I believe this is what exasound was inferring also by their statements about their playpointe working with their dac.
 
Also, what is all this talk about sotm mods and clocks sent to various devices (router, player, dac).
 
I don't understand much if any of this stuff, nor do i really care to, but "reading between the lines" makes me believe we are conitinuing to advance in this area inre clocks.
 

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2 hours ago, jabbr said:

Clocks are an established technology.

 

below is some of the mumbo-jumbo going on in the 190+ page sotm thread....

 

Based on the Hans channel raving review of the SOTM, and all the talk about the SOTM lately, and other things i have read and heard about at recent audio meetings about clocking.....I am a believer in recent advancements inre clocks....

 

My main question is there something we should look for in marketing of future network players that would suggest they have embraced these new advancements in layman's terms.

 

For example, i know if i buy a new usb dac, that i would likely want it to have "galvanic isolation"....what could/should i look for in the purchase of a network player inre clocks?

 

 

 

------

austinpop

Clock Distribution and Termination

 

I wanted to update this thread with some information I have gleaned from recent discussions with Kenji Hasegawa-san of Cybershaft, May from SOtM, as well as @zephyr24069, who has provided me very valuable advice with regards to clocks.

 

Important Considerations with Clock Distribution

 

With all the interest in the SOtM sCLK-EX and master reference clocks, it's important not to lost sight of the basic tenets of clock distribution. At the frequencies of interest here, in the 10-54 MHz range, a clock cable acts as a transmission line. Transmission lines are defined by their characteristic impedance. For the SOtM, Mutec, and Cybershaft being discussed here, they are designed to use cables with 50 or 75 ohm characteristic impedance. It is also necessary for clock cables to be terminated at both ends, with the correct impedance (50 or 75 ohm). Proper termination is necessary to minimize reflections, which occurs on the transmission line if there is an impedance mismatch.

 

Point to Point

 

We have almost exclusively been discussing point to point clock connections in this thread. Examples of this are:

Cybershaft clock <-> tX-USBultra master clock input via 50 ohm BNC

Mutec Ref 10 <-> Mutec MC-3+ USB via 75 ohm BNC

sCLK-EX clock point <-> modded component (switch, router, sMS-200, etc) via 50 ohm SMB

In all these cases, it's important to know that the source and target connections are internally terminated. In scenario 1, for example, the Cybershaft output is terminated with a 50 ohm impedance, as is the master clock input of the tX-USBultra. I have confirmed this with both Cybershaft and SOtM. The Mutec Ref 10 uses an internal distribution amp to provide 8 independent clock outputs, but each of these is internally terminated, and expects a properly terminated target as well.

 

In case you are wondering, SOtM handles the termination internally when you send them components to mod. For each sCLK-EX clock point, both the source and the target are appropriately terminated.

 

But what about the case, where you're a cheapskate like me, who doesn't want to spring for multi-output clocks like the Ref 10 or the upcoming SOtM sMS-OCX10? Can I use a single high-quality clock like the OP-14 and drive multiple outputs?

 

This is where things get interesting.

 

Daisy Chaining

 

Yes, you can daisy chain, but you have to consider the entire length of the cable across the chain as a single transmission line, and you must have termination on each end equal to the characteristic impedance of the cable. For this to work, you have to have devices whose inputs can be selectively configured to be terminated (i.e. have an input impedance of 50 or 75 ohms as needed), or unterminated, in which case the input impedance of the input is very high. In the quote from Kenji below, he calls this "Hi-Z."

 

Regarding distribution of clock T plugs, it is possible under certain conditions.

For example, in the case of a daisy chain

 

1.

Clock output(50ohm) ------T--------T--------T-(50ohm)Terminator

                                      (Hi-z)   (Hi-z)    (Hiz)

                               Device1   Device2   Device3

2.

Clock output(50ohm) ------T--------T- non

                                     (Hi-z)   (50ohm) 

                                  Device1   Device2 

 

( Hi-z = High impedance) 

Be sure to have one 50 ohm impedance at the end and the other relay point must be Hi-z.

Therefore, T plug can be used only when the clock input can be set to Hi-z.

For reference, I attach a connection diagram of CH presision CH and D1. Please be aware that each relay point is Hi-z.

If, for example, there are 50 ohm points in two places, the impedance will be 25 ohm, the current will overload and destroy the output circuit of clock due to long-term use.

SOtM tX - USBultra can not set the input impedance to Hi - z. So SOtM tX - USBultra does not use T plug in the situation.

Also, due to the use of T plugs, noises of each device can interfere and clocks that can be transmitted can not be transmitted. I do not recommend using T plug.

The best way to distribute the clock is to use an ultralow noise distribution amplifier.

However, I could not find a low-cost ultra low noise distribution amplifier of less than $ 1000 from the world market.

We are developing to sell low-cost distributors by next spring.

 

Pay particular note to his point about overloading the output circuit of the clock due to it "seeing" a lower impedance than designed. The second consequence of not paying careful attention to termination is that impedance mismatches cause reflections, that degrade the signal integrity of the clock, which negates the whole point in the first place.

 

The other point to note is that he discourages the use of daisy chaining, and promotes the use of an ultra low noise distribution amplifier. I got the same feedback from May and I believe (although I'd have to check) Mutec also discourages daisy chaining. With the Ref 10, it's self evident due to the provision of 8 clock outputs!

 

So what does this all mean

Don't daisy chain, if at all possible. Even without the other complications, daisy chains necessitate longer cable lengths, which degrades clock quality

If you must, design your chain to ensure that all devices in the chain can be configured to be unterminated, and that there is proper termination of the right impedance on both ends, using tees and terminators.

At least for the SOtM Ultra components, SOtM does not currently provide a way to switch between terminated and unterminated. I'm pretty sure that upon request, they can configure a device whichever way you want it.

For me, this means that if I get to the point where I have more than one component with a master clock input that I want to drive, I'll want to spring for a Ref 10 or OCX-10. Ouch!

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23 minutes ago, austinpop said:

You are asking the wrong people. This is a question best asked of manufacturers. The good news is that some are paying close attention. I suspect over time we will see one-box solutions that make all this spaghetti superfluous.

 

THANK YOU!

That is the exact answer i was hoping to hear....you were the right person to ask....

When it is all sorted out, i will ask again in a few months (wink)

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14 minutes ago, beerandmusic said:

 

THANK YOU!

That is the exact answer i was hoping to hear....you were the right person to ask....

When it is all sorted out, i will ask again in a few months (wink)

 

Yes. A one box solution, with decent engineering, sorts all the "problems" - these were made 30 years ago, but didn't make an impact because people weren't interested enough, they cost too much or were just too rare. Then jitter was invented as an explanation for everything that was 'wrong' with digital - and the audio world has had a merry dance "sorting this" ever since ...

 

The clock drives the key DAC circuitry 100% directly, and everything else slaves off that - super simple, and a vaguely OK clock will then do the job well enough - the OTT complexities of all the fashionable 'solutions' devised over the years can then be dumped.

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3 hours ago, mansr said:

Ethernet and USB audio implementations have flow control, so there is no need to embed a clock signal with the data stream. This is a fact just as the sun rises in the east.

 

 

does the clock in the DAC need any future improvements to improve SQ?

 

relatedly, do any >$200 DACs or universal players that can ... uh DACify external inputs... have crummy clocks in them?

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19 minutes ago, JohnSwenson said:

I've been thinking about writing a primer on crystal oscillators and digital audio and this looks like the perfect place to put it. I promise I will leave out all the complex math that most articles are filled with. I'm NOT going to go into how it all works, since most people don't care, just what makes them different and how that matters for audio.

 

A crystal oscillator is a combination of a special piece of quartz crystal and an electronic circuit, the combination produces periodic signal at a specific frequency, several things can change this frequency:

 

Thickness of the quartz piece, this is the primary determining factor in the frequency

 

Temperature of the crystal,  this is called the temperature coefficient (TEMPCO for short), it is the change in frequency for a small change in temperature. It is not constant but changes with temperature, this is the TEMPCO curve. All TEMPCO curves have a temperature where the TEMPCO is zero, this is called the inflection point. If you run the crystal at this temperature, small changes in temperature produce no change in frequency, THIS point is where you want to run a crystal oscillator. If the temperature is far away from this point a small change in temperature makes a big change in frequency, you do not want to be here.

 

Capacitance across the crystal, all crystal oscillators need some capacitance across the crystal to work, changing that capacitance changes the frequency.

 

Power flowing through the crystal. The oscillator circuit works by running power (in the form of an AC signal) through the crystal, changing the power changes the frequency.

 

TEMPCO is THE most important characteristic besides the thickness, so a lot of crystal oscillator design has to do with this.

 

Now on to "cut", this is how a slice of crystal is cut out of a block of quartz. This is all very complicated so I won't go into the details, just to say there are many ways to do this and the exact cut determines the properties of the oscillator.

 

The most common cut (BY FAR) is called the AT cut. Almost all the oscillators in your electronics devices use the AT cut. The primary reason for this is that the inflection point of its TEMPCO curve is at 25-35C, right around "normal" room temperature, especially in a box where the electronics warm it up slightly. With this cut you usually do not need to apply any temperature stabilization since it is at a point where a change in temperature makes a very small change in frequency.

 

The other cut we need to talk about is the SC cut, this is used in OCXOs, I'll talk about that later. This cut has much higher Q than the AT cut, which means much lower phase noise, BUT in order to get that the inflection point of the TEMPCO curve is at 95C. THIS is why an oven is needed, not so much to stabalize the temperature but to get the crystal to the inflection point where a change in temperature makes an extremely small change in frequency. The slope of the TEMPCO cut around the inflection point is much shallower than the AT cut, so a given change in temperature makes a much smaller change in frequency, IF it is at 95C, outside of that and it is worse than an AT. So you ONLY want to use an SC cut in an oven.

 

So what aspect of this is really important for digital audio? Most oscillator spec sheets spend a lot of time talking about their long term stability. It turns out crystals will change frequency over time (called aging). Some applications need this, digital audio does not. A 1 part per million change in frequency over  years time is completely irrelevant. Another spec that is important for some application is the TEMPCO, how much the frequency is going to change as the heater turns on and off. Again, irrelevant to digital audio. What DOES matter is phase noise. I'm not going to go into any detail on this but that is what matters. It is not a single number but a graph, you have to see the graph to really get an idea of what it is.

 

The manufacturers are starting to realize this and are now making some fairly inexpensive AT cut crystals with extremely low phase noise. They don't have great aging or great TEMPCO but they DO have great phase noise.

 

There are three common crystal oscillator configurations you will come across in digital audio:

 

XO - basic simple crystal oscillator, always uses an AT cut crystal, susceptible to the ambient temperature (remember that 25-35C) changes a fair amount over the years, has a huge range of phase noise from one model to the next. Anywhere from $0.35 to $25.

 

TCXO- Temperature Compensated Crystal Oscillator. Standard AT crystal with a temperature sensor that feeds a voltage variable capacitor across the crystal. In order to have a large enough "pull range" to handle large changes in temperature the crystal is modified so the frequency changes a lot with a given capacitance change. Unfortunately this radically increases the phase noise of the crystal. Thus TCXOs are about the worst clock you can use for digital audio. You get much better temperature stability, which you don't care about, in exchange for much worse phase noise which you DO care about. A very bad trade off. So if you see  a digital audio device with a TCXO, stay away.

 

OCXO Oven Compensated Crystal Oscillator. The oscillator sits in an oven that brings its temperature to 95C. Most writing you find on the net will say this is to stabilize the temperature, but the real reason is to bring an SC cut crystal up to 95C where its built in TEMPCO is zero. This gives extremely low frequency change with temperature, but the SC also has MUCH lower aging than the AT AND much lower phase noise than the AT. Thus the OCXO is great for both systems that require extremely low drift but also systems that require extremely low phase noise.

 

The problem is that OCXOs are not cheap, $100 and up (WAY UP). The cheapest OCXOs have about the same phase noise as the best AT cut XOs, for about 4 times the price. So for digital audio at least a low end OCXO is not particularly useful. You have to get in the $300 range to get OCXOs with significantly lower phase noise. As you go up from there you can get WAY better phase noise, but you really have to pay for it. So when looking at OCXO specs, all you need look at is the phase noise, all the stuff in PPB etc is irreverent. Don't waste money on getting the best in those specs. If a manufacturer just shows the PPB numbers and doesn't give phase noise, stay away.

 

Another thing that has been talked about is "atomic clocks". The "inexpensive" ones (less than $10k) are rubidium. These have EXTREMELY low long term drift, but very bad phase noise. There is NO reason to get one of these for digital audio. Sometimes a rubidium oscillator is paired with an OCXO, the rubidium "disciplines" the OCXO, this gives the best of both worlds, but if you spent the same amount of money on just the OCXO you could get much lower phase noise which is what matters.

 

In the next installment I'll go into frequency synthesizers and how recent changes are changing the landscape of clocks for digital audio.

 

John S.

 

 

 

Thanks for sharing...i am sure many that are more versed are much more appreciative....to me it still looks like gobbly-gook to me...

 

All i want to know is Do you believe we can expect to see a DSD network player (streamer/dac) with all the latest new advancements of noise suppressioin and midfi clocks with a "decent" dac for under $2k in near future from any decent manufacturerer?  (ps-i don't believe a manufacturer needs to be a boutique class).  Also, do you know if any of the circuitry in modern AVR's already have this "advanced stuff"?

 

Grin, and seriously, thanks!

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31 minutes ago, mansr said:

Atomic clocks and extreme temperature stability just don't make sense for audio purposes. Nobody will notice if the clock drifts a few hundred ppm over the course of an hour.

While not important I also haven't found very much drift. 

 

I recently acquired an Antelope Audio interface.  They have their fancy Oven clocks.  One of their trademark features.  I wanted it for other features, but of course don't mind.  They have the hoopla about < 1 ppm aging per year, stability of +/- .02 ppm and calibration of +/- .001 ppm.  None of which tells me anything definitive about short term phase noise. 

 

In a week vs another interface it varied by 4-5 ppb.  Meaning both were at least this stable or the much more unlikely case of them both varying over time almost exactly the same amount.  

 

I have hooked up other interfaces and weeks apart they vary at most by a few ppm usually not that much.  Some of them vary from one another by more than 100 ppm in basic clock speed, but the variance over time is not very large at all.   So I should be smart and start a company to fix this non-issue for audiophiles.  Creativity can be furthered when you are developing gear to fix issues not broken. Success would be guaranteed judging by history. 

 

beerandmusic already believes.  He doesn't know why he believes.  He does believe.  He doesn't understand what this would do for him, but he believes.  Belief is enough.  He doesn't know what bad clocking would sound like, but believes better clocking would sound........better. 

 

To paraphrase John Lennon: All you need is belief. Belief is all you need.

 

Facts???  What can you do with Facts?????????  

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22 minutes ago, esldude said:

While not important I also haven't found very much drift. 

 

I recently acquired an Antelope Audio interface.  They have their fancy Oven clocks.  One of their trademark features.  I wanted it for other features, but of course don't mind.  They have the hoopla about < 1 ppm aging per year, stability of +/- .02 ppm and calibration of +/- .001 ppm.  None of which tells me anything definitive about short term phase noise. 

 

In a week vs another interface it varied by 4-5 ppb.  Meaning both were at least this stable or the much more unlikely case of them both varying over time almost exactly the same amount.  

 

I have hooked up other interfaces and weeks apart they vary at most by a few ppm usually not that much.  Some of them vary from one another by more than 100 ppm in basic clock speed, but the variance over time is not very large at all.   So I should be smart and start a company to fix this non-issue for audiophiles.  Creativity can be furthered when you are developing gear to fix issues not broken. Success would be guaranteed judging by history. 

 

beerandmusic already believes.  He doesn't know why he believes.  He does believe.  He doesn't understand what this would do for him, but he believes.  Belief is enough.  He doesn't know what bad clocking would sound like, but believes better clocking would sound........better. 

 

To paraphrase John Lennon: All you need is belief. Belief is all you need.

 

Facts???  What can you do with Facts?????????  

 

Probably good marketing is why i believe.....but i have believed before and been wrong...maybe it is all just more hoopla, but right now I do believe....Even the main manufacturers are pushing the importance of clocking and power....more so lately.

 

I am not an audio engineer, nor do i pretend to be...i am merely trying to educate myself as little as possible so that i don't throw away good money that i don't have.

 

I wonder how this would subjectively compare to a $4K trifecta and $2K dac.

SU-G30....hmmm, product of the month....possibly worth a look, or at least what they are doing differently than before.

 

http://www.technics.com/us/products/grand-class-g30/network-audio-amplifier-su-g30.html

 

https://www.gramophone.co.uk/feature/product-of-the-month-technics-su-g30

 

su-g30-mainvisual.jpg

 

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^^^perhaps you are right, and it is just good marketing....i think time will tell if there really is anything new here...i am not jumping on any bandwagon so fast... Hell, i still haven't bought any usb toys, and i believe in them too.....i just think it should all be part of a well designed system.

 

I am going to CES this year though and hope to hear a lot of new products....I am convinced I will buy something to "complete" my system within a year though....still contemplating the Lumin D1 too.

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^^^ Actually, i had to think about it, and what got me so excited after sitting on sidelines for over the last year....

I think, more than anything, it was the Hans channel review about the SOTM Ultra.  I have tried so much stuff over the past few years, only to be left unimpressed, with so many "OMG, best thing ever reviews" that i became numb to the audio hoopla. 

 

Hans video review here, kind of summed up my thoughts about the hoopla marketing that goes on in audio....but he is convincingly unbiased (as unbiased as a reviewer can be anyway), that when he seemed so excited about the SOTM ULTRA, and i see so much talk on this site (what are we at 200 pages now), and most having to do with clocking, I guess I am just excited about "HOPE", because of being let down so many times.

 

Anyways, regardless if this is just more hoopla, or if there really is any MEAT to any of this clocking stuff, I am very close to buying something, which i plan on not upgrading again....so if i seem overly excited, or hopeful, that is probably the best context i can put it in....

I am not dishing out $4K though, and so I just want to find something i can enjoy "with belief" that i have the best i can have with my limited budget.

 

All of you don't need to worry much more, i will likely slip back into hiding off of this site (i know, never too soon for many of you...don't let the door kick me on the way out)....it's been fun and interesting to me, and I am sorry i have offended so many...it was never my intention....

 

 

 

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