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The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
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Old 11th September 2014, 04:13 PM   #21
esgigt is offline esgigt  Netherlands
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A 11.2896 Mhz perhaps?
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Old 11th September 2014, 04:23 PM   #22
Eldam is offline Eldam  France
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I'm asking if the 96 of the XX.xx96 are stable !

Quartz spec accuracy are moving with time
greater the first year of use then slower after but it moves !

Is there crystals oscillator more stable then over in time ? I assume phase noise is more important than the exact accuracy of the crystal ?

I would like to swap the four crystals of my SB Duet with the appropriates XX.xxxx Mhz range if I have money and skill! Some maid it with an hearable result... but know have more change by working on simple things like good caps for having good tonal balance and no harchness.... It makes sense to me a good dac chip with a good layout needs a good crystal to obtain a better result than middle production dacs off shelves ! But for the better ones a good crystal swap can certainly help ; Have no experience with such things ! !

Last edited by Eldam; 11th September 2014 at 04:25 PM.
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Old 11th September 2014, 10:36 PM   #23
andrea_mori is offline andrea_mori  Italy
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The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
Eldam,

at this moment I own only 2 Laptech crystals, so I use them to experiment.
If you can wait a few days, I will check if there is enough interest to ask Laptech for a quote. The minimum orderable quantity is at least 5 pieces for each frequency, and the price decreases for higher quantity (10, 20, and so on).

The long term stability is not so important in digital audio. The phase noise of an oscillator is affected mainly by the short term stability.
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Old 11th September 2014, 10:51 PM   #24
andrea_mori is offline andrea_mori  Italy
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The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
The finished oscillator.

I'm updating the PCB, the new batch will be more compact, 1.75" x 1", and Ni/Au surface finish.
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Old 12th September 2014, 11:28 AM   #25
merlin el mago is offline merlin el mago
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Congrats andrea looks very good.
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Old 12th September 2014, 11:48 AM   #26
HpW is offline HpW
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Talking My suggestion

Quote:
Originally Posted by andrea_mori View Post
To get 3V3 at the output, the 74HC04 should be replaced with a 74LVC04, and the +5V power supply should be replaced with 3V3 voltage.
Well, in my old HW days (DACXVCO) I used the HCU04 chip, while you use the inverter as an amplifier and the HCU type should be used!

On the front I used as you a similar circuit and after words the HCU04 as an amplifier with isolated powering (this power noise is critical) and for the output driver also a different IC, while the load would influence the power noise on the oscillator. Then put all in a nice CU box

PHP Code:
My HCU04 

->-+--- HCU04 ---+->-
   !             !
   +- 
-+- ---+
         
C
         
!
        
GND 
Cheers

Hp
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Old 12th September 2014, 01:17 PM   #27
peufeu is offline peufeu  France
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Very interesting !

This thread also indirectly answers one of my questions, which is : what is the added jitter of a HC logic gate ? From the tests, it seems negligible. Good news !
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Old 12th September 2014, 01:31 PM   #28
kevinkr is offline kevinkr  United States
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The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
Very nice board layout.
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Old 12th September 2014, 01:53 PM   #29
Eldam is offline Eldam  France
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Hi Andrea,

I can wait few month, not a question of time, you know I'm waiting Ian and Joro for inputs stages (but have a B plan to beginn something with spidf kits I already have), and I have no output stage yet. You have thousand less free time than me but sucees to make device like that ! Wow ! It's more about a passion to learn around my best hobby !

I read a little yesterday to try to be less fool ! Well I learn than jitter & phase noise are the same with crystals. I also read than TCXO are not as good that it seems for audio... I also read than the ppm stability is not so important, btw some manufacter provide already more stabilised Crystal than they get artificialy older with heating !

About the TDA 1541 and its simple 16 bits resolution & say 44K hz application: has it an intresec jitter or noise floor Under which the quality of phase noise can not be heard with it ?

If I look at the famous Crystek, i see than at 500 hz, the noise floor is -140 db ! Is it an usefull data or is it just the phase noise F and h2,h3... level which are important.

Sorry for my poor understanding, I assume all those concepts are near but I mix them badly....

Last edited by Eldam; 12th September 2014 at 01:57 PM.
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Old 13th September 2014, 05:31 AM   #30
1audio is offline 1audio  United States
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The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
A few questions on the oscillator. First for a 3rd overtone you usually need a trap to prevent the oscillator from operating at the wrong mode. I did not see it in your schematic.

Second use a 74AC logic gate for the lowest phase noise. It can be problematic since those can radiate with their very fast edges but they have the lowest phase noise of the TTL logic families (except perhaps the Potato stuff). Buffering and isolation is important. Modulating the load even a little will alter the frequency of the oscillator producing phase noise. i suspect a pretty simple inexpensive packaged oscillator with good isolation would make a big difference and be better than an over the top effort with poor isolation. There is a spec for reverse isolation on distribution amps for precision oscillators because of this issue. Usually way better than 100 dB for good ones. And not an easy one to meet. http://www.ko4bb.com/Manuals/05)_GPS...ction_NIST.pdf

I do not see an AGC, which is usually necessary for very low phase noise oscillators.

The AT crystal can be pretty good and is more pullable than an SC crystal but it has a lower Q which will mean higher close in phase noise.

i think this is a really interesting circuit: Low Phase Noise Design: Crystal Oscillators it uses the crystal as a bandpass filter as well as the oscillator to reduce the phase noise. There are a number of tricks worth studying.

The J310 is a good tradeoff between RF gain and noise but it will limit the possible phase noise. Usually a bipolar transistor is used to get the lowest phase noise. In this application it can be as much as 10 db lower. Its directly related to the input voltage noise. The low frequency voltage noise of the transistor will modulate the RF producing close in phase noise.

If you want to really go down the low phase noise road start here: http://www.hpl.hp.com/techreports/1999/HPL-1999-6.pdf There is some of the history in the article.

I designed a really low noise power supply for crystal oscillators here: http://www.diyaudio.com/forums/digit...ml#post2863700 It has less than 1 nV/rtHz noise, important when chasing the really low phase noise, and cheap and simple to build.

I asked Rick Karlquist about changing the crystal in an HP 10811. He said it would not work, since the crystals were very specific to work in it.

In the US you can go to Wenzel/Croven to get crystals. It will be slow and expensive but they are as good as you can get. I don't think the crystal will be a limiting factor until you get a lot of the other stuff really right.

Build 2 so you can measure the phase noise. Three if you want to use the cross correlation method.
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